feat(models): implement Google Gemma 4 architecture support (MoE, Multimodal, Reasoning, Tool-Use) (#38826)

Signed-off-by: Luciano Martins <lucianommartins@users.noreply.github.com>
Signed-off-by: Luciano Martins <lucianomartins@google.com>
Co-authored-by: Luciano Martins <lucianommartins@users.noreply.github.com>
Co-authored-by: Isotr0py <2037008807@qq.com>
(cherry picked from commit 08ed2b9688)

tests/models/multimodal/generation/test_common.py

@@ -394,6 +394,22 @@ VLM_TEST_SETTINGS = {
         vllm_runner_kwargs={"mm_processor_kwargs": {"do_pan_and_scan": True}},
         patch_hf_runner=model_utils.gemma3_patch_hf_runner,
     ),
+    "gemma4": VLMTestInfo(
+        models=["google/gemma-4-E2B-it"],
+        test_type=(VLMTestType.IMAGE, VLMTestType.MULTI_IMAGE),
+        prompt_formatter=lambda img_prompt: f"<bos><start_of_turn>user\n{img_prompt}<end_of_turn>\n<start_of_turn>model\n",  # noqa: E501
+        single_image_prompts=IMAGE_ASSETS.prompts(
+            {
+                "stop_sign": "What's the content in the center of the image?",
+                "cherry_blossom": "What is the season?",
+            }
+        ),
+        multi_image_prompt="Describe the two images in detail.",
+        max_model_len=4096,
+        max_num_seqs=2,
+        auto_cls=AutoModelForImageTextToText,
+        vllm_runner_kwargs={"limit_mm_per_prompt": {"image": 4}},
+    ),
     "granite_vision": VLMTestInfo(
         models=["ibm-granite/granite-vision-3.3-2b"],
         test_type=(VLMTestType.IMAGE),

tests/models/multimodal/processing/test_gemma4.py

@@ -0,0 +1,44 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import pytest
+
+from vllm.multimodal import MULTIMODAL_REGISTRY
+
+from ....conftest import ImageTestAssets
+from ...utils import build_model_context
+
+# TODO: to be updated to "google/gemma-4-e2b-it" once the models are available
+GEMMA4_MODEL_ID = "google/gemma-4-E2B-it"
+
+
+@pytest.mark.parametrize("model_id", [GEMMA4_MODEL_ID])
+def test_limit_mm_per_prompt(
+    image_assets: ImageTestAssets,
+    model_id: str,
+):
+    """Test that limit_mm_per_prompt accurately restricts multiple images."""
+    # We only allow 1 image
+    ctx = build_model_context(
+        model_id,
+        mm_processor_kwargs={},
+        limit_mm_per_prompt={"image": 1},
+    )
+    processor = MULTIMODAL_REGISTRY.create_processor(ctx.model_config)
+
+    # Provide 2 images in the prompt
+    prompt = "<image><image>"
+    # image_assets usually has multiple images
+    images = [asset.pil_image for asset in image_assets][:2]
+    if len(images) < 2:
+        images = [images[0], images[0]]
+
+    mm_data = {"image": images}
+
+    # Expect ValueError when exceeding limit
+    with pytest.raises(ValueError, match="At most 1 image"):
+        processor(
+            prompt,
+            mm_items=processor.info.parse_mm_data(mm_data),
+            hf_processor_mm_kwargs={},
+        )

tests/models/registry.py

@@ -277,6 +277,10 @@ _TEXT_GENERATION_EXAMPLE_MODELS = {
         "google/gemma-2-9b", extras={"tiny": "google/gemma-2-2b-it"}
     ),
     "Gemma3ForCausalLM": _HfExamplesInfo("google/gemma-3-1b-it"),
+    "Gemma4ForCausalLM": _HfExamplesInfo(
+        "google/gemma-4-E2B-it",
+        min_transformers_version="5.0.0",
+    ),
     "Gemma3nForCausalLM": _HfExamplesInfo("google/gemma-3n-E2B-it"),
     "GlmForCausalLM": _HfExamplesInfo("zai-org/glm-4-9b-chat-hf"),
     "Glm4ForCausalLM": _HfExamplesInfo("zai-org/GLM-4-9B-0414"),
@@ -805,6 +809,10 @@ _MULTIMODAL_EXAMPLE_MODELS = {
     ),
     "FuyuForCausalLM": _HfExamplesInfo("adept/fuyu-8b"),
     "Gemma3ForConditionalGeneration": _HfExamplesInfo("google/gemma-3-4b-it"),
+    "Gemma4ForConditionalGeneration": _HfExamplesInfo(
+        "google/gemma-4-E2B-it",
+        min_transformers_version="5.5.0",
+    ),
     "Gemma3nForConditionalGeneration": _HfExamplesInfo("google/gemma-3n-E2B-it"),
     "GlmAsrForConditionalGeneration": _HfExamplesInfo(
         "zai-org/GLM-ASR-Nano-2512",

tests/reasoning/test_gemma4_reasoning_parser.py

@@ -0,0 +1,196 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import pytest
+
+from tests.reasoning.utils import run_reasoning_extraction
+from vllm.reasoning import ReasoningParser, ReasoningParserManager
+
+# Using mistral tokenizer as a generic mock since the actual model is not on HF
+from vllm.tokenizers.registry import get_tokenizer
+
+parser_name = "gemma4"
+
+
+@pytest.fixture(scope="module")
+def generic_tokenizer():
+    return get_tokenizer("google/gemma-4-E2B-it")
+
+
+INVALID_SIMPLE_NONSTREAMING = {
+    "output": "This is a reasoning section<channel|>This is the rest",
+    "reasoning": "This is a reasoning section",
+    "content": "This is the rest",
+    "is_reasoning_end": True,
+}
+INVALID_SIMPLE_STREAMING = {
+    "output": "This is a reasoning section<channel|>This is the rest",
+    "reasoning": None,
+    "content": "This is a reasoning sectionThis is the rest",
+    "is_reasoning_end": True,
+}
+INVALID_COMPLETE_NONSTREAMING = {
+    "output": "This is a reasoning section<channel|>",
+    "reasoning": "This is a reasoning section",
+    "content": None,
+    "is_reasoning_end": True,
+}
+INVALID_COMPLETE_STREAMING = {
+    "output": "This is a reasoning section<channel|>",
+    "reasoning": None,
+    "content": "This is a reasoning section",
+    "is_reasoning_end": True,
+}
+NO_CONTENT = {
+    "output": "<|channel>This is reasoning",
+    "reasoning": "This is reasoning",
+    "content": None,
+    "is_reasoning_end": False,
+}
+NO_REASONING = {
+    "output": "This is content",
+    "reasoning": None,
+    "content": "This is content",
+    "is_reasoning_end": False,
+}
+REASONING_WITH_CHANNEL = {
+    "output": "<|channel>This is a reasoning section<channel|>This is the rest",
+    "reasoning": "This is a reasoning section",
+    "content": "This is the rest",
+    "is_reasoning_end": True,
+}
+COMPLETE_REASONING_WITH_CHANNEL = {
+    "output": "<|channel>This is a reasoning section<channel|>",
+    "reasoning": "This is a reasoning section",
+    "content": None,
+    "is_reasoning_end": True,
+}
+MULTIPLE_LINES_WITH_CHANNEL = {
+    "output": "<|channel>This\nThat<channel|>This is the rest\nThat",
+    "reasoning": "This\nThat",
+    "content": "This is the rest\nThat",
+    "is_reasoning_end": True,
+}
+CHANNEL_NO_END = {
+    "output": "<|channel>This is a reasoning section",
+    "reasoning": "This is a reasoning section",
+    "content": None,
+    "is_reasoning_end": False,
+}
+EMPTY = {
+    "output": "",
+    "reasoning": None,
+    "content": "",
+    "is_reasoning_end": False,
+}
+NEW_LINE_NONSTREAMING = {
+    "output": (
+        "Before\n<|channel>This is a reasoning section<channel|>\nThis is the rest"
+    ),
+    "reasoning": "This is a reasoning section",
+    "content": "\nThis is the rest",
+    "is_reasoning_end": True,
+}
+NEW_LINE_STREAMING = {
+    "output": (
+        "Before\n<|channel>This is a reasoning section<channel|>\nThis is the rest"
+    ),
+    "reasoning": "This is a reasoning section",
+    "content": "Before\n\nThis is the rest",
+    "is_reasoning_end": True,
+}
+
+TEST_CASES = [
+    pytest.param(False, INVALID_SIMPLE_NONSTREAMING, id="invalid_simple"),
+    pytest.param(True, INVALID_SIMPLE_STREAMING, id="invalid_simple_streaming"),
+    pytest.param(False, INVALID_COMPLETE_NONSTREAMING, id="invalid_complete"),
+    pytest.param(True, INVALID_COMPLETE_STREAMING, id="invalid_complete_streaming"),
+    pytest.param(False, NO_CONTENT, id="no_content"),
+    pytest.param(False, NO_REASONING, id="no_reasoning"),
+    pytest.param(False, REASONING_WITH_CHANNEL, id="reasoning"),
+    pytest.param(True, REASONING_WITH_CHANNEL, id="reasoning_streaming"),
+    pytest.param(False, COMPLETE_REASONING_WITH_CHANNEL, id="complete_reasoning"),
+    pytest.param(
+        True, COMPLETE_REASONING_WITH_CHANNEL, id="complete_reasoning_streaming"
+    ),
+    pytest.param(False, MULTIPLE_LINES_WITH_CHANNEL, id="multiple_lines"),
+    pytest.param(True, MULTIPLE_LINES_WITH_CHANNEL, id="multiple_lines_streaming"),
+    pytest.param(False, CHANNEL_NO_END, id="no_end"),
+    pytest.param(True, CHANNEL_NO_END, id="no_end_streaming"),
+    pytest.param(False, EMPTY, id="empty"),
+    pytest.param(False, NEW_LINE_NONSTREAMING, id="new_line"),
+    pytest.param(True, NEW_LINE_STREAMING, id="new_line_streaming"),
+]
+
+
+@pytest.mark.parametrize("streaming, param_dict", TEST_CASES)
+def test_gemma4_reasoning(
+    streaming: bool,
+    param_dict: dict,
+    generic_tokenizer,
+):
+    output = param_dict["output"]
+
+    # Resolve token IDs dynamically from the real tokenizer
+    vocab = generic_tokenizer.get_vocab()
+    start_token_id = vocab["<|channel>"]
+    end_token_id = vocab["<channel|>"]
+
+    index_start = output.find("<|channel>")
+    len_start = len("<|channel>")
+    index_end = output.find("<channel|>")
+    len_end = len("<channel|>")
+
+    output_tokens = []
+
+    def _encode(text: str) -> list[int]:
+        if not text:
+            return []
+        # Handle both raw transformers and vLLM wrappers
+        enc = getattr(generic_tokenizer, "tokenizer", generic_tokenizer)
+        try:
+            return enc.encode(text, add_special_tokens=False)
+        except TypeError:
+            return enc.encode(text)
+
+    if index_start != -1:
+        output_before = output[:index_start]
+        output_tokens += _encode(output_before)
+        output_tokens += [start_token_id]
+
+        if index_end != -1:
+            output_middle = output[index_start + len_start : index_end]
+            output_after = output[index_end + len_end :]
+            output_tokens += _encode(output_middle)
+            output_tokens += [end_token_id]
+            output_tokens += _encode(output_after)
+        else:
+            output_middle = output[index_start + len_start :]
+            output_tokens += _encode(output_middle)
+    elif index_end != -1:
+        output_before = output[:index_end]
+        output_after = output[index_end + len_end :]
+        output_tokens += _encode(output_before)
+        output_tokens += [end_token_id]
+        output_tokens += _encode(output_after)
+    else:
+        output_tokens += _encode(output)
+
+    parser: ReasoningParser = ReasoningParserManager.get_reasoning_parser(parser_name)(
+        generic_tokenizer
+    )
+
+    # We use the generic run_reasoning_extraction from utils
+    # Use decode per token to get standard spaces instead of
+    # SentencePiece space characters
+    output_token_strings = [generic_tokenizer.decode([t]) for t in output_tokens]
+    reasoning, content = run_reasoning_extraction(
+        parser, output_token_strings, streaming=streaming
+    )
+
+    assert reasoning == param_dict["reasoning"]
+    assert content == param_dict["content"]
+
+    # Test is_reasoning_end
+    is_reasoning_end = parser.is_reasoning_end(output_tokens)
+    assert is_reasoning_end == param_dict["is_reasoning_end"]

tests/tool_parsers/test_gemma4_tool_parser.py

@@ -0,0 +1,504 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import json
+from typing import Any
+from unittest.mock import MagicMock
+
+import pytest
+
+from vllm.entrypoints.openai.chat_completion.protocol import ChatCompletionRequest
+from vllm.tool_parsers.gemma4_tool_parser import (
+    TOOL_CALL_END,
+    TOOL_CALL_START,
+    Gemma4ToolParser,
+    _parse_gemma4_args,
+    _parse_gemma4_array,
+)
+
+# ---------------------------------------------------------------------------
+# Fixtures
+# ---------------------------------------------------------------------------
+
+
+@pytest.fixture
+def mock_tokenizer():
+    tokenizer = MagicMock()
+    tokenizer.encode.return_value = [1, 2, 3]
+    # Include the tool call start token in the vocab for the parser
+    tokenizer.get_vocab.return_value = {TOOL_CALL_START: 48, TOOL_CALL_END: 49}
+    return tokenizer
+
+
+@pytest.fixture
+def parser(mock_tokenizer):
+    return Gemma4ToolParser(mock_tokenizer)
+
+
+@pytest.fixture
+def mock_request():
+    request = MagicMock(spec=ChatCompletionRequest)
+    request.tools = []
+    request.tool_choice = "auto"
+    return request
+
+
+# ---------------------------------------------------------------------------
+# Unit tests for _parse_gemma4_args (shared parser logic)
+# ---------------------------------------------------------------------------
+
+
+class TestParseGemma4Args:
+    def test_empty_string(self):
+        assert _parse_gemma4_args("") == {}
+
+    def test_whitespace_only(self):
+        assert _parse_gemma4_args("   ") == {}
+
+    def test_single_string_value(self):
+        result = _parse_gemma4_args('location:<|"|>Paris<|"|>')
+        assert result == {"location": "Paris"}
+
+    def test_string_value_with_comma(self):
+        result = _parse_gemma4_args('location:<|"|>Paris, France<|"|>')
+        assert result == {"location": "Paris, France"}
+
+    def test_multiple_string_values(self):
+        result = _parse_gemma4_args(
+            'location:<|"|>San Francisco<|"|>,unit:<|"|>celsius<|"|>'
+        )
+        assert result == {"location": "San Francisco", "unit": "celsius"}
+
+    def test_integer_value(self):
+        result = _parse_gemma4_args("count:42")
+        assert result == {"count": 42}
+
+    def test_float_value(self):
+        result = _parse_gemma4_args("score:3.14")
+        assert result == {"score": 3.14}
+
+    def test_boolean_true(self):
+        result = _parse_gemma4_args("flag:true")
+        assert result == {"flag": True}
+
+    def test_boolean_false(self):
+        result = _parse_gemma4_args("flag:false")
+        assert result == {"flag": False}
+
+    def test_mixed_types(self):
+        result = _parse_gemma4_args(
+            'name:<|"|>test<|"|>,count:42,active:true,score:3.14'
+        )
+        assert result == {
+            "name": "test",
+            "count": 42,
+            "active": True,
+            "score": 3.14,
+        }
+
+    def test_nested_object(self):
+        result = _parse_gemma4_args('nested:{inner:<|"|>value<|"|>}')
+        assert result == {"nested": {"inner": "value"}}
+
+    def test_array_of_strings(self):
+        result = _parse_gemma4_args('items:[<|"|>a<|"|>,<|"|>b<|"|>]')
+        assert result == {"items": ["a", "b"]}
+
+    def test_unterminated_string(self):
+        """Unterminated strings should take everything after the delimiter."""
+        result = _parse_gemma4_args('key:<|"|>unterminated')
+        assert result == {"key": "unterminated"}
+
+    def test_empty_value(self):
+        """Key with no value after colon."""
+        result = _parse_gemma4_args("key:")
+        assert result == {"key": ""}
+
+
+class TestParseGemma4Array:
+    def test_string_array(self):
+        result = _parse_gemma4_array('<|"|>a<|"|>,<|"|>b<|"|>')
+        assert result == ["a", "b"]
+
+    def test_empty_array(self):
+        result = _parse_gemma4_array("")
+        assert result == []
+
+    def test_bare_values(self):
+        result = _parse_gemma4_array("42,true,3.14")
+        assert result == [42, True, 3.14]
+
+
+# ---------------------------------------------------------------------------
+# Non-streaming extraction tests
+# ---------------------------------------------------------------------------
+
+
+class TestExtractToolCalls:
+    def test_no_tool_calls(self, parser, mock_request):
+        model_output = "Hello, how can I help you today?"
+        result = parser.extract_tool_calls(model_output, mock_request)
+
+        assert result.tools_called is False
+        assert result.tool_calls == []
+        assert result.content == model_output
+
+    def test_single_tool_call(self, parser, mock_request):
+        model_output = (
+            '<|tool_call>call:get_weather{location:<|"|>London<|"|>}<tool_call|>'
+        )
+        result = parser.extract_tool_calls(model_output, mock_request)
+
+        assert result.tools_called is True
+        assert len(result.tool_calls) == 1
+        assert result.tool_calls[0].function.name == "get_weather"
+        args = json.loads(result.tool_calls[0].function.arguments)
+        assert args == {"location": "London"}
+
+    def test_multiple_arguments(self, parser, mock_request):
+        model_output = (
+            "<|tool_call>call:get_weather{"
+            'location:<|"|>San Francisco<|"|>,'
+            'unit:<|"|>celsius<|"|>}'
+            "<tool_call|>"
+        )
+        result = parser.extract_tool_calls(model_output, mock_request)
+
+        assert result.tools_called is True
+        assert len(result.tool_calls) == 1
+        assert result.tool_calls[0].function.name == "get_weather"
+        args = json.loads(result.tool_calls[0].function.arguments)
+        assert args == {"location": "San Francisco", "unit": "celsius"}
+
+    def test_text_before_tool_call(self, parser, mock_request):
+        model_output = (
+            "Let me check the weather for you. "
+            '<|tool_call>call:get_weather{location:<|"|>Paris<|"|>}'
+            "<tool_call|>"
+        )
+        result = parser.extract_tool_calls(model_output, mock_request)
+
+        assert result.tools_called is True
+        assert result.content == "Let me check the weather for you."
+        assert len(result.tool_calls) == 1
+        assert result.tool_calls[0].function.name == "get_weather"
+
+    def test_multiple_tool_calls(self, parser, mock_request):
+        model_output = (
+            '<|tool_call>call:get_weather{location:<|"|>London<|"|>}'
+            "<tool_call|>"
+            '<|tool_call>call:get_time{location:<|"|>London<|"|>}'
+            "<tool_call|>"
+        )
+        result = parser.extract_tool_calls(model_output, mock_request)
+
+        assert result.tools_called is True
+        assert len(result.tool_calls) == 2
+        assert result.tool_calls[0].function.name == "get_weather"
+        assert result.tool_calls[1].function.name == "get_time"
+
+    def test_nested_arguments(self, parser, mock_request):
+        model_output = (
+            "<|tool_call>call:complex_function{"
+            'nested:{inner:<|"|>value<|"|>},'
+            'list:[<|"|>a<|"|>,<|"|>b<|"|>]}'
+            "<tool_call|>"
+        )
+        result = parser.extract_tool_calls(model_output, mock_request)
+
+        assert result.tools_called is True
+        assert len(result.tool_calls) == 1
+        assert result.tool_calls[0].function.name == "complex_function"
+        args = json.loads(result.tool_calls[0].function.arguments)
+        assert args == {"nested": {"inner": "value"}, "list": ["a", "b"]}
+
+    def test_tool_call_with_number_and_boolean(self, parser, mock_request):
+        model_output = (
+            "<|tool_call>call:set_status{"
+            "is_active:true,"
+            "count:42,"
+            "score:3.14}"
+            "<tool_call|>"
+        )
+        result = parser.extract_tool_calls(model_output, mock_request)
+
+        assert result.tools_called is True
+        assert len(result.tool_calls) == 1
+        assert result.tool_calls[0].function.name == "set_status"
+        args = json.loads(result.tool_calls[0].function.arguments)
+        assert args == {"is_active": True, "count": 42, "score": 3.14}
+
+    def test_incomplete_tool_call(self, parser, mock_request):
+        model_output = '<|tool_call>call:get_weather{location:<|"|>London'
+        result = parser.extract_tool_calls(model_output, mock_request)
+
+        # Incomplete — no <tool_call|> end marker, regex won't match
+        assert result.tools_called is False
+        assert result.content == model_output
+
+    def test_hyphenated_function_name(self, parser, mock_request):
+        """Ensure function names with hyphens are parsed correctly."""
+        model_output = (
+            '<|tool_call>call:get-weather{location:<|"|>London<|"|>}<tool_call|>'
+        )
+        result = parser.extract_tool_calls(model_output, mock_request)
+
+        assert result.tools_called is True
+        assert result.tool_calls[0].function.name == "get-weather"
+
+    def test_dotted_function_name(self, parser, mock_request):
+        """Ensure function names with dots are parsed correctly."""
+        model_output = (
+            '<|tool_call>call:weather.get{location:<|"|>London<|"|>}<tool_call|>'
+        )
+        result = parser.extract_tool_calls(model_output, mock_request)
+
+        assert result.tools_called is True
+        assert result.tool_calls[0].function.name == "weather.get"
+
+    def test_no_arguments(self, parser, mock_request):
+        """Tool calls with empty arguments."""
+        model_output = "<|tool_call>call:get_status{}<tool_call|>"
+        result = parser.extract_tool_calls(model_output, mock_request)
+
+        assert result.tools_called is True
+        assert result.tool_calls[0].function.name == "get_status"
+        args = json.loads(result.tool_calls[0].function.arguments)
+        assert args == {}
+
+
+# ---------------------------------------------------------------------------
+# Streaming extraction tests
+# ---------------------------------------------------------------------------
+
+
+class TestStreamingExtraction:
+    """Tests for the streaming tool call extraction.
+
+    These simulate the token-by-token streaming that vLLM performs,
+    feeding incremental text to extract_tool_calls_streaming() and
+    verifying that the accumulated argument deltas form valid JSON.
+    """
+
+    def _simulate_streaming(
+        self, parser: Gemma4ToolParser, mock_request: Any, chunks: list[str]
+    ) -> list[tuple[Any, str]]:
+        """Feed chunks through the streaming parser and collect results.
+
+        Returns a list of (delta_message, accumulated_text) tuples.
+        """
+        results: list[tuple[Any, str]] = []
+        previous_text: str = ""
+        previous_token_ids: list[int] = []
+
+        for chunk in chunks:
+            current_text = previous_text + chunk
+            # Use token ID 48 for tool_call start, 49 for end, 0 otherwise
+            delta_token_ids: list[int] = []
+            if TOOL_CALL_START in chunk:
+                delta_token_ids.append(48)
+            elif TOOL_CALL_END in chunk:
+                delta_token_ids.append(49)
+            else:
+                delta_token_ids.append(0)
+
+            current_token_ids = previous_token_ids + delta_token_ids
+
+            delta = parser.extract_tool_calls_streaming(
+                previous_text=previous_text,
+                current_text=current_text,
+                delta_text=chunk,
+                previous_token_ids=tuple(previous_token_ids),
+                current_token_ids=tuple(current_token_ids),
+                delta_token_ids=tuple(delta_token_ids),
+                request=mock_request,
+            )
+            results.append((delta, current_text))
+            previous_text = current_text
+            previous_token_ids = list(current_token_ids)
+
+        return results
+
+    def _collect_arguments(self, results):
+        """Collect all argument deltas from streaming results into one string."""
+        args_text = ""
+        for delta, _ in results:
+            if delta and delta.tool_calls:
+                for tc in delta.tool_calls:
+                    func = tc.function if isinstance(tc.function, dict) else tc.function
+                    if isinstance(func, dict):
+                        arg = func.get("arguments", "")
+                    else:
+                        arg = getattr(func, "arguments", "") or ""
+                    if arg:
+                        args_text += arg
+        return args_text
+
+    def _collect_function_name(self, results):
+        """Extract the function name from streaming results."""
+        for delta, _ in results:
+            if delta and delta.tool_calls:
+                for tc in delta.tool_calls:
+                    func = tc.function if isinstance(tc.function, dict) else tc.function
+                    if isinstance(func, dict):
+                        name = func.get("name")
+                    else:
+                        name = getattr(func, "name", None)
+                    if name:
+                        return name
+        return None
+
+    def test_basic_streaming_single_tool(self, parser, mock_request):
+        """Simulate the exact streaming scenario from the bug report.
+
+        Model generates:
+        <|tool_call>call:get_weather{location:<|"|>Paris, France<|"|>}<tool_call|>
+
+        Expected: arguments should be valid JSON {"location": "Paris, France"}
+        """
+        chunks = [
+            "<|tool_call>",
+            "call:get_weather{",
+            'location:<|"|>Paris',
+            ", France",
+            '<|"|>}',
+            "<tool_call|>",
+        ]
+
+        results = self._simulate_streaming(parser, mock_request, chunks)
+
+        # Verify function name
+        name = self._collect_function_name(results)
+        assert name == "get_weather", f"Expected 'get_weather', got '{name}'"
+
+        # Verify arguments form valid JSON
+        args_text = self._collect_arguments(results)
+        assert args_text, "No arguments were streamed"
+        parsed_args = json.loads(args_text)
+        assert parsed_args == {"location": "Paris, France"}
+
+    def test_streaming_multi_arg(self, parser, mock_request):
+        """Streaming with multiple arguments."""
+        chunks = [
+            "<|tool_call>",
+            "call:get_weather{",
+            'location:<|"|>Tokyo<|"|>,',
+            'unit:<|"|>celsius<|"|>}',
+            "<tool_call|>",
+        ]
+
+        results = self._simulate_streaming(parser, mock_request, chunks)
+
+        name = self._collect_function_name(results)
+        assert name == "get_weather"
+
+        args_text = self._collect_arguments(results)
+        assert args_text
+        parsed_args = json.loads(args_text)
+        assert parsed_args == {"location": "Tokyo", "unit": "celsius"}
+
+    def test_streaming_no_extra_brace(self, parser, mock_request):
+        """Verify the closing } is NOT leaked into arguments (Bug #2)."""
+        chunks = [
+            "<|tool_call>",
+            "call:get_weather{",
+            'location:<|"|>London<|"|>}',
+            "<tool_call|>",
+        ]
+
+        results = self._simulate_streaming(parser, mock_request, chunks)
+        args_text = self._collect_arguments(results)
+        assert args_text
+
+        # The args text must be valid JSON (no extra })
+        parsed = json.loads(args_text)
+        assert parsed == {"location": "London"}
+
+        # Specifically assert no double-brace
+        assert args_text.count("}") <= 1, (
+            f"Arguments contain extra closing brace: {args_text!r}"
+        )
+
+    def test_streaming_no_unquoted_keys(self, parser, mock_request):
+        """Verify keys are properly quoted in JSON (Bug #1)."""
+        chunks = [
+            "<|tool_call>",
+            "call:get_weather{",
+            'location:<|"|>Paris<|"|>}',
+            "<tool_call|>",
+        ]
+
+        results = self._simulate_streaming(parser, mock_request, chunks)
+        args_text = self._collect_arguments(results)
+
+        # Must start with { and contain quoted key
+        assert args_text.lstrip().startswith("{"), (
+            f"Arguments don't start with '{{': {args_text!r}"
+        )
+        assert '"location"' in args_text, (
+            f"Key 'location' not properly quoted: {args_text!r}"
+        )
+
+    def test_streaming_name_no_call_prefix(self, parser, mock_request):
+        """Verify function name has no 'call:' prefix."""
+        chunks = [
+            "<|tool_call>",
+            "call:get_weather{",
+            'location:<|"|>Paris<|"|>}',
+            "<tool_call|>",
+        ]
+
+        results = self._simulate_streaming(parser, mock_request, chunks)
+        name = self._collect_function_name(results)
+        assert name == "get_weather"
+        assert not name.startswith("call:"), f"Name has 'call:' prefix: {name!r}"
+
+    def test_streaming_text_before_tool_call(self, parser, mock_request):
+        """Text before tool call should be emitted as content."""
+        chunks = [
+            "Let me check ",
+            "the weather. ",
+            "<|tool_call>",
+            "call:get_weather{",
+            'location:<|"|>London<|"|>}',
+            "<tool_call|>",
+        ]
+
+        results = self._simulate_streaming(parser, mock_request, chunks)
+
+        # First chunks should be content
+        content_parts = []
+        for delta, _ in results:
+            if delta and delta.content:
+                content_parts.append(delta.content)
+
+        assert "".join(content_parts).strip().startswith("Let me check")
+
+    def test_streaming_numeric_args(self, parser, mock_request):
+        """Streaming with numeric and boolean argument values."""
+        chunks = [
+            "<|tool_call>",
+            "call:set_config{",
+            "count:42,",
+            "active:true}",
+            "<tool_call|>",
+        ]
+
+        results = self._simulate_streaming(parser, mock_request, chunks)
+        args_text = self._collect_arguments(results)
+        if args_text:
+            parsed_args = json.loads(args_text)
+            assert parsed_args["count"] == 42
+            assert parsed_args["active"] is True
+
+    def test_streaming_empty_args(self, parser, mock_request):
+        """Tool call with no arguments."""
+        chunks = [
+            "<|tool_call>",
+            "call:get_status{}",
+            "<tool_call|>",
+        ]
+
+        results = self._simulate_streaming(parser, mock_request, chunks)
+        name = self._collect_function_name(results)
+        assert name == "get_status"

vllm/model_executor/layers/rotary_embedding/__init__.py

@@ -12,6 +12,7 @@ from .dual_chunk_rope import DualChunkRotaryEmbedding
 from .dynamic_ntk_alpha_rope import DynamicNTKAlphaRotaryEmbedding
 from .dynamic_ntk_scaling_rope import DynamicNTKScalingRotaryEmbedding
 from .fope import FourierRotaryEmbedding
+from .gemma4_rope import Gemma4RotaryEmbedding
 from .linear_scaling_rope import LinearScalingRotaryEmbedding
 from .llama3_rope import Llama3RotaryEmbedding
 from .llama4_vision_rope import Llama4VisionRotaryEmbedding
@@ -134,6 +135,17 @@ def get_rope(
                 is_neox_style,
                 dtype,
             )
+    elif scaling_type == "proportional":
+        # Proportional RoPE is used by Gemma4 for global (full) attention.
+        # Gemma4 uses a sparse/fractional RoPE with cross-mixing between halves.
+        rotary_emb = Gemma4RotaryEmbedding(
+            head_size,
+            rotary_dim,
+            max_position,
+            base,
+            is_neox_style,
+            dtype,
+        )
     elif scaling_type == "llama3":
         scaling_factor = rope_parameters["factor"]
         low_freq_factor = rope_parameters["low_freq_factor"]

vllm/model_executor/layers/rotary_embedding/gemma4_rope.py

@@ -0,0 +1,84 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Gemma4-specific Rotary Positional Embeddings (proportional scaling).
+
+Gemma4 uses "proportional" RoPE which computes inv_freq frequencies scaled
+by head_dim (not rotary_dim), and zero-pads for non-rotated dimensions when
+partial_rotary_factor < 1. The actual rotation uses standard neox-style
+rotate_half, matching HF transformers' apply_rotary_pos_emb.
+"""
+
+import torch
+
+from .base import RotaryEmbedding
+
+
+class Gemma4RotaryEmbedding(RotaryEmbedding):
+    """Gemma4 proportional RoPE.
+
+    Extends RotaryEmbedding (which provides standard neox-style rotation
+    via ops.rotary_embedding CUDA kernel) but overrides the inv_freq
+    computation to match HF's _compute_proportional_rope_parameters:
+    - Frequency exponents use head_dim (not rotary_dim) as denominator
+    - Non-rotated dims are zero-padded (cos=1, sin=0 = identity rotation)
+
+    When partial_rotary_factor=1.0 (the default for some variants), ALL dims are
+    rotated and this is equivalent to standard RotaryEmbedding with
+    head_dim-scaled frequencies.
+    """
+
+    def __init__(
+        self,
+        head_size: int,
+        rotary_dim: int,
+        max_position_embeddings: int,
+        base: float,
+        is_neox_style: bool,
+        dtype: torch.dtype,
+    ) -> None:
+        # Number of rotation angle pairs (from partial_rotary_factor)
+        self.rope_angles = rotary_dim // 2
+        # Non-rotated angle pairs per half
+        self.nope_angles = (head_size // 2) - self.rope_angles
+
+        # Important: set rotary_dim = head_size so the base class's
+        # forward_static applies rotation to ALL dims of the cos/sin cache.
+        # The non-rotated dims will have cos=1, sin=0 (identity) thanks
+        # to our _compute_inv_freq zero-padding.
+        super().__init__(
+            head_size,
+            head_size,  # rotary_dim = head_size (full application)
+            max_position_embeddings,
+            base,
+            is_neox_style,
+            dtype,
+        )
+
+    def _compute_inv_freq(self, base: float) -> torch.Tensor:
+        """Compute frequencies matching HF proportional RoPE.
+
+        Key difference from base: exponent denominator is head_size (not
+        rotary_dim), and non-rotated dims are zero-padded.
+        """
+        # HF formula: base ** (arange(0, 2*rope_angles, 2) / head_dim)
+        freq_exponents = (
+            torch.arange(0, 2 * self.rope_angles, 2, dtype=torch.float) / self.head_size
+        )
+        inv_freq = 1.0 / (base**freq_exponents)
+
+        # Zero-pad for non-rotated dims (identity rotation: cos=1, sin=0)
+        if self.nope_angles > 0:
+            inv_freq = torch.cat(
+                [
+                    inv_freq,
+                    torch.zeros(self.nope_angles, dtype=torch.float),
+                ]
+            )
+        return inv_freq
+
+    def extra_repr(self) -> str:
+        s = f"head_size={self.head_size}, rotary_dim={self.rotary_dim}"
+        s += f", rope_angles={self.rope_angles}, nope_angles={self.nope_angles}"
+        s += f", max_position_embeddings={self.max_position_embeddings}"
+        s += f", base={self.base}, is_neox_style={self.is_neox_style}"
+        return s

vllm/model_executor/models/config.py

@@ -14,6 +14,7 @@ from vllm.v1.kv_cache_interface import FullAttentionSpec, MambaSpec, MLAAttentio
 if TYPE_CHECKING:
     from vllm.config import ModelConfig, VllmConfig
 
+
 logger = init_logger(__name__)
 
 
@@ -57,6 +58,58 @@ class Gemma3TextModelConfig(VerifyAndUpdateConfig):
         hf_config.is_causal = not hf_config.use_bidirectional_attention
 
 
+class Gemma4Config(VerifyAndUpdateConfig):
+    @staticmethod
+    def verify_and_update_config(vllm_config: "VllmConfig") -> None:
+        """Force unified attention backend for models with heterogeneous
+        head dimensions.
+
+        Some Gemma4 variants use different head dimensions for
+        sliding window (head_dim) vs full attention (global_head_dim) layers.
+        When global_head_dim > 256, FlashAttention rejects those layers
+        (head_size <= 256 kernel limit), causing vLLM to select a different
+        backend for each layer type. This mixed-backend execution produces
+        numerical divergence and output corruption.
+
+        The fix detects heterogeneous head dimensions from the model config
+        and forces TRITON_ATTN (which has no head_size ceiling) for all
+        layers when the user hasn't explicitly chosen a backend.
+
+        TODO: Heterogeneous head_sizes (head_dim != global_head_dim)
+        require NixlConnector changes to support per-layer KV transfer
+        with different head dimensions for prefill-decode disaggregation.
+        """
+        hf_text_config = vllm_config.model_config.hf_text_config
+        head_dim = getattr(hf_text_config, "head_dim", None)
+        global_head_dim = getattr(hf_text_config, "global_head_dim", None)
+
+        # Only force Triton when head dimensions actually differ AND the
+        # larger one exceeds FlashAttention's kernel limit (head_size <= 256).
+        # This avoids unnecessary backend forcing on smaller models where
+        # the config carries global_head_dim but all layers can still use
+        # the same FA backend.
+        max_head_dim = max(head_dim or 0, global_head_dim or 0)
+        if (
+            head_dim is not None
+            and global_head_dim is not None
+            and head_dim != global_head_dim
+            and max_head_dim > 256
+            and vllm_config.attention_config.backend is None
+        ):
+            from vllm.v1.attention.backends.registry import (
+                AttentionBackendEnum,
+            )
+
+            vllm_config.attention_config.backend = AttentionBackendEnum.TRITON_ATTN
+            logger.info(
+                "Gemma4 model has heterogeneous head dimensions "
+                "(head_dim=%d, global_head_dim=%d). Forcing TRITON_ATTN "
+                "backend to prevent mixed-backend numerical divergence.",
+                head_dim,
+                global_head_dim,
+            )
+
+
 class GptOssForCausalLMConfig(VerifyAndUpdateConfig):
     @staticmethod
     def verify_and_update_config(vllm_config: "VllmConfig") -> None:
@@ -668,6 +721,8 @@ MODELS_CONFIG_MAP: dict[str, type[VerifyAndUpdateConfig]] = {
     "Ernie4_5_VLMoeForConditionalGeneration": Ernie4_5_VLMoeForConditionalGenerationConfig,  # noqa: E501
     "FalconMambaForCausalLM": MambaModelConfig,
     "Gemma3TextModel": Gemma3TextModelConfig,
+    "Gemma4ForCausalLM": Gemma4Config,
+    "Gemma4ForConditionalGeneration": Gemma4Config,
     "GptOssForCausalLM": GptOssForCausalLMConfig,
     "GteModel": SnowflakeGteNewModelConfig,
     "GteNewForSequenceClassification": GteNewModelConfig,

vllm/model_executor/models/gemma4_utils.py

@@ -0,0 +1,292 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# Copyright 2025 Google Inc. HuggingFace Inc. team. All rights reserved.
+
+"""Gemma4 output parsing utilities for offline inference.
+
+Standalone functions that parse decoded model text to extract structured
+thinking content and tool calls from Gemma4 models. These are pure-Python
+utilities with zero heavy dependencies — they work on raw decoded strings
+from any inference backend (vLLM, HuggingFace, TGI, etc.).
+
+Usage with vLLM offline inference::
+
+    from vllm import LLM, SamplingParams
+    from vllm.model_executor.models.gemma4_utils import (
+        parse_output,
+        parse_tool_calls,
+    )
+
+    llm = LLM(model="google/gemma-4-it")
+    outputs = llm.generate(prompt, SamplingParams(...))
+    text = tokenizer.decode(outputs[0].outputs[0].token_ids, skip_special_tokens=False)
+
+    # Extract thinking / answer (works with or without enable_thinking)
+    result = parse_output(text)
+    print(result["thinking"])  # chain-of-thought or None
+    print(result["answer"])  # final answer
+
+    # Extract tool calls
+    tool_calls = parse_tool_calls(text)
+    for tc in tool_calls:
+        print(f"{tc['name']}({tc['arguments']})")
+
+Ported from ``transformers.models.gemma4.utils_gemma4`` so that vLLM users
+do not need a transformers dependency for output parsing.
+"""
+
+import json
+
+import regex as re
+
+# ---- Thinking Mode Utility ----
+
+# Thinking delimiter tokens as they appear in decoded text.
+# Gemma4 uses <|channel> (start) and <channel|> (end) as thinking delimiters.
+_THINKING_START_TAG = "<|channel>"
+_THINKING_END_TAG = "<channel|>"
+
+# Sentinel tokens that may appear in decoded output.
+_TURN_END_TAG = "<turn|>"
+
+
+def parse_thinking_output(text: str) -> dict[str, str | None]:
+    """Parse decoded Gemma4 model output.
+
+    Use this on **all** Gemma4 output regardless of whether thinking mode
+    was enabled.  It handles three cases:
+
+    1. **Thinking enabled, tags present** — splits on ``<|channel>``/
+       ``<channel|>`` to separate chain-of-thought from the answer and
+       strips the ``thought\\n`` role label.
+    2. **Thinking disabled, spurious label** — strips the bare
+       ``thought\\n`` prefix that some Gemma4 models emit even
+       without thinking mode.
+    3. **Clean output** — returns the text unchanged.
+
+    The answer text is always cleaned of trailing sentinel tokens
+    (``<turn|>``, ``<eos>``, etc.).
+
+    Args:
+        text: Decoded model output text (from ``tokenizer.decode(...)``).
+
+    Returns:
+        A dict with keys:
+            - ``"thinking"``: The chain-of-thought text, or ``None`` if no
+              thinking delimiters were found.
+            - ``"answer"``: The final answer text.
+
+    Example::
+
+        >>> from vllm.model_executor.models.gemma4_utils import parse_thinking_output
+        >>> output_text = tokenizer.decode(outputs[0], skip_special_tokens=False)
+        >>> result = parse_thinking_output(output_text)
+        >>> print(result["thinking"])  # chain-of-thought reasoning or None
+        >>> print(result["answer"])    # final answer
+    """
+    if _THINKING_END_TAG in text:
+        parts = text.split(_THINKING_END_TAG, 1)
+        thinking_block = parts[0]
+        answer = _clean_answer(parts[1])
+
+        # Extract thinking content: strip the start tag if present
+        if _THINKING_START_TAG in thinking_block:
+            thinking = thinking_block.split(_THINKING_START_TAG, 1)[1]
+        else:
+            thinking = thinking_block
+
+        # Strip the "thought\n" channel role label the model emits inside
+        # <|channel>thought\n...<channel|> (analogous to "user\n" in
+        # <|turn>user\n...<turn|>).
+        thinking = _strip_thought_label(thinking.strip())
+        thinking = thinking.strip()
+
+        return {"thinking": thinking, "answer": answer}
+
+    # No thinking delimiters found.
+    # Strip spurious "thought\n" role label that some Gemma4 models sometimes
+    # emit even without thinking mode enabled, then clean trailing tokens.
+    answer = _strip_thought_label(text)
+    answer = _clean_answer(answer)
+    return {"thinking": None, "answer": answer}
+
+
+def _strip_thought_label(text: str) -> str:
+    """Strip the spurious ``thought\\n`` label from the start of text.
+
+    Only strips when ``thought`` appears as the very first word followed by
+    a newline — preserving the word ``thought`` in any other context.
+    """
+    if text.startswith("thought\n"):
+        return text[len("thought\n") :]
+    return text
+
+
+def _clean_answer(text: str) -> str:
+    """Clean trailing sentinel tokens from the answer text.
+
+    Strips ``<turn|>``, ``<eos>``, and surrounding whitespace that the
+    model appends at the end of its response.
+    """
+    text = text.strip()
+    # Strip trailing <turn|> (Gemma4 turn-end marker)
+    if text.endswith(_TURN_END_TAG):
+        text = text[: -len(_TURN_END_TAG)].rstrip()
+    # Strip trailing <eos> if present
+    if text.endswith("<eos>"):
+        text = text[:-5].rstrip()
+    return text
+
+
+# ---- Tool Call Parsing Utility ----
+#
+# NOTE: For the OpenAI-compatible API server tool parser (streaming +
+# non-streaming), see vllm/tool_parsers/gemma4_tool_parser.py.
+# This module provides offline inference utilities for direct user import.
+
+# Tool call delimiter tokens as they appear in decoded text.
+# Standard format: <|tool_call>call:name{args}<tool_call|>
+_TOOL_CALL_START_TAG = "<|tool_call>"
+_TOOL_CALL_END_TAG = "<tool_call|>"
+_TOOL_RESPONSE_START_TAG = "<|tool_response>"
+
+# Gemma4 escape token as it appears in decoded text.
+_ESCAPE_TOKEN = '<|"|>'
+
+
+def _parse_tool_arguments(args_str: str) -> dict[str, str]:
+    """Parse tool call arguments from the Gemma4 compact format.
+
+    Handles the ``key:<|"|>value<|"|>`` format used by Gemma4, with fallback
+    to heuristic key-value extraction. Also tolerates the slightly different
+    ``key: "value"`` format (space + plain quotes) that some chat templates
+    produce.
+
+    Args:
+        args_str: Raw argument string from inside ``call:name{...}``.
+
+    Returns:
+        Dictionary of argument name → value.
+    """
+    if not args_str or not args_str.strip():
+        return {}
+
+    # Replace Gemma4 escape tokens with standard quotes.
+    cleaned = args_str.replace(_ESCAPE_TOKEN, '"')
+
+    # Try JSON parsing first (handles nested values, arrays, etc.).
+    try:
+        parsed = json.loads("{" + cleaned + "}")
+        # Ensure all values are strings for consistency.
+        return {k: str(v) if not isinstance(v, str) else v for k, v in parsed.items()}
+    except (json.JSONDecodeError, ValueError):
+        pass
+
+    # Fallback: extract key:"value" pairs (allow optional space after colon).
+    arguments = {}
+    for key, value in re.findall(r'(\w+):\s*"([^"]*)"', cleaned):
+        arguments[key] = value
+
+    if not arguments:
+        # Last resort: extract key:value pairs (unquoted).
+        for key, value in re.findall(r"(\w+):\s*([^,}]+)", args_str):
+            arguments[key] = value.strip().strip('"').replace(_ESCAPE_TOKEN, "")
+
+    return arguments
+
+
+def parse_tool_calls(text: str, *, strict: bool = False) -> list[dict]:
+    """Parse tool calls from decoded Gemma4 model output.
+
+    Uses a tiered parsing strategy to handle known output variations in
+    Gemma4 models, which may emit
+    non-standard tool call formats.
+
+    Parsing tiers:
+        1. **Standard**: ``<|tool_call>call:name{args}<tool_call|>``
+           (special token IDs 48/49 in decoded text)
+        2. **Fallback** (when ``strict=False``): bare ``call:name{args}``
+           patterns, including ``<call>name{args}`` (fragmented tokens from
+           multimodal inputs)
+
+    Args:
+        text: Decoded model output text (from ``tokenizer.decode(...,
+            skip_special_tokens=False)``).
+        strict: If ``True``, only match the standard ``<|tool_call>`` format.
+            If ``False`` (default), also try fallback patterns for
+            known Gemma4 output variations.
+
+    Returns:
+        A list of dicts, each with keys:
+            - ``"name"``: The tool function name (e.g. ``"get_weather"``).
+            - ``"arguments"``: A dict of argument name → value.
+
+    Example::
+
+        >>> from vllm.model_executor.models.gemma4_utils import (
+        ...     parse_tool_calls
+        ... )
+        >>> output = tokenizer.decode(outputs[0], skip_special_tokens=False)
+        >>> tool_calls = parse_tool_calls(output)
+        >>> for tc in tool_calls:
+        ...     print(f"Call: {tc['name']}({tc['arguments']})")
+    """
+    results = []
+
+    # Tier 1: Standard format with special tokens.
+    # <|tool_call>call:name{args}<tool_call|>
+    # Note: Some Gemma4 models emit <turn|> instead of <tool_call|>.
+    standard_pattern = r"<\|tool_call\>call:(\w+)\{(.*?)\}(?:<tool_call\|>|<turn\|>)"
+    for match in re.finditer(standard_pattern, text, re.DOTALL):
+        name, args_str = match.group(1), match.group(2)
+        results.append(
+            {
+                "name": name,
+                "arguments": _parse_tool_arguments(args_str),
+            }
+        )
+
+    if results or strict:
+        return results
+
+    # Tier 2: Fallback for known Gemma4 output variations.
+    # Matches: <call>name{args}, call:name{args}, or bare call:name{args}<eos>
+    fallback_pattern = r"(?:<call>|(?:^|\s)call:)(\w+)\{(.*?)\}"
+    for match in re.finditer(fallback_pattern, text, re.DOTALL):
+        name, args_str = match.group(1), match.group(2)
+        results.append(
+            {
+                "name": name,
+                "arguments": _parse_tool_arguments(args_str),
+            }
+        )
+
+    return results
+
+
+def has_tool_response_tag(text: str) -> bool:
+    """Check if model output properly ends with a tool response tag.
+
+    Some Gemma4 models sometimes emit ``<eos>`` instead of
+    ``<|tool_response>`` after a tool call. This helper detects
+    whether the model used the proper termination, so callers can
+    decide whether to inject ``<|tool_response>`` into the next prompt.
+
+    Args:
+        text: Decoded model output text.
+
+    Returns:
+        ``True`` if the output ends with ``<|tool_response>``
+        (proper behavior), ``False`` otherwise.
+
+    Example::
+
+        >>> from vllm.model_executor.models.gemma4_utils import (
+        ...     has_tool_response_tag
+        ... )
+        >>> if not has_tool_response_tag(model_output):
+        ...     # Model used <eos> instead — inject <|tool_response> manually
+        ...     next_prompt = "<|tool_response>" + tool_result
+    """
+    stripped = text.rstrip()
+    return stripped.endswith(_TOOL_RESPONSE_START_TAG)

vllm/model_executor/models/registry.py

@@ -111,6 +111,7 @@ _TEXT_GENERATION_MODELS = {
     "Gemma2ForCausalLM": ("gemma2", "Gemma2ForCausalLM"),
     "Gemma3ForCausalLM": ("gemma3", "Gemma3ForCausalLM"),
     "Gemma3nForCausalLM": ("gemma3n", "Gemma3nForCausalLM"),
+    "Gemma4ForCausalLM": ("gemma4", "Gemma4ForCausalLM"),
     "Qwen3NextForCausalLM": ("qwen3_next", "Qwen3NextForCausalLM"),
     "GlmForCausalLM": ("glm", "GlmForCausalLM"),
     "Glm4ForCausalLM": ("glm4", "Glm4ForCausalLM"),
@@ -381,6 +382,7 @@ _MULTIMODAL_MODELS = {
         "gemma3n_mm",
         "Gemma3nForConditionalGeneration",
     ),
+    "Gemma4ForConditionalGeneration": ("gemma4_mm", "Gemma4ForConditionalGeneration"),
     "GlmAsrForConditionalGeneration": ("glmasr", "GlmAsrForConditionalGeneration"),
     "GLM4VForCausalLM": ("glm4v", "GLM4VForCausalLM"),
     "Glm4vForConditionalGeneration": ("glm4_1v", "Glm4vForConditionalGeneration"),

vllm/model_executor/models/utils.py

@@ -233,8 +233,15 @@ class AutoWeightsLoader:
     ):
         """
         Add tensor names that are not in the model params that may be in the
-        safetensors, e.g., batch normalization stats.
+        safetensors, e.g., batch normalization stats and registered buffers.
         """
+        # Add persistent registered buffers.
+        # Non-persistent buffers are excluded, matching PyTorch state_dict().
+        non_persistent = getattr(module, "_non_persistent_buffers_set", set())
+        for buf_name, buf in module.named_buffers(recurse=False):
+            if buf_name not in child_params and buf_name not in non_persistent:
+                child_params[buf_name] = buf
+
         if isinstance(
             module,
             (

vllm/reasoning/__init__.py

@@ -32,6 +32,10 @@ _REASONING_PARSERS_TO_REGISTER = {
         "ernie45_reasoning_parser",
         "Ernie45ReasoningParser",
     ),
+    "gemma4": (
+        "gemma4_reasoning_parser",
+        "Gemma4ReasoningParser",
+    ),
     "glm45": (
         "deepseek_v3_reasoning_parser",
         "DeepSeekV3ReasoningWithThinkingParser",

vllm/reasoning/gemma4_reasoning_parser.py

@@ -0,0 +1,193 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from collections.abc import Sequence
+from typing import TYPE_CHECKING
+
+from vllm.entrypoints.openai.engine.protocol import DeltaMessage
+from vllm.reasoning.basic_parsers import BaseThinkingReasoningParser
+from vllm.tokenizers import TokenizerLike
+
+if TYPE_CHECKING:
+    from vllm.entrypoints.openai.chat_completion.protocol import (
+        ChatCompletionRequest,
+    )
+    from vllm.entrypoints.openai.responses.protocol import ResponsesRequest
+
+# Role label that Gemma4 emits at the start of the thinking channel.
+# The model generates: <|channel>thought\n...reasoning...<channel|>
+# This prefix must be stripped to expose only the actual reasoning content.
+_THOUGHT_PREFIX = "thought\n"
+
+
+class Gemma4ReasoningParser(BaseThinkingReasoningParser):
+    """
+    Reasoning parser for Google Gemma4 thinking models.
+
+    Gemma4 uses <|channel>...<channel|> tokens to delimit reasoning/thinking
+    content within its output. Thinking mode is activated by passing
+    ``enable_thinking=True`` in the chat template kwargs, which injects a
+    system turn containing <|think|> (token 98) to trigger chain-of-thought
+    reasoning.
+
+    Output pattern when thinking is enabled::
+
+        <|channel>thought
+        ...chain of thought reasoning...<channel|>
+        Final answer text here.
+
+    The ``thought\\n`` role label inside the channel delimiters is a
+    structural artefact (analogous to ``user\\n`` in ``<|turn>user\\n...``).
+    This parser strips it so that downstream consumers see only the
+    actual reasoning text, consistent with the offline parser
+    (``vllm.reasoning.gemma4_utils._strip_thought_label``).
+    """
+
+    def __init__(self, tokenizer: TokenizerLike, *args, **kwargs):
+        super().__init__(tokenizer, *args, **kwargs)
+        # Instance state for streaming prefix stripping.
+        # Tracks only the reasoning text received from the base parser,
+        # independent of current_text (which may contain pre-reasoning
+        # content and lacks special token text due to
+        # skip_special_tokens=True).
+        self._reasoning_text: str = ""
+        self._prefix_stripped: bool = False
+
+    @property
+    def start_token(self) -> str:
+        """The token that starts reasoning content."""
+        return "<|channel>"
+
+    @property
+    def end_token(self) -> str:
+        """The token that ends reasoning content."""
+        return "<channel|>"
+
+    # ------------------------------------------------------------------
+    # Non-streaming path
+    # ------------------------------------------------------------------
+
+    def extract_reasoning(
+        self,
+        model_output: str,
+        request: "ChatCompletionRequest | ResponsesRequest",
+    ) -> tuple[str | None, str | None]:
+        """Extract reasoning, stripping the ``thought\\n`` role label."""
+        if self.start_token not in model_output and self.end_token not in model_output:
+            # Default to content history if no tags are present
+            # (or if they were stripped)
+            return None, model_output
+
+        reasoning, content = super().extract_reasoning(model_output, request)
+        if reasoning is not None:
+            reasoning = _strip_thought_label(reasoning)
+        return reasoning, content
+
+    # ------------------------------------------------------------------
+    # Streaming path
+    # ------------------------------------------------------------------
+
+    def extract_reasoning_streaming(
+        self,
+        previous_text: str,
+        current_text: str,
+        delta_text: str,
+        previous_token_ids: Sequence[int],
+        current_token_ids: Sequence[int],
+        delta_token_ids: Sequence[int],
+    ) -> DeltaMessage | None:
+        """Extract streaming reasoning, stripping ``thought\\n`` from the
+        first reasoning delta(s).
+
+        The ``thought\\n`` prefix may arrive as a single delta or split
+        across multiple deltas (e.g. ``"thought"`` then ``"\\n"``). We
+        buffer early reasoning tokens until we can determine whether the
+        prefix is present, then emit the buffered content minus the
+        prefix.
+
+        Unlike the previous implementation which reconstructed accumulated
+        reasoning from ``current_text``, this uses instance state
+        (``_reasoning_text``) to track only the reasoning content returned
+        by the base parser. This is necessary because
+        ``skip_special_tokens=True`` (the vLLM default) causes the
+        ``<|channel>`` delimiter to be invisible in ``current_text``,
+        making it impossible to separate pre-reasoning content from
+        reasoning content via string matching.
+        """
+        result = super().extract_reasoning_streaming(
+            previous_text,
+            current_text,
+            delta_text,
+            previous_token_ids,
+            current_token_ids,
+            delta_token_ids,
+        )
+        if result is None:
+            return None
+
+        if result.reasoning is None:
+            return result
+
+        # Accumulate ONLY the reasoning text from base parser results.
+        # This is immune to pre-reasoning content pollution.
+        self._reasoning_text += result.reasoning
+
+        # Once the prefix has been handled, all subsequent reasoning
+        # deltas pass through unchanged.
+        if self._prefix_stripped:
+            return result
+
+        # ---- Prefix stripping logic ----
+
+        # Case 1: We've accumulated enough to confirm the prefix is
+        # present. Strip it and pass through the remainder.
+        if self._reasoning_text.startswith(_THOUGHT_PREFIX):
+            prefix_len = len(_THOUGHT_PREFIX)
+            # How much reasoning was accumulated before this delta?
+            prev_reasoning_len = len(self._reasoning_text) - len(result.reasoning)
+            if prev_reasoning_len >= prefix_len:
+                # Prefix was already consumed by prior deltas; this
+                # delta is entirely real content — pass through.
+                self._prefix_stripped = True
+                return result
+            else:
+                # Part or all of the prefix is in this delta.
+                chars_of_prefix_in_delta = prefix_len - prev_reasoning_len
+                stripped = result.reasoning[chars_of_prefix_in_delta:]
+                if stripped:
+                    self._prefix_stripped = True
+                    result.reasoning = stripped
+                    return result
+                else:
+                    # This entire delta was prefix — suppress it.
+                    # Don't set _prefix_stripped yet; there may be more
+                    # prefix chars to consume in the next delta.
+                    if len(self._reasoning_text) >= prefix_len:
+                        self._prefix_stripped = True
+                    return None
+
+        # Case 2: Accumulated text is a strict prefix of
+        # _THOUGHT_PREFIX (e.g. we've only seen "thou" so far).
+        # Buffer by suppressing — we can't yet tell if this will
+        # become the full prefix or diverge.
+        if _THOUGHT_PREFIX.startswith(self._reasoning_text):
+            return None
+
+        # Case 3: Accumulated text doesn't match the thought prefix
+        # at all. This means prior deltas were buffered (suppressed
+        # by Case 2) but the text diverged. Re-emit the full
+        # accumulated text to avoid data loss.
+        self._prefix_stripped = True
+        result.reasoning = self._reasoning_text
+        return result
+
+
+def _strip_thought_label(text: str) -> str:
+    """Remove the ``thought\\n`` role label from the beginning of text.
+
+    Mirrors ``vllm.reasoning.gemma4_utils._strip_thought_label`` from the
+    offline parser.
+    """
+    if text.startswith(_THOUGHT_PREFIX):
+        return text[len(_THOUGHT_PREFIX) :]
+    return text

vllm/reasoning/gemma4_utils.py

@@ -0,0 +1,130 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# Copyright 2025 Google Inc. HuggingFace Inc. team. All rights reserved.
+
+"""Gemma4 thinking/reasoning output parsing utilities for offline inference.
+
+Standalone functions that parse decoded model text to extract structured
+thinking content from Gemma4 models. These are pure-Python utilities with
+zero heavy dependencies — they work on raw decoded strings from any
+inference backend (vLLM, HuggingFace, TGI, etc.).
+
+For the OpenAI-compatible API reasoning parser (streaming +
+non-streaming), see ``vllm.reasoning.gemma4_reasoning_parser``.
+For tool call parsing, see ``vllm.tool_parsers.gemma4_utils``.
+
+Usage with vLLM offline inference::
+
+    from vllm import LLM, SamplingParams
+    from vllm.reasoning.gemma4_utils import parse_thinking_output
+
+    llm = LLM(model="google/gemma-4-it")
+    outputs = llm.generate(prompt, SamplingParams(...))
+    text = tokenizer.decode(outputs[0].outputs[0].token_ids, skip_special_tokens=False)
+
+    # Extract thinking / answer (works with or without enable_thinking)
+    result = parse_thinking_output(text)
+    print(result["thinking"])  # chain-of-thought or None
+    print(result["answer"])  # final answer
+
+Ported from ``transformers.models.gemma4.utils_gemma4`` so that vLLM users
+do not need a transformers dependency for output parsing.
+"""
+
+# ---- Thinking Mode Utility ----
+
+# Thinking delimiter tokens as they appear in decoded text.
+# Gemma4 uses <|channel> (start) and <channel|> (end) as thinking delimiters.
+_THINKING_START_TAG = "<|channel>"
+_THINKING_END_TAG = "<channel|>"
+
+# Sentinel tokens that may appear in decoded output.
+_TURN_END_TAG = "<turn|>"
+
+
+def parse_thinking_output(text: str) -> dict[str, str | None]:
+    """Parse decoded Gemma4 model output.
+
+    Use this on **all** Gemma4 output regardless of whether thinking mode
+    was enabled.  It handles three cases:
+
+    1. **Thinking enabled, tags present** — splits on ``<|channel>``/
+       ``<channel|>`` to separate chain-of-thought from the answer and
+       strips the ``thought\\n`` role label.
+    2. **Thinking disabled, spurious label** — strips the bare
+       ``thought\\n`` prefix that some Gemma4 models emit even
+       without thinking mode.
+    3. **Clean output** — returns the text unchanged.
+
+    The answer text is always cleaned of trailing sentinel tokens
+    (``<turn|>``, ``<eos>``, etc.).
+
+    Args:
+        text: Decoded model output text (from ``tokenizer.decode(...)``).
+
+    Returns:
+        A dict with keys:
+            - ``"thinking"``: The chain-of-thought text, or ``None`` if no
+              thinking delimiters were found.
+            - ``"answer"``: The final answer text.
+
+    Example::
+
+        >>> from vllm.reasoning.gemma4_utils import parse_thinking_output
+        >>> output_text = tokenizer.decode(outputs[0], skip_special_tokens=False)
+        >>> result = parse_thinking_output(output_text)
+        >>> print(result["thinking"])  # chain-of-thought reasoning or None
+        >>> print(result["answer"])    # final answer
+    """
+    if _THINKING_END_TAG in text:
+        parts = text.split(_THINKING_END_TAG, 1)
+        thinking_block = parts[0]
+        answer = _clean_answer(parts[1])
+
+        # Extract thinking content: strip the start tag if present
+        if _THINKING_START_TAG in thinking_block:
+            thinking = thinking_block.split(_THINKING_START_TAG, 1)[1]
+        else:
+            thinking = thinking_block
+
+        # Strip the "thought\n" channel role label the model emits inside
+        # <|channel>thought\n...<channel|> (analogous to "user\n" in
+        # <|turn>user\n...<turn|>).
+        thinking = _strip_thought_label(thinking.strip())
+        thinking = thinking.strip()
+
+        return {"thinking": thinking, "answer": answer}
+
+    # No thinking delimiters found.
+    # Strip spurious "thought\n" role label that some Gemma4 models sometimes
+    # emit even without thinking mode enabled, then clean trailing tokens.
+    answer = _strip_thought_label(text)
+    answer = _clean_answer(answer)
+    return {"thinking": None, "answer": answer}
+
+
+def _strip_thought_label(text: str) -> str:
+    """Strip the spurious ``thought\\n`` label from the start of text.
+
+    Only strips when ``thought`` appears as the very first word followed by
+    a newline — preserving the word ``thought`` in any other context.
+    """
+    if text.startswith("thought\n"):
+        return text[len("thought\n") :]
+    return text
+
+
+def _clean_answer(text: str) -> str:
+    """Clean trailing sentinel tokens from the answer text.
+
+    Strips ``<turn|>``, ``<eos>``, and surrounding whitespace that the
+    model appends at the end of its response.
+    """
+    text = text.strip()
+    # Strip trailing <turn|> (Gemma4 turn-end marker)
+    if text.endswith(_TURN_END_TAG):
+        text = text[: -len(_TURN_END_TAG)].rstrip()
+    # Strip trailing <eos> if present
+    if text.endswith("<eos>"):
+        text = text[:-5].rstrip()
+    return text

vllm/tool_parsers/__init__.py

@@ -154,6 +154,10 @@ _TOOL_PARSERS_TO_REGISTER = {
         "functiongemma_tool_parser",
         "FunctionGemmaToolParser",
     ),
+    "gemma4": (
+        "gemma4_tool_parser",
+        "Gemma4ToolParser",
+    ),
 }
 
 

vllm/tool_parsers/gemma4_tool_parser.py

@@ -0,0 +1,724 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""
+Tool call parser for Google Gemma4 models.
+
+Gemma4 uses a custom serialization format (not JSON) for tool calls::
+
+    <|tool_call>call:func_name{key:<|"|>value<|"|>,num:42}<tool_call|>
+
+Strings are delimited by ``<|"|>`` (token 52), keys are unquoted, and
+multiple tool calls are concatenated without separators.
+
+Used when ``--enable-auto-tool-choice --tool-call-parser gemma4`` are set.
+
+For offline inference tool call parsing (direct ``tokenizer.decode()`` output),
+see ``vllm.tool_parsers.gemma4_utils.parse_tool_calls``.
+"""
+
+import json
+from collections.abc import Sequence
+
+import regex as re
+
+from vllm.entrypoints.chat_utils import make_tool_call_id
+from vllm.entrypoints.openai.chat_completion.protocol import (
+    ChatCompletionRequest,
+)
+from vllm.entrypoints.openai.engine.protocol import (
+    DeltaFunctionCall,
+    DeltaMessage,
+    DeltaToolCall,
+    ExtractedToolCallInformation,
+    FunctionCall,
+    ToolCall,
+)
+from vllm.entrypoints.openai.responses.protocol import (
+    ResponsesRequest,
+)
+from vllm.logger import init_logger
+from vllm.tokenizers import TokenizerLike
+from vllm.tool_parsers.abstract_tool_parser import ToolParser
+from vllm.tool_parsers.utils import find_common_prefix
+
+logger = init_logger(__name__)
+
+# Gemma4 special tokens for tool calls
+TOOL_CALL_START = "<|tool_call>"
+TOOL_CALL_END = "<tool_call|>"
+STRING_DELIM = '<|"|>'
+
+
+# ---------------------------------------------------------------------------
+# Gemma4 argument parser (used by both streaming and non-streaming paths)
+# ---------------------------------------------------------------------------
+
+
+def _parse_gemma4_value(value_str: str) -> object:
+    """Parse a single Gemma4 value (after key:) into a Python object."""
+    value_str = value_str.strip()
+    if not value_str:
+        return value_str
+
+    # Boolean
+    if value_str == "true":
+        return True
+    if value_str == "false":
+        return False
+
+    # Number (int or float)
+    try:
+        if "." in value_str:
+            return float(value_str)
+        return int(value_str)
+    except ValueError:
+        pass
+
+    # Bare string (no <|"|> delimiters — shouldn't happen but be safe)
+    return value_str
+
+
+def _parse_gemma4_args(args_str: str) -> dict:
+    """Parse Gemma4's custom key:value format into a Python dict.
+
+    Format examples::
+
+        location:<|"|>Tokyo<|"|>
+        location:<|"|>San Francisco<|"|>,unit:<|"|>celsius<|"|>
+        count:42,flag:true
+        nested:{inner_key:<|"|>val<|"|>}
+        items:[<|"|>a<|"|>,<|"|>b<|"|>]
+
+    Returns a dict ready for ``json.dumps()``.
+    """
+    if not args_str or not args_str.strip():
+        return {}
+
+    result: dict = {}
+    i = 0
+    n = len(args_str)
+
+    while i < n:
+        # Skip whitespace and commas
+        while i < n and args_str[i] in (" ", ",", "\n", "\t"):
+            i += 1
+        if i >= n:
+            break
+
+        # Parse key (unquoted, ends at ':')
+        key_start = i
+        while i < n and args_str[i] != ":":
+            i += 1
+        if i >= n:
+            break
+        key = args_str[key_start:i].strip()
+        i += 1  # skip ':'
+
+        # Parse value
+        if i >= n:
+            result[key] = ""
+            break
+
+        # Skip whitespace after ':'
+        while i < n and args_str[i] in (" ", "\n", "\t"):
+            i += 1
+        if i >= n:
+            result[key] = ""
+            break
+
+        # String value: <|"|>...<|"|>
+        if args_str[i:].startswith(STRING_DELIM):
+            i += len(STRING_DELIM)
+            val_start = i
+            end_pos = args_str.find(STRING_DELIM, i)
+            if end_pos == -1:
+                # Unterminated string — take rest
+                result[key] = args_str[val_start:]
+                break
+            result[key] = args_str[val_start:end_pos]
+            i = end_pos + len(STRING_DELIM)
+
+        # Nested object: {...}
+        elif args_str[i] == "{":
+            depth = 1
+            obj_start = i + 1
+            i += 1
+            while i < n and depth > 0:
+                if args_str[i:].startswith(STRING_DELIM):
+                    # Skip over string contents to avoid counting { inside strings
+                    i += len(STRING_DELIM)
+                    next_delim = args_str.find(STRING_DELIM, i)
+                    i = n if next_delim == -1 else next_delim + len(STRING_DELIM)
+                    continue
+                if args_str[i] == "{":
+                    depth += 1
+                elif args_str[i] == "}":
+                    depth -= 1
+                i += 1
+            result[key] = _parse_gemma4_args(args_str[obj_start : i - 1])
+
+        # Array: [...]
+        elif args_str[i] == "[":
+            depth = 1
+            arr_start = i + 1
+            i += 1
+            while i < n and depth > 0:
+                if args_str[i:].startswith(STRING_DELIM):
+                    i += len(STRING_DELIM)
+                    next_delim = args_str.find(STRING_DELIM, i)
+                    i = n if next_delim == -1 else next_delim + len(STRING_DELIM)
+                    continue
+                if args_str[i] == "[":
+                    depth += 1
+                elif args_str[i] == "]":
+                    depth -= 1
+                i += 1
+            arr_content = args_str[arr_start : i - 1]
+            result[key] = _parse_gemma4_array(arr_content)
+
+        # Bare value (number, boolean, etc.)
+        else:
+            val_start = i
+            while i < n and args_str[i] not in (",", "}", "]"):
+                i += 1
+            result[key] = _parse_gemma4_value(args_str[val_start:i])
+
+    return result
+
+
+def _parse_gemma4_array(arr_str: str) -> list:
+    """Parse a Gemma4 array content string into a Python list."""
+    items: list = []
+    i = 0
+    n = len(arr_str)
+
+    while i < n:
+        while i < n and arr_str[i] in (" ", ",", "\n", "\t"):
+            i += 1
+        if i >= n:
+            break
+
+        # String element
+        if arr_str[i:].startswith(STRING_DELIM):
+            i += len(STRING_DELIM)
+            end_pos = arr_str.find(STRING_DELIM, i)
+            if end_pos == -1:
+                items.append(arr_str[i:])
+                break
+            items.append(arr_str[i:end_pos])
+            i = end_pos + len(STRING_DELIM)
+
+        # Nested object
+        elif arr_str[i] == "{":
+            depth = 1
+            obj_start = i + 1
+            i += 1
+            while i < n and depth > 0:
+                if arr_str[i:].startswith(STRING_DELIM):
+                    i += len(STRING_DELIM)
+                    nd = arr_str.find(STRING_DELIM, i)
+                    i = nd + len(STRING_DELIM) if nd != -1 else n
+                    continue
+                if arr_str[i] == "{":
+                    depth += 1
+                elif arr_str[i] == "}":
+                    depth -= 1
+                i += 1
+            items.append(_parse_gemma4_args(arr_str[obj_start : i - 1]))
+
+        # Nested array
+        elif arr_str[i] == "[":
+            depth = 1
+            sub_start = i + 1
+            i += 1
+            while i < n and depth > 0:
+                if arr_str[i] == "[":
+                    depth += 1
+                elif arr_str[i] == "]":
+                    depth -= 1
+                i += 1
+            items.append(_parse_gemma4_array(arr_str[sub_start : i - 1]))
+
+        # Bare value
+        else:
+            val_start = i
+            while i < n and arr_str[i] not in (",", "]"):
+                i += 1
+            items.append(_parse_gemma4_value(arr_str[val_start:i]))
+
+    return items
+
+
+# ---------------------------------------------------------------------------
+# Parser
+# ---------------------------------------------------------------------------
+
+
+class Gemma4ToolParser(ToolParser):
+    """
+    Tool call parser for Google Gemma4 models.
+
+    Handles the Gemma4 function call format::
+
+        <|tool_call>call:func_name{key:<|"|>value<|"|>}<tool_call|>
+
+    Used when ``--enable-auto-tool-choice --tool-call-parser gemma4``
+    are set.
+
+    Streaming strategy: **accumulate-then-parse-then-diff**
+
+    Instead of trying to convert Gemma4's custom format to JSON
+    token-by-token (which fails because Gemma4 uses bare keys, custom
+    delimiters, and structural braces that differ from JSON), this parser:
+
+    1. Accumulates the raw Gemma4 argument string during streaming
+    2. Parses it with ``_parse_gemma4_args()`` into a Python dict
+    3. Converts to JSON with ``json.dumps()``
+    4. Diffs against the previously-streamed JSON string
+    5. Emits only the new JSON fragment as the delta
+
+    This follows the same pattern used by FunctionGemma, Hermes, and Llama
+    tool parsers.
+    """
+
+    def __init__(self, tokenizer: TokenizerLike):
+        super().__init__(tokenizer)
+
+        if not self.model_tokenizer:
+            raise ValueError(
+                "The model tokenizer must be passed to the ToolParser "
+                "constructor during construction."
+            )
+
+        # Token strings
+        self.tool_call_start_token = TOOL_CALL_START
+        self.tool_call_end_token = TOOL_CALL_END
+
+        # Token IDs
+        self.tool_call_start_token_id = self.vocab.get(TOOL_CALL_START)
+        self.tool_call_end_token_id = self.vocab.get(TOOL_CALL_END)
+
+        if self.tool_call_start_token_id is None:
+            raise RuntimeError(
+                "Gemma4 ToolParser could not locate the tool call start "
+                f"token '{TOOL_CALL_START}' in the tokenizer!"
+            )
+
+        # Regex for non-streaming: extract complete tool calls.
+        # Supports function names with letters, digits, underscores,
+        # hyphens, and dots (e.g. "get-weather", "module.func").
+        self.tool_call_regex = re.compile(
+            r"<\|tool_call>call:([\w\-\.]+)\{(.*?)\}<tool_call\|>",
+            re.DOTALL,
+        )
+
+        # Streaming state — reset per-request via _reset_streaming_state()
+        self._reset_streaming_state()
+
+        # Delta buffer for handling multi-token special sequences
+        self.buffered_delta_text = ""
+
+    def _reset_streaming_state(self) -> None:
+        """Reset all streaming state for a new request."""
+        self.current_tool_id = -1
+        self.current_tool_name_sent = False
+        self.prev_tool_call_arr: list[dict] = []
+        self.streamed_args_for_tool: list[str] = []
+
+    def adjust_request(
+        self, request: ChatCompletionRequest | ResponsesRequest
+    ) -> ChatCompletionRequest | ResponsesRequest:
+        request = super().adjust_request(request)
+        if (
+            isinstance(request, ChatCompletionRequest)
+            and request.tools
+            and request.tool_choice != "none"
+        ):
+            # Don't skip special tokens — <|tool_call> etc. are needed
+            request.skip_special_tokens = False
+        return request
+
+    # ------------------------------------------------------------------
+    # Delta buffering for multi-token special sequences
+    # ------------------------------------------------------------------
+
+    def _buffer_delta_text(self, delta_text: str) -> str:
+        """Buffer incoming delta text to handle multi-token special sequences.
+
+        Accumulates partial tokens that could be the start of
+        ``<|tool_call>`` or ``<tool_call|>`` and only flushes them
+        when the complete sequence is recognized or the sequence breaks.
+
+        This prevents partial special tokens (e.g., ``<|tool``) from being
+        emitted prematurely as content text.
+        """
+        combined = self.buffered_delta_text + delta_text
+
+        # Check if combined ends with a complete special token
+        if combined.endswith(TOOL_CALL_START) or combined.endswith(TOOL_CALL_END):
+            self.buffered_delta_text = ""
+            return combined
+
+        # Check if combined ends with a partial prefix of a special token
+        for tag in [TOOL_CALL_START, TOOL_CALL_END]:
+            for i in range(1, len(tag)):
+                if combined.endswith(tag[:i]):
+                    self.buffered_delta_text = combined[-i:]
+                    return combined[:-i]
+
+        # No partial match — flush everything
+        self.buffered_delta_text = ""
+        return combined
+
+    # ------------------------------------------------------------------
+    # Non-streaming extraction
+    # ------------------------------------------------------------------
+
+    def extract_tool_calls(
+        self,
+        model_output: str,
+        request: ChatCompletionRequest,
+    ) -> ExtractedToolCallInformation:
+        if self.tool_call_start_token not in model_output:
+            return ExtractedToolCallInformation(
+                tools_called=False, tool_calls=[], content=model_output
+            )
+
+        try:
+            matches = self.tool_call_regex.findall(model_output)
+            if not matches:
+                return ExtractedToolCallInformation(
+                    tools_called=False, tool_calls=[], content=model_output
+                )
+
+            tool_calls: list[ToolCall] = []
+            for func_name, args_str in matches:
+                arguments = _parse_gemma4_args(args_str)
+                tool_calls.append(
+                    ToolCall(
+                        type="function",
+                        function=FunctionCall(
+                            name=func_name,
+                            arguments=json.dumps(arguments, ensure_ascii=False),
+                        ),
+                    )
+                )
+
+            # Content = text before first tool call (if any)
+            content_end = model_output.find(self.tool_call_start_token)
+            content = model_output[:content_end].strip() if content_end > 0 else None
+
+            return ExtractedToolCallInformation(
+                tools_called=True,
+                tool_calls=tool_calls,
+                content=content if content else None,
+            )
+
+        except Exception:
+            logger.exception("Error extracting tool calls from Gemma4 response")
+            return ExtractedToolCallInformation(
+                tools_called=False, tool_calls=[], content=model_output
+            )
+
+    # ------------------------------------------------------------------
+    # Streaming extraction — accumulate-then-parse-then-diff
+    # ------------------------------------------------------------------
+
+    def extract_tool_calls_streaming(
+        self,
+        previous_text: str,
+        current_text: str,
+        delta_text: str,
+        previous_token_ids: Sequence[int],
+        current_token_ids: Sequence[int],
+        delta_token_ids: Sequence[int],
+        request: ChatCompletionRequest,
+    ) -> DeltaMessage | None:
+        # Buffer delta text to handle multi-token special sequences
+        delta_text = self._buffer_delta_text(delta_text)
+        # Reconstruct current_text after buffering to stay in sync
+        current_text = previous_text + delta_text
+
+        # If no tool call token seen yet, emit as content
+        if self.tool_call_start_token not in current_text:
+            if delta_text:
+                return DeltaMessage(content=delta_text)
+            return None
+
+        try:
+            return self._extract_streaming(
+                previous_text=previous_text,
+                current_text=current_text,
+                delta_text=delta_text,
+            )
+        except Exception:
+            logger.exception("Error in Gemma4 streaming tool call extraction")
+            return None
+
+    def _extract_streaming(
+        self,
+        previous_text: str,
+        current_text: str,
+        delta_text: str,
+    ) -> DeltaMessage | None:
+        """Tag-counting streaming parser.
+
+        Uses the proven approach from FunctionGemma/Hermes: count start/end
+        tags in previous vs current text to determine phase, then
+        accumulate-parse-diff for arguments.
+
+        Format: ``<|tool_call>call:name{args}<tool_call|>``
+        """
+        start_count = current_text.count(self.tool_call_start_token)
+        end_count = current_text.count(self.tool_call_end_token)
+        prev_start_count = previous_text.count(self.tool_call_start_token)
+        prev_end_count = previous_text.count(self.tool_call_end_token)
+
+        # Case 1: Not inside any tool call — emit as content
+        if (
+            start_count == end_count
+            and prev_end_count == end_count
+            and self.tool_call_end_token not in delta_text
+        ):
+            if delta_text:
+                return DeltaMessage(content=delta_text)
+            return None
+
+        # Case 2: Starting a new tool call
+        if start_count > prev_start_count and start_count > end_count:
+            self.current_tool_id += 1
+            self.current_tool_name_sent = False
+            self.streamed_args_for_tool.append("")
+            self.prev_tool_call_arr.append({})
+            logger.debug("Starting new tool call %d", self.current_tool_id)
+            # Don't return yet — fall through to try parsing if there's
+            # content after <|tool_call> in this same delta
+            # (but usually it's just the token itself, so return None)
+            if len(delta_text) <= len(self.tool_call_start_token):
+                return None
+
+        # Case 3: Tool call just ended
+        if end_count > prev_end_count:
+            return self._handle_tool_call_end(current_text)
+
+        # Case 4: In the middle of a tool call — parse partial content
+        if start_count > end_count:
+            return self._handle_tool_call_middle(current_text)
+
+        # Default: generate text outside tool calls
+        if delta_text:
+            text = delta_text.replace(self.tool_call_start_token, "")
+            text = text.replace(self.tool_call_end_token, "")
+            if text:
+                return DeltaMessage(content=text)
+        return None
+
+    def _extract_partial_call(self, current_text: str) -> tuple[str | None, str]:
+        """Extract function name and raw argument string from partial text.
+
+        Returns (func_name, raw_args_str) or (None, "") if not parseable yet.
+        """
+        # Get the text after the last <|tool_call> token
+        last_start = current_text.rfind(self.tool_call_start_token)
+        if last_start == -1:
+            return None, ""
+
+        partial_call = current_text[last_start + len(self.tool_call_start_token) :]
+
+        # Strip end token if present
+        if self.tool_call_end_token in partial_call:
+            partial_call = partial_call.split(self.tool_call_end_token)[0]
+
+        # Expect "call:name{args...}" or "call:name{args...}"
+        if not partial_call.startswith("call:"):
+            return None, ""
+
+        func_part = partial_call[5:]  # skip "call:"
+
+        if "{" not in func_part:
+            # Still accumulating function name, not ready yet
+            return None, ""
+
+        func_name, _, args_part = func_part.partition("{")
+        func_name = func_name.strip()
+
+        # Strip trailing '}' if present (Gemma4 structural brace)
+        if args_part.endswith("}"):
+            args_part = args_part[:-1]
+
+        return func_name, args_part
+
+    def _handle_tool_call_middle(self, current_text: str) -> DeltaMessage | None:
+        """Handle streaming when we're inside an active tool call.
+
+        Accumulates the raw Gemma4 arguments, parses them into JSON, and
+        diffs against the previously-streamed JSON to emit only the new
+        fragment.
+        """
+        func_name, args_part = self._extract_partial_call(current_text)
+
+        if func_name is None:
+            return None
+
+        # Step 1: Send function name (once)
+        if not self.current_tool_name_sent and func_name:
+            self.current_tool_name_sent = True
+            self.prev_tool_call_arr[self.current_tool_id] = {
+                "name": func_name,
+                "arguments": {},
+            }
+            return DeltaMessage(
+                tool_calls=[
+                    DeltaToolCall(
+                        index=self.current_tool_id,
+                        type="function",
+                        id=make_tool_call_id(),
+                        function=DeltaFunctionCall(
+                            name=func_name,
+                            arguments="",
+                        ).model_dump(exclude_none=True),
+                    )
+                ]
+            )
+
+        # Step 2: Parse and diff arguments
+        if self.current_tool_name_sent and args_part:
+            return self._emit_argument_diff(args_part)
+
+        return None
+
+    def _handle_tool_call_end(self, current_text: str) -> DeltaMessage | None:
+        """Handle streaming when a tool call has just completed.
+
+        Performs a final parse of the complete tool call and flushes
+        any remaining un-streamed argument fragments.
+        """
+        if self.current_tool_id < 0 or self.current_tool_id >= len(
+            self.prev_tool_call_arr
+        ):
+            logger.debug(
+                "Tool call end detected but no active tool call (current_tool_id=%d)",
+                self.current_tool_id,
+            )
+            return None
+
+        # Parse the complete tool call using regex for accuracy
+        all_matches = self.tool_call_regex.findall(current_text)
+        if self.current_tool_id < len(all_matches):
+            _, args_str = all_matches[self.current_tool_id]
+            final_args = _parse_gemma4_args(args_str)
+            final_args_json = json.dumps(final_args, ensure_ascii=False)
+
+            prev_streamed = self.streamed_args_for_tool[self.current_tool_id]
+            if len(final_args_json) > len(prev_streamed):
+                diff = final_args_json[len(prev_streamed) :]
+                self.streamed_args_for_tool[self.current_tool_id] = final_args_json
+                self.prev_tool_call_arr[self.current_tool_id]["arguments"] = final_args
+
+                return DeltaMessage(
+                    tool_calls=[
+                        DeltaToolCall(
+                            index=self.current_tool_id,
+                            function=DeltaFunctionCall(arguments=diff).model_dump(
+                                exclude_none=True
+                            ),
+                        )
+                    ]
+                )
+
+        return None
+
+    def _emit_argument_diff(self, raw_args_str: str) -> DeltaMessage | None:
+        """Parse raw Gemma4 arguments, convert to JSON, diff, and emit.
+
+        This is the core of the accumulate-then-parse-then-diff strategy:
+        1. Parse ``raw_args_str`` with ``_parse_gemma4_args()``
+        2. Convert to JSON string with ``json.dumps()``
+        3. Withhold trailing closing characters (``"}``) that may move
+           as more tokens arrive
+        4. Diff against previously streamed JSON and emit only new chars
+
+        **Why withholding is necessary:**
+
+        Gemma4's custom format produces *structurally incomplete* JSON
+        during streaming. For example, when ``<|"|>Paris`` arrives
+        without a closing delimiter, ``_parse_gemma4_args`` treats it
+        as a complete value and produces ``{"location": "Paris"}``. But
+        when ``, France<|"|>`` arrives next, the JSON becomes
+        ``{"location": "Paris, France"}``. If we had sent the closing
+        ``"}`` from the first parse, the concatenated client output
+        would be ``{"location": "Paris"}France"}``, which is garbage.
+
+        The solution: **never send trailing closing chars during
+        streaming**. They get flushed by ``_handle_tool_call_end()``
+        when the ``<tool_call|>`` end marker arrives.
+
+        Args:
+            raw_args_str: The raw Gemma4 argument text accumulated so far
+                (without the surrounding ``{`` ``}``).
+
+        Returns:
+            DeltaMessage with the argument diff, or None if no new content.
+        """
+        try:
+            current_args = _parse_gemma4_args(raw_args_str)
+        except Exception:
+            logger.debug(
+                "Could not parse partial Gemma4 args yet: %s",
+                raw_args_str[:100],
+            )
+            return None
+
+        if not current_args:
+            return None
+
+        current_args_json = json.dumps(current_args, ensure_ascii=False)
+
+        # Withhold trailing closing characters that may shift as more
+        # tokens arrive. Strip trailing '}', '"', and ']' sequences
+        # to get the "safe prefix".
+        safe_json = current_args_json
+        while safe_json and safe_json[-1] in ("}", '"', "]"):
+            safe_json = safe_json[:-1]
+
+        prev_streamed = self.streamed_args_for_tool[self.current_tool_id]
+
+        if not safe_json or safe_json == prev_streamed:
+            return None
+
+        # Use find_common_prefix to handle cases where the value changed
+        # structurally (e.g., a string grew).
+        if prev_streamed:
+            prefix = find_common_prefix(prev_streamed, safe_json)
+            sent_len = len(prev_streamed)
+            prefix_len = len(prefix)
+
+            if prefix_len < sent_len:
+                # Structure changed — we sent too much. Truncate our
+                # tracking to the common prefix and wait for the final
+                # flush in _handle_tool_call_end.
+                self.streamed_args_for_tool[self.current_tool_id] = prefix
+                return None
+
+            # Stream the new stable portion
+            diff = safe_json[sent_len:]
+        else:
+            # First emission
+            diff = safe_json
+
+        if diff:
+            self.streamed_args_for_tool[self.current_tool_id] = safe_json
+            self.prev_tool_call_arr[self.current_tool_id]["arguments"] = current_args
+
+            return DeltaMessage(
+                tool_calls=[
+                    DeltaToolCall(
+                        index=self.current_tool_id,
+                        function=DeltaFunctionCall(arguments=diff).model_dump(
+                            exclude_none=True
+                        ),
+                    )
+                ]
+            )
+
+        return None

vllm/tool_parsers/gemma4_utils.py

@@ -0,0 +1,183 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+# Copyright 2025 Google Inc. HuggingFace Inc. team. All rights reserved.
+
+"""Gemma4 tool call parsing utilities for offline inference.
+
+Standalone functions that parse decoded model text to extract tool calls
+from Gemma4 models. These are pure-Python utilities with zero heavy
+dependencies — they work on raw decoded strings from any inference
+backend (vLLM, HuggingFace, TGI, etc.).
+
+For the OpenAI-compatible API server tool parser (streaming +
+non-streaming), see ``vllm.tool_parsers.gemma4_tool_parser``.
+For thinking/reasoning output parsing, see
+``vllm.reasoning.gemma4_utils``.
+
+Usage with vLLM offline inference::
+
+    from vllm import LLM, SamplingParams
+    from vllm.tool_parsers.gemma4_utils import (
+        parse_tool_calls,
+        has_tool_response_tag,
+    )
+
+    llm = LLM(model="google/gemma-4-it")
+    outputs = llm.generate(prompt, SamplingParams(...))
+    text = tokenizer.decode(outputs[0].outputs[0].token_ids, skip_special_tokens=False)
+
+    # Extract tool calls
+    tool_calls = parse_tool_calls(text)
+    for tc in tool_calls:
+        print(f"{tc['name']}({tc['arguments']})")
+
+Ported from ``transformers.models.gemma4.utils_gemma4`` so that vLLM users
+do not need a transformers dependency for output parsing.
+"""
+
+import json
+
+import regex as re
+
+# Tool call delimiter tokens as they appear in decoded text.
+# Standard format: <|tool_call>call:name{args}<tool_call|>
+_TOOL_CALL_START_TAG = "<|tool_call>"
+_TOOL_CALL_END_TAG = "<tool_call|>"
+_TOOL_RESPONSE_START_TAG = "<|tool_response>"
+
+# Gemma4 escape token as it appears in decoded text.
+_ESCAPE_TOKEN = '<|"|>'
+
+
+def _parse_tool_arguments(args_str: str) -> dict[str, str]:
+    """Parse tool call arguments from the Gemma4 compact format.
+
+    Handles the ``key:<|"|>value<|"|>`` format used by Gemma4, with fallback
+    to heuristic key-value extraction. Also tolerates the slightly different
+    ``key: "value"`` format (space + plain quotes) that some chat templates
+    produce.
+
+    Args:
+        args_str: Raw argument string from inside ``call:name{...}``.
+
+    Returns:
+        Dictionary of argument name → value.
+    """
+    if not args_str or not args_str.strip():
+        return {}
+
+    # Replace Gemma4 escape tokens with standard quotes.
+    cleaned = args_str.replace(_ESCAPE_TOKEN, '"')
+
+    # Try JSON parsing first (handles nested values, arrays, etc.).
+    try:
+        parsed = json.loads("{" + cleaned + "}")
+        # Ensure all values are strings for consistency.
+        return {k: str(v) if not isinstance(v, str) else v for k, v in parsed.items()}
+    except (json.JSONDecodeError, ValueError):
+        pass
+
+    # Fallback: extract key:"value" pairs (allow optional space after colon).
+    arguments = {}
+    for key, value in re.findall(r'(\w+):\s*"([^"]*)"', cleaned):
+        arguments[key] = value
+
+    if not arguments:
+        # Last resort: extract key:value pairs (unquoted).
+        for key, value in re.findall(r"(\w+):\s*([^,}]+)", args_str):
+            arguments[key] = value.strip().strip('"').replace(_ESCAPE_TOKEN, "")
+
+    return arguments
+
+
+def parse_tool_calls(text: str, *, strict: bool = False) -> list[dict]:
+    """Parse tool calls from decoded Gemma4 model output.
+
+    Uses a tiered parsing strategy to handle known output variations in
+    Gemma4 models, which may emit
+    non-standard tool call formats.
+
+    Parsing tiers:
+        1. **Standard**: ``<|tool_call>call:name{args}<tool_call|>``
+           (special token IDs 48/49 in decoded text)
+        2. **Fallback** (when ``strict=False``): bare ``call:name{args}``
+           patterns, including ``<call>name{args}`` (fragmented tokens from
+           multimodal inputs)
+
+    Args:
+        text: Decoded model output text (from ``tokenizer.decode(...,
+            skip_special_tokens=False)``).
+        strict: If ``True``, only match the standard ``<|tool_call>`` format.
+            If ``False`` (default), also try fallback patterns for
+            known Gemma4 output variations.
+
+    Returns:
+        A list of dicts, each with keys:
+            - ``"name"``: The tool function name (e.g. ``"get_weather"``).
+            - ``"arguments"``: A dict of argument name → value.
+
+    Example::
+
+        >>> from vllm.tool_parsers.gemma4_utils import parse_tool_calls
+        >>> output = tokenizer.decode(outputs[0], skip_special_tokens=False)
+        >>> tool_calls = parse_tool_calls(output)
+        >>> for tc in tool_calls:
+        ...     print(f"Call: {tc['name']}({tc['arguments']})")
+    """
+    results = []
+
+    # Tier 1: Standard format with special tokens.
+    # <|tool_call>call:name{args}<tool_call|>
+    # Note: Some Gemma4 models emit <turn|> instead of <tool_call|>.
+    standard_pattern = r"<\|tool_call\>call:(\w+)\{(.*?)\}(?:<tool_call\|>|<turn\|>)"
+    for match in re.finditer(standard_pattern, text, re.DOTALL):
+        name, args_str = match.group(1), match.group(2)
+        results.append(
+            {
+                "name": name,
+                "arguments": _parse_tool_arguments(args_str),
+            }
+        )
+
+    if results or strict:
+        return results
+
+    # Tier 2: Fallback for known Gemma4 output variations.
+    # Matches: <call>name{args}, call:name{args}, or bare call:name{args}<eos>
+    fallback_pattern = r"(?:<call>|(?:^|\s)call:)(\w+)\{(.*?)\}"
+    for match in re.finditer(fallback_pattern, text, re.DOTALL):
+        name, args_str = match.group(1), match.group(2)
+        results.append(
+            {
+                "name": name,
+                "arguments": _parse_tool_arguments(args_str),
+            }
+        )
+
+    return results
+
+
+def has_tool_response_tag(text: str) -> bool:
+    """Check if model output properly ends with a tool response tag.
+
+    Some Gemma4 models sometimes emit ``<eos>`` instead of
+    ``<|tool_response>`` after a tool call. This helper detects
+    whether the model used the proper termination, so callers can
+    decide whether to inject ``<|tool_response>`` into the next prompt.
+
+    Args:
+        text: Decoded model output text.
+
+    Returns:
+        ``True`` if the output ends with ``<|tool_response>``
+        (proper behavior), ``False`` otherwise.
+
+    Example::
+
+        >>> from vllm.tool_parsers.gemma4_utils import has_tool_response_tag
+        >>> if not has_tool_response_tag(model_output):
+        ...     # Model used <eos> instead — inject <|tool_response> manually
+        ...     next_prompt = "<|tool_response>" + tool_result
+    """
+    stripped = text.rstrip()
+    return stripped.endswith(_TOOL_RESPONSE_START_TAG)

vllm/transformers_utils/model_arch_config_convertor.py

@@ -448,6 +448,16 @@ class LongCatFlashMTPModelArchConfigConvertor(ModelArchConfigConvertorBase):
         return getattr(self.hf_text_config, "num_nextn_predict_layers", 1)
 
 
+class Gemma4ModelArchConfigConvertor(ModelArchConfigConvertorBase):
+    def get_head_size(self) -> int:
+        # Gemma4 uses dual head dimensions: head_dim (sliding attention)
+        # and global_head_dim (full attention).  Return the largest so
+        # that attention backends allocate buffers large enough for both.
+        head_dim = getattr(self.hf_text_config, "head_dim", 0)
+        global_head_dim = getattr(self.hf_text_config, "global_head_dim", 0)
+        return max(head_dim, global_head_dim) or super().get_head_size()
+
+
 # hf_config.model_type -> convertor class
 MODEL_ARCH_CONFIG_CONVERTORS = {
     "cohere_asr": CohereAsrModelArchConfigConvertor,
@@ -471,4 +481,6 @@ MODEL_ARCH_CONFIG_CONVERTORS = {
     "ernie_mtp": ErnieMTPModelArchConfigConvertor,
     "pangu_ultra_moe_mtp": PanguUltraMoeMTPModelArchConfigConvertor,
     "longcat_flash_mtp": LongCatFlashMTPModelArchConfigConvertor,
+    "gemma4": Gemma4ModelArchConfigConvertor,
+    "gemma4_text": Gemma4ModelArchConfigConvertor,
 }