From 61e632aea15f76fd1c46354b00f9cac62cd28c4e Mon Sep 17 00:00:00 2001
From: Harry Mellor <19981378+hmellor@users.noreply.github.com>
Date: Tue, 3 Feb 2026 17:40:59 +0000
Subject: [PATCH] Turn `@config` into a `dataclass_transform` (#31541)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>
---
 tests/engine/test_arg_utils.py                |  26 ++--
 tests/test_config.py                          |   5 +-
 tests/tools/test_config_validator.py          |  26 ++--
 tests/v1/e2e/test_spec_decode.py              |   2 +-
 .../test_backend_guidance.py                  |   7 +-
 tools/pre_commit/validate_config.py           |  26 ++--
 vllm/config/__init__.py                       |   2 +
 vllm/config/attention.py                      |   2 -
 vllm/config/cache.py                          |   2 -
 vllm/config/compilation.py                    |   6 +-
 vllm/config/device.py                         |   4 +-
 vllm/config/ec_transfer.py                    |   3 -
 vllm/config/kv_events.py                      |   2 -
 vllm/config/kv_transfer.py                    |   3 -
 vllm/config/load.py                           |   2 -
 vllm/config/lora.py                           |   4 +-
 vllm/config/model.py                          |   4 +-
 vllm/config/multimodal.py                     |   1 -
 vllm/config/observability.py                  |   2 -
 vllm/config/parallel.py                       |   7 --
 vllm/config/pooler.py                         |   3 -
 vllm/config/profiler.py                       |   2 -
 vllm/config/scheduler.py                      |   2 -
 vllm/config/speculative.py                    |   2 -
 vllm/config/speech_to_text.py                 |   3 -
 vllm/config/structured_outputs.py             |   2 -
 vllm/config/utils.py                          | 111 ++++++++++++------
 vllm/config/vllm.py                           |  19 +--
 vllm/entrypoints/openai/cli_args.py           |   3 -
 .../configs/speculators/algos.py              |  17 +--
 .../configs/speculators/base.py               |  34 +++---
 vllm/v1/spec_decode/draft_model.py            |  10 +-
 32 files changed, 153 insertions(+), 191 deletions(-)

diff --git a/tests/engine/test_arg_utils.py b/tests/engine/test_arg_utils.py
index 2acb38bc9..d1986e0a4 100644
--- a/tests/engine/test_arg_utils.py
+++ b/tests/engine/test_arg_utils.py
@@ -3,11 +3,11 @@
 
 import json
 from argparse import ArgumentError
-from contextlib import nullcontext
-from dataclasses import dataclass, field
+from contextlib import AbstractContextManager, nullcontext
 from typing import Annotated, Literal
 
 import pytest
+from pydantic import Field
 
 from vllm.config import AttentionConfig, CompilationConfig, config
 from vllm.engine.arg_utils import (
@@ -96,7 +96,7 @@ def test_get_type(type_hints, type, expected):
     ],
 )
 def test_literal_to_kwargs(type_hints, expected):
-    context = nullcontext()
+    context: AbstractContextManager[object] = nullcontext()
     if expected is Exception:
         context = pytest.raises(expected)
     with context:
@@ -104,14 +104,12 @@ def test_literal_to_kwargs(type_hints, expected):
 
 
 @config
-@dataclass
 class NestedConfig:
     field: int = 1
     """field"""
 
 
 @config
-@dataclass
 class DummyConfig:
     regular_bool: bool = True
     """Regular bool with default True"""
@@ -119,23 +117,23 @@ class DummyConfig:
     """Optional bool with default None"""
     optional_literal: Literal["x", "y"] | None = None
     """Optional literal with default None"""
-    tuple_n: tuple[int, ...] = field(default_factory=lambda: (1, 2, 3))
+    tuple_n: tuple[int, ...] = Field(default_factory=lambda: (1, 2, 3))
     """Tuple with variable length"""
-    tuple_2: tuple[int, int] = field(default_factory=lambda: (1, 2))
+    tuple_2: tuple[int, int] = Field(default_factory=lambda: (1, 2))
     """Tuple with fixed length"""
-    list_n: list[int] = field(default_factory=lambda: [1, 2, 3])
+    list_n: list[int] = Field(default_factory=lambda: [1, 2, 3])
     """List with variable length"""
-    list_literal: list[Literal[1, 2]] = field(default_factory=list)
+    list_literal: list[Literal[1, 2]] = Field(default_factory=list)
     """List with literal choices"""
-    list_union: list[str | type[object]] = field(default_factory=list)
+    list_union: list[str | type[object]] = Field(default_factory=list)
     """List with union type"""
-    set_n: set[int] = field(default_factory=lambda: {1, 2, 3})
+    set_n: set[int] = Field(default_factory=lambda: {1, 2, 3})
     """Set with variable length"""
     literal_literal: Literal[Literal[1], Literal[2]] = 1
     """Literal of literals with default 1"""
-    json_tip: dict = field(default_factory=dict)
+    json_tip: dict = Field(default_factory=dict)
     """Dict which will be JSON in CLI"""
-    nested_config: NestedConfig = field(default_factory=NestedConfig)
+    nested_config: NestedConfig = Field(default_factory=NestedConfig)
     """Nested config"""
 
 
@@ -195,7 +193,7 @@ def test_get_kwargs():
     json_tip = "Should either be a valid JSON string or JSON keys"
     assert json_tip in kwargs["json_tip"]["help"]
     # nested config should construct the nested config
-    assert kwargs["nested_config"]["type"]('{"field": 2}') == NestedConfig(2)
+    assert kwargs["nested_config"]["type"]('{"field": 2}') == NestedConfig(2)  # type: ignore[call-arg]
 
 
 @pytest.mark.parametrize(
diff --git a/tests/test_config.py b/tests/test_config.py
index 1676598b1..f3c3003a0 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -66,9 +66,6 @@ class _TestConfigFields:
 
 
 def test_get_field():
-    with pytest.raises(ValueError):
-        get_field(_TestConfigFields, "a")
-
     b = get_field(_TestConfigFields, "b")
     assert isinstance(b, Field)
     assert b.default is MISSING
@@ -188,7 +185,7 @@ def test_get_pooling_config():
 )
 def test_get_pooling_config_from_args():
     model_id = "sentence-transformers/all-MiniLM-L12-v2"
-    pooler_config = PoolerConfig(seq_pooling_type="CLS", normalize=True)
+    pooler_config = PoolerConfig(seq_pooling_type="CLS", use_activation=False)
     model_config = ModelConfig(model_id, pooler_config=pooler_config)
 
     assert asdict(model_config.pooler_config) == asdict(pooler_config)
diff --git a/tests/tools/test_config_validator.py b/tests/tools/test_config_validator.py
index d6104dc6d..e317bf911 100644
--- a/tests/tools/test_config_validator.py
+++ b/tests/tools/test_config_validator.py
@@ -7,31 +7,22 @@ import pytest
 
 from tools.pre_commit.validate_config import validate_ast
 
-_TestConfig1 = """
+_TestConfig1 = '''
 @config
 class _TestConfig1:
-    pass
-"""
-
-_TestConfig2 = '''
-@config
-@dataclass
-class _TestConfig2:
     a: int
     """docstring"""
 '''
 
-_TestConfig3 = """
+_TestConfig2 = """
 @config
-@dataclass
-class _TestConfig3:
+class _TestConfig2:
     a: int = 1
 """
 
-_TestConfig4 = '''
+_TestConfig3 = '''
 @config
-@dataclass
-class _TestConfig4:
+class _TestConfig3:
     a: Union[Literal[1], Literal[2]] = 1
     """docstring"""
 '''
@@ -40,10 +31,9 @@ class _TestConfig4:
 @pytest.mark.parametrize(
     ("test_config", "expected_error"),
     [
-        (_TestConfig1, "must be a dataclass"),
-        (_TestConfig2, "must have a default"),
-        (_TestConfig3, "must have a docstring"),
-        (_TestConfig4, "must use a single Literal"),
+        (_TestConfig1, "must have a default"),
+        (_TestConfig2, "must have a docstring"),
+        (_TestConfig3, "must use a single Literal"),
     ],
 )
 def test_config(test_config, expected_error):
diff --git a/tests/v1/e2e/test_spec_decode.py b/tests/v1/e2e/test_spec_decode.py
index 02e152914..4905a4120 100644
--- a/tests/v1/e2e/test_spec_decode.py
+++ b/tests/v1/e2e/test_spec_decode.py
@@ -766,8 +766,8 @@ def assert_draft_model_correctness(args: ArgsTest, enforce_eager: bool):
             "max_model_len": args.max_model_len,
             "enforce_eager": enforce_eager,
             "draft_tensor_parallel_size": args.draft_tensor_parallel_size,
-            "max_num_seqs": 100,  # limit cudagraph capture runtime
         },
+        max_num_seqs=100,  # limit cudagraph capture runtime
         max_model_len=args.max_model_len,
         gpu_memory_utilization=args.gpu_memory_utilization,
         tensor_parallel_size=args.target_tensor_parallel_size,
diff --git a/tests/v1/structured_output/test_backend_guidance.py b/tests/v1/structured_output/test_backend_guidance.py
index 4c01560fc..362f75c49 100644
--- a/tests/v1/structured_output/test_backend_guidance.py
+++ b/tests/v1/structured_output/test_backend_guidance.py
@@ -26,11 +26,8 @@ def test_backend_guidance_rollback_terminated():
     # guidance backend. In that case we are in a stopped state, but
     # it should be reverted in case EOS is not accepted by the target
     # model.
-    vllm_config = VllmConfig(
-        decoding_config=StructuredOutputsConfig(
-            backend="guidance",
-        )
-    )
+    structured_outputs_config = StructuredOutputsConfig(backend="guidance")
+    vllm_config = VllmConfig(structured_outputs_config=structured_outputs_config)
     tokenizer = AutoTokenizer.from_pretrained(TOKENIZER)
 
     backend = GuidanceBackend(
diff --git a/tools/pre_commit/validate_config.py b/tools/pre_commit/validate_config.py
index fb6f0e6a9..7da32bc6b 100644
--- a/tools/pre_commit/validate_config.py
+++ b/tools/pre_commit/validate_config.py
@@ -54,24 +54,18 @@ class ConfigValidator(ast.NodeVisitor):
     def __init__(self): ...
 
     def visit_ClassDef(self, node):
-        # Validate class with both @config and @dataclass decorators
-        decorators = [
-            id
-            for d in node.decorator_list
-            if (
-                isinstance(d, ast.Name)
-                and ((id := d.id) == "config" or id == "dataclass")
-            )
-            or (
-                isinstance(d, ast.Call)
-                and (isinstance(d.func, ast.Name) and (id := d.func.id) == "dataclass")
-            )
-        ]
+        # Validate classes with a @config decorator
+        decorators = set()
+        for decorator in node.decorator_list:
+            if isinstance(decorator, ast.Call):
+                decorator = decorator.func
+            if isinstance(decorator, ast.Name) and decorator.id == "config":
+                decorators.add(decorator.id)
 
-        if set(decorators) == {"config", "dataclass"}:
+        if decorators == {"config"}:
             validate_class(node)
-        elif set(decorators) == {"config"}:
-            fail(f"Class {node.name} with config decorator must be a dataclass.", node)
+        elif "config" in decorators:
+            fail(f"config decorator for {node.name} should be used alone", node)
 
         self.generic_visit(node)
 
diff --git a/vllm/config/__init__.py b/vllm/config/__init__.py
index 7f6565053..b2044c6e1 100644
--- a/vllm/config/__init__.py
+++ b/vllm/config/__init__.py
@@ -36,6 +36,7 @@ from vllm.config.utils import (
     config,
     get_attr_docs,
     is_init_field,
+    replace,
     update_config,
 )
 from vllm.config.vllm import (
@@ -101,6 +102,7 @@ __all__ = [
     "config",
     "get_attr_docs",
     "is_init_field",
+    "replace",
     "update_config",
     # From vllm.config.vllm
     "VllmConfig",
diff --git a/vllm/config/attention.py b/vllm/config/attention.py
index ee072fb1c..9379b2878 100644
--- a/vllm/config/attention.py
+++ b/vllm/config/attention.py
@@ -4,14 +4,12 @@
 from typing import Any, Literal
 
 from pydantic import field_validator
-from pydantic.dataclasses import dataclass
 
 from vllm.config.utils import config
 from vllm.v1.attention.backends.registry import AttentionBackendEnum
 
 
 @config
-@dataclass
 class AttentionConfig:
     """Configuration for attention mechanisms in vLLM."""
 
diff --git a/vllm/config/cache.py b/vllm/config/cache.py
index abf10e21d..bf121e544 100644
--- a/vllm/config/cache.py
+++ b/vllm/config/cache.py
@@ -6,7 +6,6 @@ from dataclasses import field
 from typing import TYPE_CHECKING, Any, Literal
 
 from pydantic import Field, SkipValidation, field_validator
-from pydantic.dataclasses import dataclass
 
 from vllm.config.utils import config
 from vllm.logger import init_logger
@@ -37,7 +36,6 @@ KVOffloadingBackend = Literal["native", "lmcache"]
 
 
 @config
-@dataclass
 class CacheConfig:
     """Configuration for the KV cache."""
 
diff --git a/vllm/config/compilation.py b/vllm/config/compilation.py
index 7a69629f7..556254a65 100644
--- a/vllm/config/compilation.py
+++ b/vllm/config/compilation.py
@@ -8,8 +8,7 @@ from dataclasses import field
 from pathlib import Path
 from typing import TYPE_CHECKING, Any, ClassVar, Literal
 
-from pydantic import ConfigDict, Field, TypeAdapter, field_validator
-from pydantic.dataclasses import dataclass
+from pydantic import Field, TypeAdapter, field_validator
 
 import vllm.envs as envs
 from vllm.compilation.inductor_pass import CallableInductorPass, InductorPass
@@ -96,7 +95,6 @@ class CUDAGraphMode(enum.Enum):
 
 
 @config
-@dataclass(config=ConfigDict(extra="forbid"))
 class PassConfig:
     """Configuration for custom Inductor passes.
 
@@ -267,7 +265,6 @@ class DynamicShapesType(str, enum.Enum):
 
 
 @config
-@dataclass(config=ConfigDict(extra="forbid"))
 class DynamicShapesConfig:
     """Configuration to control/debug torch compile dynamic shapes."""
 
@@ -311,7 +308,6 @@ class DynamicShapesConfig:
 
 
 @config
-@dataclass(config=ConfigDict(extra="forbid"))
 class CompilationConfig:
     """Configuration for compilation.
 
diff --git a/vllm/config/device.py b/vllm/config/device.py
index 85662ddff..c20e4d0f2 100644
--- a/vllm/config/device.py
+++ b/vllm/config/device.py
@@ -6,7 +6,6 @@ from typing import Any, Literal
 
 import torch
 from pydantic import ConfigDict, SkipValidation
-from pydantic.dataclasses import dataclass
 
 from vllm.config.utils import config
 from vllm.utils.hashing import safe_hash
@@ -14,8 +13,7 @@ from vllm.utils.hashing import safe_hash
 Device = Literal["auto", "cuda", "cpu", "tpu", "xpu"]
 
 
-@config
-@dataclass(config=ConfigDict(arbitrary_types_allowed=True))
+@config(config=ConfigDict(arbitrary_types_allowed=True))
 class DeviceConfig:
     """Configuration for the device to use for vLLM execution."""
 
diff --git a/vllm/config/ec_transfer.py b/vllm/config/ec_transfer.py
index d95236f81..c7f56557f 100644
--- a/vllm/config/ec_transfer.py
+++ b/vllm/config/ec_transfer.py
@@ -5,8 +5,6 @@ import uuid
 from dataclasses import field
 from typing import Any, Literal, get_args
 
-from pydantic.dataclasses import dataclass
-
 from vllm.config.utils import config
 
 ECProducer = Literal["ec_producer"]
@@ -15,7 +13,6 @@ ECRole = Literal[ECProducer, ECConsumer]
 
 
 @config
-@dataclass
 class ECTransferConfig:
     """Configuration for distributed EC cache transfer."""
 
diff --git a/vllm/config/kv_events.py b/vllm/config/kv_events.py
index ce46cc03c..94da54c78 100644
--- a/vllm/config/kv_events.py
+++ b/vllm/config/kv_events.py
@@ -5,13 +5,11 @@
 from typing import Literal
 
 from pydantic import Field
-from pydantic.dataclasses import dataclass
 
 from vllm.config.utils import config
 
 
 @config
-@dataclass
 class KVEventsConfig:
     """Configuration for KV event publishing."""
 
diff --git a/vllm/config/kv_transfer.py b/vllm/config/kv_transfer.py
index 98cea821c..fe3b218fb 100644
--- a/vllm/config/kv_transfer.py
+++ b/vllm/config/kv_transfer.py
@@ -5,8 +5,6 @@ import uuid
 from dataclasses import field
 from typing import Any, Literal, get_args
 
-from pydantic.dataclasses import dataclass
-
 from vllm.config.utils import config
 from vllm.utils.hashing import safe_hash
 
@@ -16,7 +14,6 @@ KVRole = Literal[KVProducer, KVConsumer]
 
 
 @config
-@dataclass
 class KVTransferConfig:
     """Configuration for distributed KV cache transfer."""
 
diff --git a/vllm/config/load.py b/vllm/config/load.py
index 579a0bc31..64a269e98 100644
--- a/vllm/config/load.py
+++ b/vllm/config/load.py
@@ -4,7 +4,6 @@
 from typing import TYPE_CHECKING, Any
 
 from pydantic import Field, field_validator
-from pydantic.dataclasses import dataclass
 
 from vllm.config.utils import config
 from vllm.logger import init_logger
@@ -21,7 +20,6 @@ logger = init_logger(__name__)
 
 
 @config
-@dataclass
 class LoadConfig:
     """Configuration for loading the model weights."""
 
diff --git a/vllm/config/lora.py b/vllm/config/lora.py
index f15beffe1..0d310c87e 100644
--- a/vllm/config/lora.py
+++ b/vllm/config/lora.py
@@ -5,7 +5,6 @@ from typing import TYPE_CHECKING, Any, Literal
 
 import torch
 from pydantic import ConfigDict, Field, model_validator
-from pydantic.dataclasses import dataclass
 from typing_extensions import Self
 
 from vllm.config.utils import config
@@ -26,8 +25,7 @@ MaxLoRARanks = Literal[1, 8, 16, 32, 64, 128, 256, 320, 512]
 LoRAExtraVocabSize = Literal[256, 512]
 
 
-@config
-@dataclass(config=ConfigDict(arbitrary_types_allowed=True))
+@config(config=ConfigDict(arbitrary_types_allowed=True))
 class LoRAConfig:
     """Configuration for LoRA."""
 
diff --git a/vllm/config/model.py b/vllm/config/model.py
index 48ff44ac9..3bb8e7177 100644
--- a/vllm/config/model.py
+++ b/vllm/config/model.py
@@ -9,7 +9,6 @@ from typing import TYPE_CHECKING, Any, Literal, cast, get_args
 
 import torch
 from pydantic import ConfigDict, Field, field_validator, model_validator
-from pydantic.dataclasses import dataclass
 
 import vllm.envs as envs
 from vllm.config.model_arch import (
@@ -97,8 +96,7 @@ AttnTypeStr = Literal[
 ]
 
 
-@config
-@dataclass(config=ConfigDict(arbitrary_types_allowed=True))
+@config(config=ConfigDict(arbitrary_types_allowed=True))
 class ModelConfig:
     """Configuration for the model."""
 
diff --git a/vllm/config/multimodal.py b/vllm/config/multimodal.py
index f4e834f64..48eea6f4e 100644
--- a/vllm/config/multimodal.py
+++ b/vllm/config/multimodal.py
@@ -51,7 +51,6 @@ DummyOptions: TypeAlias = (
 
 
 @config
-@dataclass
 class MultiModalConfig:
     """Controls the behavior of multimodal models."""
 
diff --git a/vllm/config/observability.py b/vllm/config/observability.py
index 9700c9117..387175912 100644
--- a/vllm/config/observability.py
+++ b/vllm/config/observability.py
@@ -6,7 +6,6 @@ from typing import Any, Literal, cast
 
 from packaging.version import parse
 from pydantic import Field, field_validator, model_validator
-from pydantic.dataclasses import dataclass
 
 from vllm import version
 from vllm.config.utils import config
@@ -16,7 +15,6 @@ DetailedTraceModules = Literal["model", "worker", "all"]
 
 
 @config
-@dataclass
 class ObservabilityConfig:
     """Configuration for observability - metrics and tracing."""
 
diff --git a/vllm/config/parallel.py b/vllm/config/parallel.py
index fa1aa0312..131db50f1 100644
--- a/vllm/config/parallel.py
+++ b/vllm/config/parallel.py
@@ -3,12 +3,10 @@
 
 import os
 from collections.abc import Callable
-from dataclasses import replace
 from typing import TYPE_CHECKING, Any, Literal
 
 import torch
 from pydantic import Field, field_validator, model_validator
-from pydantic.dataclasses import dataclass
 from torch.distributed import ProcessGroup, ReduceOp
 from typing_extensions import Self
 
@@ -50,7 +48,6 @@ All2AllBackend = Literal[
 
 
 @config
-@dataclass
 class EPLBConfig:
     """Configuration for Expert Parallel Load Balancing (EP)."""
 
@@ -94,7 +91,6 @@ class EPLBConfig:
 
 
 @config
-@dataclass
 class ParallelConfig:
     """Configuration for the distributed execution."""
 
@@ -715,6 +711,3 @@ class ParallelConfig:
             )
 
         return self
-
-    def replace(self, **kwargs) -> Self:
-        return replace(self, **kwargs)
diff --git a/vllm/config/pooler.py b/vllm/config/pooler.py
index 6d87ec908..75cdc90fe 100644
--- a/vllm/config/pooler.py
+++ b/vllm/config/pooler.py
@@ -3,8 +3,6 @@
 
 from typing import Any, Literal, get_args
 
-from pydantic.dataclasses import dataclass
-
 from vllm.config.utils import config
 from vllm.logger import init_logger
 from vllm.utils.hashing import safe_hash
@@ -19,7 +17,6 @@ TOK_POOLING_TYPES: tuple[TokenPoolingType, ...] = get_args(TokenPoolingType)
 
 
 @config
-@dataclass
 class PoolerConfig:
     """Controls the behavior of output pooling in pooling models."""
 
diff --git a/vllm/config/profiler.py b/vllm/config/profiler.py
index 425f3fb6b..b3b8844f7 100644
--- a/vllm/config/profiler.py
+++ b/vllm/config/profiler.py
@@ -5,7 +5,6 @@ import os
 from typing import Any, Literal
 
 from pydantic import Field, model_validator
-from pydantic.dataclasses import dataclass
 from typing_extensions import Self
 
 from vllm.config.utils import config
@@ -32,7 +31,6 @@ def _is_uri_path(path: str) -> bool:
 
 
 @config
-@dataclass
 class ProfilerConfig:
     """Dataclass which contains profiler config for the engine."""
 
diff --git a/vllm/config/scheduler.py b/vllm/config/scheduler.py
index 5ff9fc930..5e44eb84f 100644
--- a/vllm/config/scheduler.py
+++ b/vllm/config/scheduler.py
@@ -6,7 +6,6 @@ from dataclasses import InitVar
 from typing import TYPE_CHECKING, Any, ClassVar, Literal, cast
 
 from pydantic import Field, field_validator
-from pydantic.dataclasses import dataclass
 from typing_extensions import Self
 
 from vllm.config.utils import config
@@ -24,7 +23,6 @@ SchedulerPolicy = Literal["fcfs", "priority"]
 
 
 @config
-@dataclass
 class SchedulerConfig:
     """Scheduler configuration."""
 
diff --git a/vllm/config/speculative.py b/vllm/config/speculative.py
index 966d168b4..ed3dbefb3 100644
--- a/vllm/config/speculative.py
+++ b/vllm/config/speculative.py
@@ -5,7 +5,6 @@ import ast
 from typing import TYPE_CHECKING, Any, Literal, get_args
 
 from pydantic import Field, SkipValidation, model_validator
-from pydantic.dataclasses import dataclass
 from typing_extensions import Self
 
 from vllm.config.model import ModelConfig
@@ -55,7 +54,6 @@ SpeculativeMethod = Literal[
 
 
 @config
-@dataclass
 class SpeculativeConfig:
     """Configuration for speculative decoding."""
 
diff --git a/vllm/config/speech_to_text.py b/vllm/config/speech_to_text.py
index fe3532c97..0233d3657 100644
--- a/vllm/config/speech_to_text.py
+++ b/vllm/config/speech_to_text.py
@@ -2,13 +2,10 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
 
-from pydantic.dataclasses import dataclass
-
 from vllm.config.utils import config
 
 
 @config
-@dataclass
 class SpeechToTextConfig:
     """Configuration for speech-to-text models."""
 
diff --git a/vllm/config/structured_outputs.py b/vllm/config/structured_outputs.py
index 8c060c816..c4db15989 100644
--- a/vllm/config/structured_outputs.py
+++ b/vllm/config/structured_outputs.py
@@ -4,7 +4,6 @@
 from typing import Any, Literal
 
 from pydantic import model_validator
-from pydantic.dataclasses import dataclass
 from typing_extensions import Self
 
 from vllm.config.utils import config
@@ -16,7 +15,6 @@ StructuredOutputsBackend = Literal[
 
 
 @config
-@dataclass
 class StructuredOutputsConfig:
     """Dataclass which contains structured outputs config for the engine."""
 
diff --git a/vllm/config/utils.py b/vllm/config/utils.py
index 9288948c5..e8c866f02 100644
--- a/vllm/config/utils.py
+++ b/vllm/config/utils.py
@@ -10,14 +10,17 @@ import json
 import pathlib
 import textwrap
 from collections.abc import Callable, Mapping, Sequence, Set
-from dataclasses import MISSING, Field, dataclass, field, fields, is_dataclass, replace
+from dataclasses import MISSING, Field, field, fields, is_dataclass
 from itertools import pairwise
-from typing import TYPE_CHECKING, Any, Protocol, TypeVar
+from typing import TYPE_CHECKING, Any, Protocol, TypeVar, cast
 
 import regex as re
 import torch
+from pydantic import ConfigDict
+from pydantic.dataclasses import dataclass
+from pydantic.fields import Field as PydanticField
 from pydantic.fields import FieldInfo
-from typing_extensions import runtime_checkable
+from typing_extensions import dataclass_transform, runtime_checkable
 
 from vllm.logger import init_logger
 
@@ -29,23 +32,39 @@ else:
     DataclassInstance = Any
 
 ConfigType = type[DataclassInstance]
-ConfigT = TypeVar("ConfigT", bound=ConfigType)
+ConfigT = TypeVar("ConfigT", bound=DataclassInstance)
 
 
-def config(cls: ConfigT) -> ConfigT:
-    """
-    A decorator that ensures all fields in a dataclass have default values
-    and that each field has a docstring.
+@dataclass_transform(field_specifiers=(PydanticField,))
+def config(
+    cls: type[ConfigT] | None = None,
+    *,
+    config: ConfigDict | None = None,
+    **kwargs: Any,
+) -> type[ConfigT] | Callable[[type[ConfigT]], type[ConfigT]]:
+    """Decorator to create a pydantic dataclass with default config. The default config
+    for the dataclass forbids extra fields.
 
-    If a `ConfigT` is used as a CLI argument itself, the `type` keyword argument
-    provided by `get_kwargs` will be
-    `pydantic.TypeAdapter(ConfigT).validate_json(cli_arg)` which treats the
-    `cli_arg` as a JSON string which gets validated by `pydantic`.
+    All config classes in vLLM should use this decorator.
 
-    Config validation is performed by the tools/pre_commit/validate_config.py
-    script, which is invoked during the pre-commit checks.
-    """
-    return cls
+    Args:
+        cls: The class to decorate
+        config: The pydantic ConfigDict to use. If provided, it will be merged with
+            the default config.
+        **kwargs: Additional arguments to pass to pydantic.dataclass."""
+    # Extra fields are forbidden by default
+    merged_config = ConfigDict(extra="forbid")
+    if config is not None:
+        merged_config.update(config)
+
+    def decorator(cls):
+        return dataclass(cls, config=merged_config, **kwargs)
+
+    # Called with arguments: @config(config=...)
+    if cls is None:
+        return decorator
+    # Called without arguments: @config
+    return decorator(cls)
 
 
 def get_field(cls: ConfigType, name: str) -> Field:
@@ -53,24 +72,46 @@ def get_field(cls: ConfigType, name: str) -> Field:
     default factory fields in `EngineArgs`."""
     if not is_dataclass(cls):
         raise TypeError("The given class is not a dataclass.")
-    cls_fields = {f.name: f for f in fields(cls)}
-    if name not in cls_fields:
-        raise ValueError(f"Field '{name}' not found in {cls.__name__}.")
-    named_field: Field = cls_fields[name]
-    if (default_factory := named_field.default_factory) is not MISSING:
-        return field(default_factory=default_factory)
-    if (default := named_field.default) is not MISSING:
-        if isinstance(default, FieldInfo):
-            # Handle pydantic.Field defaults
-            if default.default_factory is not None:
-                return field(default_factory=default.default_factory)
-            else:
-                default = default.default
-        return field(default=default)
+    try:
+        named_field = next(f for f in fields(cls) if f.name == name)
+    except StopIteration as e:
+        raise ValueError(f"Field '{name}' not found in {cls.__name__}.") from e
 
-    raise ValueError(
-        f"{cls.__name__}.{name} must have a default value or default factory."
-    )
+    # The arguments to copy to the new field
+    default = named_field.default
+    default_factory = named_field.default_factory
+    init = named_field.init
+
+    # Handle pydantic.Field
+    if isinstance(default, FieldInfo):
+        if default.init is not None:
+            init = default.init
+        if default.default_factory is not None:
+            default_factory = cast(Callable[[], Any], default.default_factory)
+            default = MISSING
+        else:
+            default = default.default
+
+    if default is MISSING and default_factory is MISSING:
+        logger.warning_once(
+            "%s.%s has no default or default factory.", cls.__name__, name
+        )
+    return field(default=default, default_factory=default_factory, init=init)
+
+
+def is_init_field(cls: ConfigType, name: str) -> bool:
+    return get_field(cls, name).init
+
+
+def replace(dataclass_instance: ConfigT, /, **kwargs) -> ConfigT:
+    """Like [`dataclasses.replace`](https://docs.python.org/3/library/dataclasses.html#dataclasses.replace),
+    but compatible with Pydantic dataclasses which use `pydantic.fields.Field` instead
+    of `dataclasses.field`"""
+    cls = type(dataclass_instance)
+    dataclass_dict = dataclass_instance.__dict__
+    dataclass_dict = {k: v for k, v in dataclass_dict.items() if is_init_field(cls, k)}
+    dataclass_dict.update(kwargs)
+    return cls(**dataclass_dict)
 
 
 def getattr_iter(
@@ -172,10 +213,6 @@ def get_attr_docs(cls: type[Any]) -> dict[str, str]:
     return out
 
 
-def is_init_field(cls: ConfigType, name: str) -> bool:
-    return next(f for f in fields(cls) if f.name == name).init
-
-
 @runtime_checkable
 class SupportsHash(Protocol):
     def compute_hash(self) -> str: ...
diff --git a/vllm/config/vllm.py b/vllm/config/vllm.py
index ea1338563..846ed50e0 100644
--- a/vllm/config/vllm.py
+++ b/vllm/config/vllm.py
@@ -9,7 +9,7 @@ import tempfile
 import threading
 import time
 from contextlib import contextmanager
-from dataclasses import is_dataclass, replace
+from dataclasses import is_dataclass
 from datetime import datetime
 from enum import IntEnum
 from functools import lru_cache
@@ -18,10 +18,8 @@ from typing import TYPE_CHECKING, Any, TypeVar, get_args
 
 import torch
 from pydantic import ConfigDict, Field, model_validator
-from pydantic.dataclasses import dataclass
 
 import vllm.envs as envs
-from vllm.config.speculative import EagleModelTypes
 from vllm.logger import enable_trace_function_call, init_logger
 from vllm.transformers_utils.runai_utils import is_runai_obj_uri
 from vllm.utils import random_uuid
@@ -41,9 +39,9 @@ from .observability import ObservabilityConfig
 from .parallel import ParallelConfig
 from .profiler import ProfilerConfig
 from .scheduler import SchedulerConfig
-from .speculative import SpeculativeConfig
+from .speculative import EagleModelTypes, SpeculativeConfig
 from .structured_outputs import StructuredOutputsConfig
-from .utils import SupportsHash, config
+from .utils import SupportsHash, config, replace
 
 if TYPE_CHECKING:
     from transformers import PretrainedConfig
@@ -187,8 +185,7 @@ OPTIMIZATION_LEVEL_TO_CONFIG = {
 }
 
 
-@config
-@dataclass(config=ConfigDict(arbitrary_types_allowed=True))
+@config(config=ConfigDict(arbitrary_types_allowed=True))
 class VllmConfig:
     """Dataclass which contains all vllm-related configuration. This
     simplifies passing around the distinct configurations in the codebase.
@@ -1395,14 +1392,6 @@ class VllmConfig:
         path = self.compilation_config.debug_dump_path / append_path
         return path
 
-    def replace(self, **kwargs):
-        """
-        Replace attributes of the config, and 'recompute' the config.
-        dataclass.replace() calls __init__() and __post_init__(), source:
-        https://docs.python.org/3/library/dataclasses.html#dataclasses.replace
-        """
-        return replace(self, **kwargs)
-
     def __str__(self):
         return (
             f"model={self.model_config.model!r}, "
diff --git a/vllm/entrypoints/openai/cli_args.py b/vllm/entrypoints/openai/cli_args.py
index 808c2a908..983040a89 100644
--- a/vllm/entrypoints/openai/cli_args.py
+++ b/vllm/entrypoints/openai/cli_args.py
@@ -13,8 +13,6 @@ from collections.abc import Sequence
 from dataclasses import field
 from typing import Any, Literal
 
-from pydantic.dataclasses import dataclass
-
 import vllm.envs as envs
 from vllm.config import config
 from vllm.engine.arg_utils import AsyncEngineArgs, optional_type
@@ -69,7 +67,6 @@ class LoRAParserAction(argparse.Action):
 
 
 @config
-@dataclass
 class FrontendArgs:
     """Arguments for the OpenAI-compatible frontend server."""
 
diff --git a/vllm/transformers_utils/configs/speculators/algos.py b/vllm/transformers_utils/configs/speculators/algos.py
index 88bce3d4f..60bb5d588 100644
--- a/vllm/transformers_utils/configs/speculators/algos.py
+++ b/vllm/transformers_utils/configs/speculators/algos.py
@@ -13,9 +13,10 @@ def register_speculator(name):
 
 
 @register_speculator("eagle3")
-def update_eagle3(config_dict: dict, vllm_config: dict) -> None:
+def update_eagle3(config_dict: dict, pre_trained_config: dict) -> None:
     """
-    Apply Eagle-3 specific configuration transformations.
+    Apply Eagle-3 specific configuration transformations to the `dict` used to
+    construct the Transformers PreTrainedConfig.
 
     Eagle-3 specific fields:
     - draft_vocab_size: Size of the draft model's vocabulary
@@ -27,12 +28,14 @@ def update_eagle3(config_dict: dict, vllm_config: dict) -> None:
         predictions. This is the standard field used in Eagle3 checkpoints.
     """
 
-    vllm_config["draft_vocab_size"] = config_dict.get("draft_vocab_size")
+    pre_trained_config["draft_vocab_size"] = config_dict.get("draft_vocab_size")
     if config_dict.get("target_hidden_size") is not None:
-        vllm_config["target_hidden_size"] = config_dict["target_hidden_size"]
-    vllm_config["norm_before_residual"] = config_dict.get("norm_before_residual", True)
-    vllm_config["architectures"] = ["Eagle3LlamaForCausalLM"]
+        pre_trained_config["target_hidden_size"] = config_dict["target_hidden_size"]
+    pre_trained_config["norm_before_residual"] = config_dict.get(
+        "norm_before_residual", True
+    )
+    pre_trained_config["architectures"] = ["Eagle3LlamaForCausalLM"]
     if config_dict.get("eagle_aux_hidden_state_layer_ids"):
-        vllm_config["eagle_aux_hidden_state_layer_ids"] = config_dict[
+        pre_trained_config["eagle_aux_hidden_state_layer_ids"] = config_dict[
             "eagle_aux_hidden_state_layer_ids"
         ]
diff --git a/vllm/transformers_utils/configs/speculators/base.py b/vllm/transformers_utils/configs/speculators/base.py
index bf3a5d413..a57350b09 100644
--- a/vllm/transformers_utils/configs/speculators/base.py
+++ b/vllm/transformers_utils/configs/speculators/base.py
@@ -24,13 +24,16 @@ class SpeculatorsConfig(PretrainedConfig):
         """Load speculators Eagle config and convert to vLLM format."""
         config_dict, _ = cls.get_config_dict(pretrained_model_name_or_path, **kwargs)
 
-        vllm_config = cls.extract_vllm_speculative_config(config_dict)
+        vllm_config = cls.extract_transformers_pre_trained_config(config_dict)
         return cls(**vllm_config)
 
     @classmethod
-    def extract_vllm_speculative_config(
+    def extract_transformers_pre_trained_config(
         cls, config_dict: dict[str, Any]
     ) -> dict[str, Any]:
+        """
+        Extract standard Transformers PreTrainedConfig config from speculators config.
+        """
         speculators_model_type = config_dict.get("speculators_model_type")
         if speculators_model_type not in SUPPORTED_SPECULATORS_TYPES:
             raise ValueError(
@@ -38,15 +41,23 @@ class SpeculatorsConfig(PretrainedConfig):
                 "Please ensure you're loading a speculators-format model."
             )
 
+        # Start with transformer layer configuration if present
+        pre_trained_config = config_dict.get("transformer_layer_config", {})
+        # Apply anything specific to the supported algorithm
+        algo_updater = SUPPORTED_SPECULATORS_TYPES[speculators_model_type]
+        algo_updater(config_dict=config_dict, pre_trained_config=pre_trained_config)
+        return pre_trained_config
+
+    @classmethod
+    def extract_vllm_speculative_config(
+        cls, config_dict: dict[str, Any]
+    ) -> dict[str, Any]:
+        """Extract vLLM speculative config from speculators config."""
         # validate fields
         # TODO: @dsikka - use speculators pydantic model to validate
         cls.validate_speculators_config(config_dict=config_dict)
         # Convert from speculators config -> format that can be ingested by vLLM
-        vllm_config = cls.build_vllm_speculative_config(config_dict=config_dict)
-        # Apply anything specific to the supported algorithm
-        algo_updater = SUPPORTED_SPECULATORS_TYPES[speculators_model_type]
-        algo_updater(config_dict=config_dict, vllm_config=vllm_config)
-        return vllm_config
+        return cls.build_vllm_speculative_config(config_dict=config_dict)
 
     @classmethod
     def validate_speculators_config(cls, config_dict: dict[str, Any]) -> None:
@@ -101,14 +112,7 @@ class SpeculatorsConfig(PretrainedConfig):
             )
 
         # Build base vLLM speculative configuration
-        vllm_config = {
+        return {
             "method": config_dict.get("speculators_model_type"),
             "num_speculative_tokens": num_speculative_tokens,
-            "target_model": spec_config.get("verifier")["name_or_path"],
         }
-
-        # Merge transformer layer configuration if present
-        transformer_config = config_dict.get("transformer_layer_config", {})
-        vllm_config.update(transformer_config)
-
-        return vllm_config
diff --git a/vllm/v1/spec_decode/draft_model.py b/vllm/v1/spec_decode/draft_model.py
index 9c6754013..18e98b267 100644
--- a/vllm/v1/spec_decode/draft_model.py
+++ b/vllm/v1/spec_decode/draft_model.py
@@ -4,7 +4,7 @@ from typing import Any
 
 import torch
 
-from vllm.config import VllmConfig, get_layers_from_vllm_config
+from vllm.config import VllmConfig, get_layers_from_vllm_config, replace
 from vllm.logger import init_logger
 from vllm.model_executor.layers.attention import Attention
 from vllm.model_executor.model_loader import get_model
@@ -191,10 +191,12 @@ def create_vllm_config_for_draft_model(
     old = target_model_vllm_config
     assert old.speculative_config is not None, "speculative_config is not set"
     old_spec_config = old.speculative_config
-    new_parallel_config = old_spec_config.draft_parallel_config.replace(
-        rank=old.parallel_config.rank
+    new_parallel_config = replace(
+        old_spec_config.draft_parallel_config,
+        rank=old.parallel_config.rank,
     )
-    new: VllmConfig = old.replace(
+    new: VllmConfig = replace(
+        old,
         quant_config=None,  # quant_config is recomputed in __init__()
         model_config=old_spec_config.draft_model_config,
         parallel_config=new_parallel_config,