diff --git a/tools/pre_commit/mypy.py b/tools/pre_commit/mypy.py
index a3aa54634..8d04848f8 100755
--- a/tools/pre_commit/mypy.py
+++ b/tools/pre_commit/mypy.py
@@ -36,12 +36,15 @@ FILES = [
     "vllm/transformers_utils",
     "vllm/triton_utils",
     "vllm/usage",
+    "vllm/v1/core",
+    "vllm/v1/engine",
 ]
 
 # After fixing errors resulting from changing follow_imports
 # from "skip" to "silent", move the following directories to FILES
 SEPARATE_GROUPS = [
     "tests",
+    # v0 related
     "vllm/attention",
     "vllm/compilation",
     "vllm/engine",
@@ -50,7 +53,16 @@ SEPARATE_GROUPS = [
     "vllm/model_executor",
     "vllm/plugins",
     "vllm/worker",
-    "vllm/v1",
+    # v1 related
+    "vllm/v1/attention",
+    "vllm/v1/executor",
+    "vllm/v1/kv_offload",
+    "vllm/v1/metrics",
+    "vllm/v1/pool",
+    "vllm/v1/sample",
+    "vllm/v1/spec_decode",
+    "vllm/v1/structured_output",
+    "vllm/v1/worker",
 ]
 
 # TODO(woosuk): Include the code from Megatron and HuggingFace.
diff --git a/vllm/config/vllm.py b/vllm/config/vllm.py
index f592a708a..1acac70c3 100644
--- a/vllm/config/vllm.py
+++ b/vllm/config/vllm.py
@@ -84,7 +84,9 @@ class VllmConfig:
         default_factory=StructuredOutputsConfig
     )
     """Structured outputs configuration."""
-    observability_config: ObservabilityConfig | None = None
+    observability_config: ObservabilityConfig = Field(
+        default_factory=ObservabilityConfig
+    )
     """Observability configuration."""
     quant_config: QuantizationConfig | None = None
     """Quantization configuration."""
@@ -170,10 +172,7 @@ class VllmConfig:
             vllm_factors.append(self.structured_outputs_config.compute_hash())
         else:
             vllm_factors.append("None")
-        if self.observability_config:
-            vllm_factors.append(self.observability_config.compute_hash())
-        else:
-            vllm_factors.append("None")
+        vllm_factors.append(self.observability_config.compute_hash())
         if self.quant_config:
             pass  # should be captured by model_config.quantization
         if self.compilation_config:
diff --git a/vllm/engine/protocol.py b/vllm/engine/protocol.py
index 959a03428..24fcd9fe1 100644
--- a/vllm/engine/protocol.py
+++ b/vllm/engine/protocol.py
@@ -77,6 +77,7 @@ class EngineClient(ABC):
         lora_request: LoRARequest | None = None,
         trace_headers: Mapping[str, str] | None = None,
         priority: int = 0,
+        truncate_prompt_tokens: int | None = None,
         tokenization_kwargs: dict[str, Any] | None = None,
     ) -> AsyncGenerator[PoolingRequestOutput, None]:
         """Generate outputs for a request from a pooling model."""
diff --git a/vllm/v1/core/sched/scheduler.py b/vllm/v1/core/sched/scheduler.py
index c794886bc..ad6fbee2e 100644
--- a/vllm/v1/core/sched/scheduler.py
+++ b/vllm/v1/core/sched/scheduler.py
@@ -167,7 +167,7 @@ class Scheduler(SchedulerInterface):
         self.kv_cache_manager = KVCacheManager(
             kv_cache_config=kv_cache_config,
             max_model_len=self.max_model_len,
-            enable_caching=self.cache_config.enable_prefix_caching,
+            enable_caching=bool(self.cache_config.enable_prefix_caching),
             use_eagle=self.use_eagle,
             log_stats=self.log_stats,
             enable_kv_cache_events=self.enable_kv_cache_events,
@@ -407,13 +407,13 @@ class Scheduler(SchedulerInterface):
 
                     # Get externally-cached tokens if using a KVConnector.
                     if self.connector is not None:
-                        num_external_computed_tokens, load_kv_async = (
+                        ext_tokens, load_kv_async = (
                             self.connector.get_num_new_matched_tokens(
                                 request, num_new_local_computed_tokens
                             )
                         )
 
-                        if num_external_computed_tokens is None:
+                        if ext_tokens is None:
                             # The request cannot be scheduled because
                             # the KVConnector couldn't determine
                             # the number of matched tokens.
@@ -421,6 +421,8 @@ class Scheduler(SchedulerInterface):
                             skipped_waiting_requests.prepend_request(request)
                             continue
 
+                        num_external_computed_tokens = ext_tokens
+
                     # Total computed tokens (local + external).
                     num_computed_tokens = (
                         num_new_local_computed_tokens + num_external_computed_tokens
@@ -905,13 +907,13 @@ class Scheduler(SchedulerInterface):
 
         outputs: dict[int, list[EngineCoreOutput]] = defaultdict(list)
         spec_decoding_stats: SpecDecodingStats | None = None
-        kv_connector_stats = (
+        kv_connector_stats: KVConnectorStats | None = (
             kv_connector_output.kv_connector_stats if kv_connector_output else None
         )
         if kv_connector_stats and self.connector:
-            stats = self.connector.get_kv_connector_stats()
-            if stats:
-                kv_connector_stats = kv_connector_stats.aggregate(stats)
+            kv_stats = self.connector.get_kv_connector_stats()
+            if kv_stats:
+                kv_connector_stats = kv_connector_stats.aggregate(kv_stats)
 
         failed_kv_load_req_ids = None
         if kv_connector_output and kv_connector_output.invalid_block_ids:
diff --git a/vllm/v1/engine/async_llm.py b/vllm/v1/engine/async_llm.py
index 761c37504..dc61d4501 100644
--- a/vllm/v1/engine/async_llm.py
+++ b/vllm/v1/engine/async_llm.py
@@ -6,7 +6,7 @@ import socket
 import time
 from collections.abc import AsyncGenerator, Iterable, Mapping
 from copy import copy
-from typing import Any
+from typing import Any, cast
 
 import numpy as np
 import torch
@@ -131,10 +131,9 @@ class AsyncLLM(EngineClient):
         self.output_processor = OutputProcessor(
             self.tokenizer, log_stats=self.log_stats
         )
-        if self.observability_config.otlp_traces_endpoint is not None:
-            tracer = init_tracer(
-                "vllm.llm_engine", self.observability_config.otlp_traces_endpoint
-            )
+        endpoint = self.observability_config.otlp_traces_endpoint
+        if endpoint is not None:
+            tracer = init_tracer("vllm.llm_engine", endpoint)
             self.output_processor.tracer = tracer
 
         # EngineCore (starts the engine in background process).
@@ -266,7 +265,9 @@ class AsyncLLM(EngineClient):
         if engine_core := getattr(self, "engine_core", None):
             engine_core.shutdown()
 
-        cancel_task_threadsafe(getattr(self, "output_handler", None))
+        handler = getattr(self, "output_handler", None)
+        if handler is not None:
+            cancel_task_threadsafe(handler)
 
     async def get_supported_tasks(self) -> tuple[SupportedTask, ...]:
         return await self.engine_core.get_supported_tasks_async()
@@ -314,7 +315,10 @@ class AsyncLLM(EngineClient):
                 priority,
                 data_parallel_rank,
             )
-            prompt_text = prompt if isinstance(prompt, str) else prompt.get("prompt")
+            if isinstance(prompt, str):
+                prompt_text = prompt
+            elif isinstance(prompt, Mapping):
+                prompt_text = cast(str | None, prompt.get("prompt"))
 
         if is_pooling or params.n == 1:
             await self._add_request(request, prompt_text, None, 0, queue)
@@ -436,6 +440,7 @@ class AsyncLLM(EngineClient):
                 # Note: both OutputProcessor and EngineCore handle their
                 # own request cleanup based on finished.
                 finished = out.finished
+                assert isinstance(out, RequestOutput)
                 yield out
 
         # If the request is disconnected by the client, generate()
@@ -653,7 +658,7 @@ class AsyncLLM(EngineClient):
         return self.tokenizer
 
     async def is_tracing_enabled(self) -> bool:
-        return self.observability_config.otlp_traces_endpoint is not None
+        return self.observability_config.otlp_traces_endpoint is not None  # type: ignore
 
     async def do_log_stats(self) -> None:
         if self.logger_manager:
diff --git a/vllm/v1/engine/core.py b/vllm/v1/engine/core.py
index 85cab32eb..6cbd986b3 100644
--- a/vllm/v1/engine/core.py
+++ b/vllm/v1/engine/core.py
@@ -1075,6 +1075,7 @@ class DPEngineCoreProc(EngineCoreProc):
         local_dp_rank = vllm_config.parallel_config.data_parallel_rank_local
 
         assert dp_size > 1
+        assert local_dp_rank is not None
         assert 0 <= local_dp_rank <= dp_rank < dp_size
 
         if vllm_config.kv_transfer_config is not None:
diff --git a/vllm/v1/engine/core_client.py b/vllm/v1/engine/core_client.py
index 7b554ca99..9b440505b 100644
--- a/vllm/v1/engine/core_client.py
+++ b/vllm/v1/engine/core_client.py
@@ -385,10 +385,11 @@ class BackgroundResources:
                         with contextlib.suppress(Exception):
                             task.cancel()
 
-            if in_loop(loop):
-                close_sockets_and_tasks()
-            elif loop and not loop.is_closed():
-                loop.call_soon_threadsafe(close_sockets_and_tasks)
+            if loop is not None:
+                if in_loop(loop):
+                    close_sockets_and_tasks()
+                elif not loop.is_closed():
+                    loop.call_soon_threadsafe(close_sockets_and_tasks)
             else:
                 # Loop has been closed, try to clean up directly.
                 del tasks
@@ -1044,6 +1045,7 @@ class DPAsyncMPClient(AsyncMPClient):
             return
 
         assert self.stats_update_address is not None
+        stats_addr: str = self.stats_update_address
         assert len(self.engine_ranks_managed) > 0
         # NOTE: running and waiting counts are all global from
         # the Coordinator include all global EngineCores. This
@@ -1054,9 +1056,7 @@ class DPAsyncMPClient(AsyncMPClient):
 
         async def run_engine_stats_update_task():
             with (
-                make_zmq_socket(
-                    self.ctx, self.stats_update_address, zmq.XSUB, linger=0
-                ) as socket,
+                make_zmq_socket(self.ctx, stats_addr, zmq.XSUB, linger=0) as socket,
                 make_zmq_socket(
                     self.ctx, self.first_req_sock_addr, zmq.PAIR, bind=False, linger=0
                 ) as first_req_rcv_socket,
diff --git a/vllm/v1/engine/detokenizer.py b/vllm/v1/engine/detokenizer.py
index 5f66e3689..b7a24096b 100644
--- a/vllm/v1/engine/detokenizer.py
+++ b/vllm/v1/engine/detokenizer.py
@@ -69,14 +69,21 @@ class BaseIncrementalDetokenizer(IncrementalDetokenizer, ABC):
         # Stop strings
         params = request.sampling_params
         assert params is not None
-        self.stop = stop = params.stop
+        stop_list: list[str]
+        if params.stop is None:
+            stop_list = []
+        elif isinstance(params.stop, str):
+            stop_list = [params.stop]
+        else:
+            stop_list = params.stop
+        self.stop = stop_list
         self.min_tokens = params.min_tokens
         self.include_stop_str_in_output = params.include_stop_str_in_output
 
         # Number of chars to hold back when stop strings are to be excluded
         # from streamed output.
-        if stop and not self.include_stop_str_in_output:
-            self.stop_buffer_length = max(len(s) for s in stop) - 1
+        if self.stop and not self.include_stop_str_in_output:
+            self.stop_buffer_length = max(len(s) for s in self.stop) - 1
         else:
             self.stop_buffer_length = 0
         self._last_output_text_offset: int = 0
diff --git a/vllm/v1/engine/llm_engine.py b/vllm/v1/engine/llm_engine.py
index 0fce34370..c2ca9579d 100644
--- a/vllm/v1/engine/llm_engine.py
+++ b/vllm/v1/engine/llm_engine.py
@@ -4,7 +4,7 @@
 import time
 from collections.abc import Callable, Mapping
 from copy import copy
-from typing import Any
+from typing import Any, cast
 
 import torch.nn as nn
 from typing_extensions import TypeVar
@@ -112,10 +112,9 @@ class LLMEngine:
         self.output_processor = OutputProcessor(
             self.tokenizer, log_stats=self.log_stats
         )
-        if self.observability_config.otlp_traces_endpoint is not None:
-            tracer = init_tracer(
-                "vllm.llm_engine", self.observability_config.otlp_traces_endpoint
-            )
+        endpoint = self.observability_config.otlp_traces_endpoint
+        if endpoint is not None:
+            tracer = init_tracer("vllm.llm_engine", endpoint)
             self.output_processor.tracer = tracer
 
         # EngineCore (gets EngineCoreRequests and gives EngineCoreOutputs)
@@ -259,7 +258,10 @@ class LLMEngine:
                 trace_headers,
                 priority,
             )
-            prompt_text = prompt if isinstance(prompt, str) else prompt.get("prompt")
+            if isinstance(prompt, str):
+                prompt_text = prompt
+            elif isinstance(prompt, Mapping):
+                prompt_text = cast(str | None, prompt.get("prompt"))
 
         n = params.n if isinstance(params, SamplingParams) else 1
 
@@ -285,7 +287,7 @@ class LLMEngine:
             # Add the request to EngineCore.
             self.engine_core.add_request(child_request)
 
-    def step(self) -> list[RequestOutput] | list[PoolingRequestOutput]:
+    def step(self) -> list[RequestOutput | PoolingRequestOutput]:
         if self.should_execute_dummy_batch:
             self.should_execute_dummy_batch = False
             self.engine_core.execute_dummy_batch()
diff --git a/vllm/v1/engine/output_processor.py b/vllm/v1/engine/output_processor.py
index 44e4eadce..07c8113dd 100644
--- a/vllm/v1/engine/output_processor.py
+++ b/vllm/v1/engine/output_processor.py
@@ -44,10 +44,16 @@ class RequestOutputCollector:
         if self.output is None or isinstance(output, Exception):
             self.output = output
             self.ready.set()
-        elif isinstance(self.output, (RequestOutput, PoolingRequestOutput)):
+        elif isinstance(self.output, RequestOutput) and isinstance(
+            output, RequestOutput
+        ):
             # This ensures that request outputs with different request indexes
             # (if n > 1) do not override each other.
             self.output.add(output, aggregate=self.aggregate)
+        elif isinstance(self.output, PoolingRequestOutput) and isinstance(
+            output, PoolingRequestOutput
+        ):
+            self.output = output
 
     async def get(self) -> RequestOutput | PoolingRequestOutput:
         """Get operation blocks on put event."""
@@ -408,7 +414,7 @@ class OutputProcessor:
         within the loop below.
         """
 
-        request_outputs: list[RequestOutput] | list[PoolingRequestOutput] = []
+        request_outputs: list[RequestOutput | PoolingRequestOutput] = []
         reqs_to_abort: list[str] = []
         for engine_core_output in engine_core_outputs:
             req_id = engine_core_output.request_id
diff --git a/vllm/v1/engine/parallel_sampling.py b/vllm/v1/engine/parallel_sampling.py
index 2a47befec..26ee10d2b 100644
--- a/vllm/v1/engine/parallel_sampling.py
+++ b/vllm/v1/engine/parallel_sampling.py
@@ -2,7 +2,7 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
 from copy import copy
-from typing import Optional
+from typing import Optional, cast
 
 from vllm.outputs import CompletionOutput
 from vllm.sampling_params import RequestOutputKind, SamplingParams
@@ -37,7 +37,7 @@ class ParentRequest:
 
         self.child_requests = set()
         self.output_aggregator = (
-            [None] * sampling_params.n
+            [cast(CompletionOutput, None)] * sampling_params.n
             if (sampling_params.output_kind == RequestOutputKind.FINAL_ONLY)
             else []
         )
diff --git a/vllm/v1/engine/processor.py b/vllm/v1/engine/processor.py
index de15677ae..c49fd1bde 100644
--- a/vllm/v1/engine/processor.py
+++ b/vllm/v1/engine/processor.py
@@ -3,7 +3,7 @@
 
 import time
 from collections.abc import Mapping
-from typing import Any, Literal
+from typing import Any, Literal, cast
 
 from vllm.config import VllmConfig
 from vllm.inputs import ProcessorInputs, PromptType, SingletonInputs
@@ -208,9 +208,9 @@ class Processor:
             enc = prompt.get("encoder_prompt")
             dec = prompt.get("decoder_prompt")
             if enc is not None:
-                _validate_single_prompt(enc)
+                _validate_single_prompt(cast(dict | str, enc))
             if dec is not None:
-                _validate_single_prompt(dec)
+                _validate_single_prompt(cast(dict | str, dec))
         else:
             _validate_single_prompt(prompt)  # type: ignore[arg-type]
 
@@ -332,7 +332,7 @@ class Processor:
         if not mm_data:
             return None
 
-        mm_uuids: MultiModalUUIDDict = {}
+        mm_uuids: dict[str, list[str | None] | str] = {}
         for modality, data in mm_data.items():
             n = len(data) if isinstance(data, list) else 1
             mm_uuids[modality] = [f"{request_id}-{modality}-{i}" for i in range(n)]
@@ -384,7 +384,9 @@ class Processor:
             # if provided.
             self._validate_multi_modal_uuids(prompt)
             if isinstance(prompt, dict):
-                mm_uuids = prompt.get("multi_modal_uuids")
+                mm_uuids = cast(
+                    MultiModalUUIDDict | None, prompt.get("multi_modal_uuids")
+                )
             else:
                 mm_uuids = None
 
@@ -410,20 +412,13 @@ class Processor:
         encoder_inputs, decoder_inputs = split_enc_dec_inputs(processed_inputs)
         self._validate_model_inputs(encoder_inputs, decoder_inputs)
 
-        # Mypy does not always properly infer the types of some elements of
-        # discriminated unions of TypedDicts, because of how it handles
-        # inheritance of TypedDict. If we explicitly extract the items we want
-        # we can avoid type errors from using `dict.get` later in the method.
-        prompt_token_ids = (
-            decoder_inputs["prompt_token_ids"]
-            if decoder_inputs["type"] != "embeds"
-            else None
-        )
-        prompt_embeds = (
-            decoder_inputs["prompt_embeds"]
-            if decoder_inputs["type"] == "embeds"
-            else None
-        )
+        # Mypy can be conservative for TypedDict unions; normalize access.
+        if decoder_inputs["type"] == "embeds":
+            prompt_token_ids = None
+            prompt_embeds = decoder_inputs["prompt_embeds"]
+        else:
+            prompt_token_ids = decoder_inputs["prompt_token_ids"]
+            prompt_embeds = None
 
         sampling_params = None
         pooling_params = None