[Core] add support for reasoning parser plugins (#28075)

Signed-off-by: walter beller-morales <walter.beller.morales@gmail.com>

vllm/config/structured_outputs.py

@@ -37,6 +37,9 @@ class StructuredOutputsConfig:
     reasoning_parser: str = ""
     """Select the reasoning parser depending on the model that you're using.
     This is used to parse the reasoning content into OpenAI API format."""
+    reasoning_parser_plugin: str = ""
+    """Path to a dynamically reasoning parser plugin that can be dynamically
+    loaded and registered."""
     enable_in_reasoning: bool = False
     """Whether to use structured input for reasoning."""
 
@@ -60,6 +63,22 @@ class StructuredOutputsConfig:
 
     @model_validator(mode="after")
     def _validate_structured_output_config(self) -> Self:
+        # Import here to avoid circular import
+        from vllm.reasoning.abs_reasoning_parsers import ReasoningParserManager
+
+        if self.reasoning_parser_plugin and len(self.reasoning_parser_plugin) > 3:
+            ReasoningParserManager.import_reasoning_parser(self.reasoning_parser_plugin)
+
+        valid_reasoning_parsers = ReasoningParserManager.list_registered()
+        if (
+            self.reasoning_parser != ""
+            and self.reasoning_parser not in valid_reasoning_parsers
+        ):
+            raise ValueError(
+                f"invalid reasoning parser: {self.reasoning_parser} "
+                f"(chose from {{ {','.join(valid_reasoning_parsers)} }})"
+            )
+
         if self.disable_any_whitespace and self.backend not in ("xgrammar", "guidance"):
             raise ValueError(
                 "disable_any_whitespace is only supported for "

vllm/engine/arg_utils.py

@@ -80,7 +80,6 @@ from vllm.logger import init_logger
 from vllm.platforms import CpuArchEnum, current_platform
 from vllm.plugins import load_general_plugins
 from vllm.ray.lazy_utils import is_in_ray_actor, is_ray_initialized
-from vllm.reasoning import ReasoningParserManager
 from vllm.transformers_utils.config import (
     get_model_path,
     is_interleaved,
@@ -495,7 +494,7 @@ class EngineArgs:
         VllmConfig, "structured_outputs_config"
     )
     reasoning_parser: str = StructuredOutputsConfig.reasoning_parser
-
+    reasoning_parser_plugin: str | None = None
     # Deprecated guided decoding fields
     guided_decoding_backend: str | None = None
     guided_decoding_disable_fallback: bool | None = None
@@ -707,10 +706,13 @@ class EngineArgs:
         )
         structured_outputs_group.add_argument(
             "--reasoning-parser",
-            # This choice is a special case because it's not static
-            choices=list(ReasoningParserManager.list_registered()),
+            # Choices need to be validated after parsing to include plugins
             **structured_outputs_kwargs["reasoning_parser"],
         )
+        structured_outputs_group.add_argument(
+            "--reasoning-parser-plugin",
+            **structured_outputs_kwargs["reasoning_parser_plugin"],
+        )
         # Deprecated guided decoding arguments
         for arg, type in [
             ("--guided-decoding-backend", str),
@@ -1629,6 +1631,11 @@ class EngineArgs:
         if self.reasoning_parser:
             self.structured_outputs_config.reasoning_parser = self.reasoning_parser
 
+        if self.reasoning_parser_plugin:
+            self.structured_outputs_config.reasoning_parser_plugin = (
+                self.reasoning_parser_plugin
+            )
+
         # Forward the deprecated CLI args to the StructuredOutputsConfig
         so_config = self.structured_outputs_config
         if self.guided_decoding_backend is not None:

vllm/entrypoints/openai/api_server.py

@@ -1944,13 +1944,13 @@ def validate_api_server_args(args):
             f"(chose from {{ {','.join(valid_tool_parses)} }})"
         )
 
-    valid_reasoning_parses = ReasoningParserManager.list_registered()
+    valid_reasoning_parsers = ReasoningParserManager.list_registered()
     if (
         reasoning_parser := args.structured_outputs_config.reasoning_parser
-    ) and reasoning_parser not in valid_reasoning_parses:
+    ) and reasoning_parser not in valid_reasoning_parsers:
         raise KeyError(
             f"invalid reasoning parser: {reasoning_parser} "
-            f"(chose from {{ {','.join(valid_reasoning_parses)} }})"
+            f"(chose from {{ {','.join(valid_reasoning_parsers)} }})"
         )
 
 
@@ -1964,6 +1964,9 @@ def setup_server(args):
     if args.tool_parser_plugin and len(args.tool_parser_plugin) > 3:
         ToolParserManager.import_tool_parser(args.tool_parser_plugin)
 
+    if args.reasoning_parser_plugin and len(args.reasoning_parser_plugin) > 3:
+        ReasoningParserManager.import_reasoning_parser(args.reasoning_parser_plugin)
+
     validate_api_server_args(args)
 
     # workaround to make sure that we bind the port before the engine is set up.
@@ -2013,6 +2016,9 @@ async def run_server_worker(
     if args.tool_parser_plugin and len(args.tool_parser_plugin) > 3:
         ToolParserManager.import_tool_parser(args.tool_parser_plugin)
 
+    if args.reasoning_parser_plugin and len(args.reasoning_parser_plugin) > 3:
+        ReasoningParserManager.import_reasoning_parser(args.reasoning_parser_plugin)
+
     # Load logging config for uvicorn if specified
     log_config = load_log_config(args.log_config_file)
     if log_config is not None:

vllm/entrypoints/openai/run_batch.py

@@ -334,13 +334,13 @@ async def run_request(
 
 
 def validate_run_batch_args(args):
-    valid_reasoning_parses = ReasoningParserManager.list_registered()
+    valid_reasoning_parsers = ReasoningParserManager.list_registered()
     if (
         reasoning_parser := args.structured_outputs_config.reasoning_parser
-    ) and reasoning_parser not in valid_reasoning_parses:
+    ) and reasoning_parser not in valid_reasoning_parsers:
         raise KeyError(
             f"invalid reasoning parser: {reasoning_parser} "
-            f"(chose from {{ {','.join(valid_reasoning_parses)} }})"
+            f"(chose from {{ {','.join(valid_reasoning_parsers)} }})"
         )
 
 

vllm/reasoning/basic_parsers.py

@@ -3,15 +3,21 @@
 
 from abc import abstractmethod
 from collections.abc import Sequence
+from typing import TYPE_CHECKING, Any
 
-from vllm.entrypoints.openai.protocol import (
-    ChatCompletionRequest,
-    DeltaMessage,
-    ResponsesRequest,
-)
+from vllm.entrypoints.openai.protocol import DeltaMessage
 from vllm.reasoning.abs_reasoning_parsers import ReasoningParser
 from vllm.transformers_utils.tokenizer import AnyTokenizer
 
+if TYPE_CHECKING:
+    from vllm.entrypoints.openai.protocol import (
+        ChatCompletionRequest,
+        ResponsesRequest,
+    )
+else:
+    ChatCompletionRequest = Any
+    ResponsesRequest = Any
+
 
 class BaseThinkingReasoningParser(ReasoningParser):
     """

vllm/v1/structured_output/__init__.py

@@ -64,6 +64,15 @@ class StructuredOutputManager:
             self.tokenizer = init_tokenizer_from_configs(
                 model_config=self.vllm_config.model_config
             )
+            reasoning_parser = (
+                self.vllm_config.structured_outputs_config.reasoning_parser
+            )
+            reasoning_parser_plugin = (
+                self.vllm_config.structured_outputs_config.reasoning_parser_plugin
+            )
+            if reasoning_parser_plugin and len(reasoning_parser_plugin) > 3:
+                ReasoningParserManager.import_reasoning_parser(reasoning_parser_plugin)
+
             reasoning_parser = (
                 self.vllm_config.structured_outputs_config.reasoning_parser
             )