[oai serving chat] Add argument --sampling-defaults and fix ChatCompletionRequest defaults (#11304)

python/sglang/srt/configs/model_config.py

@@ -17,7 +17,7 @@ import logging
 import math
 import os
 from enum import Enum, IntEnum, auto
-from typing import Dict, List, Optional, Set, Union
+from typing import Any, Dict, List, Optional, Set, Union
 
 import torch
 from transformers import PretrainedConfig
@@ -90,6 +90,7 @@ class ModelConfig:
         is_draft_model: bool = False,
         hybrid_kvcache_ratio: Optional[float] = None,
         model_impl: Union[str, ModelImpl] = ModelImpl.AUTO,
+        sampling_defaults: str = "openai",
     ) -> None:
         # Parse args
         self.model_path = model_path
@@ -98,6 +99,7 @@ class ModelConfig:
         self.modelopt_quant = modelopt_quant
         self.is_draft_model = is_draft_model
         self.model_impl = model_impl
+        self.sampling_defaults = sampling_defaults
 
         # Get hf config
         self._maybe_pull_model_tokenizer_from_remote()
@@ -214,6 +216,7 @@ class ModelConfig:
             modelopt_quant=server_args.modelopt_quant,
             hybrid_kvcache_ratio=server_args.hybrid_kvcache_ratio,
             model_impl=server_args.model_impl,
+            sampling_defaults=server_args.sampling_defaults,
             **kwargs,
         )
 
@@ -659,6 +662,38 @@ class ModelConfig:
                 eos_ids = eos_ids | generation_eos_ids
         return eos_ids
 
+    def get_default_sampling_params(self) -> dict[str, Any]:
+        """
+        Get default sampling parameters from the model's generation config.
+
+        This method returns non-default sampling parameters from the model's
+        generation_config.json when sampling_defaults is set to "model".
+
+        Returns:
+            A dictionary containing the non-default sampling parameters.
+        """
+        if self.sampling_defaults != "model":
+            return {}
+
+        if self.hf_generation_config is None:
+            return {}
+
+        config = self.hf_generation_config.to_dict()
+
+        available_params = [
+            "repetition_penalty",
+            "temperature",
+            "top_k",
+            "top_p",
+            "min_p",
+        ]
+
+        default_sampling_params = {
+            p: config.get(p) for p in available_params if config.get(p) is not None
+        }
+
+        return default_sampling_params
+
     def _maybe_pull_model_tokenizer_from_remote(self) -> None:
         """
         Pull the model config files to a temporary

python/sglang/srt/entrypoints/openai/protocol.py

@@ -13,6 +13,7 @@
 # ==============================================================================
 """Pydantic models for OpenAI API protocol"""
 
+import logging
 import time
 import uuid
 from dataclasses import dataclass
@@ -37,6 +38,10 @@ from pydantic import (
 )
 from typing_extensions import Literal
 
+from sglang.utils import convert_json_schema_to_str
+
+logger = logging.getLogger(__name__)
+
 DEFAULT_MODEL_NAME = "default"
 
 
@@ -445,8 +450,8 @@ class ChatCompletionRequest(BaseModel):
     stop: Optional[Union[str, List[str]]] = None
     stream: bool = False
     stream_options: Optional[StreamOptions] = None
-    temperature: float = 0.7
+    temperature: Optional[float] = None
-    top_p: float = 1.0
+    top_p: Optional[float] = None
     user: Optional[str] = None
     tools: Optional[List[Tool]] = Field(default=None, examples=[None])
     tool_choice: Union[ToolChoice, Literal["auto", "required", "none"]] = Field(
@@ -461,6 +466,47 @@ class ChatCompletionRequest(BaseModel):
         "Currently only supported for OpenAI models in the harmony path, i.e GPT-OSS models.",
     )
 
+    # Extra parameters for SRT backend only and will be ignored by OpenAI models.
+    top_k: Optional[int] = None
+    min_p: Optional[float] = None
+    min_tokens: int = 0
+    regex: Optional[str] = None
+    ebnf: Optional[str] = None
+    repetition_penalty: Optional[float] = None
+    stop_token_ids: Optional[List[int]] = None
+    no_stop_trim: bool = False
+    ignore_eos: bool = False
+    continue_final_message: bool = False
+    skip_special_tokens: bool = True
+    lora_path: Optional[Union[List[Optional[str]], Optional[str]]] = None
+    session_params: Optional[Dict] = None
+    separate_reasoning: bool = True
+    stream_reasoning: bool = True
+    chat_template_kwargs: Optional[Dict] = None
+
+    # For request id
+    rid: Optional[Union[List[str], str]] = None
+    # Extra key for classifying the request (e.g. cache_salt)
+    extra_key: Optional[Union[List[str], str]] = None
+    # Cache salt for request caching
+    cache_salt: Optional[Union[List[str], str]] = None
+    # Priority for the request
+    priority: Optional[int] = None
+
+    # For PD disaggregation
+    bootstrap_host: Optional[Union[List[str], str]] = None
+    bootstrap_port: Optional[Union[List[Optional[int]], int]] = None
+    bootstrap_room: Optional[Union[List[int], int]] = None
+
+    # OpenAI/SGLang default sampling parameters
+    _DEFAULT_SAMPLING_PARAMS = {
+        "temperature": 1.0,
+        "top_p": 1.0,
+        "top_k": -1,
+        "min_p": 0.0,
+        "repetition_penalty": 1.0,
+    }
+
     @model_validator(mode="before")
     @classmethod
     def set_tool_choice_default(cls, values):
@@ -531,37 +577,81 @@ class ChatCompletionRequest(BaseModel):
 
         return values
 
-    # Extra parameters for SRT backend only and will be ignored by OpenAI models.
+    def to_sampling_params(
-    top_k: int = -1
+        self,
-    min_p: float = 0.0
+        stop: List[str],
-    min_tokens: int = 0
+        model_generation_config: Dict[str, Any],
-    regex: Optional[str] = None
+        tool_call_constraint: Optional[Any] = None,
-    ebnf: Optional[str] = None
+    ) -> Dict[str, Any]:
-    repetition_penalty: float = 1.0
+        """
-    stop_token_ids: Optional[List[int]] = None
+        Convert request to sampling parameters.
-    no_stop_trim: bool = False
+        Priority: user value > model generation_config > OpenAI defaults
-    ignore_eos: bool = False
+        """
-    continue_final_message: bool = False
-    skip_special_tokens: bool = True
-    lora_path: Optional[Union[List[Optional[str]], Optional[str]]] = None
-    session_params: Optional[Dict] = None
-    separate_reasoning: bool = True
-    stream_reasoning: bool = True
-    chat_template_kwargs: Optional[Dict] = None
 
-    # For request id
+        def get_param(param_name: str):
-    rid: Optional[Union[List[str], str]] = None
+            value = getattr(self, param_name)
-    # Extra key for classifying the request (e.g. cache_salt)
+            if value is None:
-    extra_key: Optional[Union[List[str], str]] = None
+                return model_generation_config.get(
-    # Cache salt for request caching
+                    param_name, self._DEFAULT_SAMPLING_PARAMS[param_name]
-    cache_salt: Optional[Union[List[str], str]] = None
+                )
-    # Priority for the request
+            return value
-    priority: Optional[int] = None
 
-    # For PD disaggregation
+        sampling_params = {
-    bootstrap_host: Optional[Union[List[str], str]] = None
+            "temperature": get_param("temperature"),
-    bootstrap_port: Optional[Union[List[Optional[int]], int]] = None
+            "max_new_tokens": self.max_tokens or self.max_completion_tokens,
-    bootstrap_room: Optional[Union[List[int], int]] = None
+            "min_new_tokens": self.min_tokens,
+            "stop": stop,
+            "stop_token_ids": self.stop_token_ids,
+            "top_p": get_param("top_p"),
+            "top_k": get_param("top_k"),
+            "min_p": get_param("min_p"),
+            "presence_penalty": self.presence_penalty,
+            "frequency_penalty": self.frequency_penalty,
+            "repetition_penalty": get_param("repetition_penalty"),
+            "regex": self.regex,
+            "ebnf": self.ebnf,
+            "n": self.n,
+            "no_stop_trim": self.no_stop_trim,
+            "ignore_eos": self.ignore_eos,
+            "skip_special_tokens": self.skip_special_tokens,
+            "logit_bias": self.logit_bias,
+        }
+
+        if self.response_format and self.response_format.type == "json_schema":
+            sampling_params["json_schema"] = convert_json_schema_to_str(
+                self.response_format.json_schema.schema_
+            )
+        elif self.response_format and self.response_format.type == "json_object":
+            sampling_params["json_schema"] = '{"type": "object"}'
+        elif self.response_format and self.response_format.type == "structural_tag":
+            sampling_params["structural_tag"] = convert_json_schema_to_str(
+                self.response_format.model_dump(by_alias=True)
+            )
+
+        # Check if there are already existing output constraints
+        has_existing_constraints = (
+            sampling_params.get("regex")
+            or sampling_params.get("ebnf")
+            or sampling_params.get("structural_tag")
+            or sampling_params.get("json_schema")
+        )
+
+        if tool_call_constraint and has_existing_constraints:
+            logger.warning("Constrained decoding is not compatible with tool calls.")
+        elif tool_call_constraint:
+            constraint_type, constraint_value = tool_call_constraint
+            if constraint_type == "structural_tag":
+                sampling_params[constraint_type] = convert_json_schema_to_str(
+                    constraint_value.model_dump(by_alias=True)
+                )
+            elif constraint_type == "json_schema":
+                sampling_params[constraint_type] = convert_json_schema_to_str(
+                    constraint_value
+                )
+            else:
+                sampling_params[constraint_type] = constraint_value
+
+        return sampling_params
 
 
 class ChatMessage(BaseModel):

python/sglang/srt/entrypoints/openai/serving_chat.py

@@ -44,7 +44,6 @@ from sglang.srt.managers.io_struct import GenerateReqInput
 from sglang.srt.parser.conversation import generate_chat_conv
 from sglang.srt.parser.jinja_template_utils import process_content_for_template_format
 from sglang.srt.parser.reasoning_parser import ReasoningParser
-from sglang.utils import convert_json_schema_to_str
 
 if TYPE_CHECKING:
     from sglang.srt.managers.template_manager import TemplateManager
@@ -66,6 +65,15 @@ class OpenAIServingChat(OpenAIServingBase):
         self.tool_call_parser = self.tokenizer_manager.server_args.tool_call_parser
         self.reasoning_parser = self.tokenizer_manager.server_args.reasoning_parser
 
+        # Get default sampling parameters from model's generation config
+        self.default_sampling_params = (
+            self.tokenizer_manager.model_config.get_default_sampling_params()
+        )
+        if self.default_sampling_params:
+            logger.info(
+                f"Using default chat sampling params from model generation config: {self.default_sampling_params}",
+            )
+
     def _request_id_prefix(self) -> str:
         return "chatcmpl-"
 
@@ -137,10 +145,10 @@ class OpenAIServingChat(OpenAIServingBase):
         processed_messages = self._process_messages(request, is_multimodal)
 
         # Build sampling parameters
-        sampling_params = self._build_sampling_params(
+        sampling_params = request.to_sampling_params(
-            request,
+            stop=processed_messages.stop,
-            processed_messages.stop,
+            model_generation_config=self.default_sampling_params,
-            processed_messages.tool_call_constraint,
+            tool_call_constraint=processed_messages.tool_call_constraint,
         )
 
         # Handle single vs multiple requests
@@ -410,72 +418,6 @@ class OpenAIServingChat(OpenAIServingBase):
             stop=stop,
         )
 
-    def _build_sampling_params(
-        self,
-        request: ChatCompletionRequest,
-        stop: List[str],
-        tool_call_constraint: Optional[Any],
-    ) -> Dict[str, Any]:
-        """Build sampling parameters for the request"""
-
-        sampling_params = {
-            "temperature": request.temperature,
-            "max_new_tokens": request.max_tokens or request.max_completion_tokens,
-            "min_new_tokens": request.min_tokens,
-            "stop": stop,
-            "stop_token_ids": request.stop_token_ids,
-            "top_p": request.top_p,
-            "top_k": request.top_k,
-            "min_p": request.min_p,
-            "presence_penalty": request.presence_penalty,
-            "frequency_penalty": request.frequency_penalty,
-            "repetition_penalty": request.repetition_penalty,
-            "regex": request.regex,
-            "ebnf": request.ebnf,
-            "n": request.n,
-            "no_stop_trim": request.no_stop_trim,
-            "ignore_eos": request.ignore_eos,
-            "skip_special_tokens": request.skip_special_tokens,
-            "logit_bias": request.logit_bias,
-        }
-
-        if request.response_format and request.response_format.type == "json_schema":
-            sampling_params["json_schema"] = convert_json_schema_to_str(
-                request.response_format.json_schema.schema_
-            )
-        elif request.response_format and request.response_format.type == "json_object":
-            sampling_params["json_schema"] = '{"type": "object"}'
-        elif (
-            request.response_format and request.response_format.type == "structural_tag"
-        ):
-            sampling_params["structural_tag"] = convert_json_schema_to_str(
-                request.response_format.model_dump(by_alias=True)
-            )
-
-        # Check if there are already existing output constraints
-        has_existing_constraints = (
-            sampling_params.get("regex")
-            or sampling_params.get("ebnf")
-            or sampling_params.get("structural_tag")
-            or sampling_params.get("json_schema")
-        )
-
-        if tool_call_constraint and has_existing_constraints:
-            logger.warning("Constrained decoding is not compatible with tool calls.")
-        elif tool_call_constraint:
-            constraint_type, constraint_value = tool_call_constraint
-            if constraint_type == "structural_tag":
-                sampling_params[constraint_type] = convert_json_schema_to_str(
-                    constraint_value.model_dump(by_alias=True)
-                )
-            elif constraint_type == "json_schema":
-                sampling_params[constraint_type] = convert_json_schema_to_str(
-                    constraint_value
-                )
-            else:
-                sampling_params[constraint_type] = constraint_value
-        return sampling_params
-
     async def _handle_streaming_request(
         self,
         adapted_request: GenerateReqInput,

python/sglang/srt/server_args.py

@@ -252,6 +252,7 @@ class ServerArgs:
     reasoning_parser: Optional[str] = None
     tool_call_parser: Optional[str] = None
     tool_server: Optional[str] = None
+    sampling_defaults: str = "model"
 
     # Data parallelism
     dp_size: int = 1
@@ -1872,6 +1873,16 @@ class ServerArgs:
             default=ServerArgs.tool_call_parser,
             help=f"Specify the parser for handling tool-call interactions. Options include: {tool_call_parser_choices}.",
         )
+        parser.add_argument(
+            "--sampling-defaults",
+            type=str,
+            choices=["openai", "model"],
+            default=ServerArgs.sampling_defaults,
+            help="Where to get default sampling parameters. "
+            "'openai' uses SGLang/OpenAI defaults (temperature=1.0, top_p=1.0, etc.). "
+            "'model' uses the model's generation_config.json to get the recommended "
+            "sampling parameters if available. Default is 'model'.",
+        )
         parser.add_argument(
             "--tool-server",
             type=str,

test/srt/openai_server/basic/test_protocol.py

@@ -150,10 +150,26 @@ class TestChatCompletionRequest(unittest.TestCase):
         self.assertEqual(len(request.messages), 1)
         self.assertEqual(request.messages[0].role, "user")
         self.assertEqual(request.messages[0].content, "Hello")
-        self.assertEqual(request.temperature, 0.7)  # default
+        self.assertEqual(request.temperature, None)  # default
         self.assertFalse(request.stream)  # default
         self.assertEqual(request.tool_choice, "none")  # default when no tools
 
+    def test_sampling_param_build(self):
+        req = ChatCompletionRequest(
+            model="x",
+            messages=[{"role": "user", "content": "Hi"}],
+            temperature=0.8,
+            max_tokens=150,
+            min_tokens=5,
+            top_p=0.9,
+            stop=["</s>"],
+        )
+        params = req.to_sampling_params(["</s>"], {}, None)
+        self.assertEqual(params["temperature"], 0.8)
+        self.assertEqual(params["max_new_tokens"], 150)
+        self.assertEqual(params["min_new_tokens"], 5)
+        self.assertEqual(params["stop"], ["</s>"])
+
     def test_chat_completion_tool_choice_validation(self):
         """Test tool choice validation logic"""
         messages = [{"role": "user", "content": "Hello"}]

test/srt/openai_server/basic/test_serving_chat.py

@@ -177,28 +177,6 @@ class ServingChatTestCase(unittest.TestCase):
             self.assertNotIn("CUSTOM_STOP", result2.stop)
             self.assertEqual(conv_ins.stop_str, initial_stop_str)
 
-    # ------------- sampling-params -------------
-    def test_sampling_param_build(self):
-        req = ChatCompletionRequest(
-            model="x",
-            messages=[{"role": "user", "content": "Hi"}],
-            temperature=0.8,
-            max_tokens=150,
-            min_tokens=5,
-            top_p=0.9,
-            stop=["</s>"],
-        )
-        with patch.object(
-            self.chat,
-            "_process_messages",
-            return_value=("Prompt", [1], None, None, [], ["</s>"], None),
-        ):
-            params = self.chat._build_sampling_params(req, ["</s>"], None)
-            self.assertEqual(params["temperature"], 0.8)
-            self.assertEqual(params["max_new_tokens"], 150)
-            self.assertEqual(params["min_new_tokens"], 5)
-            self.assertEqual(params["stop"], ["</s>"])
-
     async def test_unstreamed_tool_args_completion(self):
         """Test that remaining tool call arguments are sent when generation finishes."""