Support v1/responses and use harmony in serving_chat (#8837)

Signed-off-by: Xinyuan Tong <justinning0323@outlook.com>
Signed-off-by: Xinyuan Tong <xinyuantong.cs@gmail.com>
Co-authored-by: Xinyuan Tong <justinning0323@outlook.com>
Co-authored-by: Xinyuan Tong <xinyuantong.cs@gmail.com>

python/pyproject.toml

@@ -29,6 +29,7 @@ runtime_common = [
     "modelscope",
     "msgspec",
     "ninja",
+    "openai-harmony==0.0.3",
     "orjson",
     "outlines==0.1.11",
     "packaging",
@@ -96,7 +97,7 @@ srt_cpu = ["sglang[runtime_common]", "einops"]
 # https://vllm-ascend.readthedocs.io/en/latest/installation.html
 srt_npu = ["sglang[runtime_common]"]
 
-openai = ["openai>=1.0", "tiktoken"]
+openai = ["openai>=1.99.1", "tiktoken"]
 anthropic = ["anthropic>=0.20.0"]
 litellm = ["litellm>=1.0.0"]
 torch_memory_saver = ["torch_memory_saver>=0.0.8"]

python/sglang/srt/entrypoints/context.py

+# SPDX-License-Identifier: Apache-2.0
+# Copied from vLLM
+import json
+import logging
+from abc import ABC, abstractmethod
+from typing import Union
+
+logger = logging.getLogger(__name__)
+
+try:
+    from mcp import ClientSession
+except ImportError:
+    logger.warning("Ignoring mcp import error")
+
+from openai_harmony import Author, Message, Role, StreamState, TextContent
+
+from sglang.srt.entrypoints.harmony_utils import (
+    get_encoding,
+    get_streamable_parser_for_assistant,
+    render_for_completion,
+)
+from sglang.srt.entrypoints.tool import Tool
+
+
+class ConversationContext(ABC):
+
+    @abstractmethod
+    def append_output(self, output) -> None:
+        pass
+
+    @abstractmethod
+    async def call_tool(self) -> list[Message]:
+        pass
+
+    @abstractmethod
+    def need_builtin_tool_call(self) -> bool:
+        pass
+
+    @abstractmethod
+    def render_for_completion(self) -> list[int]:
+        pass
+
+
+class SimpleContext(ConversationContext):
+
+    def __init__(self):
+        self.last_output = None
+
+    def append_output(self, output) -> None:
+        self.last_output = output
+
+    def need_builtin_tool_call(self) -> bool:
+        return False
+
+    async def call_tool(self) -> list[Message]:
+        raise NotImplementedError("Should not be called.")
+
+    def render_for_completion(self) -> list[int]:
+        raise NotImplementedError("Should not be called.")
+
+
+class HarmonyContext(ConversationContext):
+
+    def __init__(
+        self,
+        messages: list,
+        tool_sessions: dict[str, Union["ClientSession", Tool]],
+    ):
+        # TODO: Remove the hack of Union[ClientSession, Tool] by using MCP
+        # when demo.
+        self._messages = messages
+        self.tool_sessions = tool_sessions
+
+        self.parser = get_streamable_parser_for_assistant()
+        self.num_init_messages = len(messages)
+        # TODO
+        self.num_prompt_tokens = 0
+        self.num_cached_tokens = 0
+        self.num_output_tokens = 0
+        self.num_reasoning_tokens = 0
+
+    def append_output(self, output) -> None:
+        if isinstance(output, dict) and "output_ids" in output:
+            output_token_ids = output["output_ids"]
+
+            # TODO: REMOVE here:
+            # Very hacky, find the first occurrence of token 200006 and cut from there
+            try:
+                start_index = output_token_ids.index(200006)
+                output_token_ids = output_token_ids[start_index:]
+            except ValueError:
+                pass
+
+            for token_id in output_token_ids:
+                self.parser.process(token_id)
+            output_msgs = self.parser.messages
+
+            meta_info = output["meta_info"]
+
+            if isinstance(meta_info, dict):
+                if "prompt_token_ids" in meta_info:
+                    self.num_prompt_tokens = meta_info["prompt_tokens"]
+                if "cached_tokens" in meta_info:
+                    self.num_cached_tokens = meta_info["cached_tokens"]
+                if "completion_tokens" in meta_info:
+                    self.num_output_tokens += meta_info["completion_tokens"]
+
+        else:
+            output_msgs = output
+
+        self._messages.extend(output_msgs)
+
+    @property
+    def messages(self) -> list:
+        return self._messages
+
+    def need_builtin_tool_call(self) -> bool:
+        last_msg = self.messages[-1]
+        recipient = last_msg.recipient
+        return recipient is not None and (
+            recipient.startswith("browser.") or recipient.startswith("python")
+        )
+
+    async def call_tool(self) -> list[Message]:
+        if not self.messages:
+            return []
+        last_msg = self.messages[-1]
+        recipient = last_msg.recipient
+        if recipient is not None:
+            if recipient.startswith("browser."):
+                return await self.call_search_tool(
+                    self.tool_sessions["browser"], last_msg
+                )
+            elif recipient.startswith("python"):
+                return await self.call_python_tool(
+                    self.tool_sessions["python"], last_msg
+                )
+        raise ValueError("No tool call found")
+
+    def render_for_completion(self) -> list[int]:
+        return render_for_completion(self.messages)
+
+    async def call_search_tool(
+        self, tool_session: Union["ClientSession", Tool], last_msg: Message
+    ) -> list[Message]:
+        if isinstance(tool_session, Tool):
+            return await tool_session.get_result(self)
+        tool_name = last_msg.recipient.split(".")[1]
+        args = json.loads(last_msg.content[0].text)
+        result = await tool_session.call_tool(tool_name, args)
+        result_str = result.content[0].text
+        content = TextContent(text=result_str)
+        author = Author(role=Role.TOOL, name=last_msg.recipient)
+        return [Message(author=author, content=[content], recipient=Role.ASSISTANT)]
+
+    async def call_python_tool(
+        self, tool_session: Union["ClientSession", Tool], last_msg: Message
+    ) -> list[Message]:
+        if isinstance(tool_session, Tool):
+            return await tool_session.get_result(self)
+        param = {
+            "code": last_msg.content[0].text,
+        }
+        result = await tool_session.call_tool("python", param)
+        result_str = result.content[0].text
+
+        content = TextContent(text=result_str)
+        author = Author(role=Role.TOOL, name="python")
+
+        return [
+            Message(
+                author=author,
+                content=[content],
+                channel=last_msg.channel,
+                recipient=Role.ASSISTANT,
+            )
+        ]
+
+
+class StreamingHarmonyContext(HarmonyContext):
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.last_output = None
+
+        self.parser = get_streamable_parser_for_assistant()
+        self.encoding = get_encoding()
+        self.last_tok = None
+
+    @property
+    def messages(self) -> list:
+        return self.parser.messages
+
+    def append_output(self, output) -> None:
+        if isinstance(output, dict) and "output_ids" in output:
+            # RequestOutput from SGLang with outputs
+            output_token_ids = output["output_ids"]
+
+            # TODO: REMOVE here:
+            # Very hacky, find the first occurrence of token 200006 and cut from there
+            # Find the first occurrence of token 200006 and cut from there
+            try:
+                start_index = output_token_ids.index(200006)
+                output_token_ids = output_token_ids[start_index:]
+            except ValueError:
+                pass
+
+            for token_id in output_token_ids:
+                self.parser.process(token_id)
+
+        else:
+            # Handle the case of tool output in direct message format
+            assert len(output) == 1, "Tool output should be a single message"
+            msg = output[0]
+            # Sometimes the recipient is not set for tool messages,
+            # so we set it to "assistant"
+            if msg.author.role == Role.TOOL and msg.recipient is None:
+                msg.recipient = "assistant"
+            toks = self.encoding.render(msg)
+            for tok in toks:
+                self.parser.process(tok)
+            self.last_tok = toks[-1]
+
+    def is_expecting_start(self) -> bool:
+        return self.parser.state == StreamState.EXPECT_START
+
+    def is_assistant_action_turn(self) -> bool:
+        return self.last_tok in self.encoding.stop_tokens_for_assistant_actions()
+
+    def render_for_completion(self) -> list[int]:
+        # now this list of tokens as next turn's starting tokens
+        # `<|start|>assistant``,
+        # we need to process them in parser.
+        rendered_tokens = super().render_for_completion()
+
+        last_n = -1
+        to_process = []
+        while rendered_tokens[last_n] != self.last_tok:
+            to_process.append(rendered_tokens[last_n])
+            last_n -= 1
+        for tok in reversed(to_process):
+            self.parser.process(tok)
+
+        return rendered_tokens

python/sglang/srt/entrypoints/harmony_utils.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+import datetime
+import json
+from collections.abc import Iterable
+from typing import Literal, Optional, Union
+
+from openai.types.responses import (
+    ResponseOutputItem,
+    ResponseOutputMessage,
+    ResponseOutputText,
+    ResponseReasoningItem,
+)
+from openai.types.responses.response_function_tool_call import ResponseFunctionToolCall
+from openai.types.responses.response_function_web_search import (
+    ActionFind,
+    ActionOpenPage,
+    ActionSearch,
+    ResponseFunctionWebSearch,
+)
+from openai.types.responses.response_reasoning_item import (
+    Content as ResponseReasoningTextContent,
+)
+from openai.types.responses.tool import Tool
+from openai_harmony import (
+    Author,
+    Conversation,
+    DeveloperContent,
+    HarmonyEncodingName,
+    Message,
+    ReasoningEffort,
+    Role,
+    StreamableParser,
+    SystemContent,
+    TextContent,
+    ToolDescription,
+    load_harmony_encoding,
+)
+
+from sglang.srt.entrypoints.openai.protocol import ResponseInputOutputItem
+from sglang.srt.utils import random_uuid
+
+REASONING_EFFORT = {
+    "high": ReasoningEffort.HIGH,
+    "medium": ReasoningEffort.MEDIUM,
+    "low": ReasoningEffort.LOW,
+}
+
+_harmony_encoding = None
+
+
+def get_encoding():
+    global _harmony_encoding
+    if _harmony_encoding is None:
+        _harmony_encoding = load_harmony_encoding(HarmonyEncodingName.HARMONY_GPT_OSS)
+    return _harmony_encoding
+
+
+def get_system_message(
+    model_identity: Optional[str] = None,
+    reasoning_effort: Optional[Literal["high", "medium", "low"]] = None,
+    start_date: Optional[str] = None,
+    browser_description: Optional[str] = None,
+    python_description: Optional[str] = None,
+) -> Message:
+    sys_msg_content = SystemContent.new()
+    if model_identity is not None:
+        sys_msg_content = sys_msg_content.with_model_identity(model_identity)
+    if reasoning_effort is not None:
+        sys_msg_content = sys_msg_content.with_reasoning_effort(
+            REASONING_EFFORT[reasoning_effort]
+        )
+    if start_date is None:
+        start_date = datetime.datetime.now().strftime("%Y-%m-%d")
+    sys_msg_content = sys_msg_content.with_conversation_start_date(start_date)
+    if browser_description is not None:
+        sys_msg_content = sys_msg_content.with_tools(browser_description)
+    if python_description is not None:
+        sys_msg_content = sys_msg_content.with_tools(python_description)
+    sys_msg = Message.from_role_and_content(Role.SYSTEM, sys_msg_content)
+    return sys_msg
+
+
+def get_developer_message(
+    instructions: Optional[str] = None, tools: Optional[list[Tool]] = None
+) -> Message:
+    dev_msg_content = DeveloperContent.new()
+    if instructions is not None:
+        dev_msg_content = dev_msg_content.with_instructions(instructions)
+    if tools is not None:
+        function_tools = []
+        for tool in tools:
+            if tool.type in ("web_search_preview", "code_interpreter"):
+                # These are built-in tools that are added to the system message.
+                pass
+            elif tool.type == "function":
+                function_tools.append(tool)
+            else:
+                raise ValueError(f"tool type {tool.type} not supported")
+        if function_tools:
+            function_tool_descriptions = [
+                ToolDescription.new(
+                    name=tool.name,
+                    description=tool.description,
+                    parameters=tool.parameters,
+                )
+                for tool in function_tools
+            ]
+            dev_msg_content = dev_msg_content.with_function_tools(
+                function_tool_descriptions
+            )
+    dev_msg = Message.from_role_and_content(Role.DEVELOPER, dev_msg_content)
+    return dev_msg
+
+
+def get_user_message(content: str) -> Message:
+    return Message.from_role_and_content(Role.USER, content)
+
+
+def parse_response_input(
+    response_msg: ResponseInputOutputItem,
+    prev_responses: list[Union[ResponseOutputItem, ResponseReasoningItem]],
+) -> Message:
+    if not isinstance(response_msg, dict):
+        response_msg = response_msg.model_dump()
+    if "type" not in response_msg or response_msg["type"] == "message":
+        role = response_msg["role"]
+        content = response_msg["content"]
+        if role == "system":
+            # User is trying to set a system message. Change it to:
+            # <|start|>developer<|message|># Instructions
+            # {instructions}<|end|>
+            role = "developer"
+            text_prefix = "Instructions:\n"
+        else:
+            text_prefix = ""
+        if isinstance(content, str):
+            msg = Message.from_role_and_content(role, text_prefix + content)
+        else:
+            contents = [TextContent(text=text_prefix + c["text"]) for c in content]
+            msg = Message.from_role_and_contents(role, contents)
+    elif response_msg["type"] == "function_call_output":
+        call_id = response_msg["call_id"]
+        call_response: Optional[ResponseFunctionToolCall] = None
+        for prev_response in reversed(prev_responses):
+            if (
+                isinstance(prev_response, ResponseFunctionToolCall)
+                and prev_response.call_id == call_id
+            ):
+                call_response = prev_response
+                break
+        if call_response is None:
+            raise ValueError(f"No call message found for {call_id}")
+        msg = Message.from_author_and_content(
+            Author.new(Role.TOOL, f"functions.{call_response.name}"),
+            response_msg["output"],
+        )
+    elif response_msg["type"] == "reasoning":
+        content = response_msg["content"]
+        assert len(content) == 1
+        msg = Message.from_role_and_content(Role.ASSISTANT, content[0]["text"])
+    elif response_msg["type"] == "function_call":
+        msg = Message.from_role_and_content(Role.ASSISTANT, response_msg["arguments"])
+        msg = msg.with_channel("commentary")
+        msg = msg.with_recipient(f"functions.{response_msg['name']}")
+        msg = msg.with_content_type("json")
+    else:
+        raise ValueError(f"Unknown input type: {response_msg['type']}")
+    return msg
+
+
+def parse_response_output(output: ResponseOutputItem) -> Message:
+    if isinstance(output, ResponseOutputMessage):
+        role = output.role
+        contents = [TextContent(text=c.text) for c in output.content]
+        msg = Message.from_role_and_contents(role, contents)
+        return msg
+    elif isinstance(output, ResponseFunctionToolCall):
+        msg = Message.from_role_and_content(Role.ASSISTANT, output.arguments)
+        msg = msg.with_channel("commentary")
+        msg = msg.with_recipient(output.name)
+        msg = msg.with_content_type("json")
+        return msg
+    else:
+        raise ValueError(f"Unknown output type: {type(output)}")
+
+
+def parse_chat_input(chat_msg) -> Message:
+    role = chat_msg.role
+    content = chat_msg.content
+    if isinstance(content, str):
+        contents = [TextContent(text=content)]
+    else:
+        # TODO: Support refusal.
+        contents = [TextContent(text=c.text) for c in content]
+    msg = Message.from_role_and_contents(role, contents)
+    return msg
+
+
+def render_for_completion(messages: list[Message]) -> list[int]:
+    conversation = Conversation.from_messages(messages)
+    token_ids = get_encoding().render_conversation_for_completion(
+        conversation, Role.ASSISTANT
+    )
+    return token_ids
+
+
+def get_stop_tokens_for_assistant_actions() -> list[int]:
+    return get_encoding().stop_tokens_for_assistant_actions()
+
+
+def get_streamable_parser_for_assistant() -> StreamableParser:
+    return StreamableParser(get_encoding(), role=Role.ASSISTANT)
+
+
+def parse_output_message(message: Message):
+    if message.author.role != "assistant":
+        # This is a message from a tool to the assistant (e.g., search result).
+        # Don't include it in the final output for now. This aligns with
+        # OpenAI's behavior on models like o4-mini.
+        return []
+
+    output_items = []
+    recipient = message.recipient
+    if recipient is not None and recipient.startswith("browser."):
+        if len(message.content) != 1:
+            raise ValueError("Invalid number of contents in browser message")
+        content = message.content[0]
+        browser_call = json.loads(content.text)
+        # TODO: translate to url properly!
+        if recipient == "browser.search":
+            action = ActionSearch(
+                query=f"cursor:{browser_call.get('query', '')}", type="search"
+            )
+        elif recipient == "browser.open":
+            action = ActionOpenPage(
+                url=f"cursor:{browser_call.get('url', '')}", type="open_page"
+            )
+        elif recipient == "browser.find":
+            action = ActionFind(
+                pattern=browser_call["pattern"],
+                url=f"cursor:{browser_call.get('url', '')}",
+                type="find",
+            )
+        else:
+            raise ValueError(f"Unknown browser action: {recipient}")
+        web_search_item = ResponseFunctionWebSearch(
+            id=f"ws_{random_uuid()}",
+            action=action,
+            status="completed",
+            type="web_search_call",
+        )
+        output_items.append(web_search_item)
+    elif message.channel == "analysis":
+        for content in message.content:
+            reasoning_item = ResponseReasoningItem(
+                id=f"rs_{random_uuid()}",
+                type="reasoning",
+                summary=[],
+                content=[
+                    ResponseReasoningTextContent(
+                        text=content.text, type="reasoning_text"
+                    )
+                ],
+                status=None,
+            )
+            output_items.append(reasoning_item)
+    elif message.channel == "commentary":
+        if message.recipient.startswith("functions."):
+            function_name = message.recipient.split(".")[-1]
+            for content in message.content:
+                random_id = random_uuid()
+                response_item = ResponseFunctionToolCall(
+                    arguments=content.text,
+                    call_id=f"call_{random_id}",
+                    type="function_call",
+                    name=function_name,
+                    id=f"ft_{random_id}",
+                )
+                output_items.append(response_item)
+        elif message.recipient.startswith("python") or message.recipient.startswith(
+            "browser"
+        ):
+            for content in message.content:
+                reasoning_item = ResponseReasoningItem(
+                    id=f"rs_{random_uuid()}",
+                    type="reasoning",
+                    summary=[],
+                    content=[
+                        ResponseReasoningTextContent(
+                            text=content.text, type="reasoning_text"
+                        )
+                    ],
+                    status=None,
+                )
+                output_items.append(reasoning_item)
+        else:
+            raise ValueError(f"Unknown recipient: {message.recipient}")
+    elif message.channel == "final":
+        contents = []
+        for content in message.content:
+            output_text = ResponseOutputText(
+                text=content.text,
+                annotations=[],  # TODO
+                type="output_text",
+                logprobs=None,  # TODO
+            )
+            contents.append(output_text)
+        text_item = ResponseOutputMessage(
+            id=f"msg_{random_uuid()}",
+            content=contents,
+            role=message.author.role,
+            status="completed",
+            type="message",
+        )
+        output_items.append(text_item)
+    else:
+        raise ValueError(f"Unknown channel: {message.channel}")
+    return output_items
+
+
+def parse_remaining_state(parser: StreamableParser):
+    if not parser.current_content:
+        return []
+    if parser.current_role != Role.ASSISTANT:
+        return []
+    current_recipient = parser.current_recipient
+    if current_recipient is not None and current_recipient.startswith("browser."):
+        return []
+
+    if parser.current_channel == "analysis":
+        reasoning_item = ResponseReasoningItem(
+            id=f"rs_{random_uuid()}",
+            type="reasoning",
+            summary=[],
+            content=[
+                ResponseReasoningTextContent(
+                    text=parser.current_content, type="reasoning_text"
+                )
+            ],
+            status=None,
+        )
+        return [reasoning_item]
+    elif parser.current_channel == "final":
+        output_text = ResponseOutputText(
+            content=[
+                ResponseReasoningTextContent(
+                    text=parser.current_content, type="reasoning_text"
+                )
+            ],
+            annotations=[],  # TODO
+            type="output_text",
+            logprobs=None,  # TODO
+        )
+        text_item = ResponseOutputMessage(
+            id=f"msg_{random_uuid()}",
+            content=[output_text],
+            role="assistant",
+            status="completed",
+            type="message",
+        )
+        return [text_item]
+    return []
+
+
+def parse_output_into_messages(token_ids: Iterable[int]):
+    parser = get_streamable_parser_for_assistant()
+    for token_id in token_ids:
+        parser.process(token_id)
+    return parser

python/sglang/srt/entrypoints/http_server.py

@@ -32,6 +32,7 @@ from typing import AsyncIterator, Callable, Dict, Optional
 setattr(threading, "_register_atexit", lambda *args, **kwargs: None)
 
 from contextlib import asynccontextmanager
+from typing import AsyncGenerator
 
 import numpy as np
 import orjson
@@ -56,6 +57,7 @@ from sglang.srt.entrypoints.openai.protocol import (
     ErrorResponse,
     ModelCard,
     ModelList,
+    ResponsesRequest,
     ScoringRequest,
     V1RerankReqInput,
 )
@@ -147,6 +149,37 @@ async def lifespan(fast_api_app: FastAPI):
     )
 
     server_args: ServerArgs = fast_api_app.server_args
+
+    tool_server = None
+    if server_args.tool_server == "demo":
+        from sglang.srt.entrypoints.openai.tool_server import DemoToolServer
+
+        tool_server = DemoToolServer()
+    elif server_args.tool_server:
+        from sglang.srt.entrypoints.openai.tool_server import MCPToolServer
+
+        tool_server = MCPToolServer()
+        await tool_server.add_tool_server(server_args.tool_server)
+
+    try:
+        from sglang.srt.entrypoints.openai.serving_responses import (
+            OpenAIServingResponses,
+        )
+
+        fast_api_app.state.openai_serving_responses = OpenAIServingResponses(
+            _global_state.tokenizer_manager,
+            _global_state.template_manager,
+            enable_prompt_tokens_details=True,
+            enable_force_include_usage=True,
+            tool_server=tool_server,
+        )
+    except Exception as e:
+        # print stack trace
+        import traceback
+
+        traceback.print_exc()
+        logger.warning(f"Can not initialize OpenAIServingResponses, error: {e}")
+
     if server_args.warmups is not None:
         await execute_warmups(
             server_args.disaggregation_mode,
@@ -843,6 +876,42 @@ async def v1_score_request(request: ScoringRequest, raw_request: Request):
     )
 
 
+@app.post("/v1/responses", dependencies=[Depends(validate_json_request)])
+async def v1_responses_request(request: dict, raw_request: Request):
+    """Endpoint for the responses API with reasoning support."""
+
+    request_obj = ResponsesRequest(**request)
+    result = await raw_request.app.state.openai_serving_responses.create_responses(
+        request_obj, raw_request
+    )
+
+    # Handle streaming responses
+    if isinstance(result, AsyncGenerator):
+        return StreamingResponse(
+            result,
+            media_type="text/event-stream",
+            headers={"Cache-Control": "no-cache", "Connection": "keep-alive"},
+        )
+
+    return result
+
+
+@app.get("/v1/responses/{response_id}")
+async def v1_retrieve_responses(response_id: str, raw_request: Request):
+    """Retrieve a response by ID."""
+    return await raw_request.app.state.openai_serving_responses.retrieve_responses(
+        response_id
+    )
+
+
+@app.post("/v1/responses/{response_id}/cancel")
+async def v1_cancel_responses(response_id: str, raw_request: Request):
+    """Cancel a background response."""
+    return await raw_request.app.state.openai_serving_responses.cancel_responses(
+        response_id
+    )
+
+
 @app.api_route(
     "/v1/rerank", methods=["POST", "PUT"], dependencies=[Depends(validate_json_request)]
 )

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

@@ -14,9 +14,18 @@
 """Pydantic models for OpenAI API protocol"""
 
 import time
+import uuid
 from dataclasses import dataclass
-from typing import Any, Dict, List, Optional, Union
+from typing import Any, Dict, List, Optional, TypeAlias, Union
 
+from openai.types.responses import (
+    ResponseFunctionToolCall,
+    ResponseInputItemParam,
+    ResponseOutputItem,
+    ResponseReasoningItem,
+)
+from openai.types.responses.response import ToolChoice
+from openai.types.responses.tool import Tool
 from pydantic import (
     BaseModel,
     Field,
@@ -84,6 +93,7 @@ class UsageInfo(BaseModel):
     completion_tokens: Optional[int] = 0
     # only used to return cached tokens when --enable-cache-report is set
     prompt_tokens_details: Optional[Dict[str, int]] = None
+    reasoning_tokens: Optional[int] = 0
 
 
 class StreamOptions(BaseModel):
@@ -428,6 +438,13 @@ class ChatCompletionRequest(BaseModel):
         default="auto", examples=["none"]
     )  # noqa
     return_hidden_states: bool = False
+    reasoning_effort: Optional[Literal["low", "medium", "high"]] = Field(
+        default="medium",
+        description="Constrains effort on reasoning for reasoning models. "
+        "'low' is the least effort, 'high' is the most effort. Reducing reasoning effort can "
+        "result in faster responses and fewer tokens used on reasoning in a response. "
+        "Currently only supported for OpenAI models.",
+    )
 
     @model_validator(mode="before")
     @classmethod
@@ -619,6 +636,196 @@ OpenAIServingRequest = Union[
 ]
 
 
+# Response API protocol definitions
+class ResponseReasoningParam(BaseModel):
+    """Reasoning parameters for responses."""
+
+    effort: Optional[Literal["low", "medium", "high"]] = Field(
+        default="medium",
+        description="Constrains effort on reasoning for reasoning models.",
+    )
+
+
+class ResponseTool(BaseModel):
+    """Tool definition for responses."""
+
+    type: Literal["web_search_preview", "code_interpreter"] = Field(
+        description="Type of tool to enable"
+    )
+
+
+ResponseInputOutputItem: TypeAlias = Union[
+    ResponseInputItemParam,
+    "ResponseReasoningItem",
+    ResponseFunctionToolCall,
+]
+
+
+class ResponsesRequest(BaseModel):
+    """Request body for v1/responses endpoint."""
+
+    # Core OpenAI API fields (ordered by official documentation)
+    background: Optional[bool] = False
+    include: Optional[
+        List[
+            Literal[
+                "code_interpreter_call.outputs",
+                "computer_call_output.output.image_url",
+                "file_search_call.results",
+                "message.input_image.image_url",
+                "message.output_text.logprobs",
+                "reasoning.encrypted_content",
+            ]
+        ]
+    ] = None
+    input: Union[str, List[ResponseInputOutputItem]]
+    instructions: Optional[str] = None
+    max_output_tokens: Optional[int] = None
+    max_tool_calls: Optional[int] = None
+    metadata: Optional[Dict[str, Any]] = None
+    model: Optional[str] = None  # Made optional to match vLLM
+    parallel_tool_calls: Optional[bool] = True
+    previous_response_id: Optional[str] = None
+    reasoning: Optional[ResponseReasoningParam] = None
+    service_tier: Literal["auto", "default", "flex", "scale", "priority"] = "auto"
+    store: Optional[bool] = True
+    stream: Optional[bool] = False
+    temperature: Optional[float] = None
+    tool_choice: Literal["auto", "required", "none"] = "auto"
+    tools: List[ResponseTool] = Field(default_factory=list)
+    top_logprobs: Optional[int] = 0
+    top_p: Optional[float] = None
+    truncation: Optional[Literal["auto", "disabled"]] = "disabled"
+    user: Optional[str] = None
+
+    # Extra SGLang parameters
+    request_id: str = Field(
+        default_factory=lambda: f"resp_{uuid.uuid4().hex}",
+        description="The request_id related to this request. If the caller does not set it, a random uuid will be generated.",
+    )
+    priority: int = Field(default=0, description="Request priority")
+
+    # SGLang-specific sampling parameters
+    frequency_penalty: float = 0.0
+    presence_penalty: float = 0.0
+    stop: Optional[Union[str, List[str]]] = None
+    top_k: int = -1
+    min_p: float = 0.0
+    repetition_penalty: float = 1.0
+
+    # Default sampling parameters
+    _DEFAULT_SAMPLING_PARAMS = {
+        "temperature": 0.7,
+        "top_p": 1.0,
+        "top_k": -1,
+        "min_p": 0.0,
+        "repetition_penalty": 1.0,
+    }
+
+    def to_sampling_params(
+        self, default_max_tokens: int, default_params: Optional[Dict] = None
+    ) -> Dict[str, Any]:
+        """Convert to sampling parameters for generation."""
+        if default_params is None:
+            default_params = {}
+
+        # Use max_output_tokens if available, otherwise use max_tokens for backwards compatibility
+        if self.max_output_tokens is not None:
+            max_tokens = min(self.max_output_tokens, default_max_tokens)
+        else:
+            max_tokens = default_max_tokens
+
+        # Avoid exceed the context length by minus 1 token
+        max_tokens -= 1
+
+        # Get parameters with defaults
+        temperature = self.temperature
+        if temperature is None:
+            temperature = default_params.get(
+                "temperature", self._DEFAULT_SAMPLING_PARAMS["temperature"]
+            )
+
+        top_p = self.top_p
+        if top_p is None:
+            top_p = default_params.get("top_p", self._DEFAULT_SAMPLING_PARAMS["top_p"])
+
+        params = {
+            "max_new_tokens": max_tokens,
+            "temperature": temperature,
+            "top_p": top_p,
+            "frequency_penalty": self.frequency_penalty,
+            "presence_penalty": self.presence_penalty,
+            "stop": self.stop,
+            "top_k": self.top_k,
+            "min_p": self.min_p,
+            "repetition_penalty": self.repetition_penalty,
+        }
+
+        # Apply any additional default parameters
+        for key, value in default_params.items():
+            if key not in params or params[key] is None:
+                params[key] = value
+
+        return params
+
+
+class PromptTokenUsageInfo(BaseModel):
+    """Prompt token usage details."""
+
+    cached_tokens: int = 0
+
+
+class ResponsesResponse(BaseModel):
+    """Response body for v1/responses endpoint."""
+
+    id: str = Field(default_factory=lambda: f"resp_{time.time()}")
+    object: Literal["response"] = "response"
+    created_at: int = Field(default_factory=lambda: int(time.time()))
+    model: str
+
+    output: List[
+        Union[ResponseOutputItem, ResponseReasoningItem, ResponseFunctionToolCall]
+    ] = Field(default_factory=list)
+    status: Literal["queued", "in_progress", "completed", "failed", "cancelled"]
+    usage: Optional[UsageInfo] = None
+    parallel_tool_calls: bool = True
+    tool_choice: str = "auto"
+    tools: List[ResponseTool] = Field(default_factory=list)
+
+    @classmethod
+    def from_request(
+        cls,
+        request: ResponsesRequest,
+        sampling_params: Any,
+        model_name: str,
+        created_time: int,
+        output: List[
+            Union[ResponseOutputItem, ResponseReasoningItem, ResponseFunctionToolCall]
+        ],
+        status: str,
+        usage: Optional[UsageInfo],
+    ) -> "ResponsesResponse":
+        """Create a response from a request."""
+        return cls(
+            id=request.request_id,
+            created_at=created_time,
+            model=model_name,
+            output=output,
+            status=status,
+            usage=usage,
+            parallel_tool_calls=request.parallel_tool_calls or True,
+            tool_choice=request.tool_choice,
+            tools=request.tools,
+        )
+
+
+class RequestResponseMetadata(BaseModel):
+    """Metadata for request/response tracking."""
+
+    request_id: str
+    final_usage_info: Optional[UsageInfo] = None
+
+
 @dataclass
 class MessageProcessingResult:
     """Result of processing chat messages and applying templates.
@@ -645,3 +852,22 @@ class MessageProcessingResult:
     modalities: List[str]
     stop: List[str]
     tool_call_constraint: Optional[Any] = None
+
+
+class ResponseReasoningTextContent(BaseModel):
+    text: str
+    type: Literal["reasoning_text"] = "reasoning_text"
+
+
+class ResponseReasoningItem(BaseModel):
+    id: str
+    content: list[ResponseReasoningTextContent] = Field(default_factory=list)
+    summary: list = Field(default_factory=list)
+    type: Literal["reasoning"] = "reasoning"
+    encrypted_content: Optional[str] = None
+    status: Optional[Literal["in_progress", "completed", "incomplete"]]
+
+
+ResponseInputOutputItem: TypeAlias = Union[
+    ResponseInputItemParam, "ResponseReasoningItem", ResponseFunctionToolCall
+]

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

@@ -7,8 +7,18 @@ from typing import Any, AsyncGenerator, Dict, List, Optional, Union
 
 from fastapi import Request
 from fastapi.responses import ORJSONResponse, StreamingResponse
+from openai_harmony import Message as OpenAIMessage
 
 from sglang.srt.conversation import generate_chat_conv
+from sglang.srt.entrypoints.harmony_utils import (
+    get_developer_message,
+    get_stop_tokens_for_assistant_actions,
+    get_streamable_parser_for_assistant,
+    get_system_message,
+    parse_chat_input,
+    parse_output_into_messages,
+    render_for_completion,
+)
 from sglang.srt.entrypoints.openai.protocol import (
     ChatCompletionRequest,
     ChatCompletionResponse,
@@ -51,6 +61,26 @@ class OpenAIServingChat(OpenAIServingBase):
     ):
         super().__init__(tokenizer_manager)
         self.template_manager = template_manager
+        self.use_harmony = (
+            self.tokenizer_manager.model_config.hf_config.model_type == "gpt_oss"
+        )
+
+        if self.use_harmony:
+            from sglang.srt.function_call.harmony_tool_parser import (
+                HarmonyToolCallParser,
+            )
+
+            self.harmony_tool_parser = HarmonyToolCallParser()
+
+        # NOTE While OpenAI's chat completion API supports browsing
+        # for some models, currently vLLM doesn't support it. Please use the
+        # Responses API instead.
+        self.supports_browsing = False
+        self.browser_tool = None
+        # NOTE: Chat completion API does not support code interpreter.
+        # Please use the Responses API instead.
+        self.supports_code_interpreter = False
+        self.python_tool = None
 
     def _request_id_prefix(self) -> str:
         return "chatcmpl-"
@@ -77,41 +107,66 @@ class OpenAIServingChat(OpenAIServingBase):
         is_multimodal = self.tokenizer_manager.model_config.is_multimodal
 
         # Process messages and apply chat template
-        processed_messages = self._process_messages(request, is_multimodal)
-
-        # Build sampling parameters
-        sampling_params = self._build_sampling_params(
-            request, processed_messages.stop, processed_messages.tool_call_constraint
-        )
+        if not self.use_harmony:
+            processed_messages = self._process_messages(request, is_multimodal)
+
+            # Build sampling parameters
+            sampling_params = self._build_sampling_params(
+                request,
+                processed_messages.stop,
+                processed_messages.tool_call_constraint,
+            )
 
-        # Handle single vs multiple requests
-        if is_multimodal:
-            prompt_kwargs = {"text": processed_messages.prompt}
-        else:
-            if isinstance(processed_messages.prompt_ids, str):
-                prompt_kwargs = {"text": processed_messages.prompt_ids}
+            # Handle single vs multiple requests
+            if is_multimodal:
+                prompt_kwargs = {"text": processed_messages.prompt}
             else:
-                prompt_kwargs = {"input_ids": processed_messages.prompt_ids}
-
-        adapted_request = GenerateReqInput(
-            **prompt_kwargs,
-            image_data=processed_messages.image_data,
-            video_data=processed_messages.video_data,
-            audio_data=processed_messages.audio_data,
-            sampling_params=sampling_params,
-            return_logprob=request.logprobs,
-            logprob_start_len=-1,
-            top_logprobs_num=request.top_logprobs or 0,
-            stream=request.stream,
-            return_text_in_logprobs=True,
-            modalities=processed_messages.modalities,
-            lora_path=request.lora_path,
-            bootstrap_host=request.bootstrap_host,
-            bootstrap_port=request.bootstrap_port,
-            bootstrap_room=request.bootstrap_room,
-            return_hidden_states=request.return_hidden_states,
-            rid=request.rid,
-        )
+                if isinstance(processed_messages.prompt_ids, str):
+                    prompt_kwargs = {"text": processed_messages.prompt_ids}
+                else:
+                    prompt_kwargs = {"input_ids": processed_messages.prompt_ids}
+
+            adapted_request = GenerateReqInput(
+                **prompt_kwargs,
+                image_data=processed_messages.image_data,
+                video_data=processed_messages.video_data,
+                audio_data=processed_messages.audio_data,
+                sampling_params=sampling_params,
+                return_logprob=request.logprobs,
+                logprob_start_len=-1,
+                top_logprobs_num=request.top_logprobs or 0,
+                stream=request.stream,
+                return_text_in_logprobs=True,
+                modalities=processed_messages.modalities,
+                lora_path=request.lora_path,
+                bootstrap_host=request.bootstrap_host,
+                bootstrap_port=request.bootstrap_port,
+                bootstrap_room=request.bootstrap_room,
+                return_hidden_states=request.return_hidden_states,
+                rid=request.rid,
+            )
+        else:
+            processed_messages, prompt_ids = self._make_request_with_harmony(request)
+
+            adapted_request = GenerateReqInput(
+                input_ids=prompt_ids,
+                sampling_params=self._build_sampling_params(
+                    request,
+                    request.stop,
+                    tool_call_constraint=None,
+                ),
+                stream=request.stream,
+                return_logprob=request.logprobs,
+                logprob_start_len=-1,
+                top_logprobs_num=request.top_logprobs or 0,
+                return_text_in_logprobs=True,
+                lora_path=request.lora_path,
+                bootstrap_host=request.bootstrap_host,
+                bootstrap_port=request.bootstrap_port,
+                bootstrap_room=request.bootstrap_room,
+                return_hidden_states=request.return_hidden_states,
+                rid=request.rid,
+            )
 
         return adapted_request, request
 
@@ -402,6 +457,12 @@ class OpenAIServingChat(OpenAIServingBase):
         cached_tokens = {}
         hidden_states = {}
 
+        # Harmony tracking
+        if self.use_harmony:
+            harmony_parsers = [
+                get_streamable_parser_for_assistant() for _ in range(request.n)
+            ]
+
         try:
             async for content in self.tokenizer_manager.generate_request(
                 adapted_request, raw_request
@@ -449,14 +510,57 @@ class OpenAIServingChat(OpenAIServingBase):
                     yield f"data: {chunk.model_dump_json()}\n\n"
 
                 # Process content delta
-                stream_buffer = stream_buffers.get(index, "")
-                delta = content["text"][len(stream_buffer) :]
-                stream_buffers[index] = stream_buffer + delta
+                if self.use_harmony:
+                    harmony_parser = harmony_parsers[index]
+
+                    new_token_ids = content["output_ids"]
+                    for token_id in new_token_ids:
+                        harmony_parser.process(token_id)
+
+                    is_final = harmony_parser.current_channel == "final"
+                    is_analysis = harmony_parser.current_channel == "analysis"
+                    delta = harmony_parser.last_content_delta or ""
+
+                    if is_analysis:
+                        choice_data = ChatCompletionResponseStreamChoice(
+                            index=index,
+                            delta=DeltaMessage(reasoning_content=delta),
+                            finish_reason=None,
+                        )
+                        chunk = ChatCompletionStreamResponse(
+                            id=content["meta_info"]["id"],
+                            created=int(time.time()),
+                            choices=[choice_data],
+                            model=request.model,
+                        )
+                        yield f"data: {chunk.model_dump_json()}\n\n"
+                        continue
+
+                    choice_data = ChatCompletionResponseStreamChoice(
+                        index=index,
+                        delta=DeltaMessage(content=delta if delta else None),
+                        finish_reason=None,
+                        matched_stop=None,
+                        logprobs=choice_logprobs,
+                    )
+                    chunk = ChatCompletionStreamResponse(
+                        id=content["meta_info"]["id"],
+                        created=int(time.time()),
+                        choices=[choice_data],
+                        model=request.model,
+                    )
+                    yield f"data: {chunk.model_dump_json()}\n\n"
+                    continue
+                else:
+                    stream_buffer = stream_buffers.get(index, "")
+                    delta = content["text"][len(stream_buffer) :]
+                    stream_buffers[index] = stream_buffer + delta
 
                 # Handle reasoning content
                 if (
                     self.tokenizer_manager.server_args.reasoning_parser
                     and request.separate_reasoning
+                    and not self.use_harmony
                 ):
                     reasoning_text, delta = self._process_reasoning_stream(
                         index, delta, reasoning_parser_dict, content, request
@@ -475,8 +579,27 @@ class OpenAIServingChat(OpenAIServingBase):
                         )
                         yield f"data: {chunk.model_dump_json()}\n\n"
 
+                if self.use_harmony and not is_final:
+                    choice_data = ChatCompletionResponseStreamChoice(
+                        index=index,
+                        delta=DeltaMessage(reasoning_content=delta),
+                        finish_reason=None,
+                    )
+                    chunk = ChatCompletionStreamResponse(
+                        id=content["meta_info"]["id"],
+                        created=int(time.time()),
+                        choices=[choice_data],
+                        model=request.model,
+                    )
+                    yield f"data: {chunk.model_dump_json()}\n\n"
+
                 # Handle tool calls
-                if request.tool_choice != "none" and request.tools:
+                # TODO: support tool call parsing for harmony
+                if (
+                    request.tool_choice != "none"
+                    and request.tools
+                    and not self.use_harmony
+                ):
                     async for chunk in self._process_tool_call_stream(
                         index,
                         delta,
@@ -502,7 +625,7 @@ class OpenAIServingChat(OpenAIServingBase):
                     if delta:
                         choice_data = ChatCompletionResponseStreamChoice(
                             index=index,
-                            delta=DeltaMessage(content=delta if delta else None),
+                            delta=DeltaMessage(content=delta),
                             finish_reason=None,
                             matched_stop=None,
                             logprobs=choice_logprobs,
@@ -640,6 +763,76 @@ class OpenAIServingChat(OpenAIServingBase):
 
             finish_reason = ret_item["meta_info"]["finish_reason"]
             text = ret_item["text"]
+            output_ids = ret_item["output_ids"]
+
+            if self.use_harmony:
+                parser = parse_output_into_messages(output_ids)
+                output_msgs = parser.messages
+                if len(output_msgs) == 0:
+                    # The generation has stopped during reasoning.
+                    is_tool_call = False
+                    reasoning_content = parser.current_content
+                    final_content = None
+                elif len(output_msgs) == 1:
+                    # The generation has stopped during final message.
+                    is_tool_call = False
+                    reasoning_content = output_msgs[0].content[0].text
+                    final_content = parser.current_content
+                else:
+                    if len(output_msgs) != 2:
+                        raise ValueError(
+                            "Expected 2 output messages (reasoning and final), "
+                            f"but got {len(output_msgs)}."
+                        )
+                    reasoning_msg, final_msg = output_msgs
+                    reasoning_content = reasoning_msg.content[0].text
+                    final_content = final_msg.content[0].text
+                    is_tool_call = final_msg.recipient is not None
+
+                if is_tool_call:
+                    # Extract tool call information from final message
+                    tool_call = (
+                        self.harmony_tool_parser.extract_tool_calls_from_message(
+                            final_msg
+                        )
+                    )
+                    tool_calls = [tool_call] if tool_call else []
+
+                    message = ChatMessage(
+                        role="assistant",
+                        reasoning_content=reasoning_content,
+                        content=None,  # Tool calls don't have regular content
+                        tool_calls=tool_calls,
+                    )
+                else:
+                    # Normal message
+                    message = ChatMessage(
+                        role="assistant",
+                        reasoning_content=reasoning_content,
+                        content=final_content,
+                    )
+
+                if is_tool_call:
+                    finish_reason_type = "tool_calls"
+                elif finish_reason:
+                    finish_reason_type = (
+                        finish_reason["type"] if finish_reason else "stop"
+                    )
+                else:
+                    finish_reason_type = "stop"
+                choice_data = ChatCompletionResponseChoice(
+                    index=idx,
+                    message=message,
+                    logprobs=choice_logprobs,
+                    finish_reason=finish_reason_type,
+                    matched_stop=(
+                        finish_reason["matched"]
+                        if finish_reason and "matched" in finish_reason
+                        else None
+                    ),
+                )
+                choices.append(choice_data)
+                continue
 
             # Handle reasoning content
             reasoning_text = None
@@ -978,3 +1171,33 @@ class OpenAIServingChat(OpenAIServingBase):
             return f"data: {chunk.model_dump_json()}\n\n"
 
         return None
+
+    def _make_request_with_harmony(
+        self,
+        request: ChatCompletionRequest,
+    ):
+        messages: list[OpenAIMessage] = []
+
+        # Add system message.
+        # In Chat Completion API, browsing is enabled by default if the model
+        # supports it.
+        assert not self.supports_browsing
+        assert not self.supports_code_interpreter
+        sys_msg = get_system_message(
+            reasoning_effort=request.reasoning_effort,
+            browser_description=None,
+            python_description=None,
+        )
+        messages.append(sys_msg)
+
+        # Add developer message.
+        dev_msg = get_developer_message()
+        messages.append(dev_msg)
+
+        # Add user message.
+        for chat_msg in request.messages:
+            messages.append(parse_chat_input(chat_msg))
+
+        # Render prompt token ids.
+        prompt_token_ids = render_for_completion(messages)
+        return messages, prompt_token_ids

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

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+import logging
+from abc import ABC, abstractmethod
+from contextlib import AbstractAsyncContextManager, asynccontextmanager
+from typing import Any
+
+logger = logging.getLogger(__name__)
+try:
+    from mcp import ClientSession
+    from mcp.client.sse import sse_client
+    from mcp.types import ListToolsResult
+except ImportError:
+    logger.warning("Ignoring mcp import error")
+
+from openai_harmony import ToolDescription, ToolNamespaceConfig
+
+
+async def list_server_and_tools(server_url: str):
+
+    async with sse_client(url=server_url) as streams, ClientSession(
+        *streams
+    ) as session:
+        initialize_response = await session.initialize()
+        list_tools_response = await session.list_tools()
+        return initialize_response, list_tools_response
+
+
+def trim_schema(schema: dict) -> dict:
+    # Turn JSON Schema from MCP generated into Harmony's variant.
+    if "title" in schema:
+        del schema["title"]
+    if "default" in schema and schema["default"] is None:
+        del schema["default"]
+    if "anyOf" in schema:
+        # Turn "anyOf": [{"type": "type-1"}, {"type": "type-2"}]
+        # into "type": ["type-1", "type-2"]
+        # if there's more than 1 types, also remove "null" type as Harmony will
+        # just ignore it
+        types = [
+            type_dict["type"]
+            for type_dict in schema["anyOf"]
+            if type_dict["type"] != "null"
+        ]
+        schema["type"] = types
+        del schema["anyOf"]
+    if "properties" in schema:
+        schema["properties"] = {
+            k: trim_schema(v) for k, v in schema["properties"].items()
+        }
+    return schema
+
+
+def post_process_tools_description(
+    list_tools_result: "ListToolsResult",
+) -> "ListToolsResult":
+    # Adapt the MCP tool result for Harmony
+    for tool in list_tools_result.tools:
+        tool.inputSchema = trim_schema(tool.inputSchema)
+
+    # Some tools schema don't need to be part of the prompt (e.g. simple text
+    # in text out for Python)
+    list_tools_result.tools = [
+        tool
+        for tool in list_tools_result.tools
+        if getattr(tool.annotations, "include_in_prompt", True)
+    ]
+
+    return list_tools_result
+
+
+class ToolServer(ABC):
+
+    @abstractmethod
+    def has_tool(self, tool_name: str):
+        pass
+
+    @abstractmethod
+    def get_tool_description(self, tool_name: str):
+        pass
+
+    @abstractmethod
+    def get_tool_session(self, tool_name: str) -> AbstractAsyncContextManager[Any]: ...
+
+
+class MCPToolServer(ToolServer):
+
+    def __init__(self):
+        self.harmony_tool_descriptions = {}
+
+    async def add_tool_server(self, server_url: str):
+        tool_urls = server_url.split(",")
+        self.harmony_tool_descriptions = {}
+        self.urls: dict[str, str] = {}
+        for url in tool_urls:
+            url = f"http://{url}/sse"
+            initialize_response, list_tools_response = await list_server_and_tools(url)
+
+            list_tools_response = post_process_tools_description(list_tools_response)
+
+            tool_from_mcp = ToolNamespaceConfig(
+                name=initialize_response.serverInfo.name,
+                description=initialize_response.instructions,
+                tools=[
+                    ToolDescription.new(
+                        name=tool.name,
+                        description=tool.description,
+                        parameters=tool.inputSchema,
+                    )
+                    for tool in list_tools_response.tools
+                ],
+            )
+            self.harmony_tool_descriptions[tool_from_mcp.name] = tool_from_mcp
+            if tool_from_mcp.name not in self.urls:
+                self.urls[tool_from_mcp.name] = url
+            else:
+                logger.warning(
+                    "Tool %s already exists. Ignoring duplicate tool server %s",
+                    tool_from_mcp.name,
+                    url,
+                )
+
+    def has_tool(self, tool_name: str):
+        return tool_name in self.harmony_tool_descriptions
+
+    def get_tool_description(self, tool_name: str):
+        return self.harmony_tool_descriptions.get(tool_name)
+
+    @asynccontextmanager
+    async def get_tool_session(self, tool_name: str):
+        url = self.urls.get(tool_name)
+        if url:
+            async with sse_client(url=url) as streams, ClientSession(
+                *streams
+            ) as session:
+                await session.initialize()
+                yield session
+        else:
+            logger.warning("Tool %s not found", tool_name)
+
+
+class DemoToolServer(ToolServer):
+
+    def __init__(self):
+        from sglang.srt.entrypoints.tool import (
+            HarmonyBrowserTool,
+            HarmonyPythonTool,
+            Tool,
+        )
+
+        self.tools: dict[str, Tool] = {}
+        browser_tool = HarmonyBrowserTool()
+        if browser_tool.enabled:
+            self.tools["browser"] = browser_tool
+        python_tool = HarmonyPythonTool()
+        if python_tool.enabled:
+            self.tools["python"] = python_tool
+
+    def has_tool(self, tool_name: str):
+        return tool_name in self.tools
+
+    def get_tool_description(self, tool_name: str):
+        if tool_name not in self.tools:
+            return None
+        if tool_name == "browser":
+            return ToolNamespaceConfig.browser()
+        elif tool_name == "python":
+            return ToolNamespaceConfig.python()
+        else:
+            raise ValueError(f"Unknown tool {tool_name}")
+
+    @asynccontextmanager
+    async def get_tool_session(self, tool_name: str):
+        yield self.tools[tool_name]

python/sglang/srt/entrypoints/tool.py

+# SPDX-License-Identifier: Apache-2.0
+import logging
+import os
+from abc import ABC, abstractmethod
+from typing import TYPE_CHECKING, Any
+
+if TYPE_CHECKING:
+    # Avoid circular import.
+    from sglang.srt.entrypoints.context import ConversationContext
+
+logger = logging.getLogger(__name__)
+
+
+class Tool(ABC):
+
+    @abstractmethod
+    async def get_result(self, context: "ConversationContext") -> Any:
+        pass
+
+
+class HarmonyBrowserTool(Tool):
+
+    def __init__(self):
+        self.enabled = True
+        exa_api_key = os.getenv("EXA_API_KEY")
+        if not exa_api_key:
+            self.enabled = False
+            logger.warning_once("EXA_API_KEY is not set, browsing is disabled")
+            return
+
+        try:
+            from gpt_oss.tools.simple_browser import SimpleBrowserTool
+            from gpt_oss.tools.simple_browser.backend import ExaBackend
+        except ImportError:
+            self.enabled = False
+            logger.warning_once("gpt_oss is not installed, browsing is disabled")
+            return
+
+        browser_backend = ExaBackend(source="web", api_key=exa_api_key)
+        self.browser_tool = SimpleBrowserTool(backend=browser_backend)
+        logger.info_once("Browser tool initialized")
+
+    async def get_result(self, context: "ConversationContext") -> Any:
+        from sglang.srt.entrypoints.context import HarmonyContext
+
+        assert isinstance(context, HarmonyContext)
+        last_msg = context.messages[-1]
+        tool_output_msgs = []
+        async for msg in self.browser_tool.process(last_msg):
+            tool_output_msgs.append(msg)
+        return tool_output_msgs
+
+    @property
+    def tool_config(self) -> Any:
+        return self.browser_tool.tool_config
+
+
+class HarmonyPythonTool(Tool):
+
+    def __init__(self):
+        self.enabled = True
+
+        try:
+            from gpt_oss.tools.python_docker.docker_tool import PythonTool
+        except ImportError:
+            self.enabled = False
+            logger.warning_once(
+                "gpt_oss is not installed, code interpreter is disabled"
+            )
+            return
+
+        self.python_tool = PythonTool()
+        logger.info_once("Code interpreter tool initialized")
+
+    async def get_result(self, context: "ConversationContext") -> Any:
+        from sglang.srt.entrypoints.context import HarmonyContext
+
+        assert isinstance(context, HarmonyContext)
+        last_msg = context.messages[-1]
+        tool_output_msgs = []
+        async for msg in self.python_tool.process(last_msg):
+            tool_output_msgs.append(msg)
+        return tool_output_msgs
+
+    @property
+    def tool_config(self) -> Any:
+        return self.python_tool.tool_config

python/sglang/srt/function_call/harmony_tool_parser.py

+# Copyright 2023-2024 SGLang Team
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ==============================================================================
+"""Harmony tool call parser for processing tool calls in harmony models."""
+
+import uuid
+from typing import List, Optional, Tuple
+
+from sglang.srt.entrypoints.openai.protocol import (
+    ChatMessage,
+    FunctionResponse,
+    ToolCall,
+)
+
+
+class HarmonyToolCallParser:
+    """Parser for extracting tool calls from harmony model outputs."""
+
+    def extract_tool_calls_from_message(self, msg) -> Optional[ToolCall]:
+        """
+        Extract tool call from a single message if it's a tool call.
+
+        Args:
+            msg: The harmony message
+
+        Returns:
+            ToolCall if the message is a tool call, None otherwise
+        """
+        if (
+            msg.channel == "commentary"
+            and msg.recipient
+            and msg.recipient.startswith("functions.")
+        ):
+            function_name = msg.recipient.split(".")[-1]
+            arguments = msg.content[0].text if msg.content else "{}"
+
+            return ToolCall(
+                id=f"call_{uuid.uuid4().hex[:24]}",
+                function=FunctionResponse(
+                    name=function_name,
+                    arguments=arguments,
+                ),
+            )
+        return None
+
+    def process_streaming_chunk(
+        self,
+        harmony_parser,
+        index: int,
+        tool_call_trackers: dict,
+        stream_buffers: dict,
+    ) -> Tuple[Optional[dict], bool, Optional[str]]:
+        """
+        Process a streaming chunk for tool calls.
+
+        Args:
+            harmony_parser: The harmony parser instance
+            index: The choice index
+            tool_call_trackers: Dict tracking tool calls per choice
+            stream_buffers: Dict for buffering content
+
+        Returns:
+            Tuple of (tool_call_data, is_tool_call, delta)
+        """
+        # Check if we're in a tool call
+        is_tool_call = (
+            harmony_parser.current_channel == "commentary"
+            and harmony_parser.current_recipient
+            and harmony_parser.current_recipient.startswith("functions.")
+        )
+
+        delta = harmony_parser.last_content_delta or ""
+        tool_call_data = None
+
+        if is_tool_call:
+            # Handle tool call streaming
+            function_name = harmony_parser.current_recipient.split(".")[-1]
+
+            # Track tool call indices per choice
+            if index not in tool_call_trackers:
+                tool_call_trackers[index] = {"count": 0, "current_function": None}
+
+            # Check if we just started a new tool call
+            tool_call_tracker = tool_call_trackers[index]
+            if tool_call_tracker["current_function"] != function_name:
+                # New tool call started
+                tool_call_tracker["current_function"] = function_name
+                tool_call_index = tool_call_tracker["count"]
+                tool_call_tracker["count"] += 1
+
+                # Store the tool call index for this function
+                tool_call_key = f"{index}_{function_name}"
+                stream_buffers[tool_call_key] = {
+                    "index": tool_call_index,
+                    "content": "",
+                }
+
+                tool_call_data = {
+                    "id": f"call_{uuid.uuid4().hex[:24]}",
+                    "index": tool_call_index,
+                    "function_name": function_name,
+                    "arguments": delta,
+                    "is_first_chunk": True,
+                }
+            else:
+                # Subsequent chunks for the same tool call
+                tool_call_key = f"{index}_{function_name}"
+                tool_call_index = stream_buffers[tool_call_key]["index"]
+
+                tool_call_data = {
+                    "id": None,
+                    "index": tool_call_index,
+                    "function_name": None,
+                    "arguments": delta,
+                    "is_first_chunk": False,
+                }
+
+            stream_buffers[tool_call_key]["content"] += delta
+
+        return tool_call_data, is_tool_call, delta

python/sglang/srt/managers/detokenizer_manager.py

@@ -216,7 +216,7 @@ class DetokenizerManager:
             rids=recv_obj.rids,
             finished_reasons=recv_obj.finished_reasons,
             output_strs=output_strs,
-            output_ids=None,
+            output_ids=recv_obj.decode_ids,
             prompt_tokens=recv_obj.prompt_tokens,
             completion_tokens=recv_obj.completion_tokens,
             cached_tokens=recv_obj.cached_tokens,

python/sglang/srt/managers/io_struct.py

@@ -126,6 +126,9 @@ class GenerateReqInput:
     # For data parallel rank routing
     data_parallel_rank: Optional[int] = None
 
+    # For background responses (OpenAI responses API)
+    background: bool = False
+
     def contains_mm_input(self) -> bool:
         return (
             has_valid_data(self.image_data)
@@ -560,6 +563,9 @@ class EmbeddingReqInput:
     # For cross-encoder requests
     is_cross_encoder_request: bool = False
 
+    # For background responses (OpenAI responses API)
+    background: bool = False
+
     def normalize_batch_and_arguments(self):
         # at least one of text, input_ids, or image should be provided
         if self.text is None and self.input_ids is None and self.image_data is None:

python/sglang/srt/managers/scheduler_output_processor_mixin.py

@@ -571,8 +571,7 @@ class SchedulerOutputProcessorMixin:
 
                 req.send_decode_id_offset = len(decode_ids)
                 read_offsets.append(read_offset)
-                if self.skip_tokenizer_init:
-                    output_ids.append(req.output_ids[send_token_offset:])
+                output_ids.append(req.output_ids[send_token_offset:])
                 req.send_token_offset = len(req.output_ids)
                 skip_special_tokens.append(req.sampling_params.skip_special_tokens)
                 spaces_between_special_tokens.append(

python/sglang/srt/managers/tokenizer_manager.py

@@ -750,7 +750,11 @@ class TokenizerManager:
             try:
                 await asyncio.wait_for(state.event.wait(), timeout=4)
             except asyncio.TimeoutError:
-                if request is not None and await request.is_disconnected():
+                if (
+                    request is not None
+                    and not obj.background
+                    and await request.is_disconnected()
+                ):
                     # Abort the request for disconnected requests (non-streaming, waiting queue)
                     self.abort_request(obj.rid)
                     # Use exception to kill the whole call stack and asyncio task
@@ -805,7 +809,11 @@ class TokenizerManager:
             if obj.stream:
                 yield out
             else:
-                if request is not None and await request.is_disconnected():
+                if (
+                    request is not None
+                    and not obj.background
+                    and await request.is_disconnected()
+                ):
                     # Abort the request for disconnected requests (non-streaming, running)
                     self.abort_request(obj.rid)
                     # Use exception to kill the whole call stack and asyncio task
@@ -1548,8 +1556,17 @@ class TokenizerManager:
 
             if isinstance(recv_obj, BatchStrOut):
                 state.text += recv_obj.output_strs[i]
+                if state.obj.stream:
+                    state.output_ids.extend(recv_obj.output_ids[i])
+                    output_token_ids = state.output_ids[state.last_output_offset :]
+                    state.last_output_offset = len(state.output_ids)
+                else:
+                    state.output_ids.extend(recv_obj.output_ids[i])
+                    output_token_ids = state.output_ids.copy()
+
                 out_dict = {
                     "text": state.text,
+                    "output_ids": output_token_ids,
                     "meta_info": meta_info,
                 }
             elif isinstance(recv_obj, BatchTokenIDOut):

python/sglang/srt/server_args.py

@@ -274,6 +274,9 @@ class ServerArgs:
     enable_pdmux: bool = False
     sm_group_num: int = 3
 
+    # For tool server
+    tool_server: Optional[str] = None
+
     # Deprecated arguments
     enable_ep_moe: bool = False
     enable_deepep_moe: bool = False
@@ -1916,6 +1919,14 @@ class ServerArgs:
             help="Disable mmap while loading weight using safetensors.",
         )
 
+        # For tool server
+        parser.add_argument(
+            "--tool-server",
+            type=str,
+            default=None,
+            help="Either 'demo' or a comma-separated list of tool server urls to use for the model. If not specified, no tool server will be used.",
+        )
+
         # Deprecated arguments
         parser.add_argument(
             "--enable-ep-moe",

python/sglang/srt/utils.py

@@ -41,6 +41,7 @@ import tempfile
 import threading
 import time
 import traceback
+import uuid
 import warnings
 from collections import OrderedDict, defaultdict
 from contextlib import contextmanager
@@ -233,6 +234,10 @@ def is_flashinfer_available():
     return importlib.util.find_spec("flashinfer") is not None and is_cuda()
 
 
+def random_uuid() -> str:
+    return str(uuid.uuid4().hex)
+
+
 _ENABLE_TORCH_INFERENCE_MODE = get_bool_env_var(
     "SGLANG_ENABLE_TORCH_INFERENCE_MODE", "false"
 )