[Bugfix] Add Kimi-K2.5 reasoning/tool parser aliases and tool_call_id support (#37438)

Signed-off-by: DorBernsohn <dor.bernsohn@gmail.com>

tests/reasoning/test_kimi_k2_reasoning_parser.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import pytest
+
+from vllm.entrypoints.openai.chat_completion.protocol import ChatCompletionRequest
+from vllm.entrypoints.openai.engine.protocol import DeltaMessage
+from vllm.reasoning.identity_reasoning_parser import IdentityReasoningParser
+from vllm.reasoning.kimi_k2_reasoning_parser import KimiK2ReasoningParser
+from vllm.tokenizers import get_tokenizer
+
+REASONING_MODEL_NAME = "moonshotai/Kimi-K2.5"
+
+
+@pytest.fixture(scope="module")
+def kimi_k2_tokenizer():
+    return get_tokenizer(tokenizer_name=REASONING_MODEL_NAME, trust_remote_code=True)
+
+
+def test_parser_selection_thinking_enabled(kimi_k2_tokenizer):
+    parser = KimiK2ReasoningParser(
+        kimi_k2_tokenizer, chat_template_kwargs={"thinking": True}
+    )
+    assert parser._identity_parser is None
+
+
+def test_parser_selection_thinking_disabled(kimi_k2_tokenizer):
+    parser = KimiK2ReasoningParser(
+        kimi_k2_tokenizer, chat_template_kwargs={"thinking": False}
+    )
+    assert isinstance(parser._identity_parser, IdentityReasoningParser)
+
+
+def test_extract_reasoning_with_think_tags(kimi_k2_tokenizer):
+    parser = KimiK2ReasoningParser(kimi_k2_tokenizer)
+    request = ChatCompletionRequest(model="test-model", messages=[], temperature=1.0)
+
+    reasoning, content = parser.extract_reasoning(
+        "<think>step by step reasoning</think>final answer", request
+    )
+    assert reasoning == "step by step reasoning"
+    assert content == "final answer"
+
+
+def test_extract_reasoning_empty_thinking(kimi_k2_tokenizer):
+    parser = KimiK2ReasoningParser(kimi_k2_tokenizer)
+    request = ChatCompletionRequest(model="test-model", messages=[], temperature=1.0)
+
+    reasoning, content = parser.extract_reasoning(
+        "<think></think>final answer", request
+    )
+    assert reasoning == ""
+    assert content == "final answer"
+
+
+def test_extract_reasoning_implicit_start(kimi_k2_tokenizer):
+    """When there's no <think> tag, everything is treated as reasoning."""
+    parser = KimiK2ReasoningParser(kimi_k2_tokenizer)
+    request = ChatCompletionRequest(model="test-model", messages=[], temperature=1.0)
+
+    reasoning, content = parser.extract_reasoning(
+        "implicit reasoning with no tags", request
+    )
+    assert reasoning == "implicit reasoning with no tags"
+    assert content is None
+
+
+def test_extract_reasoning_tool_section_ends_reasoning(kimi_k2_tokenizer):
+    """<|tool_calls_section_begin|> implicitly ends reasoning."""
+    parser = KimiK2ReasoningParser(kimi_k2_tokenizer)
+    request = ChatCompletionRequest(model="test-model", messages=[], temperature=1.0)
+
+    text = "some reasoning<|tool_calls_section_begin|>tool call data"
+    reasoning, content = parser.extract_reasoning(text, request)
+    assert reasoning == "some reasoning"
+    assert content == "<|tool_calls_section_begin|>tool call data"
+
+
+def test_streaming_reasoning_then_content(kimi_k2_tokenizer):
+    """Token-by-token streaming: reasoning tokens then content after </think>."""
+    parser = KimiK2ReasoningParser(kimi_k2_tokenizer)
+
+    think_id = parser._start_token_id
+    end_think_id = parser._end_token_id
+    # Use a real token ID from the tokenizer for regular content
+    regular_id = kimi_k2_tokenizer.encode("hello", add_special_tokens=False)[0]
+
+    # First token: <think> — single special token should be skipped
+    result = parser.extract_reasoning_streaming(
+        previous_text="",
+        current_text="<think>",
+        delta_text="<think>",
+        previous_token_ids=[],
+        current_token_ids=[think_id],
+        delta_token_ids=[think_id],
+    )
+    assert result is None
+
+    # Reasoning token
+    result = parser.extract_reasoning_streaming(
+        previous_text="<think>",
+        current_text="<think>step one",
+        delta_text="step one",
+        previous_token_ids=[think_id],
+        current_token_ids=[think_id, regular_id],
+        delta_token_ids=[regular_id],
+    )
+    assert isinstance(result, DeltaMessage)
+    assert result.reasoning == "step one"
+    assert result.content is None
+
+    # End token </think> as single token — should be skipped
+    result = parser.extract_reasoning_streaming(
+        previous_text="<think>step one",
+        current_text="<think>step one</think>",
+        delta_text="</think>",
+        previous_token_ids=[think_id, regular_id],
+        current_token_ids=[think_id, regular_id, end_think_id],
+        delta_token_ids=[end_think_id],
+    )
+    assert result is None
+
+    # Content after </think>
+    content_id = kimi_k2_tokenizer.encode("world", add_special_tokens=False)[0]
+    result = parser.extract_reasoning_streaming(
+        previous_text="<think>step one</think>",
+        current_text="<think>step one</think>answer",
+        delta_text="answer",
+        previous_token_ids=[think_id, regular_id, end_think_id],
+        current_token_ids=[think_id, regular_id, end_think_id, content_id],
+        delta_token_ids=[content_id],
+    )
+    assert isinstance(result, DeltaMessage)
+    assert result.content == "answer"
+
+
+def test_streaming_tool_section_ends_reasoning(kimi_k2_tokenizer):
+    """<|tool_calls_section_begin|> in delta ends reasoning during streaming."""
+    parser = KimiK2ReasoningParser(kimi_k2_tokenizer)
+
+    think_id = parser._start_token_id
+    tool_begin_id = parser._tool_section_start_token_id
+    regular_id = kimi_k2_tokenizer.encode("hello", add_special_tokens=False)[0]
+
+    # Tool section token arrives — should transition from reasoning to content
+    result = parser.extract_reasoning_streaming(
+        previous_text="<think>thinking",
+        current_text="<think>thinking<|tool_calls_section_begin|>",
+        delta_text="<|tool_calls_section_begin|>",
+        previous_token_ids=[think_id, regular_id],
+        current_token_ids=[think_id, regular_id, tool_begin_id],
+        delta_token_ids=[tool_begin_id],
+    )
+    assert isinstance(result, DeltaMessage)
+    assert result.content == "<|tool_calls_section_begin|>"

vllm/entrypoints/chat_utils.py

@@ -1660,6 +1660,20 @@ def get_history_tool_calls_cnt(conversation: list[ConversationMessage]):
     return idx
 
 
+_KIMI_MODEL_TYPES = ("kimi_k2", "kimi_k25")
+
+
+def get_tool_call_id_type(model_config: ModelConfig) -> str:
+    """Return the tool-call ID type for a given model configuration."""
+    hf_overrides = getattr(model_config, "hf_overrides", None)
+    if model_config.hf_text_config.model_type in _KIMI_MODEL_TYPES or (
+        isinstance(hf_overrides, dict)
+        and hf_overrides.get("model_type") in _KIMI_MODEL_TYPES
+    ):
+        return "kimi_k2"
+    return "random"
+
+
 def make_tool_call_id(id_type: str = "random", func_name=None, idx=None):
     if id_type == "kimi_k2":
         return f"functions.{func_name}:{idx}"

vllm/entrypoints/openai/chat_completion/serving.py

@@ -19,6 +19,7 @@ from vllm.entrypoints.chat_utils import (
     ChatTemplateContentFormatOption,
     ConversationMessage,
     get_history_tool_calls_cnt,
+    get_tool_call_id_type,
     make_tool_call_id,
 )
 from vllm.entrypoints.logger import RequestLogger
@@ -152,15 +153,7 @@ class OpenAIServingChat(OpenAIServing):
                 get_stop_tokens_for_assistant_actions()
             )
 
-        # Handle tool call ID type for Kimi K2 (supporting test mocking via overrides)
-        hf_overrides = getattr(self.model_config, "hf_overrides", None)
-        if self.model_config.hf_text_config.model_type == "kimi_k2" or (
-            isinstance(hf_overrides, dict)
-            and hf_overrides.get("model_type") == "kimi_k2"
-        ):
-            self.tool_call_id_type = "kimi_k2"
-        else:
-            self.tool_call_id_type = "random"
+        self.tool_call_id_type = get_tool_call_id_type(self.model_config)
 
         # NOTE(woosuk): While OpenAI's chat completion API supports browsing
         # for some models, currently vLLM doesn't support it. Please use the

vllm/entrypoints/openai/responses/serving.py

@@ -46,6 +46,7 @@ from vllm.engine.protocol import EngineClient
 from vllm.entrypoints.chat_utils import (
     ChatCompletionMessageParam,
     ChatTemplateContentFormatOption,
+    get_tool_call_id_type,
 )
 from vllm.entrypoints.logger import RequestLogger
 from vllm.entrypoints.mcp.tool_server import ToolServer
@@ -241,15 +242,7 @@ class OpenAIServingResponses(OpenAIServing):
                 get_stop_tokens_for_assistant_actions()
             )
 
-        # Handle tool call ID type for Kimi K2 (supporting test mocking via overrides)
-        hf_overrides = getattr(self.model_config, "hf_overrides", None)
-        if self.model_config.hf_text_config.model_type == "kimi_k2" or (
-            isinstance(hf_overrides, dict)
-            and hf_overrides.get("model_type") == "kimi_k2"
-        ):
-            self.tool_call_id_type = "kimi_k2"
-        else:
-            self.tool_call_id_type = "random"
+        self.tool_call_id_type = get_tool_call_id_type(self.model_config)
 
         self.enable_auto_tools = enable_auto_tools
         # HACK(woosuk): This is a hack. We should use a better store.