[Tool] `adjust_request` to reasoning parser, and Gemma4 fixes (#39027)

Signed-off-by: Ben Browning <bbrownin@redhat.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Cursor <cursoragent@cursor.com>

examples/tool_chat_template_gemma4.jinja

+{%- macro format_parameters(properties, required) -%}
+    {%- set standard_keys = ['description', 'type', 'properties', 'required', 'nullable'] -%}
+    {%- set ns = namespace(found_first=false) -%}
+    {%- for key, value in properties | dictsort -%}
+        {%- set add_comma = false -%}
+        {%- if key not in standard_keys -%}
+            {%- if ns.found_first %},{% endif -%}
+            {%- set ns.found_first = true -%}
+            {{ key }}:{
+            {%- if value['description'] -%}
+                description:<|"|>{{ value['description'] }}<|"|>
+                {%- set add_comma = true -%}
+            {%- endif -%}
+            {%- if value['nullable'] %}
+                {%- if add_comma %},{%- else -%} {%- set add_comma = true -%} {% endif -%}
+                nullable:true
+            {%- endif -%}
+            {%- if value['type'] | upper == 'STRING' -%}
+                {%- if value['enum'] -%}
+                    {%- if add_comma %},{%- else -%} {%- set add_comma = true -%} {% endif -%}
+                    enum:{{ format_argument(value['enum']) }}
+                {%- endif -%}
+            {%- elif value['type'] | upper == 'OBJECT' -%}
+                ,properties:{
+                {%- if value['properties'] is defined and value['properties'] is mapping -%}
+                    {{- format_parameters(value['properties'], value['required'] | default([])) -}}
+                {%- elif value is mapping -%}
+                    {{- format_parameters(value, value['required'] | default([])) -}}
+                {%- endif -%}
+                }
+                {%- if value['required'] -%}
+                    ,required:[
+                    {%- for item in value['required'] | default([]) -%}
+                        <|"|>{{- item -}}<|"|>
+                        {%- if not loop.last %},{% endif -%}
+                    {%- endfor -%}
+                    ]
+                {%- endif -%}
+            {%- elif value['type'] | upper == 'ARRAY' -%}
+                {%- if value['items'] is mapping and value['items'] -%}
+                    ,items:{
+                    {%- set ns_items = namespace(found_first=false) -%}
+                    {%- for item_key, item_value in value['items'] | dictsort -%}
+                        {%- if item_value is not none -%}
+                            {%- if ns_items.found_first %},{% endif -%}
+                            {%- set ns_items.found_first = true -%}
+                            {%- if item_key == 'properties' -%}
+                                properties:{
+                                {%- if item_value is mapping -%}
+                                    {{- format_parameters(item_value, value['items']['required'] | default([])) -}}
+                                {%- endif -%}
+                                }
+                            {%- elif item_key == 'required' -%}
+                                required:[
+                                {%- for req_item in item_value -%}
+                                    <|"|>{{- req_item -}}<|"|>
+                                    {%- if not loop.last %},{% endif -%}
+                                {%- endfor -%}
+                                ]
+                            {%- elif item_key == 'type' -%}
+                                {%- if item_value is string -%}
+                                    type:{{ format_argument(item_value | upper) }}
+                                {%- else -%}
+                                    type:{{ format_argument(item_value | map('upper') | list) }}
+                                {%- endif -%}
+                            {%- else -%}
+                                {{ item_key }}:{{ format_argument(item_value) }}
+                            {%- endif -%}
+                        {%- endif -%}
+                    {%- endfor -%}
+                    }
+                {%- endif -%}
+            {%- endif -%}
+            {%- if add_comma %},{%- else -%} {%- set add_comma = true -%} {% endif -%}
+            type:<|"|>{{ value['type'] | upper }}<|"|>}
+        {%- endif -%}
+    {%- endfor -%}
+{%- endmacro -%}
+{%- macro format_function_declaration(tool_data) -%}
+    declaration:{{- tool_data['function']['name'] -}}{description:<|"|>{{- tool_data['function']['description'] -}}<|"|>
+    {%- set params = tool_data['function']['parameters'] -%}
+    {%- if params -%}
+        ,parameters:{
+        {%- if params['properties'] -%}
+            properties:{ {{- format_parameters(params['properties'], params['required']) -}} },
+        {%- endif -%}
+        {%- if params['required'] -%}
+            required:[
+            {%- for item in params['required'] -%}
+                <|"|>{{- item -}}<|"|>
+                {{- ',' if not loop.last -}}
+            {%- endfor -%}
+            ],
+        {%- endif -%}
+        {%- if params['type'] -%}
+            type:<|"|>{{- params['type'] | upper -}}<|"|>}
+        {%- endif -%}
+    {%- endif -%}
+    {%- if 'response' in tool_data['function'] -%}
+        {%- set response_declaration = tool_data['function']['response'] -%}
+        ,response:{
+        {%- if response_declaration['description'] -%}
+            description:<|"|>{{- response_declaration['description'] -}}<|"|>,
+        {%- endif -%}
+        {%- if response_declaration['type'] | upper == 'OBJECT' -%}
+            type:<|"|>{{- response_declaration['type'] | upper -}}<|"|>}
+        {%- endif -%}
+    {%- endif -%}
+    }
+{%- endmacro -%}
+{%- macro format_argument(argument, escape_keys=True) -%}
+    {%- if argument is string -%}
+        {{- '<|"|>' + argument + '<|"|>' -}}
+    {%- elif argument is boolean -%}
+        {{- 'true' if argument else 'false' -}}
+    {%- elif argument is mapping -%}
+        {{- '{' -}}
+        {%- set ns = namespace(found_first=false) -%}
+        {%- for key, value in argument | dictsort -%}
+            {%- if ns.found_first %},{% endif -%}
+            {%- set ns.found_first = true -%}
+            {%- if escape_keys -%}
+                {{- '<|"|>' + key + '<|"|>' -}}
+            {%- else -%}
+                {{- key -}}
+            {%- endif -%}
+            :{{- format_argument(value, escape_keys=escape_keys) -}}
+        {%- endfor -%}
+        {{- '}' -}}
+    {%- elif argument is sequence -%}
+        {{- '[' -}}
+        {%- for item in argument -%}
+            {{- format_argument(item, escape_keys=escape_keys) -}}
+            {%- if not loop.last %},{% endif -%}
+        {%- endfor -%}
+        {{- ']' -}}
+    {%- else -%}
+        {{- argument -}}
+    {%- endif -%}
+{%- endmacro -%}
+{%- macro strip_thinking(text) -%}
+    {%- set ns = namespace(result='') -%}
+    {%- for part in text.split('<channel|>') -%}
+        {%- if '<|channel>' in part -%}
+            {%- set ns.result = ns.result + part.split('<|channel>')[0] -%}
+        {%- else -%}
+            {%- set ns.result = ns.result + part -%}
+        {%- endif -%}
+    {%- endfor -%}
+    {{- ns.result | trim -}}
+{%- endmacro -%}
+
+{%- macro format_tool_response_block(tool_name, response) -%}
+    {{- '<|tool_response>' -}}
+    {%- if response is mapping -%}
+        {{- 'response:' + tool_name + '{' -}}
+        {%- for key, value in response | dictsort -%}
+            {{- key -}}:{{- format_argument(value, escape_keys=False) -}}
+            {%- if not loop.last %},{% endif -%}
+        {%- endfor -%}
+        {{- '}' -}}
+    {%- else -%}
+        {{- 'response:' + tool_name + '{value:' + format_argument(response, escape_keys=False) + '}' -}}
+    {%- endif -%}
+    {{- '<tool_response|>' -}}
+{%- endmacro -%}
+
+{%- set ns = namespace(prev_message_type=None) -%}
+{%- set loop_messages = messages -%}
+{{ bos_token }}
+{%- if (enable_thinking is defined and enable_thinking) or tools or messages[0]['role'] in ['system', 'developer'] -%}
+    {{- '<|turn>system\n' -}}
+
+    {%- if enable_thinking is defined and enable_thinking -%}
+        {{- '<|think|>' -}}
+        {%- set ns.prev_message_type = 'think' -%}
+    {%- endif -%}
+
+    {%- if messages[0]['role'] in ['system', 'developer'] -%}
+        {{- messages[0]['content'] | trim -}}
+        {%- set loop_messages = messages[1:] -%}
+    {%- endif -%}
+
+    {%- if tools -%}
+        {%- for tool in tools %}
+            {{- '<|tool>' -}}
+            {{- format_function_declaration(tool) | trim -}}
+            {{- '<tool|>' -}}
+        {%- endfor %}
+        {%- set ns.prev_message_type = 'tool' -%}
+    {%- endif -%}
+
+    {{- '<turn|>\n' -}}
+{%- endif %}
+
+{%- set ns_turn = namespace(last_user_idx=-1) -%}
+{%- for i in range(loop_messages | length) -%}
+    {%- if loop_messages[i]['role'] == 'user' -%}
+        {%- set ns_turn.last_user_idx = i -%}
+    {%- endif -%}
+{%- endfor -%}
+
+{%- for message in loop_messages -%}
+    {%- if message['role'] != 'tool' -%}
+    {%- set ns.prev_message_type = None -%}
+    {%- set role = 'model' if message['role'] == 'assistant' else message['role'] -%}
+    {#- OpenAI may emit multiple assistant messages in one tool loop (user → asst → tool → asst → tool).
+        Only the first of those should open <|turn>model; later ones continue the same model turn. -#}
+    {%- set prev_nt = namespace(role=None, found=false) -%}
+    {%- if loop.index0 > 0 -%}
+        {%- for j in range(loop.index0 - 1, -1, -1) -%}
+            {%- if not prev_nt.found -%}
+                {%- if loop_messages[j]['role'] != 'tool' -%}
+                    {%- set prev_nt.role = loop_messages[j]['role'] -%}
+                    {%- set prev_nt.found = true -%}
+                {%- endif -%}
+            {%- endif -%}
+        {%- endfor -%}
+    {%- endif -%}
+    {%- set continue_same_model_turn = (role == 'model' and prev_nt.role == 'assistant') -%}
+    {%- if not continue_same_model_turn -%}
+        {{- '<|turn>' + role + '\n' }}
+    {%- endif -%}
+
+    {%- if message.get('reasoning') and loop.index0 > ns_turn.last_user_idx and message.get('tool_calls') -%}
+        {{- '<|channel>thought\n' + message['reasoning'] + '\n<channel|>'}}
+    {%- endif -%}
+
+            {%- if message['tool_calls'] -%}
+                {%- for tool_call in message['tool_calls'] -%}
+                    {%- set function = tool_call['function'] -%}
+                    {{- '<|tool_call>call:' + function['name'] + '{' -}}
+                    {%- if function['arguments'] is mapping -%}
+                        {%- set ns_args = namespace(found_first=false) -%}
+                        {%- for key, value in function['arguments'] | dictsort -%}
+                            {%- if ns_args.found_first %},{% endif -%}
+                            {%- set ns_args.found_first = true -%}
+                            {{- key -}}:{{- format_argument(value, escape_keys=False) -}}
+                        {%- endfor -%}
+                    {%- elif function['arguments'] is string -%}
+                        {{- function['arguments'] -}}
+                    {%- endif -%}
+                    {{- '}<tool_call|>' -}}
+                {%- endfor -%}
+                {%- set ns.prev_message_type = 'tool_call' -%}
+            {%- endif -%}
+
+            {%- set ns_tr_out = namespace(flag=false) -%}
+            {%- if message.get('tool_responses') -%}
+                {#- Legacy: tool_responses embedded on the assistant message -#}
+                {%- for tool_response in message['tool_responses'] -%}
+                    {{- format_tool_response_block(tool_response['name'] | default('unknown'), tool_response['response']) -}}
+                    {%- set ns_tr_out.flag = true -%}
+                    {%- set ns.prev_message_type = 'tool_response' -%}
+                {%- endfor -%}
+            {%- elif message.get('tool_calls') -%}
+                {#- OpenAI Chat Completions: consecutive following messages with role "tool" (no break/continue; range scan) -#}
+                {%- set ns_tool_scan = namespace(stopped=false) -%}
+                {%- for k in range(loop.index0 + 1, loop_messages | length) -%}
+                    {%- if ns_tool_scan.stopped -%}
+                    {%- elif loop_messages[k]['role'] != 'tool' -%}
+                        {%- set ns_tool_scan.stopped = true -%}
+                    {%- else -%}
+                        {%- set follow = loop_messages[k] -%}
+                        {%- set ns_tname = namespace(name=follow.get('name') | default('unknown')) -%}
+                        {%- for tc in message['tool_calls'] -%}
+                            {%- if tc.get('id') == follow.get('tool_call_id') -%}
+                                {%- set ns_tname.name = tc['function']['name'] -%}
+                            {%- endif -%}
+                        {%- endfor -%}
+                        {%- set tool_body = follow.get('content') -%}
+                        {%- if tool_body is string -%}
+                            {{- format_tool_response_block(ns_tname.name, tool_body) -}}
+                        {%- elif tool_body is sequence and tool_body is not string -%}
+                            {%- set ns_txt = namespace(s='') -%}
+                            {%- for part in tool_body -%}
+                                {%- if part.get('type') == 'text' -%}
+                                    {%- set ns_txt.s = ns_txt.s + (part.get('text') | default('')) -%}
+                                {%- endif -%}
+                            {%- endfor -%}
+                            {{- format_tool_response_block(ns_tname.name, ns_txt.s) -}}
+                        {%- else -%}
+                            {{- format_tool_response_block(ns_tname.name, tool_body) -}}
+                        {%- endif -%}
+                        {%- set ns_tr_out.flag = true -%}
+                        {%- set ns.prev_message_type = 'tool_response' -%}
+                    {%- endif -%}
+                {%- endfor -%}
+            {%- endif -%}
+
+            {%- if message['content'] is string -%}
+                {%- if role == 'model' -%}
+                    {{- strip_thinking(message['content']) -}}
+                {%- else -%}
+                    {{- message['content'] | trim -}}
+                {%- endif -%}
+            {%- elif message['content'] is sequence -%}
+                {%- for item in message['content'] -%}
+                    {%- if item['type'] == 'text' -%}
+                        {%- if role == 'model' -%}
+                            {{- strip_thinking(item['text']) -}}
+                        {%- else -%}
+                            {{- item['text'] | trim -}}
+                        {%- endif -%}
+                    {%- elif item['type'] == 'image' -%}
+                        {{- '\n\n<|image|>\n\n' -}}
+                        {%- set ns.prev_message_type = 'image' -%}
+                    {%- elif item['type'] == 'audio' -%}
+                        {{- '<|audio|>' -}}
+                        {%- set ns.prev_message_type = 'audio' -%}
+                    {%- elif item['type'] == 'video' -%}
+                        {{- '\n\n<|video|>\n\n' -}}
+                        {%- set ns.prev_message_type = 'video' -%}
+                    {%- endif -%}
+                {%- endfor -%}
+            {%- endif -%}
+
+        {%- if not (ns_tr_out.flag and not message.get('content')) -%}
+            {{- '<turn|>\n' -}}
+        {%- endif -%}
+    {%- endif -%}
+{%- endfor -%}
+
+{%- if add_generation_prompt -%}
+    {%- if ns.prev_message_type != 'tool_response' -%}
+        {{- '<|turn>model\n' -}}
+    {%- endif -%}
+    {%- if not enable_thinking | default(false) -%}
+        {{- '<|channel>thought\n<channel|>' -}}
+    {%- endif -%}
+{%- endif -%}

tests/reasoning/test_gemma4_reasoning_parser.py

@@ -4,6 +4,9 @@
 import pytest
 
 from tests.reasoning.utils import run_reasoning_extraction
+from vllm.entrypoints.openai.chat_completion.protocol import (
+    ChatCompletionRequest,
+)
 from vllm.reasoning import ReasoningParser, ReasoningParserManager
 
 # Using mistral tokenizer as a generic mock since the actual model is not on HF
@@ -100,6 +103,39 @@ NEW_LINE_STREAMING = {
     "is_reasoning_end": True,
 }
 
+THOUGHT_PREFIX = {
+    "output": "<|channel>thought\nActual reasoning here<channel|>Final answer",
+    "reasoning": "Actual reasoning here",
+    "content": "Final answer",
+    "is_reasoning_end": True,
+}
+THOUGHT_PREFIX_ONLY = {
+    "output": "<|channel>thought\n<channel|>",
+    "reasoning": "",
+    "content": None,
+    "is_reasoning_end": True,
+}
+THOUGHT_PREFIX_MULTILINE = {
+    "output": "<|channel>thought\nLine1\nLine2<channel|>Answer",
+    "reasoning": "Line1\nLine2",
+    "content": "Answer",
+    "is_reasoning_end": True,
+}
+# "thousand" starts like "thought" but diverges — exercises Case 2→3 in streaming.
+THOUGHT_PREFIX_DIVERGE = {
+    "output": "<|channel>thousand reasons<channel|>Done",
+    "reasoning": "thousand reasons",
+    "content": "Done",
+    "is_reasoning_end": True,
+}
+# The model isn't reasoning if we're generating tool calls.
+TOOL_CALL_STARTED = {
+    "output": "<|tool_call>",
+    "reasoning": None,
+    "content": "<|tool_call>",
+    "is_reasoning_end": True,
+}
+
 TEST_CASES = [
     pytest.param(False, INVALID_SIMPLE_NONSTREAMING, id="invalid_simple"),
     pytest.param(True, INVALID_SIMPLE_STREAMING, id="invalid_simple_streaming"),
@@ -120,17 +156,22 @@ TEST_CASES = [
     pytest.param(False, EMPTY, id="empty"),
     pytest.param(False, NEW_LINE_NONSTREAMING, id="new_line"),
     pytest.param(True, NEW_LINE_STREAMING, id="new_line_streaming"),
+    pytest.param(False, THOUGHT_PREFIX, id="thought_prefix"),
+    pytest.param(True, THOUGHT_PREFIX, id="thought_prefix_streaming"),
+    pytest.param(False, THOUGHT_PREFIX_ONLY, id="thought_prefix_only"),
+    pytest.param(True, THOUGHT_PREFIX_ONLY, id="thought_prefix_only_streaming"),
+    pytest.param(False, THOUGHT_PREFIX_MULTILINE, id="thought_prefix_multiline"),
+    pytest.param(
+        True, THOUGHT_PREFIX_MULTILINE, id="thought_prefix_multiline_streaming"
+    ),
+    pytest.param(False, THOUGHT_PREFIX_DIVERGE, id="thought_prefix_diverge"),
+    pytest.param(True, THOUGHT_PREFIX_DIVERGE, id="thought_prefix_diverge_streaming"),
+    pytest.param(False, TOOL_CALL_STARTED, id="tool_call_started"),
+    pytest.param(True, TOOL_CALL_STARTED, id="tool_call_started_streaming"),
 ]
 
 
-@pytest.mark.parametrize("streaming, param_dict", TEST_CASES)
-def test_gemma4_reasoning(
-    streaming: bool,
-    param_dict: dict,
-    generic_tokenizer,
-):
-    output = param_dict["output"]
-
+def gemma4_encode_output(generic_tokenizer, output: str) -> list[int]:
     # Resolve token IDs dynamically from the real tokenizer
     vocab = generic_tokenizer.get_vocab()
     start_token_id = vocab["<|channel>"]
@@ -176,6 +217,18 @@ def test_gemma4_reasoning(
     else:
         output_tokens += _encode(output)
 
+    return output_tokens
+
+
+@pytest.mark.parametrize("streaming, param_dict", TEST_CASES)
+def test_gemma4_reasoning(
+    streaming: bool,
+    param_dict: dict,
+    generic_tokenizer,
+):
+    output = param_dict["output"]
+    output_tokens = gemma4_encode_output(generic_tokenizer, output)
+
     parser: ReasoningParser = ReasoningParserManager.get_reasoning_parser(parser_name)(
         generic_tokenizer
     )
@@ -194,3 +247,29 @@ def test_gemma4_reasoning(
     # Test is_reasoning_end
     is_reasoning_end = parser.is_reasoning_end(output_tokens)
     assert is_reasoning_end == param_dict["is_reasoning_end"]
+
+
+def test_gemma4_adjust_request(generic_tokenizer):
+    parser: ReasoningParser = ReasoningParserManager.get_reasoning_parser(parser_name)(
+        generic_tokenizer
+    )
+
+    request = ChatCompletionRequest(messages=[], model="test-model")
+    assert request.skip_special_tokens is True
+
+    result = parser.adjust_request(request)
+    assert result.skip_special_tokens is False
+    assert result is request
+
+
+def test_gemma4_previous_turn_reasoning_is_reasoning_end(generic_tokenizer):
+    output = (
+        "<|channel>thought\n1st thought<channel|>1st content<turn|>\n"
+        "<|turn>user\nThanks<|turn>model\n"
+    )
+    output_tokens = gemma4_encode_output(generic_tokenizer, output)
+    parser: ReasoningParser = ReasoningParserManager.get_reasoning_parser(parser_name)(
+        generic_tokenizer
+    )
+    is_reasoning_end = parser.is_reasoning_end(output_tokens)
+    assert not is_reasoning_end

tests/renderers/test_gemma4_chat_template.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+"""Tests for Gemma4 chat template rendering."""
+
+from pathlib import Path
+
+import jinja2.sandbox
+import pytest
+
+TEMPLATE_PATH = (
+    Path(__file__).resolve().parent.parent.parent
+    / "examples"
+    / "tool_chat_template_gemma4.jinja"
+)
+
+
+@pytest.fixture(scope="module")
+def gemma4_template():
+    """Load and compile the Gemma4 chat template."""
+    template_str = TEMPLATE_PATH.read_text()
+    env = jinja2.sandbox.ImmutableSandboxedEnvironment()
+    return env.from_string(template_str)
+
+
+def _render(template, messages, **kwargs):
+    """Render the template with sensible defaults."""
+    kwargs.setdefault("bos_token", "<bos>")
+    kwargs.setdefault("add_generation_prompt", False)
+    return template.render(messages=messages, **kwargs)
+
+
+class TestGemma4ChatTemplate:
+    def test_basic_multiturn_thinking_disabled(self, gemma4_template):
+        """With enable_thinking=False (default), generation prompt ends with
+        an empty thought channel to suppress thinking."""
+        messages = [
+            {"role": "user", "content": "Hello"},
+            {"role": "assistant", "content": "Hi there!"},
+            {"role": "user", "content": "How are you?"},
+        ]
+        result = _render(gemma4_template, messages, add_generation_prompt=True)
+        assert "<|turn>user\n" in result
+        assert "<|turn>model\n" in result
+        assert "Hello" in result
+        assert "Hi there!" in result
+        assert "How are you?" in result
+        assert result.rstrip("\n").endswith("<|channel>thought\n<channel|>")
+
+    def test_basic_multiturn_thinking_enabled(self, gemma4_template):
+        """With enable_thinking=True, generation prompt ends with model
+        turn opener (no thought suppression)."""
+        messages = [
+            {"role": "user", "content": "Hello"},
+            {"role": "assistant", "content": "Hi there!"},
+            {"role": "user", "content": "How are you?"},
+        ]
+        result = _render(
+            gemma4_template,
+            messages,
+            add_generation_prompt=True,
+            enable_thinking=True,
+        )
+        assert "<|turn>user\n" in result
+        assert "<|turn>model\n" in result
+        assert "Hello" in result
+        assert "Hi there!" in result
+        assert "How are you?" in result
+        assert result.rstrip("\n").endswith("<|turn>model")
+
+    def test_system_message(self, gemma4_template):
+        messages = [
+            {"role": "system", "content": "You are helpful."},
+            {"role": "user", "content": "Hi"},
+        ]
+        result = _render(gemma4_template, messages)
+        assert "<|turn>system\n" in result
+        assert "You are helpful." in result
+
+    def test_thinking_enabled(self, gemma4_template):
+        messages = [{"role": "user", "content": "Think about this"}]
+        result = _render(
+            gemma4_template,
+            messages,
+            add_generation_prompt=True,
+            enable_thinking=True,
+        )
+        assert "<|think|>" in result
+        assert "<|turn>system\n" in result
+
+    def test_tool_declarations(self, gemma4_template):
+        tools = [
+            {
+                "type": "function",
+                "function": {
+                    "name": "get_weather",
+                    "description": "Get weather for a city",
+                    "parameters": {
+                        "type": "object",
+                        "properties": {
+                            "city": {
+                                "type": "string",
+                                "description": "City name",
+                            }
+                        },
+                        "required": ["city"],
+                    },
+                },
+            }
+        ]
+        messages = [{"role": "user", "content": "What is the weather?"}]
+        result = _render(
+            gemma4_template,
+            messages,
+            tools=tools,
+            add_generation_prompt=True,
+        )
+        assert "<|tool>" in result
+        assert "declaration:get_weather" in result
+        assert "<tool|>" in result
+        assert '<|"|>City name<|"|>' in result
+
+    def test_tool_calls_in_assistant(self, gemma4_template):
+        messages = [
+            {"role": "user", "content": "Weather in London?"},
+            {
+                "role": "assistant",
+                "content": "",
+                "tool_calls": [
+                    {
+                        "id": "call_1",
+                        "function": {
+                            "name": "get_weather",
+                            "arguments": {"city": "London"},
+                        },
+                    }
+                ],
+            },
+        ]
+        result = _render(gemma4_template, messages)
+        assert "<|tool_call>call:get_weather{" in result
+        assert "}<tool_call|>" in result
+        assert '<|"|>London<|"|>' in result
+
+    def test_tool_responses_openai_style(self, gemma4_template):
+        """role='tool' messages are formatted as <|tool_response> blocks
+        with content dumped as-is."""
+        messages = [
+            {"role": "user", "content": "Weather?"},
+            {
+                "role": "assistant",
+                "content": "",
+                "tool_calls": [
+                    {
+                        "id": "call_1",
+                        "function": {
+                            "name": "get_weather",
+                            "arguments": {"city": "London"},
+                        },
+                    }
+                ],
+            },
+            {
+                "role": "tool",
+                "tool_call_id": "call_1",
+                "content": '{"temperature": 15, "condition": "sunny"}',
+            },
+        ]
+        result = _render(gemma4_template, messages, add_generation_prompt=True)
+        assert "<|tool_response>" in result
+        assert "response:get_weather{" in result
+        assert "<tool_response|>" in result
+        assert '"temperature": 15' in result
+
+    def test_tool_responses_legacy_style(self, gemma4_template):
+        """tool_responses embedded on the assistant message."""
+        messages = [
+            {"role": "user", "content": "Weather?"},
+            {
+                "role": "assistant",
+                "content": "",
+                "tool_calls": [
+                    {
+                        "function": {
+                            "name": "get_weather",
+                            "arguments": {"city": "London"},
+                        },
+                    }
+                ],
+                "tool_responses": [
+                    {
+                        "name": "get_weather",
+                        "response": {"temperature": 20},
+                    }
+                ],
+            },
+        ]
+        result = _render(gemma4_template, messages)
+        assert "<|tool_response>" in result
+        assert "response:get_weather{" in result
+        assert "temperature:" in result
+
+    def test_generation_prompt_not_after_tool_response(self, gemma4_template):
+        """add_generation_prompt=True should NOT add <|turn>model when the
+        last message type was tool_response (the model turn continues)."""
+        messages = [
+            {"role": "user", "content": "Weather?"},
+            {
+                "role": "assistant",
+                "content": "",
+                "tool_calls": [
+                    {
+                        "id": "call_1",
+                        "function": {
+                            "name": "get_weather",
+                            "arguments": {"city": "London"},
+                        },
+                    }
+                ],
+            },
+            {
+                "role": "tool",
+                "tool_call_id": "call_1",
+                "content": "sunny",
+            },
+        ]
+        result = _render(gemma4_template, messages, add_generation_prompt=True)
+        assert not result.strip().endswith("<|turn>model\n")
+
+    def test_reasoning_in_tool_chains(self, gemma4_template):
+        """reasoning field on assistant with tool_calls after last user
+        message emits <|channel>thought\\n...<channel|>."""
+        messages = [
+            {"role": "user", "content": "Calculate something"},
+            {
+                "role": "assistant",
+                "content": "",
+                "reasoning": "Let me think about this...",
+                "tool_calls": [
+                    {
+                        "function": {
+                            "name": "calculator",
+                            "arguments": {"expr": "2+2"},
+                        },
+                    }
+                ],
+            },
+        ]
+        result = _render(gemma4_template, messages)
+        assert "<|channel>thought\n" in result
+        assert "Let me think about this..." in result
+        assert "<channel|>" in result
+
+    def test_reasoning_not_before_last_user(self, gemma4_template):
+        """reasoning on assistant BEFORE the last user message is dropped."""
+        messages = [
+            {"role": "user", "content": "First"},
+            {
+                "role": "assistant",
+                "content": "Response",
+                "reasoning": "Old reasoning that should be dropped",
+                "tool_calls": [
+                    {
+                        "function": {
+                            "name": "fn",
+                            "arguments": {},
+                        },
+                    }
+                ],
+            },
+            {"role": "user", "content": "Second"},
+        ]
+        result = _render(gemma4_template, messages, add_generation_prompt=True)
+        assert "Old reasoning" not in result
+
+    def test_strip_thinking_in_model_content(self, gemma4_template):
+        """<|channel>...<channel|> in model content is stripped by the
+        strip_thinking macro."""
+        messages = [
+            {"role": "user", "content": "Hi"},
+            {
+                "role": "assistant",
+                "content": ("<|channel>internal thought<channel|>Visible answer"),
+            },
+        ]
+        result = _render(gemma4_template, messages)
+        assert "internal thought" not in result
+        assert "Visible answer" in result
+
+    def test_multi_turn_tool_chain(self, gemma4_template):
+        """assistant->tool->assistant->tool produces exactly one
+        <|turn>model (later assistants continue the same turn)."""
+        messages = [
+            {"role": "user", "content": "Do two things"},
+            {
+                "role": "assistant",
+                "content": "",
+                "tool_calls": [
+                    {
+                        "id": "c1",
+                        "function": {"name": "step1", "arguments": {}},
+                    },
+                ],
+            },
+            {"role": "tool", "tool_call_id": "c1", "content": "result1"},
+            {
+                "role": "assistant",
+                "content": "",
+                "tool_calls": [
+                    {
+                        "id": "c2",
+                        "function": {"name": "step2", "arguments": {}},
+                    },
+                ],
+            },
+            {"role": "tool", "tool_call_id": "c2", "content": "result2"},
+        ]
+        result = _render(gemma4_template, messages, add_generation_prompt=True)
+        assert result.count("<|turn>model\n") == 1
+
+    def test_format_argument_types(self, gemma4_template):
+        """Strings wrapped in <|"|>, booleans as true/false, numbers bare."""
+        messages = [
+            {"role": "user", "content": "Test"},
+            {
+                "role": "assistant",
+                "content": "",
+                "tool_calls": [
+                    {
+                        "function": {
+                            "name": "test_fn",
+                            "arguments": {
+                                "name": "Alice",
+                                "active": True,
+                                "count": 42,
+                            },
+                        },
+                    }
+                ],
+            },
+        ]
+        result = _render(gemma4_template, messages)
+        assert '<|"|>Alice<|"|>' in result
+        assert "active:true" in result
+        assert "count:42" in result

tests/tool_parsers/test_gemma4_tool_parser.py

@@ -114,6 +114,19 @@ class TestParseGemma4Args:
         result = _parse_gemma4_args("key:")
         assert result == {"key": ""}
 
+    def test_empty_value_partial_withheld(self):
+        """Key with no value is withheld in partial mode to avoid premature emission."""
+        result = _parse_gemma4_args("key:", partial=True)
+        assert result == {}
+        # also with a space after the colon
+        result = _parse_gemma4_args("key: ", partial=True)
+        assert result == {}
+
+    def test_empty_value_after_other_keys_partial_withheld(self):
+        """Trailing key with no value is withheld; earlier keys are kept."""
+        result = _parse_gemma4_args('name:<|"|>test<|"|>,flag:', partial=True)
+        assert result == {"name": "test"}
+
 
 class TestParseGemma4Array:
     def test_string_array(self):
@@ -636,3 +649,30 @@ class TestStreamingExtraction:
             '    <meta charset="UTF-8">\n'
             '    <meta name="viewport" content="width=device-width">\n'
         )
+
+    def test_streaming_trailing_bare_bool_not_duplicated(self, parser, mock_request):
+        """Trailing bare boolean must not be streamed twice."""
+        chunks = [
+            "<|tool_call>",
+            "call:Edit{",
+            'file_path:<|"|>src/env.py<|"|>,',
+            'old_string:<|"|>old_val<|"|>,',
+            'new_string:<|"|>new_val<|"|>,',
+            "replace_all:",
+            "false}",
+            "<tool_call|>",
+        ]
+
+        results = self._simulate_streaming(parser, mock_request, chunks)
+        args_text = self._collect_arguments(results)
+        assert args_text, "No arguments were streamed"
+
+        parsed_args = json.loads(args_text)
+        assert parsed_args == {
+            "file_path": "src/env.py",
+            "old_string": "old_val",
+            "new_string": "new_val",
+            "replace_all": False,
+        }
+
+        assert args_text.count("replace_all") == 1

vllm/entrypoints/anthropic/serving.py

@@ -170,7 +170,8 @@ class AnthropicServingMessages(OpenAIServingChat):
             else:
                 cls._convert_message_content(msg, openai_msg, openai_messages)
 
-            openai_messages.append(openai_msg)
+            if not (msg.role == "user" and "content" not in openai_msg):
+                openai_messages.append(openai_msg)
 
     @classmethod
     def _convert_message_content(

vllm/entrypoints/openai/api_server.py

@@ -379,6 +379,7 @@ async def init_app_state(
         enable_auto_tools=args.enable_auto_tool_choice,
         exclude_tools_when_tool_choice_none=args.exclude_tools_when_tool_choice_none,
         tool_parser=args.tool_call_parser,
+        reasoning_parser=args.structured_outputs_config.reasoning_parser,
         default_chat_template_kwargs=args.default_chat_template_kwargs,
         log_error_stack=args.log_error_stack,
     )
@@ -481,6 +482,7 @@ async def init_render_app_state(
         enable_auto_tools=args.enable_auto_tool_choice,
         exclude_tools_when_tool_choice_none=args.exclude_tools_when_tool_choice_none,
         tool_parser=args.tool_call_parser,
+        reasoning_parser=args.structured_outputs_config.reasoning_parser,
         default_chat_template_kwargs=args.default_chat_template_kwargs,
         log_error_stack=args.log_error_stack,
     )

vllm/entrypoints/openai/responses/serving.py

@@ -594,6 +594,7 @@ class OpenAIServingResponses(OpenAIServing):
             default_template_kwargs=None,
             tool_dicts=tool_dicts,
             tool_parser=self.parser.tool_parser_cls if self.parser else None,
+            reasoning_parser=self.parser.reasoning_parser_cls if self.parser else None,
         )
         return messages, engine_inputs
 
@@ -618,6 +619,7 @@ class OpenAIServingResponses(OpenAIServing):
             default_template_kwargs=None,
             tool_dicts=tool_dicts,
             tool_parser=tool_parser,
+            reasoning_parser=self.parser.reasoning_parser_cls if self.parser else None,
         )
         return engine_inputs
 

vllm/entrypoints/serve/render/serving.py

@@ -44,6 +44,7 @@ from vllm.inputs import (
 )
 from vllm.logger import init_logger
 from vllm.parser import ParserManager
+from vllm.reasoning.abs_reasoning_parsers import ReasoningParser
 from vllm.renderers import BaseRenderer, merge_kwargs
 from vllm.renderers.inputs.preprocess import (
     extract_prompt_components,
@@ -74,6 +75,7 @@ class OpenAIServingRender:
         enable_auto_tools: bool = False,
         exclude_tools_when_tool_choice_none: bool = False,
         tool_parser: str | None = None,
+        reasoning_parser: str | None = None,
         default_chat_template_kwargs: dict[str, Any] | None = None,
         log_error_stack: bool = False,
     ) -> None:
@@ -94,6 +96,11 @@ class OpenAIServingRender:
             enable_auto_tools=enable_auto_tools,
             model_name=model_config.model,
         )
+        self.reasoning_parser: type[ReasoningParser] | None = (
+            ParserManager.get_reasoning_parser(
+                reasoning_parser_name=reasoning_parser,
+            )
+        )
         self.default_chat_template_kwargs: dict[str, Any] = (
             default_chat_template_kwargs or {}
         )
@@ -245,6 +252,7 @@ class OpenAIServingRender:
                 default_template_kwargs=self.default_chat_template_kwargs,
                 tool_dicts=tool_dicts,
                 tool_parser=tool_parser,
+                reasoning_parser=self.reasoning_parser,
             )
         else:
             # For GPT-OSS.
@@ -503,6 +511,7 @@ class OpenAIServingRender:
         default_template_kwargs: dict[str, Any] | None,
         tool_dicts: list[dict[str, Any]] | None = None,
         tool_parser: type[ToolParser] | None = None,
+        reasoning_parser: type[ReasoningParser] | None = None,
         *,
         skip_mm_cache: bool = False,
     ) -> tuple[list[ConversationMessage], list[EngineInput]]:
@@ -539,6 +548,10 @@ class OpenAIServingRender:
             skip_mm_cache=skip_mm_cache,
         )
 
+        if reasoning_parser is not None:
+            tokenizer = renderer.get_tokenizer()
+            request = reasoning_parser(tokenizer).adjust_request(request=request)
+
         # tool parsing is done only if a tool_parser has been set and if
         # tool_choice is not "none" (if tool_choice is "none" but a tool_parser
         # is set, we want to prevent parsing a tool_call hallucinated by the LLM

vllm/parser/abstract_parser.py

@@ -496,6 +496,15 @@ class DelegatingParser(Parser):
         # No tool calls
         return [], content
 
+    def adjust_request(
+        self, request: ChatCompletionRequest | ResponsesRequest
+    ) -> ChatCompletionRequest | ResponsesRequest:
+        if self._reasoning_parser is not None:
+            request = self._reasoning_parser.adjust_request(request)
+        if self._tool_parser is not None:
+            request = self._tool_parser.adjust_request(request)
+        return request
+
     def extract_reasoning_streaming(
         self,
         previous_text: str,

vllm/reasoning/abs_reasoning_parsers.py

@@ -6,7 +6,7 @@ import os
 from abc import abstractmethod
 from collections.abc import Callable, Iterable, Sequence
 from functools import cached_property
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, cast
 
 from vllm.entrypoints.mcp.tool_server import ToolServer
 from vllm.logger import init_logger
@@ -150,6 +150,12 @@ class ReasoningParser:
         previously been parsed and extracted (see constructor)
         """
 
+    def adjust_request(
+        self, request: "ChatCompletionRequest | ResponsesRequest"
+    ) -> "ChatCompletionRequest | ResponsesRequest":
+        """Adjust request parameters; override in subclasses as needed."""
+        return request
+
     def prepare_structured_tag(
         self,
         original_tag: str | None,
@@ -298,7 +304,7 @@ class ReasoningParserManager:
             if isinstance(name, str):
                 names = [name]
             elif is_list_of(name, str):
-                names = name
+                names = cast(list[str], name)
             else:
                 names = [class_name]
 

vllm/reasoning/gemma4_reasoning_parser.py

@@ -52,6 +52,16 @@ class Gemma4ReasoningParser(BaseThinkingReasoningParser):
         # skip_special_tokens=True).
         self._reasoning_text: str = ""
         self._prefix_stripped: bool = False
+        self.new_turn_token_id = self.vocab["<|turn>"]
+        self.tool_call_token_id = self.vocab["<|tool_call>"]
+        self.tool_response_token_id = self.vocab["<|tool_response>"]
+
+    def adjust_request(
+        self, request: "ChatCompletionRequest | ResponsesRequest"
+    ) -> "ChatCompletionRequest | ResponsesRequest":
+        """Disable special-token stripping to preserve boundary tokens."""
+        request.skip_special_tokens = False
+        return request
 
     @property
     def start_token(self) -> str:
@@ -63,6 +73,29 @@ class Gemma4ReasoningParser(BaseThinkingReasoningParser):
         """The token that ends reasoning content."""
         return "<channel|>"
 
+    def is_reasoning_end(self, input_ids: Sequence[int]) -> bool:
+        start_token_id = self.start_token_id
+        end_token_id = self.end_token_id
+        new_turn_token_id = self.new_turn_token_id
+        tool_call_token_id = self.tool_call_token_id
+        tool_response_token_id = self.tool_response_token_id
+
+        # Search from the end of input_ids to find the last match.
+        for i in range(len(input_ids) - 1, -1, -1):
+            if input_ids[i] == start_token_id:
+                return False
+            if input_ids[i] == tool_call_token_id:
+                # We're generating a tool call, so reasoning must be ended.
+                return True
+            if input_ids[i] in (new_turn_token_id, tool_response_token_id):
+                # We found a new turn or tool response token so don't consider
+                # reasoning ended yet, since the model starts new reasoning
+                # after these tokens.
+                return False
+            if input_ids[i] == end_token_id:
+                return True
+        return False
+
     # ------------------------------------------------------------------
     # Non-streaming path
     # ------------------------------------------------------------------
@@ -159,11 +192,10 @@ class Gemma4ReasoningParser(BaseThinkingReasoningParser):
                     result.reasoning = stripped
                     return result
                 else:
-                    # This entire delta was prefix — suppress it.
-                    # Don't set _prefix_stripped yet; there may be more
-                    # prefix chars to consume in the next delta.
                     if len(self._reasoning_text) >= prefix_len:
                         self._prefix_stripped = True
+                        result.reasoning = ""
+                        return result
                     return None
 
         # Case 2: Accumulated text is a strict prefix of

vllm/tool_parsers/gemma4_tool_parser.py

@@ -122,14 +122,16 @@ def _parse_gemma4_args(args_str: str, *, partial: bool = False) -> dict:
 
         # Parse value
         if i >= n:
-            result[key] = ""
+            if not partial:
+                result[key] = ""
             break
 
         # Skip whitespace after ':'
         while i < n and args_str[i] in (" ", "\n", "\t"):
             i += 1
         if i >= n:
-            result[key] = ""
+            if not partial:
+                result[key] = ""
             break
 
         # String value: <|"|>...<|"|>