fix(gemini): read the minimal thinking floor from the cost map and cover the /v1/messages bridge

litellm/llms/openai/chat/gpt_5_transformation.py

@@ -4,9 +4,9 @@ from typing import Final
 
 import litellm
 from litellm.utils import (
-    _is_explicitly_disabled_factory,
     _supports_factory,
     declared_value_factory,
+    is_explicitly_disabled_factory,
 )
 
 from .gpt_transformation import OpenAIGPTConfig
@@ -192,7 +192,7 @@ class OpenAIGPT5Config(OpenAIGPTConfig):
 
         Use this for opt-out checks where unknown models should be allowed through.
         """
-        return _is_explicitly_disabled_factory(
+        return is_explicitly_disabled_factory(
             model=cls._model_map_lookup_name(model),
             custom_llm_provider=None,
             key=f"supports_{level}_reasoning_effort",

litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py

@@ -79,6 +79,7 @@ from litellm.utils import (
     CustomStreamWrapper,
     ModelResponse,
     is_base64_encoded,
+    is_explicitly_disabled_factory,
     supports_reasoning,
 )
 
@@ -110,7 +111,6 @@ else:
 
 
 SUPPORTED_REASONING_EFFORTS: Final = ("minimal", "low", "medium", "high", "none", "disable")
-GEMINI_FLASH_MODELS_WITHOUT_MINIMAL_THINKING: Final = ("gemini-3.7-flash", "gemini-3.8-flash")
 
 
 def _unsupported_reasoning_effort(reasoning_effort: str) -> UnsupportedParamsError:
@@ -865,7 +865,9 @@ class VertexGeminiConfig(VertexAIBaseConfig, BaseConfig):
     def _supports_minimal_thinking_level(model: str) -> bool:
         lowered: Final = model.lower()
         is_gemini3flash: Final = "gemini-3" in lowered and "flash" in lowered
-        return is_gemini3flash and not any(m in lowered for m in GEMINI_FLASH_MODELS_WITHOUT_MINIMAL_THINKING)
+        return is_gemini3flash and not is_explicitly_disabled_factory(
+            model=model, custom_llm_provider=None, key="supports_minimal_reasoning_effort"
+        )
 
     @staticmethod
     def _map_reasoning_effort_to_thinking_level(

litellm/model_prices_and_context_window_backup.json

@@ -25159,6 +25159,7 @@
         "supports_pdf_input": true,
         "supports_prompt_caching": true,
         "supports_reasoning": true,
+        "supports_minimal_reasoning_effort": false,
         "supports_response_schema": true,
         "supports_system_messages": true,
         "supports_tool_choice": true,
@@ -25216,6 +25217,7 @@
         "supports_pdf_input": true,
         "supports_prompt_caching": true,
         "supports_reasoning": true,
+        "supports_minimal_reasoning_effort": false,
         "supports_response_schema": true,
         "supports_system_messages": true,
         "supports_tool_choice": true,
@@ -27081,6 +27083,7 @@
         "supports_pdf_input": true,
         "supports_prompt_caching": true,
         "supports_reasoning": true,
+        "supports_minimal_reasoning_effort": false,
         "supports_response_schema": true,
         "supports_system_messages": true,
         "supports_tool_choice": true,
@@ -27140,6 +27143,7 @@
         "supports_pdf_input": true,
         "supports_prompt_caching": true,
         "supports_reasoning": true,
+        "supports_minimal_reasoning_effort": false,
         "supports_response_schema": true,
         "supports_system_messages": true,
         "supports_tool_choice": true,
@@ -27555,6 +27559,7 @@
         "supports_pdf_input": true,
         "supports_prompt_caching": true,
         "supports_reasoning": true,
+        "supports_minimal_reasoning_effort": false,
         "supports_response_schema": true,
         "supports_system_messages": true,
         "supports_tool_choice": true,
@@ -27612,6 +27617,7 @@
         "supports_pdf_input": true,
         "supports_prompt_caching": true,
         "supports_reasoning": true,
+        "supports_minimal_reasoning_effort": false,
         "supports_response_schema": true,
         "supports_system_messages": true,
         "supports_tool_choice": true,

litellm/utils.py

@@ -2675,7 +2675,7 @@ def declared_value_factory(model: str, custom_llm_provider: str | None, key: str
     """Return a string value the model map declares for *key*, or ``None`` when it says nothing.
 
     The string-valued sibling of :func:`_supports_factory` and
-    :func:`_is_explicitly_disabled_factory`, public where those two are not because it is read
+    :func:`is_explicitly_disabled_factory`, public like the latter because both are read
     from the provider configs rather than from this module, sharing their
     ``get_llm_provider`` -> ``_get_model_info_helper`` chain and their unprefixed-twin
     fallback (#20885), so a provider-prefixed entry that omits the key still answers
@@ -2711,7 +2711,7 @@ def declared_value_factory(model: str, custom_llm_provider: str | None, key: str
         return None
 
 
-def _is_explicitly_disabled_factory(model: str, custom_llm_provider: str | None, key: str) -> bool:
+def is_explicitly_disabled_factory(model: str, custom_llm_provider: str | None, key: str) -> bool:
     """Return True only when the model map explicitly sets *key* to ``False``.
 
     This is the opt-out mirror of :func:`_supports_factory`.  Where
@@ -2830,7 +2830,7 @@ def is_vision_explicitly_disabled(model: str, custom_llm_provider: str | None =
     The opt-out mirror of :func:`supports_vision`: a missing declaration reads as not
     disabled, so unknown or newly added models stay eligible for image routing.
     """
-    return _is_explicitly_disabled_factory(model, custom_llm_provider, "supports_vision")
+    return is_explicitly_disabled_factory(model, custom_llm_provider, "supports_vision")
 
 
 def supports_vision(model: str, custom_llm_provider: str | None = None) -> bool:

model_prices_and_context_window.json

@@ -25159,6 +25159,7 @@
         "supports_pdf_input": true,
         "supports_prompt_caching": true,
         "supports_reasoning": true,
+        "supports_minimal_reasoning_effort": false,
         "supports_response_schema": true,
         "supports_system_messages": true,
         "supports_tool_choice": true,
@@ -25216,6 +25217,7 @@
         "supports_pdf_input": true,
         "supports_prompt_caching": true,
         "supports_reasoning": true,
+        "supports_minimal_reasoning_effort": false,
         "supports_response_schema": true,
         "supports_system_messages": true,
         "supports_tool_choice": true,
@@ -27081,6 +27083,7 @@
         "supports_pdf_input": true,
         "supports_prompt_caching": true,
         "supports_reasoning": true,
+        "supports_minimal_reasoning_effort": false,
         "supports_response_schema": true,
         "supports_system_messages": true,
         "supports_tool_choice": true,
@@ -27140,6 +27143,7 @@
         "supports_pdf_input": true,
         "supports_prompt_caching": true,
         "supports_reasoning": true,
+        "supports_minimal_reasoning_effort": false,
         "supports_response_schema": true,
         "supports_system_messages": true,
         "supports_tool_choice": true,
@@ -27555,6 +27559,7 @@
         "supports_pdf_input": true,
         "supports_prompt_caching": true,
         "supports_reasoning": true,
+        "supports_minimal_reasoning_effort": false,
         "supports_response_schema": true,
         "supports_system_messages": true,
         "supports_tool_choice": true,
@@ -27612,6 +27617,7 @@
         "supports_pdf_input": true,
         "supports_prompt_caching": true,
         "supports_reasoning": true,
+        "supports_minimal_reasoning_effort": false,
         "supports_response_schema": true,
         "supports_system_messages": true,
         "supports_tool_choice": true,

tests/test_litellm/llms/openai/test_gpt5_transformation.py

@@ -8,7 +8,7 @@ from litellm.litellm_core_utils.get_model_cost_map import get_model_cost_map
 from litellm.llms.openai.chat.gpt_5_transformation import OpenAIGPT5Config
 from litellm.llms.openai.openai import OpenAIConfig
 from litellm.utils import (
-    _is_explicitly_disabled_factory,
+    is_explicitly_disabled_factory,
     peek_reasoning_summary_aliases,
     strip_reasoning_summary_aliases_from_optional_params,
 )
@@ -524,19 +524,19 @@ def test_gpt5_minimal_explicitly_disabled_check(gpt5_config: OpenAIGPT5Config):
 
 
 def test_is_explicitly_disabled_factory_minimal():
-    """_is_explicitly_disabled_factory returns True only for explicit False entries.
+    """is_explicitly_disabled_factory returns True only for explicit False entries.
 
     Verifies the shared helper used by _is_reasoning_effort_level_explicitly_disabled
     directly — so future changes to the helper are caught without going through the
     method wrapper.
     """
     key = "supports_minimal_reasoning_effort"
-    assert _is_explicitly_disabled_factory("gpt-5.4-mini", None, key)
-    assert _is_explicitly_disabled_factory("gpt-5.4-nano", None, key)
-    assert _is_explicitly_disabled_factory("openai/gpt-5.4-mini", None, key)
-    assert _is_explicitly_disabled_factory("gpt-5.4", None, key)
-    assert _is_explicitly_disabled_factory("gpt-5.4-pro", None, key)
-    assert not _is_explicitly_disabled_factory("gpt-5.4-turbo-preview", None, key)
+    assert is_explicitly_disabled_factory("gpt-5.4-mini", None, key)
+    assert is_explicitly_disabled_factory("gpt-5.4-nano", None, key)
+    assert is_explicitly_disabled_factory("openai/gpt-5.4-mini", None, key)
+    assert is_explicitly_disabled_factory("gpt-5.4", None, key)
+    assert is_explicitly_disabled_factory("gpt-5.4-pro", None, key)
+    assert not is_explicitly_disabled_factory("gpt-5.4-turbo-preview", None, key)
 
 
 def test_gpt5_unknown_model_passes_through_minimal(config: OpenAIConfig):

tests/test_litellm/llms/vertex_ai/gemini/test_vertex_and_google_ai_studio_gemini.py

@@ -5,11 +5,14 @@ from copy import deepcopy
 from typing import Final, List, cast
 from unittest.mock import MagicMock, patch
 
+import httpx
 import pytest
 from pydantic import BaseModel
 
 import litellm
 from litellm import ModelResponse, completion
+from litellm.llms.anthropic.experimental_pass_through.messages import handler as anthropic_messages_handler
+from litellm.llms.custom_httpx.http_handler import AsyncHTTPHandler
 from litellm.llms.gemini.chat.transformation import GoogleAIStudioGeminiConfig
 from litellm.llms.vertex_ai.common_utils import VertexAIError
 from litellm.llms.vertex_ai.gemini.vertex_and_google_ai_studio_gemini import (
@@ -2683,7 +2686,7 @@ def test_reasoning_effort_maps_to_thinking_level_gemini_3():
     [
         "gemini-3.7-flash",
         "vertex_ai/gemini-3.8-flash",
-        "gemini-3.8-flash-preview",
+        "gemini/gemini-3.8-flash",
     ],
 )
 @pytest.mark.parametrize(
@@ -2691,7 +2694,7 @@ def test_reasoning_effort_maps_to_thinking_level_gemini_3():
     [("minimal", True), ("none", False), ("disable", False)],
 )
 def test_gemini_37_38_flash_floor_minimal_thinking_level(
-    model, reasoning_effort, include_thoughts
+    local_model_cost_map, model, reasoning_effort, include_thoughts
 ):
     result = VertexGeminiConfig._map_reasoning_effort_to_thinking_level(
         reasoning_effort, model
@@ -2717,7 +2720,7 @@ def test_gemini_37_38_flash_floor_minimal_thinking_level(
     ],
 )
 def test_gemini_flash_minimal_thinking_support(
-    model, reasoning_effort, expected_level, include_thoughts
+    local_model_cost_map, model, reasoning_effort, expected_level, include_thoughts
 ):
     result = VertexGeminiConfig._map_reasoning_effort_to_thinking_level(
         reasoning_effort, model
@@ -2727,7 +2730,7 @@ def test_gemini_flash_minimal_thinking_support(
     assert result["includeThoughts"] is include_thoughts
 
 
-def test_gemini_38_flash_feature_flag_uses_low_thinking_level(monkeypatch):
+def test_gemini_38_flash_feature_flag_uses_low_thinking_level(local_model_cost_map, monkeypatch):
     monkeypatch.setattr(litellm, "enable_gemini_default_thinking_level_low", True)
     thinking_param = {"type": "enabled", "budget_tokens": 1024}
 
@@ -2742,7 +2745,7 @@ def test_gemini_38_flash_feature_flag_uses_low_thinking_level(monkeypatch):
     assert result_36["thinkingLevel"] == "minimal"
 
 
-def test_gemini_38_flash_public_reasoning_effort_none_uses_low():
+def test_gemini_38_flash_public_reasoning_effort_none_uses_low(local_model_cost_map):
     result = VertexGeminiConfig().map_openai_params(
         non_default_params={"reasoning_effort": "none"},
         optional_params={},
@@ -2756,6 +2759,40 @@ def test_gemini_38_flash_public_reasoning_effort_none_uses_low():
     }
 
 
+@pytest.mark.asyncio
+async def test_gemini_38_flash_messages_bridge_thinking_disabled_sends_low_thinking_level(local_model_cost_map):
+    captured: dict[str, dict] = {}
+
+    def upstream(request: httpx.Request) -> httpx.Response:
+        captured["body"] = json.loads(request.content)
+        return httpx.Response(
+            200,
+            json={
+                "candidates": [{"content": {"parts": [{"text": "hi"}], "role": "model"}, "finishReason": "STOP"}],
+                "usageMetadata": {"promptTokenCount": 1, "candidatesTokenCount": 1, "totalTokenCount": 2},
+            },
+            request=request,
+        )
+
+    client = AsyncHTTPHandler()
+    client.client = httpx.AsyncClient(transport=httpx.MockTransport(upstream))
+
+    await anthropic_messages_handler.anthropic_messages(
+        max_tokens=16,
+        messages=[{"role": "user", "content": "hi"}],
+        model="gemini/gemini-3.8-flash",
+        custom_llm_provider="gemini",
+        thinking={"type": "disabled"},
+        api_key="fake-gemini-key",
+        client=client,
+    )
+
+    assert captured["body"]["generationConfig"]["thinkingConfig"] == {
+        "thinkingLevel": "low",
+        "includeThoughts": False,
+    }
+
+
 def test_reasoning_effort_dict_format_gemini_3():
     """
     Test that reasoning_effort works when passed as dict format from OpenAI Agents SDK.