fix(gemini): skip thinking config for image models

docs/my-website/docs/providers/gemini.md

@@ -74,6 +74,10 @@ Note: Reasoning cannot be turned off on Gemini 2.5 Pro models.
 For **Gemini 3+ models** (e.g., `gemini-3-pro-preview`), LiteLLM automatically maps `reasoning_effort` to the new `thinking_level` parameter instead of `thinking_budget`. The `thinking_level` parameter uses `"low"` or `"high"` values for better control over reasoning depth.
 :::
 
+:::warning Image Models
+**Gemini image models** (e.g., `gemini-3-pro-image-preview`, `gemini-2.0-flash-exp-image-generation`) do **not** support the `thinking_level` parameter. LiteLLM automatically excludes image models from receiving thinking configuration to prevent API errors.
+:::
+
 **Mapping for Gemini 2.5 and earlier models**
 
 | reasoning_effort | thinking | Notes |

litellm/llms/vertex_ai/gemini/vertex_and_google_ai_studio_gemini.py

@@ -904,13 +904,15 @@ def map_openai_params(  # noqa: PLR0915
         if VertexGeminiConfig._is_gemini_3_or_newer(model):
             if "temperature" not in optional_params:
                 optional_params["temperature"] = 1.0
-            thinking_config = optional_params.get("thinkingConfig", {})
-            if (
-                "thinkingLevel" not in thinking_config
-                and "thinkingBudget" not in thinking_config
-            ):
-                thinking_config["thinkingLevel"] = "low"
-                optional_params["thinkingConfig"] = thinking_config
+            # Only add thinkingLevel if model supports it (exclude image models)
+            if "image" not in model.lower():
+                thinking_config = optional_params.get("thinkingConfig", {})
+                if (
+                    "thinkingLevel" not in thinking_config
+                    and "thinkingBudget" not in thinking_config
+                ):
+                    thinking_config["thinkingLevel"] = "low"
+                    optional_params["thinkingConfig"] = thinking_config
 
         return optional_params
 

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

@@ -1967,3 +1967,98 @@ def test_media_resolution_per_part():
     assert "inline_data" in image2_part
     assert image2_part["inline_data"]["mediaResolution"] == "high"
 
+
+def test_gemini_3_image_models_no_thinking_config():
+    """
+    Test that Gemini 3 image models do NOT receive automatic thinkingConfig.
+
+    Related issue: https://github.com/BerriAI/litellm/issues/17013
+    gemini-3-pro-image-preview does not support thinking_level parameter
+    and returns BadRequestError: "Thinking level is not supported for this model"
+    """
+    from litellm.llms.vertex_ai.gemini.vertex_and_google_ai_studio_gemini import (
+        VertexGeminiConfig,
+    )
+
+    v = VertexGeminiConfig()
+
+    # Test gemini-3-pro-image-preview (the specific model from the bug report)
+    model = "gemini-3-pro-image-preview"
+    optional_params = {}
+    non_default_params = {}
+
+    result = v.map_openai_params(
+        non_default_params=non_default_params,
+        optional_params=optional_params,
+        model=model,
+        drop_params=False,
+    )
+
+    # Should NOT have thinkingConfig automatically added
+    assert "thinkingConfig" not in result
+    # But should still get temperature=1.0 for Gemini 3
+    assert result["temperature"] == 1.0
+
+
+def test_gemini_3_text_models_get_thinking_config():
+    """
+    Test that Gemini 3 text models DO receive automatic thinkingConfig.
+    This ensures we didn't break the existing behavior for non-image models.
+    """
+    from litellm.llms.vertex_ai.gemini.vertex_and_google_ai_studio_gemini import (
+        VertexGeminiConfig,
+    )
+
+    v = VertexGeminiConfig()
+
+    # Test gemini-3-pro-preview (text model, should get thinking)
+    model = "gemini-3-pro-preview"
+    optional_params = {}
+    non_default_params = {}
+
+    result = v.map_openai_params(
+        non_default_params=non_default_params,
+        optional_params=optional_params,
+        model=model,
+        drop_params=False,
+    )
+
+    # Should have thinkingConfig automatically added
+    assert "thinkingConfig" in result
+    assert result["thinkingConfig"]["thinkingLevel"] == "low"
+    assert result["temperature"] == 1.0
+
+
+def test_gemini_image_models_excluded_from_thinking():
+    """
+    Test that any Gemini model with 'image' in the name is excluded from thinking config.
+    This covers current and future image models.
+    """
+    from litellm.llms.vertex_ai.gemini.vertex_and_google_ai_studio_gemini import (
+        VertexGeminiConfig,
+    )
+
+    v = VertexGeminiConfig()
+
+    # Test various image model patterns
+    image_models = [
+        "gemini-3-pro-image-preview",
+        "gemini-3-pro-image-generation",
+        "gemini-3-flash-image-preview",
+        "gemini/gemini-3-image-edit",
+    ]
+
+    for model in image_models:
+        optional_params = {}
+        non_default_params = {}
+
+        result = v.map_openai_params(
+            non_default_params=non_default_params,
+            optional_params=optional_params,
+            model=model,
+            drop_params=False,
+        )
+
+        # None of these should have thinkingConfig
+        assert "thinkingConfig" not in result, f"Model {model} should not have thinkingConfig"
+