diff --git a/providers/gemini.py b/providers/gemini.py
index 90831ab..fc142c6 100644
--- a/providers/gemini.py
+++ b/providers/gemini.py
@@ -173,6 +173,15 @@ class GeminiModelProvider(RegistryBackedProviderMixin, ModelProvider):
         # Create contents structure
         contents = [{"parts": parts}]
 
+        # Gemini 3 Pro Preview currently rejects medium thinking budgets; bump to high.
+        effective_thinking_mode = thinking_mode
+        if resolved_model_name == "gemini-3-pro-preview" and thinking_mode == "medium":
+            logger.debug(
+                "Overriding thinking mode 'medium' with 'high' for %s due to launch limitation",
+                resolved_model_name,
+            )
+            effective_thinking_mode = "high"
+
         # Prepare generation config
         generation_config = types.GenerateContentConfig(
             temperature=temperature,
@@ -184,12 +193,12 @@ class GeminiModelProvider(RegistryBackedProviderMixin, ModelProvider):
             generation_config.max_output_tokens = max_output_tokens
 
         # Add thinking configuration for models that support it
-        if capabilities.supports_extended_thinking and thinking_mode in self.THINKING_BUDGETS:
+        if capabilities.supports_extended_thinking and effective_thinking_mode in self.THINKING_BUDGETS:
             # Get model's max thinking tokens and calculate actual budget
             model_config = capability_map.get(resolved_model_name)
             if model_config and model_config.max_thinking_tokens > 0:
                 max_thinking_tokens = model_config.max_thinking_tokens
-                actual_thinking_budget = int(max_thinking_tokens * self.THINKING_BUDGETS[thinking_mode])
+                actual_thinking_budget = int(max_thinking_tokens * self.THINKING_BUDGETS[effective_thinking_mode])
                 generation_config.thinking_config = types.ThinkingConfig(thinking_budget=actual_thinking_budget)
 
         # Retry logic with progressive delays
@@ -279,7 +288,7 @@ class GeminiModelProvider(RegistryBackedProviderMixin, ModelProvider):
                 friendly_name="Gemini",
                 provider=ProviderType.GOOGLE,
                 metadata={
-                    "thinking_mode": thinking_mode if capabilities.supports_extended_thinking else None,
+                    "thinking_mode": effective_thinking_mode if capabilities.supports_extended_thinking else None,
                     "finish_reason": finish_reason_str,
                     "is_blocked_by_safety": is_blocked_by_safety,
                     "safety_feedback": safety_feedback_details,