From e13dfb030c4dd30393f0da8b867cf4ebcb285274 Mon Sep 17 00:00:00 2001
From: Roo Code <roomote@roocode.com>
Date: Wed, 24 Dec 2025 20:29:13 +0000
Subject: [PATCH] fix: clarify Gemini thinkingConfig support guard to prevent
 400 errors

---
 src/api/transform/reasoning.ts | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/api/transform/reasoning.ts b/src/api/transform/reasoning.ts
index e726ce3223..887810db00 100644
--- a/src/api/transform/reasoning.ts
+++ b/src/api/transform/reasoning.ts
@@ -131,6 +131,11 @@ export const getGeminiReasoning = ({
 	reasoningEffort,
 	settings,
 }: GetModelReasoningOptions): GeminiReasoningParams | undefined => {
+	// Only send thinkingConfig to models that advertise support for it; Gemini 3 rejects
+	// the field and returns 400 otherwise.
+	const supportsThinkingConfig =
+		typeof model.maxThinkingTokens === "number" || model.supportsReasoningBudget || model.supportsReasoningEffort
+
 	// Budget-based (2.5) models: use thinkingBudget, not thinkingLevel.
 	if (shouldUseReasoningBudget({ model, settings })) {
 		return { thinkingBudget: reasoningBudget!, includeThoughts: true }
@@ -150,6 +155,11 @@ export const getGeminiReasoning = ({
 		return undefined
 	}
 
+	// Skip thinking config for models that don't advertise support (e.g., Gemini 3).
+	if (!supportsThinkingConfig) {
+		return undefined
+	}
+
 	// Effort-based models on Google GenAI support minimal/low/medium/high levels.
 	if (!isGeminiThinkingLevel(selectedEffort)) {
 		return undefined