diff --git a/internal/util/gemini_thinking.go b/internal/util/gemini_thinking.go
index 19397f0dc..8e76f3bc7 100644
--- a/internal/util/gemini_thinking.go
+++ b/internal/util/gemini_thinking.go
@@ -71,10 +71,13 @@ func ApplyGeminiThinkingConfig(body []byte, budget *int, includeThoughts *bool)
 		incl = &defaultInclude
 	}
 	if incl != nil {
-		valuePath := "generationConfig.thinkingConfig.include_thoughts"
-		rewritten, err := sjson.SetBytes(updated, valuePath, *incl)
-		if err == nil {
-			updated = rewritten
+		if !gjson.GetBytes(updated, "generationConfig.thinkingConfig.includeThoughts").Exists() &&
+			!gjson.GetBytes(updated, "generationConfig.thinkingConfig.include_thoughts").Exists() {
+			valuePath := "generationConfig.thinkingConfig.include_thoughts"
+			rewritten, err := sjson.SetBytes(updated, valuePath, *incl)
+			if err == nil {
+				updated = rewritten
+			}
 		}
 	}
 	return updated
@@ -99,10 +102,13 @@ func ApplyGeminiCLIThinkingConfig(body []byte, budget *int, includeThoughts *boo
 		incl = &defaultInclude
 	}
 	if incl != nil {
-		valuePath := "request.generationConfig.thinkingConfig.include_thoughts"
-		rewritten, err := sjson.SetBytes(updated, valuePath, *incl)
-		if err == nil {
-			updated = rewritten
+		if !gjson.GetBytes(updated, "request.generationConfig.thinkingConfig.includeThoughts").Exists() &&
+			!gjson.GetBytes(updated, "request.generationConfig.thinkingConfig.include_thoughts").Exists() {
+			valuePath := "request.generationConfig.thinkingConfig.include_thoughts"
+			rewritten, err := sjson.SetBytes(updated, valuePath, *incl)
+			if err == nil {
+				updated = rewritten
+			}
 		}
 	}
 	return updated
@@ -130,15 +136,15 @@ func ApplyGeminiThinkingLevel(body []byte, level string, includeThoughts *bool)
 		incl = &defaultInclude
 	}
 	if incl != nil {
-		valuePath := "generationConfig.thinkingConfig.includeThoughts"
-		rewritten, err := sjson.SetBytes(updated, valuePath, *incl)
-		if err == nil {
-			updated = rewritten
+		if !gjson.GetBytes(updated, "generationConfig.thinkingConfig.includeThoughts").Exists() &&
+			!gjson.GetBytes(updated, "generationConfig.thinkingConfig.include_thoughts").Exists() {
+			valuePath := "generationConfig.thinkingConfig.includeThoughts"
+			rewritten, err := sjson.SetBytes(updated, valuePath, *incl)
+			if err == nil {
+				updated = rewritten
+			}
 		}
 	}
-	if it := gjson.GetBytes(body, "generationConfig.thinkingConfig.include_thoughts"); it.Exists() {
-		updated, _ = sjson.DeleteBytes(updated, "generationConfig.thinkingConfig.include_thoughts")
-	}
 	if tb := gjson.GetBytes(body, "generationConfig.thinkingConfig.thinkingBudget"); tb.Exists() {
 		updated, _ = sjson.DeleteBytes(updated, "generationConfig.thinkingConfig.thinkingBudget")
 	}
@@ -167,15 +173,15 @@ func ApplyGeminiCLIThinkingLevel(body []byte, level string, includeThoughts *boo
 		incl = &defaultInclude
 	}
 	if incl != nil {
-		valuePath := "request.generationConfig.thinkingConfig.includeThoughts"
-		rewritten, err := sjson.SetBytes(updated, valuePath, *incl)
-		if err == nil {
-			updated = rewritten
+		if !gjson.GetBytes(updated, "request.generationConfig.thinkingConfig.includeThoughts").Exists() &&
+			!gjson.GetBytes(updated, "request.generationConfig.thinkingConfig.include_thoughts").Exists() {
+			valuePath := "request.generationConfig.thinkingConfig.includeThoughts"
+			rewritten, err := sjson.SetBytes(updated, valuePath, *incl)
+			if err == nil {
+				updated = rewritten
+			}
 		}
 	}
-	if it := gjson.GetBytes(body, "request.generationConfig.thinkingConfig.include_thoughts"); it.Exists() {
-		updated, _ = sjson.DeleteBytes(updated, "request.generationConfig.thinkingConfig.include_thoughts")
-	}
 	if tb := gjson.GetBytes(body, "request.generationConfig.thinkingConfig.thinkingBudget"); tb.Exists() {
 		updated, _ = sjson.DeleteBytes(updated, "request.generationConfig.thinkingConfig.thinkingBudget")
 	}