diff --git a/packages/core/src/services/modelConfigService.ts b/packages/core/src/services/modelConfigService.ts
index d92532fd3a..949529b87e 100644
--- a/packages/core/src/services/modelConfigService.ts
+++ b/packages/core/src/services/modelConfigService.ts
@@ -488,6 +488,14 @@ export class ModelConfigService {
       );
     }
 
+    // Automatically strip thinkingConfig if the model does not support thinking.
+    const modelDefinition = this.getModelDefinition(resolved.model);
+    if (modelDefinition && modelDefinition.features?.thinking === false) {
+      if (resolved.generateContentConfig.thinkingConfig) {
+        delete resolved.generateContentConfig.thinkingConfig;
+      }
+    }
+
     // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
     return {
       model: resolved.model,