diff --git a/.env.example b/.env.example
index 6884e29..6e74a4d 100644
--- a/.env.example
+++ b/.env.example
@@ -66,12 +66,12 @@ OLD_S3_FORCE_PATH_STYLE=true
 OLD_S3_ACCESS_KEY_ID=
 OLD_S3_SECRET_ACCESS_KEY=
 
-# AI product generation (use Groq free tier or OpenAI)
-AI_PROVIDER=groq
+# AI product / category generation (OpenAI preferred; Groq optional fallback)
+AI_PROVIDER=openai
+OPENAI_API_KEY=
+OPENAI_MODEL=gpt-4.1-nano
 GROQ_API_KEY=
 GROQ_MODEL=llama-3.3-70b-versatile
-OPENAI_API_KEY=
-OPENAI_MODEL=gpt-4o-mini
 
 MEDIA_MAX_FILE_SIZE_MB=10
 
diff --git a/src/common/ai-provider.util.ts b/src/common/ai-provider.util.ts
index c47f6ff..e8ea92d 100644
--- a/src/common/ai-provider.util.ts
+++ b/src/common/ai-provider.util.ts
@@ -38,31 +38,47 @@ export function resolveAiProvider(config: ConfigService): AiProviderConfig {
   return {
     apiKey: openAiKey,
     baseUrl: 'https://api.openai.com/v1',
-    model: config.get<string>('OPENAI_MODEL')?.trim() || 'gpt-4o-mini',
+    model: config.get<string>('OPENAI_MODEL')?.trim() || 'gpt-4.1-nano',
   };
 }
 
+function supportsCustomTemperature(model: string): boolean {
+  // gpt-5 / o-series chat models only accept the API default temperature.
+  const id = model.trim().toLowerCase();
+  return !(
+    id.startsWith('gpt-5') ||
+    id.startsWith('o1') ||
+    id.startsWith('o3') ||
+    id.startsWith('o4')
+  );
+}
+
 export async function requestAiJsonCompletion(
   provider: AiProviderConfig,
   systemPrompt: string,
   userPrompt: string,
   temperature = 0.4,
 ): Promise<string> {
+  const body: Record<string, unknown> = {
+    model: provider.model,
+    response_format: { type: 'json_object' },
+    messages: [
+      { role: 'system', content: systemPrompt },
+      { role: 'user', content: userPrompt },
+    ],
+  };
+
+  if (supportsCustomTemperature(provider.model)) {
+    body.temperature = temperature;
+  }
+
   const response = await fetch(`${provider.baseUrl}/chat/completions`, {
     method: 'POST',
     headers: {
       Authorization: `Bearer ${provider.apiKey}`,
       'Content-Type': 'application/json',
     },
-    body: JSON.stringify({
-      model: provider.model,
-      temperature,
-      response_format: { type: 'json_object' },
-      messages: [
-        { role: 'system', content: systemPrompt },
-        { role: 'user', content: userPrompt },
-      ],
-    }),
+    body: JSON.stringify(body),
   });
 
   if (!response.ok) {