BYOK Gemini Flash 3.8 Unauthorized User API key

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1

Using BYOK, Gemini Flash 3.8 throws an “Unauthorized User API key” while Gemini Flash 3.7 has no issues whatsoever.

4

Yes facing the same issue

6

same please solve this

7

Hey, thanks for the report, and you described everything correctly.

With a personal Google API key enabled, the Gemini 3.8 Flash model is currently failing with “Unauthorized User API key”. At the same time, 3.7 Flash and the other Gemini models work fine with the same key. This is a known issue on our side with how requests are routed to 3.8 Flash when using a personal key. Your key is fine, and you don’t need to change anything in your setup. I’ve shared this with the team and we’re tracking it.

For now, you’ve got two options:

  1. Stay on Gemini 3.7 Flash with your key, like you’re doing now.
  2. If you want 3.8 Flash, temporarily turn off the Google API Key toggle in Cursor Settings > Models > API Keys. Then 3.8 Flash will use your Cursor plan instead of your key.

I’ll reply here once there’s an update.

8

Hi Dean,

Thanks for the detailed explanation and appreciate the clarity on the current workaround and that the issue is already being tracked internally.

Could you share whether there is any priority assigned to the fix for BYO Google API Key support for Gemini 3.8 Flash? Additionally, do you have an estimated timeframe or typical release cadence for resolving issues like this? Understanding the expected window would help me plan model usage on my end.

9

Hey John. I don’t have an exact ETA for you, and we don’t share internal priorities or timelines publicly. I also don’t want to give an estimate I can’t stand behind. What I can say is that we’re tracking this issue, and as soon as there’s an update on a fix, I’ll reply right here in this thread.

Until the fix is out, the workaround still works:

  • Keep using Gemini 3.7 Flash with your own key.
  • Or for 3.8 Flash, temporarily turn off the Google API Key toggle in Cursor Settings > Models > API Keys. Then 3.8 Flash will use your Cursor plan instead of your personal key.

Let me know if the workaround isn’t working for any reason.

14

Hey @bbbhhh,

Quick update on this one. The “Unauthorized User API key” error when using Gemini 3.8 Flash with your own Google API key has been addressed on our side, and the change will be rolled out soon if it hasn’t been already.

Could you switch back to 3.8 Flash with the Google API Key toggle enabled and let me know if the error still shows up? If it does, please include the request ID from the error message so we can take a look.

Thanks for the report and for your patience here.

cc @SamPat @Guven @johnchung

15

Error’s gone. Thanks for following up.