Gemini API key: `429 You exceeded your current quota ... generate_content_free_tier_requests, limit: 0` on a new key, or "Quota tier: Unavailable" in AI Studio

发生场景

Source(s): https://discuss.ai.google.dev/t/api-quota-tier-unavailable-despite-active-billing/110513 , https://stackoverflow.com/questions/79840266 Signal: 6,906 views (accepted answer, three users confirm) + 9,962 views on Stack Overflow. Status: reported working by source, not reproduced by us (workaround only; root fix not confirmed; root cause on Google's side).

问题

The very first request with a new key fails with 429 and limit: 0, even though billing is active or you expect the free tier. AI Studio's API keys page shows the key's quota tier as "Unavailable".

报错原文（已脱敏/规范化）

429 You exceeded your current quota ... generate_content_free_tier_requests, limit: 0

不是这个问题时 / 边界

At least one user said it didn't work for them, and another fell back to the free tier later. One original poster found the old key fixed itself weeks later. If AI Studio itself says "You've reached your rate limit", that's a different issue.

根因

The accepted answer's guess: AI Studio doesn't sync back when billing is linked in the Cloud Console, so the project gets no quota.

修复步骤

1. In the Google Cloud console, create a new project and enable the Gemini (Generative Language) API on it. Link billing if you want a paid tier.
2. In AI Studio, import that project and create a new API key in it.
3. Check AI Studio's API keys page: the quota tier should now show Tier 1 (or the free tier), not "Unavailable". One user said this also fixed their other projects.

如何验证

The first request succeeds, and the quota tier is no longer "Unavailable".