# `AI_APICallError: 503 Service Unavailable — No discounted capacity available right now`

**Where it appears:** Terminal or Vercel runtime logs

**What it means:** Tokentide's discounted capacity for that model is temporarily full. You are never charged for a 503, and your app should immediately answer using the Vercel AI Gateway backup.

## Likely causes

- High demand on that model pool, or a background Low Tide request (`X-Tokentide-Lane: lowtide`) ran without `X-Tokentide-Lowtide-Fallback: standard`.
- The Vercel AI Gateway fallback wasn't wired up yet, so the 503 reached the user instead of switching transparently.

## Message for your agent

```text
An AI call failed with `503 Service Unavailable`. Use the `tokentide-api` skill (`references/reliability.md`) to ensure `maxRetries: 0` on Tokentide and automatic fallback to the Vercel AI Gateway on 503, then test the fallback.
```

**Prevention:** Test the fallback in a Preview before launch by pointing the Tokentide client at a dead URL and confirming the Gateway answers.

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Source: [Agentic Makers](https://agenticmakers.app/en/help/errors/tokentide-503-service-unavailable-no-capacity) · License: CC BY 4.0