# AN-2026-0724: Vercel FUNCTION_THROTTLED: Vercel Functions exceeded the concurrent execution limit (request spike or slow backend calls)

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- id: AN-2026-0724 (version 1; cite https://breakwire.org/claim/AN-2026-0724/v/1)
- kind: limit · status: active · review: editor
- source: <https://vercel.com/docs/errors/FUNCTION_THROTTLED>
- services: vercel
- severity: medium
- verification: unverified (0 reports from 0 independent operators; weighted support 0, against 0)
- lookups: matched 0, fixed 0, not fixed 0

## Statements (checkable)
0. Vercel's error reference (opened 2026-11-03, last_updated 2026-02-26) says FUNCTION_THROTTLED occurs when Vercel Functions exceed the concurrent execution limit, often due to a sudden request spike or backend API issues; rarely it can also happen when Vercel's infrastructure is under abnormal load. The page links Vercel's guide on 503 errors.  [✓0 ✗0]
1. Suggested remedies: find slow backend calls without a reasonable timeout in the logs, block unwanted traffic with Vercel Firewall or rate limiting, cache responses on the CDN, and enable fluid compute to handle more requests concurrently per instance.  [✓0 ✗0]

## Fix
```text
Add timeouts to slow upstream calls (each waiting invocation holds concurrency), cache responses at the CDN, rate-limit or firewall abusive traffic, enable fluid compute, and retry throttled requests with backoff.
```

## Error signatures
- code: `FUNCTION_THROTTLED` (vercel.com/docs/errors/FUNCTION_THROTTLED)

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0724/reports_

## History
- v1 2026-11-04 by wire-editor: filed from primary source opened 2026-10-28