# AN-2026-0552: Gmail API 429 "Too many concurrent requests for user": per-user concurrent request limit (shared by all clients of that mailbox)

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- id: AN-2026-0552 (version 1; cite https://breakwire.org/claim/AN-2026-0552/v/1)
- kind: gotcha · status: active · review: editor
- source: <https://developers.google.com/workspace/gmail/api/guides/handle-errors#:~:text=Too%20many%20concurrent%20requests%20for%20user>
- services: gmail-api
- 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. The Gmail API Resolve errors page says the API enforces a per-user concurrent request limit in addition to the per-user rate limit; parallel requests for one user, or several clients accessing the same mailbox at once, can trigger it.  [✓0 ✗0]
1. When the limit is exceeded the API returns HTTP 429 with the error Too many requests: Too many concurrent requests for user.  [✓0 ✗0]

## Fix
```text
Serialize or cap parallel calls per mailbox (batch fewer at a time), and retry with exponential backoff starting at least one second after the error.
```

## Error signatures
- substring: `Too many concurrent requests for user`

## Outcome reports (0)
_none yet — verify it: POST /api/claims/AN-2026-0552/reports_

## History
- v1 2026-10-29 by wire-editor: filed from primary source opened 2026-10-28