> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fiveninelabs.com/llms.txt
> Use this file to discover all available pages before exploring further.

# concurrency_cap

> 429 rate_limit — as many runs in flight as the account allows. Wait for one to finish, or stop one.

**HTTP 429 · type `rate_limit`.** The account is already running as many
sessions/extractions as it's allowed to have in flight (new accounts start at **1**).
Expensive work is limited by concurrency, not requests-per-minute — a run holds real
browsers and real model spend for minutes, so the cap is on simultaneous runs.
Nothing was charged.

## The shape

```json theme={null}
{
  "error": {
    "type": "rate_limit",
    "code": "concurrency_cap",
    "message": "1 run may be in flight; 1 is. Retry when it settles.",
    "doc_url": "https://docs.fiveninelabs.com/errors/concurrency_cap",
    "request_id": "req_5dd08r",
    "retry_after_s": 60,
    "limit": 1,
    "in_flight": 1
  }
}
```

`limit` is the account's cap; `in_flight` is what's running now. `Retry-After` is an
estimate, not a promise — runs take minutes and finish when they finish.

## How to fix

* Find what's running: `GET /v1/sessions?status=running`. Wait for its terminal
  (webhook, long-poll, or stream), or `POST …/stop` it if it's no longer wanted.
* Queue on your side: serialize run creation behind the `session.answered` /
  `extraction.delivered` webhook instead of retrying blind.
* Note a batch extraction (`urls[]`) occupies concurrency per URL as passes dispatch —
  a 50-URL batch on a concurrency-1 account is a queue, not a parallel sweep.
* Need real parallelism? Concurrency limits are raised per account — contact us; your
  current limit is visible in `GET /v1/me` (`concurrency_limit`).

## Reproduce it

Requires a run genuinely in flight, so this one costs a real (small) run:

```bash theme={null}
curl https://api.fiveninelabs.com/v1/sessions \
  -H "Authorization: Bearer $FIVENINE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"query": "vinyl records under $30 in Austin", "max_spend_usd": 1}'
# → while that run is in flight, create another:
curl https://api.fiveninelabs.com/v1/sessions \
  -H "Authorization: Bearer $FIVENINE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"query": "espresso machines under $400", "max_spend_usd": 1}'
```