---
title: "concurrency_limit_exceeded — concurrent task slots are full"
url: https://lumean.app/en/developers/docs/errors/concurrency-limit-exceeded
locale: en
description: "The fourth of the five 429 sources. The body has only `message` and `reason`; there is no `Retry-After` header."
generated: 2026-10-17
---

# concurrency_limit_exceeded — concurrent task slots are full

- HTTP: `429`

- `reason`: `concurrency_limit_exceeded`

- `Retry-After` header: no

## What happened

The fourth of the five 429 sources. The body has only `message` and `reason`; there is no `Retry-After` header.

## Why

What is limited is neither the number of requests nor the generation volume, but the number of your orders IN PROGRESS AT THE SAME TIME. A batch of hundreds of orders sent in one burst hits exactly this limit — even with completely free quotas and no rate limit at all.

## What to do

Wait for YOUR OWN active orders to finish — that takes minutes, not until the end of the billing period: a retry right after any of them reaches a terminal status will go through. Pauses between requests do not help: a slot is freed by a finished task, not by silence on the wire. The right client design is a queue with a cap on the number of concurrent orders, not exponential backoff.

## Next request

`GET /usage` — the entry with `limit_type: "concurrent"` shows the ceiling and the current active count (its `period_start`/`period_end`/`resets_in` are `null`: this kind of limit has no period). What exactly is occupying the slots — `GET /orders?status=in_progress`. It is more convenient to catch a slot being freed via a WebSocket event than by polling.

## Related

- [Guide: limits and the 429 code](https://lumean.app/en/developers/docs/guide/limits)
- [Guide: the async model](https://lumean.app/en/developers/docs/guide/async)
- [GET /usage](https://lumean.app/en/developers/docs/api/get-usage)
- [GET /orders](https://lumean.app/en/developers/docs/api/get-orders)
- [Account limits](https://lumean.app/en/limits)

---

- This page in the browser: https://lumean.app/en/developers/docs/errors/concurrency-limit-exceeded
- Full machine-readable reference: https://api.lumean.app/docs/llm.md