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

# Errors & limits

> Concurrency tiers, rate limits, and HTTP 429 handling.

apisale enforces three independent limits:

## 1. Organization concurrency

Maximum **parallel runs** per organization (statuses: `pending`, `assigned`, `processing`).

| Tier    | Lifetime top-ups | Concurrent runs |
| ------- | ---------------- | --------------- |
| starter | \$0              | 10              |
| growth  | ≥ \$350          | 25              |
| pro     | ≥ \$1,400        | 50              |
| scale   | ≥ \$7,000        | 100             |

When exceeded:

```json theme={null}
{
  "error": {
    "code": "concurrency_limit_exceeded",
    "message": "Organization concurrency limit reached (10/10). Tier=starter.",
    "scope": "organization",
    "limit": 10,
    "in_flight": 10
  }
}
```

HTTP **429 Too Many Requests**

## 2. API key concurrency

Each key has `max_concurrency` (default **10**). A single key cannot exceed its own cap even if the org has headroom.

`scope: "api_key"` in the error body.

## 3. Rate limit

Each key has `rate_limit_per_minute` (default **120**). Exceeding it returns:

```json theme={null}
{
  "error": "rate_limit_exceeded",
  "message": "API key rate limit exceeded (120/minute)"
}
```

## Client recommendations

1. Read `X-Concurrency-Remaining` on submit responses
2. Poll [`GET /v1/account`](/get-started/account-and-monitoring) for proactive backoff
3. Use exponential backoff on 429
4. Distribute load across multiple keys only within org policy

## Insufficient balance

Submitting a run with insufficient `available_usd` returns **400** with an insufficient balance message. Top up in the [Console](https://apisale.ai/console/billing).