Principle:Langchain ai Langchain Rate Limiting
| Knowledge Sources | |
|---|---|
| Domains | Concurrency, API_Management |
| Last Updated | 2026-02-11 00:00 GMT |
Overview
A concurrency control mechanism that limits the rate of API requests to prevent exceeding provider rate limits and ensure fair resource usage.
Description
Rate limiting in LangChain is integrated directly into the chat model invocation path. When a rate_limiter is attached to a model, every call to invoke(), stream(), or their async equivalents acquires a permit from the rate limiter before proceeding to the API call. If the rate limit is exceeded, the call blocks until a permit becomes available.
This prevents HTTP 429 (Too Many Requests) errors from providers and enables smooth, predictable throughput in high-concurrency applications.
Usage
Attach a rate limiter when:
- Running batch inference with many concurrent requests
- Operating near a provider's rate limit
- Sharing API keys across multiple applications
Theoretical Basis
LangChain's rate limiting is based on the token bucket algorithm:
Where B is the bucket capacity, r is the refill rate (requests per second), and is the elapsed time.
# Abstract algorithm (not real code)
if bucket.tokens >= 1:
bucket.tokens -= 1
proceed_with_request()
else:
wait_until(bucket.tokens >= 1)
proceed_with_request()