Question 1

Do I get charged for API calls that return a 429 rate limit error?

Accepted Answer

No — 429 (Too Many Requests) errors are rejected before processing and you are not charged for them. However, you do pay for any tokens that were processed before the error (if the provider uses streaming and charges on partial output) and you waste the latency of the failed attempt. The real cost is the extra retry logic, delayed responses, and sometimes duplicate completions if retry logic has bugs.

Question 2

What is exponential backoff and why does it increase latency cost?

Accepted Answer

Exponential backoff means waiting 1s, 2s, 4s, 8s... between retry attempts. For a time-sensitive API call, a single 429 with 2 retries adds 3–7 seconds of latency. If your users or downstream systems have SLAs, this hidden latency has real operational cost even if the token cost is zero.

Question 3

How do retries cause duplicate charges?

Accepted Answer

If a request succeeds but times out before the response arrives, a naive retry will resend — and if the first succeeded, you pay for two completions. This is common with slow LLM responses on large context windows. Always use idempotency keys or check for existing results before retrying on timeout.

Question 4

What is the average 429 rate for LLM APIs?

Accepted Answer

Rate limit hit rates depend heavily on your traffic pattern and tier. Bursty traffic (sending 100 requests at once) can hit 10–30% error rates. Steady traffic well below limits typically sees <0.1%. Most providers now use token-per-minute limits, which punish large-context requests more than request-count limits.

Question 5

How do I reduce API retry costs?

Accepted Answer

Four approaches: (1) Rate limit locally — use a token bucket to stay under provider limits before sending. (2) Use a queue with controlled concurrency instead of parallel bursts. (3) Set up webhooks or async processing so retries happen in the background without user-facing latency. (4) Cache responses for identical prompts to avoid the API call entirely.

API レート制限の再試行コスト計算ツール

再試行によって実際に費用がかかるのは何でしょうか?

よくある質問