anthropic-rate-limits

name	Anthropic-Rate-Limits
description	Anthropic API rate limit handling - retry logic, backoff, throttling for batch workloads against Claude models

Anthropic API Rate Limits

When writing code that calls the Anthropic API (especially batch/bulk workloads), you must handle rate limits correctly. The org c68886dd-ecbd-45f6-83c8-0c5af631b760 has a 10,000 output tokens per minute limit on Haiku.

Instructions

1. Always retry 429 responses. The API returns HTTP 429 when rate-limited. This is transient and must be retried with backoff — never treat it as a fatal error.

2. Respect retry-after header. If the 429 response includes a retry-after header (seconds), use that value. Otherwise fall back to exponential backoff.

3. Use exponential backoff with jitter. Start at 2s, double each retry, cap at ~60s. Add small random jitter to avoid thundering herd.

4. Throttle proactively between batches. Don't just react to 429s — add a delay between batches to stay under the limit. For Haiku with 10k output tokens/min:

   • Each batch of 20 addresses produces ~150 output tokens
   • That's ~66 batches before hitting the limit
   • A 1-second delay between batches keeps throughput safe

5. Retry these status codes: 429 (rate limit), 529 (overloaded), 500 (server error). Fail immediately on 400 (bad request) and 401 (auth).

6. Cap retries. Use a maximum of 8 retries. After that, fail the batch and continue with the next one — don't block the entire job.

7. Log retries to stderr. Always log the status code, retry delay, and attempt number so the user can see what's happening.

Examples

Example 1: C# HttpClient with rate limit retry

User: Write code to call the Anthropic API with retry logic

Claude: I'll add exponential backoff for 429/529/500 with retry-after header support:

[Provides implementation using the C# Retry Pattern below]

Example 2: Batch processing with throttle

User: Process 1000 items through the Anthropic API

Claude: With the 10k output token/min limit, I'll add a 1-second delay between
batches to stay under the limit, plus 429 retry as a safety net.

[Adds Task.Delay(1000) between batches in the processing loop]

---

Reference Implementation Details

C# Retry Pattern

Purpose: Retry with exponential backoff, respecting retry-after header

const int maxRetries = 8;

for (var attempt = 0; ; attempt++)
{
    var response = await _http.PostAsync(url, content);

    if (response.IsSuccessStatusCode)
        return await response.Content.ReadAsStringAsync();

    var status = (int)response.StatusCode;

    // Fail immediately on non-retryable errors
    if (status == 400 || status == 401)
    {
        var errorBody = await response.Content.ReadAsStringAsync();
        throw new HttpRequestException($"API error {status}: {errorBody}");
    }

    // Retry on 429 (rate limit), 529 (overloaded), or 500
    if ((status == 429 || status == 529 || status == 500) && attempt < maxRetries)
    {
        var delay = 2000 * (1 << attempt); // 2s, 4s, 8s, 16s, ...
        if (response.Headers.TryGetValues("retry-after", out var values) &&
            int.TryParse(values.FirstOrDefault(), out var retryAfter))
        {
            delay = retryAfter * 1000;
        }

        Console.Error.WriteLine(
            $"API returned {status}, retrying in {delay / 1000}s (attempt {attempt + 1}/{maxRetries})...");
        await Task.Delay(delay);
        content = new StringContent(json, Encoding.UTF8, "application/json");
        continue;
    }

    var body = await response.Content.ReadAsStringAsync();
    throw new HttpRequestException($"API error {status} after {attempt + 1} attempts: {body}");
}

Rate Limits Quick Reference

Model	Output tokens/min	Requests/min	Input tokens/min
Haiku 4.5	10,000	varies	varies

Key Points:

• The output token limit is usually the bottleneck for batch workloads
• 429 errors are normal and expected under load — always handle them
• Proactive throttling (delay between batches) is better than reactive retry