Claude API 413 request_too_large and image/PDF size limits: how large can a Messages request, image, or batch be, and how do I shrink or upload files instead?

Cause: A 413 with error type request_too_large means the request body exceeded the maximum number of bytes for that endpoint. Per Claude's docs the first-party limits are 128 MB for the Messages API (and token counting), 256 MB for the Batch API and 500 MB for the Files API; on the first-party API the 413 is returned by Cloudflare before the request reaches the API servers. Images add their own limits: up to 8000x8000 px per image, about 10 MB (base64-encoded) per image on the Claude API (5 MB on Amazon Bedrock), up to 600 images per request (100 for models with a 200k-token window), and a stricter per-image dimension limit applies to every image when a request has more than 20 images (the error references "many-image requests"). Base64 inflates files by about a third, so a 90 MB file can already exceed 128 MB. Fix (best first): 1. Upload large files once through the Files API and reference them by file_id instead of embedding base64 in every request. 2. Downscale images before sending (Claude resizes large images anyway, so you pay bytes for nothing); keep each side at or below 3,000 px if you may send more than 20 images. 3. Send fewer images or document pages per request, or split the work into several requests or a batch. 4. Remove old images and large tool results from resent history, and use compaction or context editing for long conversations. 5. If you are going through a proxy or gateway, check its own body-size cap (nginx client_max_body_size, API gateway limits); it may reject before Anthropic does. Raise it deliberately rather than bypassing it. 6. On other platforms (Bedrock, Google Cloud) limits are lower and differ; consult that platform's page. Verify: The request body size (after base64) is under the endpoint limit and the call returns 200; log the request-id header from failures for support. Sources: https://platform.claude.com/docs/en/api/errors https://platform.claude.com/docs/en/build-with-claude/vision https://platform.claude.com/docs/en/build-with-claude/context-windows