Claude API raises its request size limit from 32 MB to 128 MB, but cloud platforms and agent endpoints stay at 20–32 MB

Anthropic has quadrupled the maximum request size for the Messages API and the Token Counting API on the first-party Claude API, from 32 MB to 128 MB. The change is dated October 28 in the Claude Platform release notes; the ClaudeDevs account announced it the following evening.

The stated reason is mundane and familiar to anyone who has built an agent that looks at a screen. Image-heavy requests, such as long computer-use sessions and big PDFs, were running into the 32 MB ceiling "with plenty of context window left". In other words, the bottleneck was the size of the HTTP payload, not what the model could actually read.

The second change: bigger images in crowded requests

In a follow-up post, Anthropic said that for requests with more than 20 images, the per-image dimension limit goes up from 2000 px to 3000 px. The vision documentation explains why this matters more than it sounds. Once a request crosses 20 images, the stricter limit applies to every image in it, and the count includes images from earlier turns that you resend and screenshots nested inside tool_result blocks. A computer-use agent that keeps its screenshot history in context crosses that line quickly, and an oversized image gets the whole request rejected with an invalid_request_error that mentions "many-image requests". The docs now advise keeping each image under 3,000 px on its longest side or sticking to 20 or fewer image and document blocks.

The ordinary per-image limits are unchanged: up to 8000×8000 px and 10 MB base64-encoded on the Claude API, with up to 600 images per request (100 for models with a 200k-token context window).

Where the new limit does not apply

The 128 MB figure is specific to Anthropic's own API, and only to two endpoints. The API overview lists the rest:

Two details stand out. Anthropic's Sessions, Agents and Environments endpoints stay at 32 MB, even though long agent sessions are exactly the workload the announcement uses as its example. And the gap between platforms has widened: a request that the first-party API now accepts can be more than six times the size Bedrock allows. Code that is tested against Anthropic directly and deployed through a cloud provider will need its own size checks.

Some back-of-the-envelope arithmetic shows why the payload limit was the one people hit. At the 10 MB maximum per image, 32 MB fit three such images; 128 MB fits twelve. The 600-image cap is still far out of reach for large images, so for heavy visual workloads the request size remains the practical ceiling. For many images, the docs recommend uploading them through the Files API and referencing them by file_id, while warning that requests with many large images can still fail before reaching the 600-image count.