Claude API files now carry C2PA credentials: the fourteen signed formats

Published 20 September 2026

Anthropic's developer documentation now states which files the Claude API signs. Image, video and audio files that Claude produces in the code execution sandbox carry C2PA Content Credentials when downloaded through the Files API. Fourteen formats are listed: PNG, JPEG, GIF, WebP, TIFF, HEIC, AVIF, SVG, MP4, MOV, MP3, WAV, FLAC and M4A. Text files, PDFs and office documents are not signed[13].

What changed

Until this section appeared, the help article said that generated .svg, .png and .jpg files carry C2PA metadata and left the rest open[1]. The developer documentation, as read on 18 September 2026, gives the full list and says what the credential contains: a cryptographically signed manifest naming Anthropic as the issuer, a timestamp, and the action description "Claude provided this file at the request of a user and may have created or modified the file contents". Nothing about the user, their organisation or their request is recorded[13].

What it means

If your application passes generated files through to users, those files identify Anthropic as their origin to any C2PA-aware reader, including Anthropic's own Content Checker[11]. The credential is metadata beside the pixels, so it survives the file being passed on intact and is lost on screenshot or re-encode. How the credential differs from the text watermark.

What is still not known

The documentation covers files produced in the code execution sandbox. Whether other routes that yield a file behave the same way is not stated, and we have not tested it. What to assume, and what you cannot check.

Last verified against primary sources: 2026-09-18