“We’re adding marking to Claude’s output to comply with the EU AI Act, and other labs are taking similar steps,” Anthropic said. “It’s hard to identify AI-generated text, and this gives people better tools for identification. Text from supported Claude models, including output from Claude Code, will carry an invisible watermark, and it doesn’t change the meaning, quality, or readability of Claude’s responses. We also plan to ship a text detection API so users can do more of this themselves.”

The fun is just starting

In the EU, transparency requirements are meant to ensure AI tools like Claude don’t upset “the integrity and trust in the information ecosystem, raising new risks of misinformation and manipulation at scale, fraud, impersonation, and consumer deception.” One EU support article forecasted that the obligations would be the “primary compliance challenge” for many AI firms.

“People should know when they are interacting with AI or exposed to AI-generated content,” the European Commission’s guidelines said. “This will help them make informed decisions, calibrate their trust and reliance on AI, and avoid misinformation or deception.” Still, it’s hard to square this with the fact that a wholly generated article on a matter of public interest gets a watermark, but not a reader-facing label, if an editor properly reviews it.

AI firms like Anthropic are best positioned to develop watermarking solutions, the EU expects, since AI moves fast and there will be an ongoing “need for new methods and techniques to trace origin of information.”

But that largely leaves the societal value of such marks up to tech firms to decide, with the EU only stipulating that “techniques and methods should be sufficiently reliable, interoperable, effective and robust as far as this is technically feasible.”

In its post, Anthropic said it plans to continue working on its watermarks and detection methods that meet the EU’s demands. If Claude’s labels fail, the AI Act carries steep penalties for violations, including fines up to 15 million euros, or 3 percent of a company’s worldwide annual revenue.

Ars Editor-in-Chief Ken Fisher contributed to this report. This story was updated on August 13 to add a statement from Anthropic.