Is there a reliable way to tell something was written by AI?
If Claude wrote it, the answer is now "yes," says AI researcher Mustafa Ocal.
Anthropic announced this summer that it is watermarking all text produced by Claude to comply with the new EU AI Act. The mark is now integrated into Claude's newer models. Implementation for older models is on the way.
The watermark aids in the detection of Claude-generated text — but is "indistinguishable" to human readers, according to a company release.
"It's brilliant," says Ocal, a professor who researches AI detection at FIU's Knight Foundation School of Computing & Information Sciences. "People think, 'I can just get rid of the watermark by deleting em dashes.' But it's much more complex than that. It is never, ever going to be human detectable."
The text watermarking technique is not new. Google pioneered it in 2024 and is already using it. However, Ocal says that Anthropic's approach goes further because the company is implementing the watermark universally in its latest models while sharing a way to check for it: a proprietary scanner restricted to certain organizations. This has important practical implications, he says.
Ocal has spent weeks combing through Anthropic's recent publications and speaking with colleagues in the industry. He offers his analysis on the watermark — and why he thinks it will usher in a new era of AI transparency — in a Q&A for FIU News.
