There exist methods to detect what kind of watermarking tool that someone is using, and most of the big tools have specific signatures that you can look for.

For Anthropic, it’s highly likely that the watermark is a SynthID type mark similar to the one that Sean is talking about (I actually ran the analysis here https://johnjwang.com/post/2026/08/12/how-claude-watermarkin...). When we get confirmation of whether all models actually are watermarked, I think we’ll be even more confident.

Of course it’s always possible that Anthropic has come up with a proprietary scheme, but I think it’s definitely harder to implement.

I think the game will be a cat and mouse game similar to LinkedIn and other websites trying to block scrapers: each iteration makes it harder for someone to figure out the watermarking scheme, but likely not impossible