The evidence is Anthropic's own reporting [1]. You may doubt that they're telling the truth, but that's what they're reporting.

[1] https://www.anthropic.com/news/detecting-and-preventing-dist...

I'm supposed to believe that DeepSeek distilled a 300B-1T param model with 150,000 requests? Lol.

"Distillation attacks", and it's just the exact same thing they did to the rest of the web and all human works.