There is a lot that is added to the prompt to lower friction, which in a lot of cases is really useful even if the user doesn't realise it. I think an Anthropic dev explained somewhere else in this thread that they added it for the model not to try to hallucinate your idendity when committing on git.

It's the same thing with web browsers. The browser adds my preferred language and operating system to the user-agent header, this way I can access the right content and download the right version of software quicker. I wouldn't want it to share my social security number but some sharing is alright to me. The problem here is people didn't know it was happening.