I think if you were going to send the same harness/prompt traffic as Claude Code, then you’d just use Claude Code. Alternatives generally are trying to do something different, thus are going to be easy to detect.

From the Claude Code codemap leak, it seems like Claude Code is sending metadata about the binary that is sending HTTP requests

I wouldn’t imagine that fingerprinting them based on request patterns is very difficult.

They can just look at the system prompt or tool definitions.

they but "minimal dump DRM" into their client (supposedly, from people which leaked the linked source code, no me)

easy to circumvent

but would fall under "circumventing security protections"/"hacking their API"/etc. And due to the sometimes very unreasonable laws the US has in that area they can use that to go after anyone providing a workaround.

Through that maybe won't work well for the EU, I'm not sure how much the laws have been undermined in recent years but we had laws which made it explicitly legal to circumvent DRM iff it's for the sake of producing compatibility (with some caveats).