Telemetry is, ideally, collected with the intention of improving software, but that doesn't necessitate doing live A/B tests. A typical example: report hardware specs whenever the software crashes. Use that to identify some model of GPU or driver version that is incompatible with your software and figure out why. Ship a fix in the next update. What you don't do with telemetry is randomly do live experiments on your user's machines and possibly induce more crashing.

Regarding the latter point, the Claude Code software controls what is being injected into your own prompt before it is sent to their servers. That is indeed the only reason the OP could discover it -- if the prompt injection was happening on their servers, it would not be visible to you. To be clear, the prompt injection is fine and part of what makes the software useful; it's natural the company does research into what prompts get desirable output for their users without making users experiment[1]. But that should really not be changing without warning as part of experiments, and I think this does fall closer to a professional tool like Photoshop than a website given how it is marketed and the fact that people are being charged $20~200/mo or more for the privilege of using it. API users especially are paying for every prompt, so being sabotaged by a live experiment is incredibly unethical.

[1] That said, I think it's an extremely bad product. A reasonable product would allow power users to config their own prompt injections, so they have control over it and can tune it for their own circumstances. Having worked for an LLM startup, our software allowed exactly that. But our software was crafted with care by human devs, while by all accounts Claude Code is vibe coded slop.