I would actually disagree with the final conclusion here; despite claiming to offer the same models, Copilot seems very much nerfed — cross-comparing the Copilotified LLM and the same LLM through OpenRouter, the Copilot one seems to fail much harder. I'm not an expert in the details of LLMs but I guess there might be some extra system prompt, I also notice the context window limit is much lower, which kinda suggests it's been partially pre-consumed.

In case it matters, I was using Copilot that is for 'free' because my dayjob is open source, and the model was Claude Sonnet 3.7. I've not yet heard anyone else saying the same as me which is kind of peculiar.