There's something in the prompting, tooling, heuristics inside the Claude Code CLI itself that makes it more than just the model it's talking to and that becomes clear if you point your ANTROPHIC_URL at another model. The results are often almost equivalent.

Whereas I tried Kilo Code and CoPilot and JetBrain's agent and others direct against Sonnet 4 and the output was ... not good ... in comparison.

I have my criticisms of Claude but still find it very impressive.