Claude Code and Gemini CLI (and OpenAI Codex) are first party from the respective companies. But also kind of products - in extreme cases people pay $200/month for Claude Code and get $thousands and thousands of usage. There's product bundling there beyond just the interface.

I think Claude Code specifically has a reputation for being a 1st class citizen - as in the model is trained and evalled on that specific toolcall syntax.

Claude Code uses Claude, Gemini CLI uses Gemini, and this one can be configured to use any model you want.