I stumbled on this page and it seems to imply that Claude Code calls other models like Qwen, not just Anthropic's

Is that commonly done. Presumably this is from people customizing their installs - is that correct?

You can do it with ENV cars for local models, but search tool does not work

Anthropic has partnerships, for example Claude Desktop has a provider selection now that allows you to use Vertex AI instead, even for Claude models (same price, more reliable)