Claude Code uses sub-agents, some of which use Haiku for operations that benefit from a cheaper, faster model. That's not new, they've done that since the start. Here's a trace I captured on June 2nd https://
static.simonwillison.net/static/2025/lo
g-2025-06-02-17-10-25.html
… – see also

→ View original post on X — @simonw,