Simon Willison’s Weblog

While Sonnet 4.5 remains the default [in Claude Code], Haiku 4.5 now powers the Explore subagent which can rapidly gather context on your codebase to build apps even faster.

You can select Haiku 4.5 to be your default model in /model. When selected, you’ll automatically use Sonnet 4.5 in Plan mode and Haiku 4.5 for execution for smarter plans and faster results.

— Catherine Wu, Claude Code PM, Anthropic