Use Haiku 5.5 for the subagents that find files and read docs; keep edits on Sonnet or Opus

Anthropic's launch post draws the line itself. Haiku 5.5 "pairs well with Opus 5.5 and Sonnet 5.5 as a subagent", while for complex agentic coding "Sonnet 5.5 and Opus 5.5 remain better choices". The numbers behind that: Terminal-Bench 4.0 is 39.2% for Haiku 5.5 and 70.6% for Sonnet 5.5. Per million input tokens Haiku costs $0.10 and Sonnet $2. There is no reason to pay 20x to check whether a file exists.

So split the roles. Exploration and doc lookups go to Haiku; edits and tests stay on Sonnet or Opus. Haiku 5.5 is the first Haiku with an effort setting, so the explorer runs on low.

<!-- .claude/agents/explorer.md -->
---
name: explorer
description: Finds the files, symbols and docs relevant to a task and reports paths with a one-line reason each. Use before editing.
tools: Read, Grep, Glob, WebFetch
model: haiku
effort: low
---
Report only what the main agent needs to start editing: file paths, the function or section to look at, and why. Do not propose changes.

Leaving Edit and Write out of tools means Haiku never touches code. In the main session say "use the explorer subagent to find this first" or mention it as @explorer. The haiku alias points at Haiku 5.5 from v2.1.293.