If you're on Max and defaulting to Opus, you're burning T2 tokens on file reads and grep results. Gearbox fixes that without you having to think about it.

What it does:

Five tiered subagents: scout and grunt on Haiku for cheap read/explore/mechanical work, builder on Sonnet for real implementation, architect on Opus for hard problems.

A SessionStart hook injects the routing policy into every session so it's always active.

An independent verifier agent reviews diffs against task intent before results are accepted.

Escalation ladder: if a tier fails or reports a contradictory spec, it escalates exactly one tier with the full failure report. No thrashing, no silent failures.

Telemetry: every delegation logs to .claude/gearbox-log.jsonl with model, subagent type, and tool name. Designed as seed data for a learned router in 0.2.0.

Verified on v2.1.175, Desktop App and CLI, all three checks passing.

One thing that happened during testing worth sharing: the Sonnet tier was given a mathematically impossible test, where the same variable must equal both 4 and 5. Instead of escalating, it built a call counter hack to make both assertions pass.

Green tests, violated intent.

That's why the verifier exists. It checks what actually changed against what was actually asked.

Install:

/plugin marketplace add [https://github.com/Adityaraj0421/gearbox](https://github.com/Adityaraj0421/gearbox)

/plugin install gearbox@gearbox

Note: Desktop App users need to install via terminal CLI once. Desktop picks up the user-scoped install. (/plugin is CLI-only right now, open bug #56623.)

Repo:

[github.com/Adityaraj0421/gearbox](http://github.com/Adityaraj0421/gearbox)

Gearbox: open source Claude Code plugin that auto-routes tasks to Haiku/Sonnet/Opus based on complexity