efficient-dispatch - routed, measured, verified

The main model is the orchestrator and Q&A reviewer. Mechanical work runs on cheaper models - and unlike guidance-only approaches, every claim here is checkable against your own ax graph.

The split

Two axes. First, main model vs subagent: the main model orchestrates and reviews; mechanical work goes to subagents. Second, and the one that actually controls spend - the tier of each subagent dispatch:

• Implementer subagents (well-specified plan tasks, mechanical edits, search, bulk transforms) → dispatch with model: sonnet (or haiku for pure search/locate, per the table).
• Reviewer / judgment subagents (quality / PR / final / adversarial / code review, design, audit, architect, critique, judge) → keep the strong model: inherit the main model, or set model: opus/fable explicitly. Review is the catch-rate gate; a cheap reviewer misses real bugs.

Get this backwards and you pay twice: in one ax session implementers ran on the expensive inherited model while reviewers were sent to a cheap one - ~$130 over, weaker catch rate, three fix rounds (memory feedback-review-gets-strong-model). The default-inherit trap is implementers, not reviewers: a forgotten model: on an implement … dispatch silently runs expensive. Set it.

Main model keeps (never dispatched at all): decomposition, architecture and product tradeoffs, plan synthesis, judging conflicting subagent reports, final integration, taste-heavy design/copy.

Isolate heavy context (the second reason to dispatch)

Cost-tier is one reason to dispatch. The other is context isolation - and it applies even when the work needs the strong model. A large input read into the main thread does not cost once: it sits in the context window and is re-sent as input on every later turn. A 0.5 MB screenshot Read on turn 5 of a 40-turn session is re-billed ~35 times and crowds out earlier reasoning.

The biggest offender is images. Reading screenshots for visual judgment (does this match the spec? rate this design, find the visual bug) floods the main context with vision tokens that persist for the rest of the session. Route it:

• Dispatch a subagent that returns the judgment as text. The subagent pays the vision tokens in its own short-lived context and returns a verdict; the main thread keeps the cheap text, never the image bytes. Use the strong model for the subagent if the judgment is hard - the win here is isolation, not tier.
• When to route: the image (or any large output) would otherwise persist across many later main-thread turns AND the question is a returnable verdict.
• When NOT to: tightly iterative visual exploration (look, tweak, look again interleaved with main reasoning - the round-trips cost more than they save), read-once-then-done short sessions (no persistence tail), or when you cannot state the judgment criteria up front (the text verdict is lossy).

Same logic applies to any bulky tool output you only need a conclusion from: giant logs, large query dumps, full-file reads for one fact. If you need the answer, not the bytes, dispatch for it.

Routing table

Source of truth: ~/.ax/hooks/routing-table.json (regenerate with ax dispatches compile-routing). Consult it when present; these built-ins mirror it:

<!-- ax:routing-table -->

class	description pattern	model
spec-review	^spec review	sonnet
search-locate	^(pattern-find|locate|find|map|sweep|grep)	haiku
research	^(research|investigate docs|study)	sonnet
well-specified-impl	^implement	sonnet
bulk-mechanical	^(write announcements|regenerate|standardize|merge main)	sonnet
task-N-impl	^Task \d+:	sonnet
bug-fix	^Fix\s	sonnet
feature-add	^Add\s	sonnet
agent types	Explore, codebase-locator, codebase-pattern-finder → haiku; codebase-analyzer → sonnet

<!-- /ax:routing-table -->

Anything unmatched: leave the model unset only if the work genuinely needs main-model judgment - otherwise pick sonnet.

Dispatch discipline

1. Decompose into independent slices BEFORE reading everything yourself; run slices as parallel subagents in isolated worktrees when they edit files.
2. Every brief is self-contained: repo path, exact objective, in/out of scope, evidence format to return (files, line refs, commands, diffs, failures), verification commands, stop conditions.
3. Set model: explicitly on every mechanical dispatch. The route-dispatch hook is quota-aware and ADVISORY (Claude Code hooks cannot enforce model on subagent dispatches - they can only inject context via additionalContext): in conserve mode it advises re-dispatching a forgotten mechanical dispatch with model:<cheaper>; near a 7d quota reset (splurge) it stays quiet so work runs on the strong inherited model; it advises when judgment work (review/design/audit) is sent on a cheap model. Real enforcement is your discipline + setting model: explicitly on every dispatch. Treat the advisory as a re-dispatch signal, not noise.
4. Workflow scripts (.claude/workflows/*.js) run sandboxed and cannot import ax code. Set model: on every agent(...) call by hand, per ax routing show: mechanical stages → model: 'sonnet'; judgment/review stages → keep the strong model. routing-tune.workflow.js is the reference. In-tree Effect/axctl code that dispatches should call resolveDispatchModel (from @ax/hooks-sdk) instead of hardcoding.
5. Treat subagent reports as leads. Before acting on a high-impact finding or declaring done, reopen the cited files and re-run the key verification yourself. Expect to find one real bug per delegated phase.

Measure (what guidance-only skills can't do)

• ax dispatches --days=7 - your inherit rate (target: explicit model on all mechanical classes)
• ax dispatches --candidates - missed routings + est savings, repriced from real token buckets
• ax cost split --days=7 - main vs subagent spend by model; the dominant cost is usually main-loop cache reads, so move tool-heavy loops (build/test cycles, browser QA) into subagents entirely
• ax cost images --days=7 - image-read context per session, main vs subagent. High main-thread MB = screenshots persisting in the main window; route that visual judgment to a subagent (see "Isolate heavy context" above)
• ax improve recommend - surfaces a routing proposal automatically when missed savings accumulate

Verify

After adopting this skill, compare windows: ax cost split + inherit rate before vs after. If the inherit rate doesn't drop, the routing isn't happening - check ax hooks backtest ~/.ax/hooks/route-dispatch.ts --days=7 and whether dispatches are bypassing the table.