# Model tiers Read when you pick a model for a spawn or a delegate call. mu passes the model through and never picks one; the choice is yours. Recipes name a tier (cheap, mid, strong, frontier) and say which one their roles need; this file says how to tell a model's tier. ## Tiers Rank a model within its own family. The model-id prefix in `pi --list-models` (`anthropic/`, `openai/`, `google/`) names the family when it names a lab; the provider column is often one shared gateway, so it does not tell families apart. | Tier | Where it sits in its family | Names as of 2026-10 | | --- | --- | --- | | **frontier** | an exceptional tier above the lab's normal flagship, priced well above it, often gated | fable, astra | | **strong** | the lab's normal flagship | opus, sol | | **mid** | the everyday default | sonnet, terra | | **cheap** | the lab's small, fast hosted model | haiku, luna, flash, mini, nano, lite | | **local** | runs on this machine (ollama, lmstudio, llama.cpp) | qwen, gemma, gpt-oss | Names go stale within months; the position in the family does not. Rank a model you cannot place by the lab's own description of its lineup (flagship, balanced, fast). `pi --list-models` shows context and max output, not price or quality, and siblings often share both. Still unsure: run it on a small slice of the real work and compare it with a model you can place. Until then, pick conservatively: a model you know is strong enough for the work, and for a checker never one that might sit below the author. Thinking effort strengthens a model within its tier. It does not change the tier, and it does not stand in for another family. ## Local models are a last resort A hosted cheap model beats a small local one at agent work: tool calls, long briefs, multi-step edits. Small local models lose the thread of a brief and fake tool results; in `pi --list-models` they tend to show thinking `no` and small context and output limits. Use one only when no hosted model is available, or the work must stay on the machine, and then only for cheap-tier work whose output something stronger checks. A local model never reviews, refutes or judges. ## Roles | Work | Tier | | --- | --- | | fan-out scouting (listing units), searchers collecting quoted claims, watchers, first-pass finders | cheap | | building, refactoring, tests, routine fixes | mid | | review, refute, judge, audit, synthesize | the tier of whoever wrote the thing being checked, or higher; another family when one exists | | design, plans, incidents, root cause, final synthesis of a large run | strong | | a strong attempt failed, or the final judge of a close call | frontier; none available: the strongest model, from a family not yet used on the job | Cheap work suits bounded tasks whose output can be checked: a searcher's claim carries a quote a checker verifies. A cheap finder's misses stay missed, since refuters only test what was reported. When an omission is costly (a security audit, a coverage sweep), run the finders mid or strong, or add a second finder from another family. ## Checkers A checker (reviewer, refuter, judge, auditor) must not share the author's blind spots. The author is whoever wrote the thing being checked: the worker for a diff, the planner for a brief, the finder for a finding. - **Level or up.** At least the author's tier; never down. - **Another family when one exists**, at that tier. One model's blind spot repeated is still one blind spot. - **No peer in another family**: the same model, fresh context, higher thinking unless at max. A delegate with no `model` runs the cli's configured default, which is your own model only if you are on that default. When the tier or family matters, pass `model`. ## How to pass a model and effort level pi takes both in one `--model` value: `:`, where the thinking (effort) level is one of `off`, `minimal`, `low`, `medium`, `high`, `xhigh`, `max`. Leave `:` off to keep the model's default. With `:`, pi reads the first segment as the provider, so copy `/` exactly from `pi --list-models`. Through a gateway that is `modelbridge/anthropic/claude-sonnet-5-5:high`; `anthropic/…:high` fails with "No API key". - `mu_delegate`: `model: "/:high"`. - Spawn: `mu agent spawn r -w --command "pi --model /:high"`. - A `cli` key (`--cli pi_big`) works only if `$MU__COMMAND` is set in the environment; check before you rely on one. - herdr refuses a command override, so neither model nor level can be set per agent there: every helper runs the cli's default. The only independence left is fresh context; say so in the verdict. Probe a model you have not used this session (`pi --model -p "say ok"`); `ctl: ok` after spawn does not test the model. Done when the chosen `model` is placed in a tier, a checker is at the author's tier or higher and from another family (or the verdict says why not), and a model new this session answered `pi --model -p "say ok"`.