model-routing

Model Routing

The expensive model thinks, cheaper models grind. The main-session model cannot be switched by Claude - routing works through subagent delegation (the model param of the Agent tool, or the agents bundled with this plugin).

Routing makes a dispatch cheaper; it does not make dispatching cheap. A subagent starts empty, so everything it reads is a cache write, while the main session pays cache read - 12.5x less - for context it already holds. That penalty is paid whether or not the tier is routed down, so the rules below only pay off on work that was going to be delegated anyway. On one wide-reading session, three runs: doing it inline cost $1.36 and delegating with the tier routed down $1.68, both measured; delegating at the session tier comes to $2.01, which is those same measured subagent tokens repriced at the higher tier rather than a run of its own. Route every dispatch - roughly a sixth off work already leaving the session - and do not manufacture dispatches to collect it.

Tiers

Think in tiers, not model names - names rot, tiers do not:

• strongest - the main-session model the user picked (Fable, Opus, whatever their plan offers). Highest reasoning quality, highest cost.
• mid - one step down (e.g. Opus when the session runs Fable, Sonnet when the session runs Opus).
• cheap - Sonnet/Haiku class. Mechanical work.

Effort, not just tier

Model tier is one knob; reasoning effort is the second, and it moves cost as hard as tier does. The same model at low effort can cost a fraction of max and still clear a task that was never hard - a strong model thinking lightly often beats a weaker model thinking hard. Pick both: which model, and how hard it thinks.

The full ladder is low / medium / high / xhigh / max. On every model that supports effort the default is high - an unset effort IS high effort, not medium, and there is no exception. Opus 4.7 and 4.8 are often misread as one: they RECOMMEND starting at xhigh for coding and agentic work, which is a value you have to pass, not what runs when you pass nothing. Which levels exist at all is a per-model list rather than a version cutoff, and setting a level the model does not support runs the highest supported level at or below it. The per-model recommendation moves with the generation: Opus 4.7 and 4.8 are told to start coding and agentic work at xhigh, while Opus 5 is told to start at high, step up to xhigh for demanding coding and agentic work, and use low and medium liberally as the primary control for token cost and response time wherever evals show quality holds. The step down got cheaper, not the step up. xhigh is also the newest level and absent on some models that support max (e.g. the 4.6 generation), so check the model's own docs when in doubt - and re-sweep effort on your own evals after a model change instead of carrying old settings across generations. This plugin tunes for cost: pins sit at the lowest level the task shape allows and step up on evidence (a weak result retries one step up). That deliberate step below the product default, wherever the task allows one, is where the effort savings come from.