@reasoning-router/pi

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A Pi extension that asks a classifier how much reasoning each Claude request needs and lets Pi place that effort without breaking the prompt cache. Requires Pi 1.0.0 or later and Node.js 24.x.

export REASONING_ROUTER_CLASSIFIER_API_KEY=your-jev-key
pi install npm:@reasoning-router/pi
pi --model reasoning-router/claude-opus-5-5

The * peer range on @earendil-works/pi-coding-agent does not enforce Pi 1.0.0. An older Pi fails to load the extension because it has no registerVirtualModel.

The extension adds a virtual model reasoning-router/<id> for each Claude model the router knows. Each request runs on the matching anthropic/<id> model with your existing Anthropic login or key; the router only picks its thinking level. For these mid-conversation-effort models Pi pins output_config.effort: "high" and states the chosen effort in an effort-only system message, so changing effort keeps the cached prefix.

• User turns and continuations are classified. A retry reuses the failed attempt's thinking level. Direct requests, such as compaction, use REASONING_ROUTER_BASE_EFFORT, or the model's base effort; the variable affects only those requests, not the pinned high above.
• The last classified effort is stored in the session, per virtual model, so previous fallback survives a restart.
• A model that Pi lacks, or that Pi cannot give mid-conversation effort, is rejected with reasoning-router unsupported_model: .... In Pi 1.0.0 and 1.0.4 that includes claude-mythos-5-1.
• A classification failure in error fallback mode rejects the request with reasoning-router classification_failed: .... Cancelling a request never falls back. The messages carry no HTTP status codes, because Pi retries errors that look like transient provider failures.
• The classifier endpoint receives the most recent user text, the most recent assistant text, and the names and output excerpts of recent tool results. System messages, thinking blocks, and tool-call arguments are not sent.

OpenAI models are not routed yet.

Environment

The extension reads the proxy's variables on the first routed request, not when Pi loads it. The virtual models are always listed. A missing classifier key, a legacy variable such as TYPESAFE_API_KEY, or another invalid value fails that request with reasoning-router invalid_config: ...; Pi keeps running, and the next request reads the variables again until they are valid.

See docs/environment.md for the classifier credentials. The decision log holds metadata only: model, effort, classifier latency and attempts, fallback, token usage including cache reads, and outcome, with no prompt text or credentials.

License

MIT