@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.

GPT-6 models (gpt-6-astra, gpt-6-sol, gpt-6-luna, gpt-6.1-sol) are routed the same way, to openai/<id>, on a Pi release that includes pi#10930. Pi then pins reasoning.effort and sends the chosen effort as configuration_update items. Older Pi rejects them with unsupported_model. They need an OpenAI API key: Sign in with ChatGPT is rejected with unsupported_model, because Pi then changes the request's effort and misses the cache. A none decision on gpt-6-luna or gpt-6-sol is also sent as request-level effort and misses the cache. openai-codex models are not routed.

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.

| Variable | Default | Purpose | | --- | --- | --- | | REASONING_ROUTER_CLASSIFIER | jev | Classifier provider name, such as jev (see classifiers). | | REASONING_ROUTER_CLASSIFIER_API_KEY | none | Classifier credential, if the provider needs one. | | REASONING_ROUTER_CLASSIFIER_BASE_URL | provider default | Classifier endpoint; defaults to the provider's. | | REASONING_ROUTER_CLASSIFIER_ACCOUNT_ID | none | Account ID, for providers that take one. | | REASONING_ROUTER_CLASSIFIER_MODEL | none | Classifier model, for providers that take one. | | REASONING_ROUTER_CLASSIFICATION_TIMEOUT_MS | 4000 | Total classification budget, including retries. | | REASONING_ROUTER_MAX_RETRIES | 1 | Classifier retries after a retryable error (0–10). | | REASONING_ROUTER_FALLBACK_MODE | fixed | On failure: fixed, previous (last classified effort, else fixed), or error. | | REASONING_ROUTER_FALLBACK_EFFORT | high | Effort for fixed fallback. | | REASONING_ROUTER_BASE_EFFORT | model default | Effort for direct requests. | | REASONING_ROUTER_DECISIONS_LOG_PATH | none | Absolute path for a JSONL log of decisions. |

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