Pi custom / variant model

When to use

Pi's saved default only loads if the exact provider/id exists in its model registry. Pi ships a static bundled list per provider — so OpenRouter routing-shortcut variants (:nitro = sort by throughput, :floor = cheapest, :exacto = quality tool-use) and any brand-new slug are NOT in it. When the default doesn't resolve, Pi silently falls through to its built-in per-provider default (for openrouter that's moonshotai/kimi-k2.6) — looking like Pi "reset" your model. Fix = register the slug as a custom model so find(provider, id) matches.

Files (global)

• ~/.pi/agent/settings.json — defaultProvider, defaultModel, defaultThinkingLevel
• ~/.pi/agent/models.json — custom models, keyed by provider
• ~/.pi/agent/auth.json — provider credentials (check the provider key exists)

Steps

1. Confirm the slug is real before adding it (e.g. check the OpenRouter model/variant exists). A typo'd id also silently falls back.
2. Confirm auth. The provider must have a key in auth.json (or an env var like OPENROUTER_API_KEY). No auth → the model is registered but unavailable → still falls back.
3. Add the model to models.json under providers.<provider>.models. For a built-in provider (openrouter, anthropic, etc.) you only supply metadata — api, baseUrl, and auth are inherited from the bundled defaults. Example:

   {
     "providers": {
       "openrouter": {
         "models": [
           {
             "id": "z-ai/glm-5.2:nitro",
             "name": "Z.ai: GLM 5.2 (nitro)",
             "reasoning": true,
             "thinkingLevelMap": { "xhigh": "xhigh" },
             "input": ["text"],
             "cost": { "input": 0.95, "output": 3, "cacheRead": 0.18, "cacheWrite": 0 },
             "contextWindow": 1048576,
             "maxTokens": 32768,
             "compat": { "supportsDeveloperRole": false, "thinkingFormat": "openrouter" }
           }
         ]
       }
     }
   }

   Copy cost/contextWindow/compat from the base model (the variant shares them) — find the bundled entry in <pi-pkg>/node_modules/@earendil-works/pi-ai/dist/providers/<provider>.models.js. Don't hardcode generic 128k/16k if the real model is bigger.
4. Set the default in settings.json: defaultProvider + defaultModel = the exact id. Leave defaultThinkingLevel as the user has it.
5. Verify: pi --list-models | grep <id> shows it, and JSON parses. Optionally smoke-test: pi --provider <p> --model "<id>" "which model are you?".

Quirks

• Exact match only. find() is exact provider+id — no fuzzy/colon-stripping for the saved default path. The slug in settings.json and models.json must be byte-identical.
• Silent fallback. Pi prints no error when the default doesn't resolve; it just shows a different model in the footer. That's the tell.
• Don't edit settings.json alone. Setting defaultModel to an unregistered slug does nothing — models.json is the actual fix.
• enabledModels (optional) pins the model picker so Ctrl+P cycling can't drift back: "enabledModels": ["<provider>/<id>:<thinking>"].
• Project override. A repo's .pi/settings.json overrides global. If a default reverts only inside one project, check that file first.
• Restart Pi fully — the registry loads at startup.