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.
~/.pi/agent/models.json — custom models, keyed by provider
~/.pi/agent/auth.json — provider credentials (check the provider key exists)
Steps
Confirm the slug is real before adding it (e.g. check the OpenRouter model/variant exists). A typo'd id also silently falls back.
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.
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:
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.
Set the default in settings.json: defaultProvider + defaultModel = the exact id. Leave defaultThinkingLevel as the user has it.
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.
Limitations
Adapted from davidondrej/skills; verify local paths, tools, credentials, and agent features before acting.
For commands, remote access, scheduling, browser automation, or file-changing workflows, get explicit user approval and confirm the target environment first.