Bring your own key to Pi

Pi has no bundled plan, no free tier, and no subscription of its own to sell you. Every session runs against a model you pay for directly - bring-your-own-key, in the fullest sense. That’s a deliberate consequence of the same minimalism the loop lesson walks through: Pi doesn’t want to be in the business of managing your billing relationship with a model provider, any more than it wants to carry a bloated standing system prompt you didn’t ask for.

The two ways in

Inside the running prompt - with Pi installed and launched in your project - /login walks you through the options:

> /login

You’ve got two shapes of authentication, and they’re not interchangeable:

• An API key, exported as an environment variable before you launch Pi - ANTHROPIC_API_KEY, OPENAI_API_KEY, and so on, depending on the provider. You pay that provider per token, directly, at their published rate.
• OAuth into a subscription you already have - /login supports signing in against a handful of subscription-based providers this way, including Anthropic’s Claude Pro/Max plans, OpenAI’s ChatGPT plans, and GitHub Copilot.

A third case appears in the table below and fits neither shape: a local model (Ollama and its kin) needs no credential at all. It is configured where providers are defined, in models.json, and the local-models lesson covers it properly - noted here only so the table has no orphan row. The aggregator row, by contrast, belongs to the API-key shape: OpenRouter issues you a key of its own, and Pi treats it like any other provider’s - that row exists because the billing cushion and the extra hop differ, not the authentication mechanism.

Here’s what “per token” means on a concrete example from this course: the first-fix lesson closes its fix in five tool calls - two reads, of stash/extract.py (stash is the course’s running example, a small FastAPI feed reader) and tests/test_extract.py; one edit, to the first of those files; and two pytest runs, the focused file first and then the full suite. Every one of those five is a fresh round trip that resends the whole growing conversation back to whichever provider you picked.

Under API-key billing, all five round trips are metered at that provider’s published rate - check it before you rely on a long session, because it compounds with every read you ask for. stash itself doesn’t care which path you choose: pytest still runs locally, free, on your own machine, either way. What changes is only what you pay to have the model read the files, propose the diff, and re-check its own work.

For stash, either path gets you to a working session. What matters is which provider you pick, and how:

Path	Who pays	Billing unit	Predictability
API key (Anthropic, OpenAI, others)	You, directly to the provider	Per token, at that provider’s published rate	Fully metered - cost scales with what you send and receive
OAuth into Claude Pro/Max	You, through your existing subscription	Per token, from “extra usage” - Pi’s own provider docs describe third-party harness calls as billed this way, not against your plan’s included usage	Same metering as an API key, despite the subscription login - verify against Anthropic’s current terms before you count on it
OAuth into ChatGPT or Copilot plans	You, through your existing subscription	Provider-specific and not detailed in Pi’s docs	Unknown until you read that provider’s current terms yourself
Local model via Ollama	Nobody, per call	None - your own compute	Free, with trade-offs you’ll weigh properly in a later module
Aggregator (OpenRouter)	You, via the aggregator	Full per-token API rate, no subscription cushion underneath	Same as a direct API key, plus one extra hop

Anthropic subscription + Pi: check current billing and terms

The table above states Pi’s own feature description of Claude Pro/Max support, not Anthropic’s terms or pricing - either can change independently of Pi, and the description is not a substitute for reading both yourself before you rely on subscription auth for a long-running workflow.

The most predictable path for this course is API-key billing - export ANTHROPIC_API_KEY and pay per token. Subscription auth is also documented by Pi, but its billing and policy are provider-specific; read the current provider terms yourself before standardizing on it. That billing shape is the one real restriction this lesson’s label names: a subscription login does not draw on your plan’s included usage - it meters per token, from “extra usage”.

What this means for today

None of this blocks you from working on stash right now. Either of the two paths above gets you a working session today - pick the one whose terms you’re already comfortable with, not the one this page recommends by default. The table’s remaining rows are paths their own lessons map out.

Pick whichever path gets a model responding, and confirm it landed:

> what model am I talking to right now?

You’re authenticated, and Pi has a model to call. Before you hand it the actual bug, spend two minutes watching how a single request through Pi actually behaves - because the shape of that loop is the one piece of trust you need before the real fix. Next: understand one turn of the loop.