The buying decision
Use Pi's supported authentication for native subscriptions. For a separate compatible API account, configure models.json and verify the provider's model appears before starting a task.
API credentials are not chat login credentials
Buying a chat subscription does not automatically supply a transferable API key. Pi supports particular provider authentication flows and custom API providers; use the flow documented for your chosen provider. Do not paste a browser session token into a generic API field. If you prefer a separate monthly API budget, compare the allowance and supported model protocol rather than the word subscription alone.
Where a custom provider goes
Pi documents custom providers in ~/.pi/agent/models.json. The provider entry includes baseUrl and an API protocol, with a models array naming the model IDs. Standard Compute's Chat Completions base is https://api.stdcmpt.com/v1 and its router model ID is standardcompute. Pi names this protocol openai-completions. Merge the entry into your existing file and configure authentication locally.
Avoid the invisible-model trap
The current Pi docs explain that a model configuration can load before authentication is available, while model selection still needs a usable credential. If your provider does not appear in /model, check the config location, provider ID and credential resolution before assuming the gateway is down. Consult the value-resolution rules for environment-variable references and avoid storing real secrets in shared examples.
Measure the whole parent task
Extensions can add tool calls or child sessions. For a cost comparison, count the parent task and all child requests, compaction, retries and failures. Keep the Pi version and extension set fixed. Pi and oh-my-pi are separate projects; a Pi recipe should not be assumed to configure every fork unchanged. Test the client you actually intend to use.
Run your own comparison
Use the same task, starting revision and acceptance check. Record every retry and failed attempt so the result reflects the work you actually paid for.