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Usage is metered on the audio your calls process, billed against your plan and prepaid credits. This page explains what each product meters; for current rates, always see the live pricing page, it is the single source of truth and avoids stale numbers.
Rates change as we improve the platform. We intentionally keep figures out of the docs so you never act on a stale number, the pricing page and your console usage are always current.

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The units header

Billed responses carry an x-pyai-units header reporting exactly what was metered for that request (e.g. the amount of audio synthesized or transcribed). Read it to reconcile your own usage accounting against ours.

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Credits and spend caps

  • Account signup creates a sandbox key. It does not guarantee promotional credit.
  • Live keys consume prepaid credit. Phone verification may unlock promotional credit under the current graduated-signup rules.
  • Per-key budgets, set a monthly spend cap on any key in the console.
  • Org credit gate, when prepaid credit is exhausted, billed calls return 402 until you top up.

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Sandbox tier (no billing)

A pyai_test_ key works instantly against production models with hard daily caps (requests/day, concurrent sessions, audio minutes/day) and never touches billing. Use it for evals and CI so a first call never hits the credit gate.

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402 semantics

A 402 means a billing limit was reached, it is not a broken key: Do not retry a 402, the call will keep failing until the underlying limit changes. See Errors & limits for the full catalog.