List engines, what each can do, and what each costs

The engine registry as it is configured right now: which engines are live, which one you get when you omit engine, and the BILLING MULTIPLIER applied to each. Until this endpoint existed the multipliers lived only in prose, so a caller sizing a budget had to trust a table that could go stale the moment pricing changed. features tells you what each engine may be asked to do — note that stream appears on v4 only, which is why every stream is charged at the v4 rate regardless of what you send. No authentication required.