Azure Speech Services (F0 free tier)

The F0 free tier offers 500,000 characters of neural text-to-speech synthesis per month, valid long-term with no expiration

Roughly equivalent to 10 hours of audio per month. The quota doesn't roll over and can't be exceeded by paying extra — once used up, requests are rate-limited or rejected, generating no extra charges.

⚠️Registering an Azure account itself generally requires linking a credit card for identity verification (the free tier itself isn't charged).