What's free
3,000 minutes (50 hours)/month speech-to-text + 1,000,000 characters (~20 hrs)/month text-to-speech
Rate limits
2 concurrent real-time sessions on the free plan
The catch
No credit card required to start; add a card only when you exceed the free limit. Recurring monthly allowance covering both STT and TTS. Commercial-use permission not explicitly stated on the pricing page.