AssemblyAI Speech-to-Text (Universal) vs Soniox Speech-to-Text

AssemblyAI Speech-to-Text (Universal)

OpenAPI 3.1 file with typed inputs and error responses on every operation. Two outages of an hour or more in the last 90 days, on 31 July and 16 September 2026.

Soniox Speech-to-Text

About $0.10 an hour async and $0.12 real time, with diarisation, language ID and translation included. No free credits for new accounts since October 2025.

AssemblyAI Speech-to-Text (Universal)

1. Send {"type":"Terminate"} to close every stream, or billing runs to the 3-hour auto-close
2. Use speech_models (plural). The singular speech_model now returns 400 for current model names
3. Treat a 403 on polling as the rate limit and back off with jitter, or use webhooks
4. Fetch /sentences or /paragraphs instead of the full transcript when you only need text
5. Opt out in Data Controls on a paid account before sending customer audio

Soniox Speech-to-Text

1. Pass audio_url for public files and skip the upload step. Delete uploaded files or they count against the 10 GB quota for 30 days
2. Use the context field for names and domain terms
3. Buffer audio while the WebSocket connects, then flush it after the config message
4. Split anything over 300 minutes. The cap is fixed
5. Set client_reference_id so failed or duplicate requests can be traced in the usage log