The short answer
AssemblyAI is billed per minute (usage-based). It has a free tier: $50 one-time credit. The paid plans we list start at $4.50/hr ($0.075/min) (Voice Agent API).
Plans and prices
| Plan | Price | What it covers |
|---|---|---|
| Free credits | $50 free | No credit card required; 5 new streams/min concurrency limit. Self-serve signup. |
| Universal-2 (async STT) | $0.15/hr | Pre-recorded transcription, billed per second; lowest base rate tier. |
| Universal-3 Pro (async STT) | $0.21/hr | Higher-accuracy async model (~5.6% mean WER, keyterm prompting). |
| Universal-Streaming | $0.15/hr | Real-time English/multilingual; billed per WebSocket session duration. |
| Voice Agent API | $4.50/hr ($0.075/min) | All-inclusive STT + LLM + TTS + turn detection + tool calling. |
| Enterprise | Custom | 99.9% uptime SLA, custom SLOs, volume pricing, committed-use; 600M+ monthly inference calls capacity. |
How AssemblyAI bills you
The pricing model is per minute (usage-based). Research-driven STT with the Universal and Slam-1 models and a deep audio-intelligence add-on stack (sentiment, topics, LeMUR LLM). Best suited to: accurate stt plus audio intelligence.
What to watch for on the bill
- Add-on features (diarization, entity detection, redaction, translation) stack on the base rate, pushing effective cost well above the $0.15/hr headline (~$0.35/hr in independent estimates)
- Cost becomes expensive at high audio volume for usage-heavy apps
- Billing-UX friction reported (e.g. difficulty removing a card or disabling autopay)
The pricing page we read
Source: https://www.assemblyai.com/pricing. Prices change, so confirm there before you commit.
Compare AssemblyAI with alternatives
- Deepgram vs AssemblyAI pricing
- AssemblyAI vs OpenAI Whisper / GPT-4o Transcribe pricing
- AssemblyAI vs Google Cloud Speech-to-Text pricing
Other speech-to-text apis: Deepgram, OpenAI Whisper / GPT-4o Transcribe, Google Cloud Speech-to-Text, Amazon Transcribe, Speechmatics.
Looking at quality rather than price? See the AssemblyAI score on APIbenchmarks. Full entry: AssemblyAI pricing.