AssemblyAI Universal-Streaming $0.15 vs 3.6 Pro $0.45: 250 hours

AssemblyAI lists its Universal-Streaming models at $0.15 per hour and Universal-3.6 Pro Realtime at $0.45 per hour, so the Pro model costs three times as much. Over a month with 250 session hours, that is $37.50 against $112.50, a difference of $75. AssemblyAI says streaming is billed on session duration, the time the WebSocket is open, so the 250 hours means connection time, not speech time.

Prices were read on AssemblyAI's page on 2026-10-09. Sume STT is a batch service and is shown only for the after-the-fact case.

The month in numbers

The comparison includes AssemblyAI's streaming add-ons where they apply. Speaker diarization is +$0.12 per hour on streaming. Keyterms prompting is included on U3.6 Pro and Multilingual but +$0.04 per hour on Universal-Streaming English.

Choosing between the two tiers

The extra $0.30 per hour buys whatever the Pro model does better on your audio. The price page does not say how much better, so a trial on your own calls is the only way to know. A quick test: stream the same ten recordings through both and count the words you would have to correct.

Keep in mind that keyterms are bundled into the Pro price but extra on the English Universal-Streaming model. If you were going to use keyterms anyway, the Pro model costs $0.45 against $0.19, and the real gap is $0.26 per hour, or $65 over 250 hours.

Where Sume fits

Sume does not offer live transcription, so it is not a substitute for either streaming row. It can transcribe the recorded sessions afterward in ten-minute jobs at $0.01 a minute. That makes sense only if the transcript is the first step of a longer Sume workflow, such as captioned replay clips. For a transcript alone, the batch prices on AssemblyAI's own page are lower than $0.60 an hour.

• Cap session length in your own code to stop forgotten connections.
• Log open and close times so you can reconcile the invoice.
• Use the cheaper tier for rough live captions and the Pro tier only where accuracy matters.

Planning a month of sessions

Count session hours from your calendar, not from speech. 250 session hours is a bit over ten days of one connection open around the clock, or 2,500 sessions of six minutes. Short sessions are cheap one by one but add up, and a pool of agents that keep sockets open between calls multiplies the hours.

If your usage is spiky, set an alert on spend per day. A bug that reconnects in a loop can open many sessions at once, and on a session-duration basis each of them bills until it closes.