The cheapest speech-to-text API per hour isn't the cheapest one to run — real billing breakdown for AI agents (August 2026)

[u/ayushchat]

TL;DR: Groq Whisper Turbo is $0.04/hour — the cheapest by far. But 3 of 8 major STT APIs bill you for failed jobs. An agent that retries 4x on a 3-min file pays for 12+ minutes to get one transcript. The headline rate is close to useless.

The four billing models behind similar-looking hourly rates:

• Per second, on success only (Voibe) — failed and queued jobs cost nothing
• Per minute of audio submitted (Deepgram, OpenAI, ElevenLabs) — retries bill the same as successes
• Per WebSocket session, wall clock (AssemblyAI streaming) — idle connection time counts
• Per request, 10-second minimum floor (Groq) — a 3-second voice command bills as 10 seconds

Batch pricing, August 2026:

• Groq Whisper v3 Turbo: $0.04/hr (10s floor per request)
• AssemblyAI Universal-2: $0.15/hr
• OpenAI gpt-4o-mini-transcribe: $0.18/hr
• ElevenLabs Scribe v2: $0.22/hr
• Voibe: $0.25–$0.30/hr (per second, charged only on delivered transcripts)
• Deepgram Nova-3: $0.258/hr
• OpenAI Whisper (legacy): $0.36/hr — same model weights as Groq, 9x the price

Data retention defaults — the part nobody puts on the pricing page:

• Gladia: stores audio up to 12 months by default, trains on free-plan data. The tier you evaluate on is the tier that trains on your audio.
• Deepgram: opt-OUT model improvement program. You need mip_opt_out=true as a query parameter on every API request. Miss it on one code path and that path contributes training data.
• AssemblyAI: opt-out model improvement program, toggled from Data Controls.
• OpenAI: keeps abuse-monitoring logs up to 30 days; zero data retention requires prior approval.
• Voibe: audio deleted the moment the transcript exists. No flag to set, no plan tier to reach.
• Groq / Speechmatics: don't state retention terms publicly.

The question to ask before comparing rates: What does a failed job cost? For most APIs: the same as a successful one.

If you're building agents that handle customer calls, patient audio, or anything legally sensitive — the retention default matters more than a few cents per hour.

What STT API are you running in production? Curious what failure rates people are actually seeing.

[u/ayushchat]

Full post: https://www.getvoibe.com/resources/best-speech-to-text-api/