Voice APIs Converge on Per-Minute Billing
Seventeen corpus companies bill on media-minutes — per-minute or per-hour — as a primary unit, and among dedicated voice and audio AI vendors the per-minute meter is near-universal. The shift from per-character (batch TTS era) to per-minute (agent call era) reflects the dominant use case moving from content generation to real-time conversational AI.
What's happening — and why
What's happening: the standard billing unit for voice AI has converged on media-minutes — per-minute or per-hour — rather than per-character or per-request. Seventeen corpus companies use media-minutes as a primary unit, and per-minute is the default across dedicated voice and audio APIs.
Why: the dominant voice AI use case shifted. In the batch TTS era, producers turned text into audio files; the natural unit was the characters being spoken. In the agent call era, voice is deployed in real-time phone calls, voicebots, and conversational interfaces — where wall-clock time, not text volume, is the cost driver. Telephony and call-center buyers already think in minutes; per-minute aligns vendor pricing with buyer mental models.
ElevenLabs is the clearest example: it charges per-minute for Conversational AI (agent calls) and per-character for Studio TTS (batch). The two units coexist for the two use cases.
How it works
Evidence over time
30 supporting · 1 counter — hover or tap a point for detail, click to jump to the row.
Evidence
| Company | Date | What happened |
|---|---|---|
| assemblyai | Jul 2026 | Launched a standalone Voice Agent API at $1.50/hr ($0.075/min) — a per-minute/per-hour rate for a proprietary end-to-end voice stack built on its Realtime STT. A brand-new voice product priced per-minute from day one. |
| speechmatics | Jul 2026 | Cut real-time enhanced STT (the live-voice-agent SKU) $0.56→$0.43/hr and added a multilingual Batch Melia 1 model at $0.129/hr — all on the per-hour audio meter; per-minute/per-hour remains the only billing unit across the Pro tier. |
| bland-ai | Jun 2024 | Billed entirely on media-minutes; phone-agent model fits per-minute naturally |
| elevenlabs | May 2026 | Conversational AI (agent calls) price cut to per-minute rate; retains per-character for Studio TTS. Both units coexist in billing. |
| cartesia | Feb 2026 | Voice Agents GA at flat per-minute rate; prior API used credits/requests |
| deepgram | Jan 2025 | Transcription and TTS both per-minute; Nova-2 ASR $0.0043/min, Aura TTS $0.0150/min |
| tavus | Jan 2025 | Entire model is hybrid access fee + pay-as-you-go video minutes; per-minute is the only consumption unit |
| speechmatics | Jun 2025 | Per-hour STT, per-character TTS — both units present; moving toward per-minute for real-time |
| murf-ai | Jun 2026 | Murf API launched with per-character and per-minute lanes; Studio plans cap on minutes |
| rev-ai | Jan 2025 | Pure usage per-minute; transcription billed in 15-second increments |
| krisp | Jun 2025 | Call Center product bills on accent-minutes; per-agent seats plus minute consumption |
| synthesia | May 2026 | Video-minute credits drive all plan tiers; minutes are the primary consumption signal |
| twelve-labs | Jun 2025 | Video understanding billed per video-minute indexed; minutes is the primary query unit |
| wellsaid | Jun 2026 | Annual download quotas expressed as minutes per plan tier; per-seat+minutes model |
| hedra | Dec 2025 | Credits map to video/audio seconds; effectively per-minute billing abstracted through credits |
| fal-ai | Jun 2025 | Audio/video models billed per second of output; effectively per-minute at scale |
| retell-ai | Jun 2026 | Voice-agent minute itemized into Voice Infra ($0.055/min) + LLM + TTS + telephony; calls metered to the nearest second |
| vapi | Jun 2026 | $0.05/min hosting fee with model and telephony passed through at cost — the minute is the platform's only unit |
| synthflow | Jun 2025 | No-platform-fee PAYG billing the Voice Engine, LLM and telephony as three separate per-minute meters |
| livekit | Jun 2026 | Realtime agent transport billed in participant-minutes plus bandwidth — the WebRTC layer under voice agents meters minutes too |
| daily | Jan 2026 | Pipecat Cloud and transport billed per participant-minute with published automatic volume discounts ($0.004 falling ~63% to $0.0015 past 50M min/mo) |
| hume-ai | Jun 2026 | EVI voice agent per-minute, falling by generation: ~$0.102/min (EVI 1) → ~$0.072 (EVI 2) → $0.04/min Business-tier overage |
| vapi | Jun 2026 | Build tier: $0.05/min Vapi hosting plus at-cost passthrough of STT/LLM/TTS/telephony — pure per-minute developer API with a Scale annual-commit tier on top. |
| retell-ai | Feb 2024 | Launched with true pay-as-you-go per-minute voice agents; no platform fee, no contract — the clearest developer-first per-minute billing in the voice-agent segment. |
| synthflow | Jun 2024 | Subscription tiers bundle minutes (Starter 50 min, Pro 2,000 min) with per-minute overage ($0.12–$0.13/min) — subscription wrapping a per-minute consumption unit. |
| polyai | Jun 2026 | Per-minute enterprise billing (sales-gated); third-party reports ~$150K annual minimum; media-minutes is the stated unit even at fully gated enterprise tier. |
| livekit | Jun 2026 | Multi-dimension metering bundles agent-session minutes ($0.01/min overage) and WebRTC media minutes ($0.0004–$0.0005/min) as two separate per-minute meters — one for AI agent orchestration, one for real-time media. |
| hume-ai | Mar 2024 | EVI 1 launched at $0.102/min; EVI 2 cut to ~$0.072/min (Sept 2024); EVI 3 overage $0.07/min, EVI 4 MINI $0.04/min — a per-minute voice model that has deflated ~60% in two years. |
| gladia | Jun 2026 | STT/transcription billed per audio-minute; free 10 hours/month then pay-as-you-go — per-minute is the primary unit for the ASR segment. |
| playht | Mar 2023 | Early plans were per-character; API pivoted toward per-request and agent voice as the voice-agent market matured, illustrating the per-character → per-minute migration path. |
Counterexamples
- lmnt · — — Charges per character for TTS only — no per-minute lane. Serves batch text-to-speech, not agent calls.
- wellsaid · — — Per-seat + annual quota model dilutes the pure per-minute signal; enterprise customers are quota-capped, not metered.
- descript · Jun 2025 — Media hours billed at tier level, not granularly per-minute; subscription model with hour pools
Trivia
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Wave 27 (June 2026) grew the media-minutes cohort from 15 to 26 corpus companies in one intake — and 23 of the 26 (88%) publish per-minute rates self-serve, making voice one of the most price-transparent AI categories despite its enterprise contact-center wing being fully gated.
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Daily (verified 2026-06-09) publishes the steepest automatic volume curve in the voice cohort: its participant-minute rate falls ~63% — from $0.004 to $0.0015 — once a customer crosses 50M minutes/month, with no negotiation, after the company dropped subscription plans entirely in June 2022.
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Hume's EVI shows the per-minute price deflating by model generation like tokens do: ~$0.102/min (EVI 1, 2024) → ~$0.072/min (EVI 2, ~30% cut) → $0.04/min Business-tier overage by 2026 — a 61% decline across three generations of the same voice-agent product.
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AssemblyAI's 2026-07-06 Voice Agent launched at exactly $0.075/min ($1.50/hr) — the same per-minute rate Vapi charges for its hosting fee — showing the ~$0.05–$0.08/min band has become the reference price for an end-to-end voice-agent minute even as the underlying STT beneath it kept falling (Speechmatics cut real-time enhanced -23% the very same day). A new voice product now launches straight onto the per-minute meter rather than testing per-character or per-request.
For buyers
Budget voice workloads in minutes, not characters. For batch content generation, characters may still be the efficient unit (WellSaid, LMNT). For agent calls and real-time voice, per-minute is the standard — model your cost on expected call durations and call volumes, not script length.
For vendors
If you are building a voice AI product, per-minute pricing aligns with the call-center and telephony mental model your buyers already use. If you serve both batch TTS and agent use cases, maintain both units (ElevenLabs' model): per-character for Studio, per-minute for Conversational.
Outlook — what to watch
As agent voice becomes the dominant voice AI use case, per-minute will further displace per-character. The holdout (LMNT, characters-only) is a batch-focused product. Watch for per-second granularity appearing in cost-sensitive high-volume deployments.
Bottom line
Voice AI billing has converged on media-minutes. Seventeen corpus companies use it as a primary unit, driven by the shift from batch TTS to real-time agent calls.
FAQ
How do voice AI APIs charge for usage?
Almost universally per-minute or per-hour of audio. Seventeen corpus companies bill on media-minutes; among dedicated voice vendors per-minute is near-universal, with LMNT (per character, batch TTS) the main exception.
Why per-minute instead of per-character?
Real-time agent calls — the dominant voice use case — are bounded by wall-clock time, not text volume. Per-minute aligns with telephony buyer mental models and the actual cost driver.
Does ElevenLabs charge per minute or per character?
Both. Conversational AI (agent calls) is priced per minute; Studio TTS (batch text-to-speech) is priced per character. The two billing units coexist for the two use cases.