Comparison of estimated costs per hour for active conversation across major providers as of 2026.
| Model/Provider | Est. Cost/Hour | Notes/Assumptions | Connection Specs | Source |
|---|---|---|---|---|
| Vowel Core Realtime API | $1.50/hr | Feature's vowel's prime one voice model with world class voice to voice responsive times. SOTA level LLM inference priced flat per hour of interaction. | OpenAI connection spec, ephemeral tokens | vowel Pricing |
| OpenAI Realtime API (GPT-4o realtime, latest 2026 rates) | ~$30–$60/hr | Based on $32/1M audio input tokens + $64/1M audio output tokens. Assumes ~30 min user speech + 30 min AI speech per hour, ~1,667 tokens/min for audio. Real-world tests often report $0.50–$1.00 per minute for balanced conversations. | OpenAI connection spec, ephemeral tokens | Official Pricing |
| Google Gemini Live API (Gemini 2.x Flash Live) | ~$5–$15/hr | Token-based: audio input ~$2.10/1M tokens, audio output ~$8.50/1M tokens (32 tokens/second). Rough estimates: ~$0.35/hr pure input audio, ~$1.40/hr pure output audio; balanced conversation with text tokens adds cost. Some reports include ~$0.025/min session fee. Significantly cheaper than OpenAI for similar usage. | Proprietary connection spec, REMOVED ephemeral tokens | Official Docs |
| Cartesia Sonic (end-to-end realtime TTS) | ~$8–$20/hr | TTS-focused at ~$0.038/1,000 characters. For full realtime voice agent (with STT/LLM), depends on pipeline; character-based output for AI speech typically yields low per-hour costs in balanced talk time. | Cartesia connection spec | Cartesia Pricing |
| Deepgram Aura (enterprise realtime TTS) | ~$6–$15/hr | $0.030/1,000 characters. Similar to Cartesia; very cost-effective for output-heavy realtime voice when paired with cheap STT/LLM. | Deepgram connection spec | Deepgram Pricing |
Vowel's prime one architecture delivers production, secure, realtime voice at 1.5, beating other voice APIs by 7–30× in most scenarios.
OpenAI's Realtime API becomes prohibitively expensive for long sessions due to high output token costs.
Gemini Live offers a middle ground, significantly cheaper than OpenAI but still more expensive than optimized pipelines.