The complete cost and streaming latency ranking for AI phone bots, conversational agents, and audio generation. Compare Cartesia, ElevenLabs, OpenAI, and Deepgram.
The new king of conversational voice AI. Offers blistering sub-135ms WebSocket latency, natural inflection, and an unbeatable $0.007 per 1k characters (over 50% cheaper than ElevenLabs Flash).
ElevenLabs' dedicated low-latency model engineered for real-time conversational agents. Retains rich emotional timbre and voice cloning accuracy while cutting latency down to ~200ms.
OpenAI's built-in voice endpoint with 6 high-quality preset voices (Alloy, Echo, Fable, Onyx, Nova, Shimmer). Simple REST interface without custom clone setup.
Designed to run alongside Deepgram Nova-3. Simplifies infrastructure by allowing voice agent builders to use a single API key and shared WebSocket stream for both transcription and voice synthesis.
| Provider & Model | Cost / 1,000 Chars | Cost / 100k Chars | Est. Cost / Audio Min | Streaming Latency (TTFB) | Emotional Naturalness | Best For |
|---|---|---|---|---|---|---|
| Cartesia Sonic | $0.0070 | $0.70 | ~$0.0065 / min | ~135ms | 9.1 / 10 | Ultra-low latency conversational bots |
| ElevenLabs Flash v2.5 | $0.0150 | $1.50 | ~$0.0135 / min | ~200ms | 9.5 / 10 | Fast interactive voice with top emotion |
| OpenAI TTS-1 | $0.0150 | $1.50 | ~$0.0135 / min | ~350ms | 8.7 / 10 | General app narration, podcasts |
| Deepgram Aura | $0.0150 | $1.50 | ~$0.0135 / min | ~180ms | 8.9 / 10 | Unified Deepgram STT/TTS pipelines |
| PlayHT 2.0 Turbo | $0.0160 | $1.60 | ~$0.0145 / min | ~280ms | 8.8 / 10 | Character voices & game development |
| ElevenLabs Turbo v2.5 | $0.0300 | $3.00 | ~$0.0270 / min | ~320ms | 9.8 / 10 | Luxury executive AI receptionists |
| OpenAI TTS HD | $0.0300 | $3.00 | ~$0.0270 / min | ~500ms | 9.3 / 10 | Audiobook publishing & marketing videos |
In a phone conversation, humans expect a turn-taking response within 400ms to 600ms. If your voice pipeline uses an STT endpoint taking 250ms, an LLM taking 300ms, and a TTS endpoint taking 450ms, total system latency reaches 1,000ms (1 second). This causes awkward conversational pauses and frequent cross-talk interruptions.
By migrating to Cartesia Sonic ($0.007/1k chars, ~135ms TTFB), total pipeline turn latency drops below 650ms, making your voice bot feel genuinely human while cutting audio synthesis bills by over 50% compared to ElevenLabs.