The voice is now streaming at the speed of a blink
the voice is now streaming at the speed of a blink: cartesia sonic 4 hits about 40 milliseconds to first audio, inworld’s realtime tts-2 runs p99 under 100 milliseconds with a flash tier under 25, and elevenlabs flash v2.5 sits near 75, while emotion steering in plain language is standard. the gap between synthetic and human speech closed faster than anyone priced.
latency is the new accent.
Context
ElevenLabs' docs list Eleven Flash v2.5 at about 75 ms latency. Inworld says its Realtime TTS-2 and TTS-2 Flash deliver 100 ms and under 25 ms time to first byte at P99.
Inworld's comparison pages say Cartesia Sonic 3.5 reaches about 40 ms time to first byte on its Turbo variant.
The ElevenLabs 75 ms and Inworld 100 ms and 25 ms figures match, but Inworld's numbers are vendor claims. The Cartesia 40 ms figure is for Sonic 3.5 Turbo in the sources, and Sonic 4 by name was not seen in the sources read, so unsupported here, not refuted. A later Inworld page refers to Cartesia Sonic 3.6 leading an Artificial Analysis arena on Sep 2, 2026.
Related work
- ElevenLabs Docs: Models ↗Flash v2.5 latency.
- Inworld vs ElevenLabs: realtime TTS compared ↗Vendor figures.
- Inworld TTS-2 vs Cartesia Sonic 3.6 ↗Arena ranking.
Watch next
- Look for an independent latency benchmark across the three.
Sources
- ElevenLabs Docselevenlabs.io
- Inworld, Feb 6, 2026inworld.ai
- Inworld, May 28, 2026inworld.ai
Provenance
The note above is reproduced unedited from the original post, first published on Threads on 2 October 2026 at 22:36 IST. Sources are the papers and datasets the note draws on.
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