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The Humanness Index™
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The Humanness Index™

The open benchmark for how human voice AI sounds. Built and operated by Vapi.

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Code is Apache-2.0. Standings data is CC BY 4.0. Audio clips and source voices are licensed recordings, all rights reserved. Provider logomarks belong to their respective owners and are used nominatively. “The Humanness Index™” name and logo are Vapi trademarks; see TRADEMARKS.md.

  1. Humanness Index™
  2. Gradium

Humanness Index™ · Provider

Gradium

Gradium

gradium.ai

Gradium is the commercial company from the founders of Kyutai, the Paris open research lab that shipped the first real time conversational speech model.

Best ranked model
#20 Gradium TTS
Humanness
24

Standings as of Jun 13, 2026, 01:14 UTC

Gradium
Models on the Index
1
Languages
5
Price / 1M chars
$58
Visit Gradium

Gradium models on the Humanness Index™

RankModelHumannessLatencyLanguagesPrice / 1M chars
#20Gradium TTS24332 ms5$58

Compare against the full Humanness Index™ rankings

About Gradium

Gradium is the commercial company from the founders of Kyutai, the Paris open research lab that shipped the first real time conversational speech model. Founded in September 2025 by generative audio pioneers from Google DeepMind and Meta, it raised a $70M seed led by FirstMark and Eurazeo, with angels including Yann LeCun.

Sources: gradium.ai, slator.com

Production speech APIs

Gradium came out of stealth with production speech APIs in December 2025, built on a decade of generative audio research spanning neural codecs, audio LLMs, and Moshi. Its text to speech streams from servers in Europe and the US, speaks five languages, and clones a voice from a ten second sample.

Sources: docs.gradium.ai

Gradium stats

Languages
51
Price / 1M chars
$582
  1. docs.gradium.ai/api-reference/endpoint/tts-post (checked 2026-06-10) English, French, Spanish, Portuguese, and German.
  2. gradium.ai/pricing (checked 2026-06-10) 1 credit per character (docs.gradium.ai/guides/credits); entry XS plan is $13/mo for 225k credits, a $58 per 1M effective rate.

Other providers on the Index

ElevenLabsElevenLabsBest ranked model #5 · Eleven v3CartesiaCartesiaBest ranked model #3 · Sonic 3.5xAIxAIBest ranked model #1 · Grok TTSMiniMaxMiniMaxBest ranked model #8 · Speech 2.5Canopy LabsCanopy LabsBest ranked model #4 · OrpheusInworldInworldBest ranked model #9 · TTS-2Smallest.aiSmallest.aiBest ranked model #14 · Lightning v3.1NeuphonicNeuphonicBest ranked model #13 · neu_hq

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