# Cartesia

Canonical page: https://technooptimist.io/companies/cartesia
Cartesia builds very fast speech models for live voice agents: Sonic turns text into speech and Ink turns speech into text. Founded by Stanford researchers behind state space models, an alternative to transformers.

## In brief

- Sonic-3.6 (Aug 2026) tops Artificial Analysis's text-to-speech leaderboards, starting to speak in under 90 ms.
- Co-founder Albert Gu co-invented Mamba; the team builds on state space models, which keep a fixed-size memory.
- Raised $91M by its 2025 Series A (Kleiner Perkins), and a reported $100M Series B in Oct 2025.

## Facts

- Founded: 2023
- Headquarters: US
- Status: private
- Raised: $186M
- Website: https://cartesia.ai
- Frontiers: [AI](https://technooptimist.io/ai.md) (Voice & music)

## Programs

- [Sonic](https://technooptimist.io/ai/sonic.md) (AI): Scaling. Sonic-3.6 out Aug 2026; #1 on Artificial Analysis voice boards; 61 locales.

## Technical approach

- **Architecture: State space models**: Instead of re-reading everything said so far like a transformer, the model updates a fixed-size summary, so cost grows linearly with length.
- **Latency: Speak within a blink**: Streaming the first audio in under 90 ms keeps a phone-agent conversation from feeling like it lags.
- **Full stack: Ears and voice**: Ink transcribes the caller and detects when they finished speaking; Sonic answers. Both are tuned for live agents.

## Open problems

- **Turn-taking** (active research): Knowing when a caller has really finished, not just paused, still causes agents to interrupt or wait too long.
- **Fixed memory recall** (active research): A fixed-size state must compress everything; Cartesia's own Mamba-3 post notes such models lag transformers on exact recall.

## Latest updates

- **27 Aug 2026**: Cartesia ships Sonic-3.6, topping Artificial Analysis text-to-speech rankings. Two months after Sonic-3.5, Cartesia rebuilt data, architecture, training and evaluation for Sonic-3.6. ([our story](https://technooptimist.io/stories/cartesia-ships-sonic-3-6-topping-artificial-analysis-text-to-speech-dbbf267d.md) · [original source](https://cartesia.ai/blog/sonic-3.6))
- **9 Jul 2026**: Cartesia releases Ink-2, a speech-to-text model for live voice agents. Ink-2 transcribes speech as it streams and decides when the speaker has finished from meaning rather than silence. ([our story](https://technooptimist.io/stories/cartesia-releases-ink-2-a-speech-to-text-model-for-live-voice-agents-347c61d1.md) · [original source](https://cartesia.ai/blog/ink-2))
- **11 Mar 2025**: Cartesia raises $64M Series A led by Kleiner Perkins and launches Sonic 2.0. Cartesia raised $64 million led by Kleiner Perkins, for $91 million raised in total, and released Sonic 2.0 on its state space architecture. ([our story](https://technooptimist.io/stories/cartesia-raises-64m-series-a-led-by-kleiner-perkins-and-launches-sonic-c493a296.md) · [original source](https://cartesia.ai/blog/series-a))

## Funding

| Date | Round | Amount | Post-money | Leads |
| --- | --- | --- | --- | --- |
| Oct 2025 | Series B | $100M |   | Kleiner Perkins |
| 11 Mar 2025 | Series A | $64M |   | Kleiner Perkins |
| 12 Dec 2024 | Seed | $22M |   | Index Ventures |

## Partners, customers and investors

- Kleiner Perkins (investor): Led the $64M Series A (March 2025).
- Index Ventures (investor): Led the $22M seed extension (Dec 2024).
- NVIDIA (investor): Strategic investor in the October 2025 Series B.

## People

- Karan Goel, Co-founder & CEO
- Albert Gu, Co-founder & Chief Scientist

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