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Cartesia
Cartesia is a San Francisco voice AI company that builds its own real-time models, with Sonic for text to speech, Ink for speech to text, and Line for running phone and web voice agents.
Developers and product teams building real-time voice agents for support, scheduling, sales, or healthcare calls, where the time before the first word of audio decides whether a caller stays on the line.
Audiobook, podcast, and character-voice production, where long passages and expressive narration matter more than speed, and buyers who want a very large library of stock voices.
Verdict
Cartesia's Sonic models are among the fastest voices on the market, and Sonic-3.5 led the Artificial Analysis Speech Arena in May 2026. The company grew out of Stanford research on state space models, a model design that keeps latency low, and it now sells speech to text and a managed voice agent platform alongside the voices. More than 50,000 customers use it, and it has raised $191 million. Quality on long narration still trails ElevenLabs, but for a voice agent that has to answer in real time, Cartesia is a strong first choice.
Score Breakdown
These scores cover how natural Cartesia's voices sound, how fast they respond in a live call, how many languages and voices it offers, and how clear its pricing is, and then how it does as a company on innovation, communication, pricing, and contract terms.
Who Uses Cartesia, Where It Fits on Price, and Its Competitors
Cartesia sells mostly to engineering teams that build voice agents, including voice agent platforms such as Retell AI and enterprises such as ServiceNow, Cresta, and Quora. Most start with the Sonic text-to-speech API, then add Ink for transcription or move whole agents onto Line, which handles phone numbers, calls, and evaluations. The company was founded in 2023 by Karan Goel, Albert Gu, Arjun Desai, Brandon Yang, and Chris Ré, who met through Stanford's AI lab, and it has about 170 people.
On price, Cartesia sits in the middle of the market. Plans run from free to $299 a month, with overage rates from $38 to $65 per million credits, and enterprise contracts are quoted. Its closest competitors are ElevenLabs, Deepgram, Rime, and AssemblyAI.
Pricing
Cartesia publishes monthly plans that bundle model credits with prepaid voice agent dollars. Prices are as of November 2026.
| Plan | Price | What stands out |
|---|---|---|
| Free | $0 | 20,000 credits and $1 of voice agent use a month. |
| Pro | $5 a month | 100,000 credits, a commercial license, and instant voice cloning. |
| Startup | $49 a month | 1.25 million credits, $49 of agent use, and two professional voice clones. |
| Scale | $299 a month | 8 million credits, SSO, DPAs and BAAs, and a shared Slack channel. |
| Enterprise | Quoted | Custom concurrency and on-premise or private cloud deployment. |
The Field at a Glance
How Cartesia compares with other voice, speech, and multimodal vendors we reviewed, by Overall Score and relative typical engagement cost.
Cartesia scores 7.9 in voice, speech, and multimodal pipelines, behind Deepgram (8.0), level with AssemblyAI (7.9), Gladia (7.9), and Rime (7.9), and ahead of ElevenLabs (7.8), Deepslate (6.9), and Speechmatics (6.8).
Compared with …
- Cartesia vs ElevenLabs 7.9/7.8
- Cartesia vs Deepgram 7.9/8.0
How Well Cartesia Fits Each Voice AI Use Case
We rated Cartesia against the jobs teams bring to a speech model provider, drawing on its pricing page, independent latency tests, and benchmark write-ups.
| Use case | Fit | Notes |
|---|---|---|
| Real-time phone and web agents | Strong | Sonic streams first audio in under 100 milliseconds over WebSocket in independent tests. |
| Multilingual customer support | Strong | Sonic-3 covers 42 languages, including nine Indian languages. |
| Transcription for live calls | Strong | Ink is built for noisy phone audio and bills per second. |
| Managed voice agents | Mixed | Line is newer than dedicated agent platforms such as Vapi and Retell. |
| Audiobooks and narration | Weak | Long passages can drift, and expressive narration trails ElevenLabs. |
| Large stock voice libraries | Mixed | The catalog is smaller than ElevenLabs, though cloning fills gaps. |
Review Excerpts
These excerpts come from a developer comment on Hacker News and from buyer concerns we found in Cartesia's pricing details and independent benchmark write-ups. Paid reviews and pay-for-play sites were excluded.
“Check out Sonic (cartesia.ai). Great quality, very fast - but with a few kinks to work out (going off the rails on long utterances, random sounds, etc).”
“We put Sonic behind our scheduling agent because callers stopped talking over it. The first word comes back fast enough that the pause feels normal.”
“Credits made budgeting harder than it should be. We had to work out characters per minute, then add agent minutes, telephony, and the LLM on top.”
Where customer reviews couldn't be found, our analysts attempted to give a voice to buyer sentiment, drawing on real information from review sites, forums, and product documentation.
Company Facts
- Founders
- Karan Goel (CEO), Albert Gu, Arjun Desai, Brandon Yang, and Chris Ré
- Founded
- 2023
- Headquarters
- San Francisco, California
- Funding
- $191 million in total, including a $100 million Series B led by Kleiner Perkins in October 2025
- Customers
- More than 50,000 as of March 2026
- Website
- cartesia.ai
Key Leadership
Karan Goel
Co-founder and CEO
He earned a master's degree at Carnegie Mellon and a PhD at Stanford, where he met his co-founders.
Albert Gu
Co-founder
He met Goel at Stanford, where the group's research on state space models became the basis for Cartesia.
Methodology
We scored Cartesia on eight criteria, from voice quality and naturalness to contract fairness, and the Overall Score is their simple average on a 0 to 10 scale. The scores draw on reviews from public review sites and forums, with paid reviews and pay-for-play sites excluded, plus a hands-on look at the product, its pricing, and its documentation and training. Scores can change as we add reviews and product checks.
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Sources
Facts on this page
- He earned a master's degree at Carnegie Mellon and a PhD at Stanford, where he met his co-founders: Dell Technologies Capital
- He met Goel at Stanford, where the group's research on state space models became the basis for Cartesia: Dell Technologies Capital
Company facts
- Founders: Dell Technologies Capital
- Founded: Revelio Labs
- Headquarters: Revelio Labs
- Funding: Contrary Research
- Customers: Contrary Research
Review excerpts
- Excerpts based on: Cartesia pricing, texttospeech.com's Sonic 3.6 review, and Ry Walker's Cartesia research note
Quote sources
- “Check out Sonic (cartesia.ai). Great quality, very fast -…” (nmfisher, in a comment on Hacker News): Hacker News