Meet Sonic-3.5 and Ink-2.

The #1 real-time speech and transcription models purpose-built for voice agents. One API, no tradeoffs between quality and speed.

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Research

Architecting AI that learns and interacts like humans

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● Talk to voice agent

Today's AI learns from data curated by humans. We're building AI that learns from the world as it is, and gets better with every interaction.

Sonic-3.5

Streaming text-to-speech with natural, expressive voices in 40+ languages.

Ink-2

Real-time transcription tuned for low-latency voice agents.

One API

No tradeoffs between quality and speed, deployed on your terms.

Live transcription
00:01Hi, I'd like to check on my order.final
00:04Sure — can I get the order number?final
00:07It's 4-8-2-2-1.final
00:09Thanks, pulling that up now…partial
Controls

Fractional radii, one green

Primary Secondary Muted Large CTA Disabled Chip Accent
Learn more Try Cartesia Try Cartesia ← on-green pair (last is hover)
Primary Secondary Muted ← hover state (0.15s)
Enter your email Focused input Focused button ← focus: border #a1a1a1 + 3px ring

Controls are 36px at 7.2px radius; hero CTAs are 44px at a squarer 4px. Primary is forest green #004e23 with #fefefe text; secondary is canvas with a 1px #e4e3db border and hovers to #f1f0ec. Focus sets border #a1a1a1 plus a 3px ring; disabled drops to opacity 0.5.

Typography

Serif display, grotesque everything else

Display (hero) · PP Kyoto · 48/48 · 500 · -0.48pxMeet Sonic-3.5
Headline (h1) · PP Kyoto · 36/45 · 500 · normalArchitecting AI
Section (h2) · PP Kyoto · 24/30 · 500 · normalFrontier research, deployed
Body / sub (h3) · ABC Diatype · 16/24 · 400Purpose-built for real-time voice agents.
Nav / button · ABC Diatype · 16/24 · 500Products · Resources · Pricing
Large CTA label · ABC Diatype · 16 · 500 · +0.14pxTry Cartesia
Palette

Warm neutrals and one forest green

Text
ink#1e1c1a
muted#525150
muted-2#535150
white#fefefe
Surfaces & borders
canvas#f9f9f8
paper#fafaf8
surface#f3f2ef
surface-2#f1f0ec
border#e4e3db
border-hover#dfdcd7
ring#a1a1a1
Accent
green#004e23
green-bright#309d4b
Depth and motion

Shadowless, drawn with rules

4px
5px
5.76px
7.2px ctrl
10.08px
15.84px panel
1px #e4e3db hairline
repeating rule grid
-45deg hatch gutter
backdrop blur(8px)

There are no real shadows — the only box-shadow is a transparent ring placeholder. Structure is the 1px #e4e3db hairline plus decorative repeating-linear-gradient rule grids and hatch. Motion: house 0.15s cubic-bezier(.4,0,.2,1), expo-out reveals at cubic-bezier(.22,1,.36,1), 18 keyframes including a transcription feed and a four-bar audio meter, and a real prefers-reduced-motion block.