Cartesia

Cartesia attacks the hardest constraint in voice AI: latency. Phone conversations break when responses lag past ~500ms; Cartesia's Sonic models generate natural speech in tens of milliseconds, low enough that AI agents can hold live calls without the awkward gaps that betray them. The research pedigree is serious — the founders created Mamba, the state-space architecture now used across the industry.

For developers building voice agents (call centers, tutoring, live translation, gaming), Cartesia is becoming the default pick where ElevenLabs is tuned more toward studio-quality narration. Voice cloning and changing round out the platform with consent-verified flows. The trade: an API-first product with no consumer app, and cloning guardrails mean tighter verification than casual tools. When your agent needs to speak — now — this is the infrastructure layer.