Cartesia Sonic
Ultra-low-latency commercial TTS API — expressive voices in under 90ms, built on state-space models.
About
Cartesia Sonic is a commercial text-to-speech API built on state-space models (SSMs, from the Mamba lineage — Cartesia's founding team). The headline is latency: under 90ms to first audio (provider-claimed), with expressive prosody, emotion/speed control, instant voice cloning, and an on-device option that runs with no internet connection. Sonic 2 is the current model generation.
It is closed and commercial — API-only (plus on-device licensing), billed per character, with a free tier (provider states 30k characters/month on free). The use case is realtime voice agents, IVR, and conversational AI where latency dominates. Independent third-party preference tests (Labelbox, cited by Cartesia) reportedly favored it on quality — treat vendor-cited evaluations with appropriate skepticism. Evaluate against ElevenLabs and Deepgram Aura for your latency/quality/cost tradeoff.
Specs
Context window
Pricing
Free quota
API access
Weights
Released
Benchmarks
Provider-cited (Labelbox blind preference tests): wins on voice quality, stability, and accuracy vs competitors — treat as vendor-cited, not independent. Latency <90ms to first audio is provider-claimed. No standardized public TTS benchmark scores.
Provider-reported unless a source says otherwise. Benchmarks are marketing-adjacent by nature — treat them as directional.
Use cases
Trust score — 6/10
Scored 6/10 (metrics tier). Serious team (Mamba/SSM lineage), genuinely distinctive latency story, and real commercial traction in voice agents. Docked four points: (1) closed and commercial — no weights, per-character metered pricing; (2) headline latency and quality claims are provider-claimed or vendor-cited, not independently verified; (3) as a 2024-era API generation the maintenance signal is aging (Sonic 2 is current but undated); (4) free-tier limits and pricing details change — verify before budgeting.
How the trust score is built
Full methodology →- Adoption · stars/downloads, log-scaled vs peers
- 8.0/10
- Maintenance · recency, releases, issue load
- 4.0/10
- Openness · license + docs
- 5.9/10
- Manual review · sanity read + red-flag check
- 7.0/10
- · provider-tier estimate — thinner evidence (no public adoption metric)
- · notable commercial voice-AI provider (Cartesia); no public adoption metric
- · released 895 days ago
- · manual review: real SSM-latency story and commercial traction; latency/quality claims provider-claimed or vendor-cited; license: closed commercial API — no weights; per-character billing