Data read October 27, 2026
Gradium TTS vs Cartesia Sonic 3.5: TTS API comparison
On P95 latency, Gradium TTS is faster: 104.3 ms for Gradium TTS against 390.5 ms for Cartesia Sonic 3.5.
On Artificial Analysis listener Elo (1,174 against 1,190) the 95% intervals overlap, so the two are statistically tied. List price per million characters: $36 to $57.80 for Gradium TTS, $39.20 to $50 for Cartesia Sonic 3.5.
Gradium TTS is ranked 1 of 23; Cartesia Sonic 3.5 is ranked 15 of 23. Every comparison on this site uses Gradium TTS as its fixed reference, and no page says either model is better overall.
| Measure | Gradium TTS | Cartesia Sonic 3.5 | Ahead |
|---|---|---|---|
| Rank in the multilingual speed ranking | 1 | 15 | n/a |
| Speed tier | Headroom | Visible delay | n/a |
| Median time to first audio (ms), lower is faster | 53.7 | 279.3 | Gradium TTS |
| P95 time to first audio (ms), lower is faster | 104.3 | 390.5 | Gradium TTS |
| Listener Elo (Artificial Analysis) | 1,174 | 1,190 | Tie |
| Customer-service Elo (Artificial Analysis) | 1,241 | 1,203 | Tie |
| Naturalness (Speko) | 1,592 | 1,574 | Gradium TTS |
| Naturalness estimate (Cekura, 1 to 5) | 4.51 | 4.41 | Gradium TTS |
| Reading accuracy (Cekura) | 79.5% | 73.1% | Gradium TTS |
| Hard passages judged correct (Artificial Analysis) | n/a | 68.8% | n/a |
| Lowest list price per 1M characters (lower is cheaper) | $36 to $57.80 | $39.20 to $50 | Gradium TTS |
| Languages tested (Artificial Analysis, Speko) | 4 | 15 | Cartesia Sonic 3.5 |
| Access | Proprietary | Proprietary | n/a |
| Streaming status | Measured | Measured | n/a |
Ahead is computed from the figures only. A latency gap under 10 ms is a tie; listener Elo values whose 95% intervals overlap are a tie. A measure one benchmark does not hold is n/a for that model and is never estimated. See the methodology and each model page for sources.
Frequently asked questions
- Is Gradium TTS faster than Cartesia Sonic 3.5?
- On P95 latency, Gradium TTS is faster: 104.3 ms for Gradium TTS against 390.5 ms for Cartesia Sonic 3.5.
- How do Gradium TTS and Cartesia Sonic 3.5 compare on voice quality?
- On Artificial Analysis listener Elo (1,174 against 1,190) the 95% intervals overlap, so the two are statistically tied.
- Which is cheaper, Gradium TTS or Cartesia Sonic 3.5?
- List price per million characters: $36 to $57.80 for Gradium TTS, $39.20 to $50 for Cartesia Sonic 3.5.