TTS API comparison 2026
Gradium TTS vs Out of Set Airy TTS Gradium vs Out of Set · text-to-speech for voice agents
Gradium TTS is in the Headroom speed tier (P95 under 120 ms); Out of Set Airy TTS is in the Visible delay speed tier (P95 over 293 ms). Below, each measure side by side with its source; a model leads on a measure only beyond the tie rule. No combined score, no overall winner.
Figures as of October 27, 2026 · Coval, Speko, Artificial Analysis, Cekura
Side by side
| Measure | Gradium TTS | Out of Set Airy TTS |
|---|---|---|
| Speed tierCoval P95, 30 days | Headroom | Visible delay |
| Median time to first audioCoval, 30-day window | 54 ms | 212 ms |
| P95 time to first audio (slow turns)Coval, 30-day window | 104 ms | 454 ms |
| Time to first audio, board chartSpeko, US East | 55 ms | 146 ms |
| Time to first audio, full sentence (median)Cekura | 76 ms | — |
| Time to first audio, text streamed word by word (median)Cekura | -64 ms | — |
| Naturalness EloSpeko | 1,592 | 1,416 |
| Listener Elo (95% interval)Artificial Analysis | 1,174 ±13 | not rated |
| Numbers and dates (0 to 1)Speko | 0.27 | 0.5 |
| Hard passages pronounced correctly (95% interval)Artificial Analysis, human reviewers | not tested | not tested |
| Reading accuracy on hard textCekura, transcriber-scored | 79.5% | not rated |
| List price per 1M charactersCoval, Speko, Artificial Analysis, Cekura | $36 to $57.8 | $3.67 |
In bold: the model ahead on that measure. “tie”: latencies within 10 ms, or Elo scores whose 95% intervals overlap.
Where Gradium TTS is ahead
- →Median time to first audio: 54 ms vs 212 ms (Coval, 30-day window)
- →P95 time to first audio (slow turns): 104 ms vs 454 ms (Coval, 30-day window)
- →Time to first audio, board chart: 55 ms vs 146 ms (Speko, US East)
- →Naturalness Elo: 1,592 vs 1,416 (Speko)
Where Out of Set Airy TTS is ahead
- →Numbers and dates (0 to 1): 0.5 vs 0.27 (Speko)
- →List price per 1M characters: $3.67 vs $36 to $57.8 (Coval, Speko, Artificial Analysis, Cekura)
Frequently asked questions
- What is the difference between Gradium TTS and Out of Set Airy TTS?
- Gradium TTS (Gradium) is in the Headroom speed tier (P95 under 120 ms); Out of Set Airy TTS (Out of Set) is in the Visible delay speed tier (P95 over 293 ms). Gradium TTS leads on median time to first audio, P95 time to first audio (slow turns), time to first audio, board chart and naturalness Elo; Out of Set Airy TTS leads on numbers and dates (0 to 1) and list price per 1M characters. No combined score is computed.
- Which is faster for real-time voice agents, Gradium TTS or Out of Set Airy TTS?
- On Coval's 30-day window as of October 27, 2026, the median time to first audio is 54 ms for Gradium TTS and 212 ms for Out of Set Airy TTS (Gradium TTS ahead by 159 ms); the P95, the slow turn, is 104 ms and 454 ms (Gradium TTS ahead by 350 ms). Gaps under 10 ms are ties.
- Which sounds more natural, Gradium TTS or Out of Set Airy TTS?
- Speko naturalness: 1,592 for Gradium TTS, 1,416 for Out of Set Airy TTS. Artificial Analysis listener Elo: 1,174 ±13 and not rated. The two sources use different listeners and can disagree.
- How are these two text-to-speech APIs compared?
- Speed first, on Coval's median and P95 time to first audio; then voice quality (Speko, Artificial Analysis), accuracy on numbers and dates (Speko) and list price. Latencies within 10 ms and Elo scores whose intervals overlap are ties. Scores from different benchmarks are never added into one number.
- Can these numbers be checked?
- Yes. Each model page lists every measurement with its source and the date of the reading, and links to the benchmark page it comes from. The rules are on the methodology page.