TTS API comparison 2026
Gradium TTS Beta vs async Flash v1.5 Gradium vs Async · text-to-speech for voice agents
Gradium TTS Beta ranks 1st of 112 with 76.8/100; async Flash v1.5 ranks 44th with 9.7/100: a gap of 67.1 points on the same public rules, built on Coval, Speko and Artificial Analysis.
Data checked on September 30, 2026 · Coval 30-day window ending October 1, 2026 · updated after each benchmark capture
Side-by-side benchmark
| Measure | Gradium TTS Beta | async Flash v1.5 |
|---|---|---|
| Overall score | 76.8/100 | 9.7/100 |
| Rank | 1st of 112 | 44th of 112 |
| Real-time speed /60 | 58.7 | 0 |
| Voice quality /20 | 7.8 | 7.6 |
| Accuracy /15 | 9.8 | 0 |
| Price /5 | 0.5 | 2.1 |
| P50 / median time-to-first-audio Coval, 30-day window | 47.2 ms | not measured |
| P99 time-to-first-audio (slowest turns) Coval, 30-day window | 108.8 ms | not measured |
| Latency consistency (standard deviation) Coval, 30-day window | 16.6 ms | not measured |
| P50 time-to-first-audio, US East Speko | 100 ms | not measured |
| Accuracy: word error rate (WER) Coval, 30-day window | 4.5% | not measured |
| Pronunciation robustness (0 to 1) Speko | 0.3 | not measured |
| Speech Arena Elo (blind listener preference) Artificial Analysis | not measured | 1133 |
| Naturalness (Elo) Speko | 1579 | not measured |
| Price per 1M characters Artificial Analysis | not measured | 10.1 USD |
Choose Gradium TTS Beta if…
- → Ranks 1st of 112 in the overall benchmark, against 44th for async Flash v1.5
Choose async Flash v1.5 if…
On the published benchmarks, async Flash v1.5 wins none of the measurements above against Gradium TTS Beta. This says nothing about features the benchmarks do not measure.
async Flash v1.5: all measurements →Frequently asked questions
- What is the difference between Gradium TTS Beta and async Flash v1.5?
- In the 2026 TTS API benchmark, Gradium TTS Beta ranks 1st of 112 with 76.8/100 and async Flash v1.5 ranks 44th with 9.7/100, a gap of 67.1 points on the same rules.
- Which is faster for real-time voice agents, Gradium TTS Beta or async Flash v1.5?
- On Coval's 30-day window ending October 1, 2026, the P50 time-to-first-audio is 47.2 ms for Gradium TTS Beta and not measured for async Flash v1.5; the P99 is 108.8 ms and not measured.
- On which criteria does async Flash v1.5 beat Gradium TTS Beta?
- async Flash v1.5 scores higher on Price (2.1 vs 0.5 out of 5).
- How are these two text-to-speech APIs scored?
- Both are scored by the same public rules: 4 criteria, 100 points (Real-time speed 60, Voice quality 20, Accuracy 15, Price 5), computed from three independent benchmarks: Coval, Speko and Artificial Analysis. A measurement a benchmark does not publish counts zero, and the model page says why.
- Can these numbers be checked?
- Yes. Each model page lists every measurement with its source and date, and links to the benchmark page it comes from. The rules are on the methodology page.