TTS API comparison 2026
Deepgram Flux TTS vs OpenAI GPT-4o mini TTS Deepgram vs OpenAI · text-to-speech for voice agents
Deepgram Flux TTS is in the Fast enough speed tier (P95 from 138 ms to 263 ms); OpenAI GPT-4o mini TTS is in the Visible delay speed tier (P95 of 320 ms or more). 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.
Data read October 22, 2026 · Coval, Speko, Artificial Analysis
Side by side
| Measure | Deepgram Flux TTS | OpenAI GPT-4o mini TTS |
|---|---|---|
| Speed tierCoval P95, 30 days | Fast enough | Visible delay |
| Median time to first audioCoval, 30-day window | 200 ms | 950 ms |
| P95 time to first audio (slow turns)Coval, 30-day window | 263 ms | 5,055 ms |
| Time to first audio, board chartSpeko, US East | 118 ms | 518 ms |
| Naturalness EloSpeko | 1,550 | 1,424 |
| Listener Elo (95% interval)Artificial Analysis | 1,052 ±13 | not rated |
| Numbers and dates (0 to 1)Speko | 0.2 | 0.44 |
| List price per 1M charactersCoval, Speko, Artificial Analysis | $45 | $20 |
In bold: the model ahead on that measure. “tie”: latencies within 10 ms, or Elo scores whose 95% intervals overlap.
Where Deepgram Flux TTS is ahead
- →Median time to first audio: 200 ms vs 950 ms (Coval, 30-day window)
- →P95 time to first audio (slow turns): 263 ms vs 5,055 ms (Coval, 30-day window)
- →Time to first audio, board chart: 118 ms vs 518 ms (Speko, US East)
- →Naturalness Elo: 1,550 vs 1,424 (Speko)
Where OpenAI GPT-4o mini TTS is ahead
- →Numbers and dates (0 to 1): 0.44 vs 0.2 (Speko)
- →List price per 1M characters: $20 vs $45 (Coval, Speko, Artificial Analysis)
Frequently asked questions
- What is the difference between Deepgram Flux TTS and OpenAI GPT-4o mini TTS?
- Deepgram Flux TTS (Deepgram) is in the Fast enough speed tier (P95 from 138 ms to 263 ms); OpenAI GPT-4o mini TTS (OpenAI) is in the Visible delay speed tier (P95 of 320 ms or more). Deepgram Flux TTS leads on median time to first audio, P95 time to first audio (slow turns), time to first audio, board chart and naturalness Elo; OpenAI GPT-4o mini 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, Deepgram Flux TTS or OpenAI GPT-4o mini TTS?
- On Coval's 30-day window read on October 22, 2026, the median time to first audio is 200 ms for Deepgram Flux TTS and 950 ms for OpenAI GPT-4o mini TTS (Deepgram Flux TTS ahead by 750 ms); the P95, the slow turn, is 263 ms and 5,055 ms (Deepgram Flux TTS ahead by 4,792 ms). Gaps under 10 ms are ties.
- Which sounds more natural, Deepgram Flux TTS or OpenAI GPT-4o mini TTS?
- Speko naturalness: 1,550 for Deepgram Flux TTS, 1,424 for OpenAI GPT-4o mini TTS. Artificial Analysis listener Elo: 1,052 ±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.