OpenAI GPT-4o mini TTS OpenAI · text-to-speech (TTS) API

Speed

On Coval's 30-day window ending October 22, 2026 (3,145 runs from US East), OpenAI GPT-4o mini TTS starts speaking after 949.5 ms on a typical turn (median) and 5,054.7 ms on a slow turn (P95, the slowest one in twenty). That P95 is 32nd lowest of the 32 models Coval measures, which puts it in the Visible delay tier: the voice becomes a visible part of the delay. Speko's board plots it at 518 ms time to first audio from US East; its model page reports a 691 ms sweep.

Voice quality

Speko rates its naturalness at 1,424 Elo from blind A/B votes on phone-agent lines (36th highest of the 43 models Speko rates).

Numbers and dates

Speko's pronunciation test on numbers, dates and currency scores it 0.44 on a 0-to-1 scale (11th highest of the 30 models Speko scores). This is the accuracy measure used here; Coval's word error rate separates models too little to compare them.

Price

Speko lists about $20. List prices, as each source prints them.

Languages tested

Tested in Spanish, German, French, Japanese, Chinese, Korean, Filipino, Norwegian and Thai by Artificial Analysis or Speko. A language missing here was not tested, which does not mean it is unsupported.