One conversational turn, voice-to-voice
same six builds as the cost table · request sent to response complete · cascade bars sum per-leg medians (n=3)
STT
LLM
TTS
speech-to-speech
green bar ends at the slowest measured turn; the dashed line inside marks the fastest
0
1
2
3
4
5
6
7
8
Cascade, budget
qwen3-asr + deepseek + google-std
1.6 s
2.6 s
0.7 s
4.9 s
Cascade, mainstream
4o-mini-transcribe + deepseek + tts-1
0.8 s
2.6 s
2.2 s
5.6 s
Speech-to-speech, mini
gpt-realtime-2.1-mini, 4 live turns
1.6–2.1 s
Cascade, SOTA brain
4o-mini-transcribe + gpt-5.6 + tts-1
0.8 s
2.7 s
2.2 s
5.7 s
Cascade, premium
whisper-1 + gemini-3.7 + chirp3-hd
1.9 s
4.5 s
1.3 s
7.7 s
Speech-to-speech, 2.1
gpt-realtime-2.1, 8 live turns
1.7–2.1 s
seconds
Measured 2026-08-17 through the Synthorai gateway · before VAD end-of-speech wait and playback · streaming legs can overlap the LLM and TTS segments