Voice agent cost
A voice agent is four paid services stacked on a phone call: listen (STT) → think (LLM) → speak (TTS) → the line itself (telephony). The LLM is often less than half the bill.
Turns = how many times the agent thinks per call. More agentic = more turns.
The formula
minutes = calls/day × call_length × 30
llm = calls × turns × tokIn/1M × P_in + calls × turns × tokOut/1M × P_out
stt = minutes × STT_rate tts = minutes × TTS_rate tel = minutes × tel_rate
per_call = (llm + stt + tts + tel) / (calls × 30)
Defaults reflect mainstream hosted APIs as of : Whisper-class STT, mid-tier neural TTS (~450 chars/min), typical US inbound voice-API rate. Token prices update daily from OpenRouter's API. Barge-in (interrupted speech) typically cuts billed minutes 10–20% — not modeled; treat the result as the conservative case.