No system runs on a single model. Each one is a composition of these six layers, chosen so that latency, cost, and consequence are matched to the task.
Fast general LLM
0.4–2sDrafting, classification, qualification, and short-form replies where a response has to land in under two seconds.
Typical models: Gemini 2.5 Flash class
Most revenue-critical steps — qualify a lead, write a text-back, tag an inbound — are short, well-specified tasks. A fast model with a tight prompt beats a slow model with a vague one, and the cost per action stays low enough to run on every inbound.
Reasoning LLM
3–20sMulti-step work: proposal drafting, objection handling, long-context summarisation, and anything where a wrong answer is expensive.
Typical models: Gemini 2.5 Pro / GPT-5 class
Used only where the extra thinking pays for itself. A quote follow-up that reasons about the job scope converts better than a template; a missed-call text does not need to reason at all.
Embedding model
<200msTurning your documents, past jobs, price lists, and won deals into vectors so the system can retrieve the right context before it writes.
Typical models: Text embedding models, 768–3072 dimensions
This is what stops the AI inventing your prices. Retrieval grounds each response in your own approved material rather than the model's memory of the internet.
Speech-to-text
~300ms streamingTranscribing inbound calls and voicemails in real time so a voice agent can act on what was actually said.
Typical models: Whisper-class streaming ASR
Trade accuracy against latency deliberately: a live voice agent needs streaming partial transcripts, while an after-hours voicemail can use the slower, more accurate batch pass.
Text-to-speech
~200ms to first audioSpeaking the agent's side of a phone call in a consistent, named voice.
Typical models: Neural TTS with cloned or stock voices
Time-to-first-audio matters more than raw fidelity on the phone. Silence over 800ms reads as a dropped call and callers hang up.
Deterministic rules & scoring
<10msBusiness logic that must never vary: budget thresholds, service areas, compliance blocks, routing, and escalation.
Typical models: Plain code, no model
Anything with a legal, financial, or safety consequence is coded, not prompted. A model decides how to phrase it; code decides whether it is allowed to happen.