Voice Provider Layer

The table nobody publishes

A 10-minute session, 20 turns:

| Arrangement | Cost | Latency | | |---|---|---|---| | Free / keyless | $0.0000 | ~1050ms | no key, on-device | | Fully on-device | $0.0000 | ~1050ms | audio never leaves the machine | | Cheapest hosted | $0.1278 | ~480ms | | | Balanced | $0.2167 | ~960ms | | | Fastest (realtime) | $3.0000 | ~320ms | |

Realtime costs 23× the cheapest hosted pipeline — and it is the default arrangement in most voice-assistant code. Sometimes that latency is worth paying for. It should be a decision, not a default you inherited.

The counterintuitive finding

The voice can cost more than the intelligence. On a balanced 20-turn session, TTS runs $0.12 and the model runs $0.09. Everyone assumes the LLM is the expensive part, so nobody scrutinizes the TTS choice — and the premium voice option is roughly 12× the alternatives. Hearing, meanwhile, is nearly free.

What you get

• One interface over STT, LLM, TTS, and bundled realtime providers.
• A pricing catalog with per-stage cost, typical latency, keyless/on-device flags, and an honest caveat on every "free" or "best" option — browser speech quality varies by browser, small local models can't tool-call reliably, premium voices are priced like it.
• `estimateCost(stack, session)` for your session shape, `recommendStack(preference)` across six preferences, and `compareStacks()` which generates the table above.

Honest about the numbers

Every catalog entry carries `asOf` and its pricing source. List prices move; these are estimates for comparison and the code never presents them as a bill.

Proof

149 tests, including guards that the estimator throws on an unknown provider rather than silently costing zero, and refuses a provider used in the wrong stage.

Delivery

Source delivered as a private repository invite within 24 hours of purchase. Single-product commercial license: use and modify in any number of products; no redistribution or resale of the source.

Interface

What you call, and what comes back. Types and signatures only — the implementation ships with the source.

  export const byStage = (stage: ProviderInfo["stage"]): CatalogEntry[];
  export const findProvider = (id: string): CatalogEntry | undefined;
  export function estimateCost(choice: StackChoice, session: SessionShape = TYPICAL_SESSION): CostBreakdown;
  export function recommendStack(preference: Preference): StackChoice;
  export function compareStacks(session: SessionShape = TYPICAL_SESSION): StackComparison[];

  export type Stage = "stt" | "llm" | "tts" | "realtime";
  export type AnyProvider = SttProvider | LlmProvider | TtsProvider | RealtimeProvider;