Cost & caching

Dustav runs a frontier model over every email a business receives, and bills for exactly what that costs. That makes cost a first-class engineering surface — not because we build cheap, but because a metered product has to be worth its meter, visibly.

The price is part of the product

Every model call is priced as it happens and written to the same records that render Usage & cost — the headline and the per-call detail are computed from one source, so they can't disagree. Showing the price is a forcing function we point at ourselves: a $0.02 read that saved you ten minutes of data entry argues for itself; a read that costs too much for what it did is a bug we can see as fast as you can.

The cached prefix — why reading is cheap

The dominant cost lever in an agent is how much context each call re-sends. Model providers discount cached prefixes steeply — but only if the bytes are identical, in order, every time. So Dustav's contexts are built as deliberate spans:

• The universal span — the tool definitions and operating rules shared by every business — is byte-identical across the whole platform, and therefore one warm cache entry for everyone. Your 9am email rides a prefix already warmed by the platform itself.
• The per-business span — your facts, your workflows, your voice — caches per business, stable across a sync's reads.
• The volatile tail — this email, this thread — is the only part paid at full rate.

Keeping those spans stable is a real discipline (a single byte of drift cold-starts the cache), and it's the difference between "a frontier model on every email" being a stunt and being a viable product.

Bounded, always

The other half of cost engineering is the ceiling. Every unit of work — a chat turn, a single email's read — is gated against your balance before it starts and debited after it completes; per-task caps bound the pathological case beneath that. There is no path that bills while nothing is watching.

What we won't do

We don't degrade the reading to save money — no skimming mode, no cheap-model triage deciding what deserves the real read. Dustav is premium on purpose: the fidelity is the product, and the engineering above is what makes fidelity affordable, rather than economizing it away.