What a live LLM simulation actually costs
A Parlour party runs five or six minutes on roughly 250–300 evaluation calls of about 3,000 input tokens each, which is three to four cents. Every watcher of a room shares one party, so the bill does not grow with the audience.
- A live party
- ~250–300 calls, ≈3–4¢
- Per call
- ~3,000 input tokens, input-billed only
- Headless dry-run
- 146 calls, ≈1.8¢
- The village
- ≈£0.40 an hour at full tilt
- Cost per extra watcher
- zero
Why the audience is free
A room is one party held in server memory and streamed to everyone looking at it. The model is paid for once per beat however many people are watching, so the marginal cost of a watcher is a socket.
That is a design decision with teeth. It is why the site can be public with no login, and why the app is pinned to one replica.
Where the tokens go
Almost all of it is input. Each call sends one character's view of the room (their condition, who is reachable, what they have seen, the arithmetic) and gets back nine scored answers, which is a trivial payload. Jev bills input only, so the cost is essentially how much state you show, times how often you ask.
Both of those are the tuning dials. Asking more people more often is the expensive direction, which is why the village budgets its brain instead of asking four hundred people anything.
Putting it on screen
The running total sits on the party UI like a buy-in. A cost you can watch accumulate is an honest thing to show, and in practice it is the best argument that the simulation is small: a night out for eight people, for the price of nothing.
Read next
Two guard rails on a public LLM toy
Nothing ticks in a room nobody has opened. A party already under way plays to its end and then stops. A rolling hourly cap drops a room to the house brain past a fixed dollar figure.
Running it through the Vercel AI Gateway
Parlour reaches Jev through the Vercel AI Gateway with one server-side key, and reads live per-token prices from the Gateway's model catalogue, so the cost counter on screen is a real number and not a constant.
One party in memory, streamed to everyone
A room is a single party held in server memory and streamed to every watcher, so everybody sees the same betrayal at the same moment and the model is paid for once per beat however many people are looking.
Four hundred agents, a few dozen guts
The village asks the model about roughly thirty people on a cadence, plus anyone at all who is facing a real choice, capped at two calls a second across the whole valley.