You pay per token, quoted per-million (per Mtok), at two rates: input (read) and output (written, ~5× dearer). Two ratios run the whole page — output ≈ 5× input, and the strong tier costs 15–75× the cheap tier. Every cost lever below is one of three numbers getting bigger: tier, input tokens, output tokens.
Two levers set your bill: output tokens cost ~5× input tokens, and the strong tier costs up to 15× the cheap tier — model choice is the biggest single knob.
Every provider prices by the token, quoted per million tokens (per Mtok), with two rates: one for input (tokens the model reads) and a higher one for output (tokens it writes). The bill for one call is just:
Two facts fall out of this and drive every optimization in the rest of the page. First, output is the expensive half — roughly 5× the input rate across the frontier lineups. Second, the model tier matters enormously: the strongest models cost 15–75× the cheapest. Here is Firstpass's built-in default price table (a calibration knob you override in config — real prices move, so treat these as illustrative defaults):
Model
Input · $/Mtok
Output · $/Mtok
Tier
anthropic/claude-haiku-4-5
1.00
5.00
cheap
anthropic/claude-sonnet-5
3.00
15.00
mid
anthropic/claude-opus-4-8
15.00
75.00
strong
openai/gpt-4.1-mini
0.40
1.60
cheap
openai/gpt-5.5
5.00
15.00
strong
google/gemini-3.1-flash
0.35
1.05
cheap
google/gemini-3.1-pro
3.50
10.50
mid
Put numbers on it. That first /orders question — 32 in, 14 out — costs almost nothing on any model. But the ratio between tiers is the whole game: send it to the strong model instead of the cheap one and you pay ~15× more for a one-line answer you'd have gotten either way.
$0.0001
the /orders question on haiku (32 in · 14 out)
$0.0015
same question on opus — ~15× more, same answer
$0.0102
a 200-in / 2 000-out reply on haiku
98%
of that reply's cost is the output half
The module that carries the whole page A model call's cost is set by three numbers you can influence: which tier you send it to, how many input tokens you make it re-read, and how many output tokens it writes. Every module below is one of those three quietly getting bigger — and every Firstpass move in Part B is one of them getting smaller.
Common mistake “Send everything to the best model, it's only fractions of a cent.” True for one call — that opus answer above is $0.0005. But an agent makes hundreds of calls, each re-reading a growing transcript (multi-turn), and the easy calls vastly outnumber the hard ones. Paying the 15–75× tier premium on every one of them is how a fractions-of-a-cent call becomes a four-figure monthly bill. The premium is only worth it on the calls that actually need it.
Cost = tier × (input tokens + ~5× output tokens); the strong tier is 15–75× the cheap one, so which model answers is the biggest single lever.