Per million tokens
How model prices are quoted: dollars per million tokens, charged separately for what you send and what comes back.
Also written: per mtok, /MTok, per 1M tokens.
Prices are quoted per million tokens, in each direction. A model at $3 in and $15 out charges you $3 for every million tokens you send it and $15 for every million it generates.
Two things surprise people. First, output is usually three to five times the input rate, so a model that is cheap to ask can be expensive to answer — a long reply costs more than a long question. Second, a million tokens is not very much: it is roughly one mid-sized codebase, or one long afternoon with a coding agent.