Token (the unit AI reads and writes text in)
Japanese トークン
A token is the small chunk of text an AI model reads and writes. Prices and how much text fits at once are counted in tokens.
An AI does not read text letter by letter or word by word. It cuts the text into small chunks called tokens and reads and writes those. Just as a book can be counted in pages, the amount of text is counted in tokens. OpenAI's documentation gives roughly 4 characters per token for English, and the real number depends on the model and the language. The question and the answer together cannot go past the model's maximum length.
Watch out Prices are usually the token count multiplied by a per-token rate. The same text can become a different number of tokens on a different model. To get an exact count, use the token-counting tool the service provider offers.
Source: OpenAI API docs, Key concepts; Anthropic, Glossary