Input token
Also: input tokens, prompt tokens
A piece of text you send to the model, including documents and instructions.
The fuller definition
An input token is a token supplied to a model as part of the material it processes, such as instructions, conversation, or source text.
2,000
8,000
4,000
2,000
A hypothetical 16,000-token budget. Real limits and token accounting depend on the model. Saving a file outside this budget does not mean it is present in the current context, and a passage inside it is not guaranteed equal attention.
A concrete example
A long uploaded passage can add many input tokens even when the question is short.
The distinction that matters
The application's file size and the exact model input are not necessarily the same thing.
Related terms
Token
A piece of text, often part of a word, that the model actually works with. Models read and write tokens, not whole words.
Prompting & contextOutput token
A piece of text the model writes. Output is usually priced higher than input.
FoundationsContext window
How much text the model can hold in mind at once: your question, the documents you added, and the conversation so far. Anything outside it is invisible to the model.
Where it is taught
Give AI a brief it can actually followSource and further reading
Anthropic · Context engineeringThe definition and example are written for this library. The link gives background, official documentation or legal authority as labelled. Legal scope depends on the jurisdiction and current text; product features depend on release and settings.