# Input tokens

Concept · [Building with AI](https://ecosystem.samcarlton.com/ai)

Also called: input token, prompt tokens, tokens in, input cost, input pricing

The [tokens](https://ecosystem.samcarlton.com/token) an AI product sends to the model on each request: the [instructions](https://ecosystem.samcarlton.com/prompt), the [conversation](https://ecosystem.samcarlton.com/session) so far, files and [tool results](https://ecosystem.samcarlton.com/tool-result). Providers charge less for them than for output, but they add up, because the whole conversation is usually sent again with every request.

**For example:** A chat that has run for an hour sends its long history along with every new question, so most of the bill is input tokens rather than answers.

## Connects to (9)

- [Token](https://ecosystem.samcarlton.com/token): In AI, a small chunk of text, roughly a word or a piece of a word, that an LLM reads and writes.
- [Output tokens](https://ecosystem.samcarlton.com/output-tokens): The tokens the model writes back.
- [Cache tokens](https://ecosystem.samcarlton.com/cache-tokens): Input tokens the provider did not need to process again because they matched the start of a recent request in its cache.
- [Prefix cache](https://ecosystem.samcarlton.com/prefix-cache): A provider feature that remembers the opening of a request it has just handled.
- [Context window](https://ecosystem.samcarlton.com/context-window): How much text an LLM can take into account at one time.
- [Model provider request](https://ecosystem.samcarlton.com/model-provider-request): One trip from an AI product to the model provider and back.
- [Usage-based pricing](https://ecosystem.samcarlton.com/usage-based-pricing): A way to charge where the bill follows how much the customer uses, instead of a flat fee.
- [Stateless](https://ecosystem.samcarlton.com/stateless): Describes something that keeps nothing between uses.
- [Tool result](https://ecosystem.samcarlton.com/tool-result): What comes back to the model after it uses a tool: a file's contents, the output of a command, a search result or an error.

Map view: https://ecosystem.samcarlton.com/input-tokens