Token
The unit AI models count text in. A token is a chunk of a word, sometimes a whole short word, sometimes a piece of a long one. Tokens are what you pay for and what the context window counts, which is why limits are stated in tokens and never in words or pages.
In plain English
The model doesn’t read words. It reads chunks. “Unbelievable” might be three chunks. “The” is one. Those chunks are tokens, and everything about AI pricing and limits is counted in them.1
In the real world
- The usage meter in your account.
- “Context window: 200K tokens” on a pricing page.
- The moment a long chat says you’ve hit a limit.
When to use it
- Reading a pricing page. Input and output tokens are often priced differently.
- Estimating whether a document fits. The system prompt, your files, the history, and the reply all count.2
When not to use it
Don’t try to count them by hand. Nobody does. Know that long pastes and long answers cost more, and move on.
Good, bad, ugly
- Good: a fair unit. You pay for what the model actually processes.
- Bad: it’s invisible until the bill or the limit shows up.
- Ugly: the same text costs a different number of tokens on different models, so comparisons are never clean.1
Key facts
- One token is
- Part of a word, usually. How many characters it covers depends on the model and the language.
- Shows up in
- Pricing, usage meters, and context window limits
- Both directions
- Your input and the model's reply are both counted
Common questions
How many tokens is a page?
It depends on the model and the language, so no fixed number. Anthropic notes newer Claude models count tokens differently from older ones. Treat any rule of thumb as rough.
Why does it matter to me?
Because limits and bills are in tokens. A long paste eats the context window and the budget, and so does a long reply.
Do images and files use tokens?
Yes. Attached documents and images count toward the context window alongside your text.
References
- Glossary: TokensAnthropic, Claude Platform DocsView source
- Context windowsAnthropic, Claude Platform DocsView source