Tokens & Pricing
Context window
The maximum number of tokens a model can consider at once — input plus output combined. It's the model's working memory for a single call. Go over it and the request fails or silently drops the oldest content.
Example
A model with a 200,000-token context window can hold roughly 150,000 words in mind at once — a small book. A long agent run that keeps appending to the conversation can fill that window and start paying to re-send the same history on every step.
Related terms
Token
The unit AI models read and write, and the unit you're billed in. A token is a chunk of text — often a word, a piece of a word, or a punctuation mark. Models don't see letters or words; they see tokens.
Prompt compression
Shrinking a prompt to fewer tokens without losing what the model needs — trimming boilerplate, deduplicating context, summarizing history — so you pay for less input.
AI agent
An AI system that doesn't just answer once but works toward a goal over multiple steps — planning, calling tools, reacting to results, and looping until done. Because an agent can make many calls per task, it can spend far more than a single prompt, and it spends without a human watching each step.