Agent memory vs Context window

Why they differ

The context window is what the model sees right now and is lost when the chat ends; agent memory is stored outside and survives to be read in again.

Agent memory

Agents & tools

Notes an AI agent saves outside the model and reads back later, so it can carry facts and past work from one chat to the next.

Formal

Storage outside the model - plain files, a database or a vector database - into which an agent writes facts, choices and summaries, and from which the most useful items are fetched back into the context window at the start of later tasks.

In plain English

Like a nurse's notebook passed between shifts - whoever starts work reads the notes first, because nobody remembers yesterday on their own.

In practice

A developer at a pension fund works with a coding assistant that saves notes such as “member numbers must never appear in logs”; a week later, in a fresh chat, it reads them back before touching the code.

Why it matters

It makes agents more useful over time, but saved notes are trusted later - a planted false note or a stored secret can outlive the chat that caused it.

Context window

Language models

The most text, counted in tokens, that a language model can take in and keep in view at one time, including its own answer.

Formal

The fixed limit on how many tokens a language model can handle in one go; the prompt, earlier turns of the chat, added documents and the answer must all fit inside it.

In plain English

Like the size of a desk - everything the model is working on has to fit on it, and when it is full, something has to be cleared away to make room.

In practice

A clerk in a region works with an AI assistant through a long afternoon; it starts ignoring the format rules given at the start, because the chat app has cut the oldest messages to keep the rest inside the context window.

Why it matters

It limits how much a model can weigh in one answer, and everything inside it - including text from a file nobody checked - shapes that answer.

Shared connections

Context engineering