---
title: Context — Claude basics, lesson 2
description: Context is everything Claude can see right now, its working memory for the session: what fills the window, what the summary keeps, and three commands.
url: https://instibrain.ai/guides/claude-basics/context
updated: 2026-10-28
site: https://instibrain.ai/llms.txt
---

lesson 2 of 7 · claude basics

# Context.

Context is everything Claude can see right now. It is Claude's working memory for this session.

## new words

**Context window**
The space that holds the context. It has a fixed size.

**Token**
A small piece of a word. Claude measures the window in tokens.

**Summary**
When the window is almost full, Claude replaces the old conversation with a short summary of it. Claude Code calls this compaction.

## the lesson

Everything goes into the window: your messages, Claude's answers, every file Claude reads, the output of every command, and the instructions it loads at the start.

When the window is almost full, Claude writes the summary and goes on from it. The summary keeps your requests. Details from early in the conversation can get lost.

A new session starts empty. Claude does not remember yesterday's conversation. Anything that must hold every day belongs on a page, never only in the chat.

| Command | What it does |
| `/context` | Shows what fills the window now. |
| `/compact` | Writes the summary now. Add what to keep: `/compact keep the pricing page work`. |
| `/clear` | Starts an empty conversation. Use it when you switch to a different task. |

An example session on Opus 5.5, whose window holds 1 million tokens. The split is an example, not a measured session.

## try it

In your Claude window, type this and press Enter:

```
/context
```

## you should see

- A grid of coloured squares, then a list of what uses the space.
- Under Memory files, the instruction files that loaded at the start. Lesson 4 explains them.

---

instibrain is made by WebWork AI, Inc. Everyone uses the same models · the difference is what yours knows.