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The short answer
The context window is how much text Claude can consider at once — your conversation, uploaded documents and its own replies, all together.
Claude Opus 5 and Sonnet 5 support a 1M-token context window on all paid plans. Older models get 500K, and outside those the standard is 200K — roughly 500 pages of text.
| Model | Context window | Availability |
|---|---|---|
| Opus 5, Sonnet 5 | 1M tokens | All paid plans |
| Opus 4.8 / 4.7 / 4.6, Sonnet 4.6 | 500K tokens | All paid plans |
| Other models | 200K tokens | Standard |
What a token is, briefly
A token is roughly three-quarters of a word. So:
- 200K tokens ≈ 500 pages — a long book
- 500K tokens ≈ 1,250 pages
- 1M tokens ≈ 2,500 pages, or a substantial codebase
Everything counts against it: your messages, uploaded files, and Claude's own responses. A long conversation consumes the window even without attachments.
In Claude Code
When using Claude Code on Pro, Max, Team or Enterprise, the 1M-token window is available on Sonnet 5, Fable 5, Opus 5, and the 4.6–4.8 Opus models.
One wrinkle worth knowing: Pro users need usage credits enabled to access the 1M window on Opus models. If you're on Pro and it seems unavailable, that's usually why.
Why bigger isn't automatically better
Two reasons people miss.
It costs you. Every message re-sends the whole conversation. A thread that has filled a large window is expensive per reply, which is a common and invisible cause of hitting usage limits. Starting a fresh conversation when you change topic genuinely saves allowance.
Signal-to-noise. Filling a window with marginally relevant material doesn't reliably improve answers. Ten pages of exactly the right context beats a thousand pages of nearly-right context.
Better than filling the window: put reference material in a Project. Retrieval pulls the relevant parts as needed instead of carrying everything in every message.
On the API
Building on the platform rather than using the app: premium pricing applies to prompts over 200K tokens — $10 per million input tokens and $37.50 per million output.
Worth designing around. Retrieval that sends 50K relevant tokens is dramatically cheaper than sending 500K and hoping.
Common questions
How big is Claude's context window?
How many pages is 1M tokens?
Does a longer conversation cost more?
Why can't I access the 1M context window on Pro?
Try it on a real document
The free tier is enough to see how Claude handles a long document — that's the fastest way to judge whether the bigger window matters to you.