Anthropic held the context window at 200K for 20 months
How has Claude's context window actually changed?
Every lab talks about context windows as though they climb steadily. Anthropic's did not. It moved three times in forty months, and between the second and third move it sat at exactly 200,000 tokens across seven consecutive releases.
That stretch covers Claude 3 Opus through Claude Opus 4.5 — twenty months in which the model got substantially better at almost everything else and the context window did not move at all. Then, in February 2026, it went to a million in one step.
The table below is generated from the dataset, so it stays correct as records are added. Every value links to the Anthropic announcement or model card it came from.
| Date | Model | Context window | Change |
|---|---|---|---|
| 2023-03-14 | Claude 1 | 9K | first recorded |
| 2023-07-11 | Claude 2 | 100K | 11.1× |
| 2024-03-04 | Claude 3 Opus | 200K | 2× |
| 2024-06-21 | Claude 3.5 Sonnet | 200K | — |
| 2025-02-24 | Claude 3.7 Sonnet | 200K | — |
| 2025-05-22 | Claude Opus 4 | 200K | — |
| 2025-09-29 | Claude Sonnet 4.5 | 200K | — |
| 2025-10-15 | Claude Haiku 4.5 ⚠︎ | 200K | — |
| 2025-11-24 | Claude Opus 4.5 | 200K | — |
| 2026-02-05 | Claude Opus 4.6 | 1M | 5× |
| 2026-02-17 | Claude Sonnet 4.6 | 1M | — |
| 2026-04-16 | Claude Opus 4.7 | 1M | — |
| 2026-05-28 | Claude Opus 4.8 | 1M | — |
| 2026-06-09 | Claude Fable 5 | 1M | — |
| 2026-06-09 | Claude Mythos 5 | 1M | — |
| 2026-06-30 | Claude Sonnet 5 | 1M | — |
| 2026-07-24 | Claude Opus 5 | 1M | — |
| 2026-09-01 | Claude Fable 5.1 ⚠︎ | 1M | — |
| 2026-09-01 | Claude Mythos 5.1 ⚠︎ | 1M | — |
| 2026-09-22 | Claude Opus 5.5 ⚠︎ | 1M | — |
| 2026-09-28 | Claude Sonnet 5.5 ⚠︎ | 1M | — |
| 2026-10-07 | Claude Haiku 5.5 ⚠︎ | 1M | — |
Every change, and the document behind it
- 9K → 100K, Jul 11, 2023 (Claude 2)
- https://www.anthropic.com/news/claude-2
- 100K → 200K, Mar 4, 2024 (Claude 3 Opus)
- https://www.anthropic.com/news/claude-3-family
- 200K → 1M, Feb 5, 2026 (Claude Opus 4.6)
- https://www.anthropic.com/news/claude-opus-4-6
- https://platform.claude.com/docs/en/about-claude/models/overview
What this does not claim
- 6 values marked ⚠︎ are in the dataset but not yet traced to a primary source.