If you’re using the Claude API with the extended context window — today’s the day you need to act. Anthropic is retiring the 1M token context window beta for Claude Sonnet 4 and Claude Sonnet 4.5 on April 30, 2026.
What Changes
The beta header context-1m-2025-08-07 no longer has any effect on Sonnet 4 and Sonnet 4.5 as of today. Requests that exceed the standard 200,000 token context window will return an error. Requests under 200K tokens continue to work — so this isn’t a model retirement, just the end of the context extension.
The Migration Path
The good news: the switch is straightforward. Claude Sonnet 4.6 and Claude Opus 4.6 support the full 1M token context window — without any beta header, at standard pricing. Since March 13, the 1M window has been GA (Generally Available) on these models, and the previous long-context premium was completely removed.
The Timeline
The two legacy Sonnets (4 and 4.5) will remain available on their standard context window until June 15, 2026. On that same date, the base Sonnet 4 and Opus 4 models will also be permanently retired.
What You Should Do Now
If you have the beta header in your code: remove it and migrate to Sonnet 4.6 or Opus 4.6. In most cases, it’s a one-liner — change the model name, done. The newer models are more capable anyway, and you get the large context at no premium.
Quick tip: test beforehand that your prompts show the same behavior with the newer models. Usually they do, but for edge cases, a brief check is worth it.