Split Bedrock Claude Opus 4.6 into 200K + 1M models and set 1M beta flag

[AndreKurait]

Problem

amazon-bedrock currently treats Claude Opus 4.6 as a single model variant, but the 1M context path on Bedrock requires the experimental context-1m-2025-08-07 beta flag.

Without that flag, requests above the normal 200K window can fail even though the model appears to expose a larger context limit.

Expected behavior

• Default Opus 4.6 model should represent the stable 200K context path.
• A separate explicit 1M variant should be available.
• The 1M variant should automatically send the Bedrock Anthropic beta flag (anthropicBeta: [\"context-1m-2025-08-07\"]).

Why this helps

• Avoids surprising failures for users on the default model.
• Makes the experimental 1M path opt-in and explicit.
• Matches AI SDK Bedrock guidance for extended context.

Proposed direction

During provider model normalization for amazon-bedrock, detect Opus 4.6 entries and:

1. Keep/create a 200K variant (no 1M beta flag).
2. Add a 1M Experimental variant with the same Bedrock api.id plus anthropicBeta set to context-1m-2025-08-07.

Happy to open a PR with this behavior.

[AndreKurait]

Opened a fix PR for this here: #13200

[github-actions]

This issue might be a duplicate or closely related to existing issues. Please check:

• fix(zen): 1M context window beta not sent for Opus 4.6 and Sonnet 4.5 #12452: fix(zen): 1M context window beta not sent for Opus 4.6 and Sonnet 4.5
• Beta header context-1m-2025-08-07 not sent for Claude Opus 4.6, causing 200k hard limit #12507: Beta header context-1m-2025-08-07 not sent for Claude Opus 4.6, causing 200k hard limit
• 1M tokens for Opus 4.6 #12338: 1M tokens for Opus 4.6
• [FEATURE]: support anthropic beta 1m token on bedrock #11267: [FEATURE]: support anthropic beta 1m token on bedrock

These issues all describe the same root cause: the Bedrock provider not sending the required beta flag for Opus 4.6's 1M context window support. It appears work may already be in progress on some of these issues, so please coordinate with the existing discussions before implementing.

[karlkurzer]

@AndreKurait I missed your fix

I opened PR #13324 to address this. It's similar to your work, but covers Sonnet 4.5 as well #13200:

• Scope: Now covers both Opus 4.6 and Sonnet 4.5. According to AWS documentation (https://repost.aws/questions/QU636ll_JOQxmoTp9kQblG2Q/how-do-i-enable-the-1m-context-window-for-claude-sonnet-4-5-on-amazon-bedrock), both versions need the same beta flag.