[FEATURE] Add support for 1M Context on Claude Sonnet 4.5

[AntonioIbarraOrtiz]

Preflight Checklist

• I have searched existing requests and this feature hasn't been requested yet
• This is a single feature request (not multiple features)

Problem Statement

Add support for 1M Context on Claude Sonnet 4.5

Proposed Solution

To use the 1M token context window, include the context-1m-2025-08-07 beta header in your API requests

Alternative Solutions

No response

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

No response

Additional Context

No response

[github-actions]

Found 3 possible duplicate issues:

1. Feature: Long-context (≈1M) support for Claude Sonnet 4 in Claude Code #5832
2. Feature Request: Enable 1M Context Window for Claude Code #5644
3. [Feature Request] Expand Claude Code Context Window to 1M Tokens #7190

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🤖 Generated with Claude Code

[AntonioIbarraOrtiz]

This beta header flag (context-1m-2025-08-07) need to be set on Claude Sonnet 4.5 model.
https://www.anthropic.com/news/1m-context

[dicksontsai]

We are currently limiting access "in public beta on the Claude Developer Platform for customers with Tier 4 and custom rate limits" as well as some Claude Max 20x users.

[AntonioIbarraOrtiz]

I have Tier 4

[dicksontsai]

Can you screenshot what you see with /model? You should see a Sonnet (1M Context) option if your organization is Tier 4. Otherwise, you can always configure your model as /model sonnet[1m]. https://docs.claude.com/en/docs/claude-code/model-config#extended-context-with-%5B1m%5D

[silver-epsilo]

Look like it still not work for Max 20x

/model sonnet[1m]
⎿ Set model to sonnet[1m] (claude-sonnet-4-20250514[1m])

hello
⎿ API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"The long context
beta is not yet available for this subscription."},"request_id":"req_011CTdp6B5hciTqYYxehWAh6"}

/model
⎿ Set model to Default (Opus 4.1 for up to 50% of usage limits, then use Sonnet 4)

[silver-epsilo]

Wait, if it now use Sonnet 4.5 then it have 1M context?

[silver-epsilo]

Hmm, look like no, claude code still use claude-sonnet-4-20250514

/model
⎿ Set model to sonnet (claude-sonnet-4-20250514)

[silver-epsilo]

Okay, I can specific model, and 4.5 still 200k token

/model claude-sonnet-4-5
⎿ Set model to claude-sonnet-4-5

hello

⏺ Hello! How can I help you today?

which model you are?

⏺ I'm powered by Claude Sonnet 4.5 (model ID: claude-sonnet-4-5).

how much context window you have?

⏺ Claude Sonnet 4.5 has a 200,000 token context window.

[AntonioIbarraOrtiz]

Is working, I set the model with "/model sonnet[1m]" and now I have 1M context.

Thanks