feat: Add Claude Sonnet 4.5 1M context window support for Claude Code…

[ColbySerpa]

feat: Add Claude Sonnet 4.5 1M context window support for Claude Code provider

Related GitHub Issue

Closes: #8585

Roo Code Task Context (Optional)

Description

Adds support for Claude Sonnet 4.5 with 1M token context window to the Claude Code provider.

Changes made in packages/types/src/providers/claude-code.ts:

• Added new model ID: claude-sonnet-4-5-20250929[1m]
• Set contextWindow: 1_000_000 (overrides default 200K from base anthropic model)
• All other properties inherited from base claude-sonnet-4-5 model

Implementation Details:
This follows the same pattern used by Bedrock and Anthropic API providers for 1M context support:

1. The model definition spreads properties from the base anthropic model (which has contextWindow: 200_000)
2. Our explicit contextWindow: 1_000_000 overrides the inherited value
3. The ClaudeCodeHandler's getModel() method returns the full ModelInfo object with the overridden contextWindow
4. The sliding window truncation logic in src/core/sliding-window/index.ts uses this contextWindow value to determine when to truncate messages

When users select this model via /model sonnet[1m] in Claude Code:

• The system retrieves the model definition with contextWindow: 1_000_000
• Messages won't be auto-truncated until they exceed 1M tokens (instead of 200K)
• The truncation calculation respects the full 1M token context window

Test Procedure

Manual Verification:

1. Select the model using /model sonnet[1m] in Claude Code
2. Verify the model is loaded with correct contextWindow in developer tools
3. Create a conversation with context approaching 1M tokens
4. Confirm truncation doesn't occur until exceeding 1M tokens (previously would truncate at ~200K)

Code Review:

• Verified model definition follows TypeScript type constraints (satisfies Record<string, ModelInfo>)
• Confirmed contextWindow override pattern matches existing 1M implementations in:
  • webview-ui/src/components/ui/hooks/useSelectedModel.ts (lines 203-211 for Bedrock)
  • webview-ui/src/components/ui/hooks/useSelectedModel.ts (lines 367-397 for Anthropic)
• Confirmed the spread operator pattern correctly overrides the contextWindow property

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue (see "Related GitHub Issue" above).
• Scope: My changes are focused on the linked issue (one major feature/fix per PR).
• Self-Review: I have performed a thorough self-review of my code.
• Testing: New and/or updated tests have been added to cover my changes (if applicable).
• Documentation Impact: I have considered if my changes require documentation updates (see "Documentation Updates" section below).
• Contribution Guidelines: I have read and agree to the Contributor Guidelines.

Screenshots / Videos

N/A - This is a backend model configuration change with no UI modifications.

Documentation Updates

• Yes, documentation updates may be helpful to inform users about the new 1M context model availability via the [1m] suffix in Claude Code.

Additional Notes

This implementation adds the model definition but relies on the existing infrastructure:

• The ClaudeCodeHandler.getModel() method already properly returns model info with all properties
• The sliding window truncation logic already uses the contextWindow property from model info
• No additional changes needed to support the 1M context - the existing code paths handle it automatically

Get in Touch

Discord:

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Important

Adds claude-sonnet-4-5-20250929[1m] model with 1M token context window to Claude Code provider, overriding default 200K token limit.

• Behavior:
  • Adds support for claude-sonnet-4-5-20250929[1m] model with 1M token context window in claude-code.ts.
  • Overrides default contextWindow of 200K tokens to 1M tokens.
  • Truncation logic in src/core/sliding-window/index.ts respects the 1M token limit.
• Implementation:
  • Model inherits properties from claude-sonnet-4-5 and overrides contextWindow.
  • getModel() method in ClaudeCodeHandler returns model info with updated context window.
• Testing:
  • Manual verification includes loading model and checking truncation at 1M tokens.
  • Code review confirms TypeScript type constraints and contextWindow override pattern.

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[roomote]

I found some issues that need attention before this can be merged.

[roomote]

Critical: Model ID naming inconsistency. The model ID "claude-sonnet-4-5-20250929[1m]" includes a date (20250929) that doesn't exist in the base anthropic models. The base model being spread is "claude-sonnet-4-5" (no date), not "claude-sonnet-4-5-20250929".

This creates confusion because:

1. The date in the model ID suggests it's based on a dated model variant
2. But it's actually spreading from the undated "claude-sonnet-4-5" base model
3. This inconsistency could lead to maintenance issues

Consider either:

• Using "claude-sonnet-4-5[1m]" to match the base model name, OR
• Documenting why the date is included if it has semantic meaning for Claude Code

[roomote]

Major: Missing pricing information for 1M context. The base claude-sonnet-4-5 model in anthropic.ts has tiered pricing for 1M context (lines 21-29 in anthropic.ts):

• Input: $6 per million tokens (vs $3 for ≤200K)
• Output: $22.50 per million tokens (vs $15 for ≤200K)
• Cache writes: $7.50 per million tokens (vs $3.75 for ≤200K)
• Cache reads: $0.60 per million tokens (vs $0.30 for ≤200K)

The current implementation inherits the base pricing ($3/$15) which is incorrect for 1M context usage. You should either:

1. Override the pricing fields to match the 1M tier pricing, OR
2. Document that Claude Code uses different pricing than the Anthropic API

[roomote]

Minor: Consider adding a test case for the new 1M context model in __tests__/claude-code.spec.ts to verify:

1. The model ID is valid and can be retrieved
2. The contextWindow is correctly set to 1_000_000
3. The model properly inherits other properties from the base model