feat: add 1M context support for Claude Sonnet 4.5 via env vars #6660
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- Add ANTHROPIC_1M_CONTEXT env var for Anthropic direct API - Add VERTEX_ANTHROPIC_1M_CONTEXT env var for Vertex AI Anthropic - Only applies to Claude Sonnet 4.5 models (not Opus 4 or Haiku) - Sets context limit to 1,000,000 tokens when enabled - Adds context-1m-2025-08-07 beta header when enabled
This was referenced Jan 3, 2026
code-yeongyu
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Jan 3, 2026
… vars (#450) - Update preemptive-compaction hook to use 1M limit when env vars set - Update dynamic-truncator to use 1M limit for output truncation - Update context-window-monitor to use 1M limit for usage tracking Previously hardcoded 200k limits caused compaction at 140k tokens even with 1M context enabled. Now respects env vars consistently with base opencode implementation. Fixes compaction triggering too early with Claude Sonnet 4.5 1M context. Related to anomalyco/opencode#6660
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Summary
This PR adds support for enabling 1M token context windows for Claude Sonnet 4.5 through environment variables for both Anthropic direct and Vertex AI Anthropic providers.
Note: Currently only Claude Sonnet 4.5 supports 1M token context windows. All other Claude models (Opus 4, Haiku 4.5, etc.) remain at 200K tokens according to models.dev.
Changes
Anthropic Direct: Add
ANTHROPIC_1M_CONTEXT=trueenv var to enable 1M context for Sonnet 4.5context-1m-2025-08-07beta when enabledVertex AI Anthropic: Add
VERTEX_ANTHROPIC_1M_CONTEXT=trueenv var to enable 1M context for Sonnet 4.5anthropic-beta: context-1m-2025-08-07header when enabledModel Detection: Regex pattern specifically matches Claude Sonnet 4.5 variants only
claude-sonnet-4.5,claude-sonnet-4-5,claude-sonnet-4.5-20250929Testing
Usage
```bash
For Anthropic direct (Sonnet 4.5 only)
export ANTHROPIC_1M_CONTEXT=true
For Vertex AI Anthropic (Sonnet 4.5 only)
export VERTEX_ANTHROPIC_1M_CONTEXT=true
```