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Claude Code Issues / #36584

Opus 4.6 1M context window disappeared — was working, now gone

Resolved 💬 6 comments Opened Mar 20, 2026 by GerardTaus Closed Mar 20, 2026

Description

I had the 1M context window working with claude-opus-4-6 for the past several days (confirmed via /context showing 1M). Today it reverted back to 200k with no changes on my end.

Environment

  • Product: Claude Code Desktop (GUI, macOS)
  • Model: claude-opus-4-6
  • Platform: macOS Darwin 25.3.0

What I tried

  • Setting ANTHROPIC_DEFAULT_OPUS_MODEL=claude-opus-4-6[1m] in ~/.claude/settings.json under env — no effect
  • Restarting Claude Code Desktop — still 200k
  • /context confirms 200k context window

Expected behavior

1M context window should still be available as it was in previous days.

Questions

  • Is there a known issue or rollback affecting 1M availability?
  • Is there a correct way to opt back in from Claude Code Desktop?
  • Is 1M context supported in Claude Code Desktop, or only CLI?

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