Claude Code --resume bug silently drops 1M context window to 200K behind third-party gateways
DimitarKrastev · ghdev · 2026-09-09
A repro'd bug report on anthropics/claude-code: when ANTHROPICBASEURL points to a non-first-party host (corporate gateway/proxy) and the session model differs from the settings default, claude --resume restores the model as bare claude-fable-5-1 with a 200K context window instead of claude-fable-5-1[1m] with 1M.
- The resumed session also stops sending the context-1m-2025-08-07 beta header, so the API works with a 200K window and auto-compaction kicks in early.
- Likely cause: resume falls back to the API-echoed model id in assistant messages (which never includes [1m]) instead of the transcript's modelId record.
- The bug is masked on api.anthropic.com, where the bare id already implies 1M.
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