Source Intelligence
Follow Discord

DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

← All of v2.1.138 Home All releases ←olderv2.1.137 v2.1.139newer→
Claude Code v2.1.138

Advanced Mid-Conversation System Beta Override

What

Claude Code now allows the CLAUDE_CODE_MID_CONVERSATION_SYSTEM environment override to enable the mid-conversation-system-2026-04-07 beta even when ANTHROPIC_BASE_URL is set to a non-default host.

Usage
ANTHROPIC_BASE_URL=https://your-compatible-endpoint.example \
CLAUDE_CODE_MID_CONVERSATION_SYSTEM=claude-sonnet-4-5 \
claude
Details
  • This is not a new public command or setting; the environment variable already existed in 2.1.137.
  • In 2.1.137, the mid-conversation beta check returned false whenever the base URL was not api.anthropic.com.
  • In 2.1.138, that base URL check is bypassed when CLAUDE_CODE_MID_CONVERSATION_SYSTEM is present.
  • The beta is still constrained by the surrounding provider and model checks, and CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS can still disable experimental betas.
Evidence

Mid-conversation beta gate now checks (!If() && !process.env.CLAUDE_CODE_MID_CONVERSATION_SYSTEM) before adding mid-conversation-system-2026-04-07 (search for "CLAUDE_CODE_MID_CONVERSATION_SYSTEM" and "mid-conversation-system-2026-04-07").

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

See this entry in the whole of v2.1.138 →