Claude Code v2.1.316 Adds New Environment Variable and Fixes Several Bugs

At a glance

Anthropic has released v2.1.316, a new version of its AI coding tool Claude Code. The update adds a few configuration options and fixes errors that occurred with shell commands and in several connection situations. It includes both new features and fixes.

Key points

1. 1

   The CLAUDE_CODE_DISABLE_ULTRATHINK setting lets you turn off the ultrathink keyword (a command that tells the model to think especially deeply).

2. 2

   The fast mode of the Opus 4.8 model (a feature that returns responses more quickly) will be discontinued on November 30, 2026. After that, users need to switch to Opus 5.5 to keep the same speed improvement.

3. 3

   A problem where shell commands left running when Claude Code exited kept running on macOS and Linux has been fixed.

4. 4

   Several bugs have been fixed, including one where PowerShell hooks (tasks that run automatically in specific situations) got stuck on exit code 2.

Why it matters

Developers who use Claude Code should know the fast mode end date and the new configuration options in advance.