Claude Code v2.1.216 Sweeps Away Long-Session Slowdowns and Security Loopholes!

Hey everyone, it's me! I've been checking out the latest Claude Code release, so let's dive in!

Claude Code Release github.com

What was announced?

Claude Code Release published the latest version of the Claude Code CLI, v2.1.216. The GitHub Releases page lists nearly 40 changes — one new setting, plus a dense batch of performance, security, and UI fixes.

The story so far

Until now, Claude Code had a handful of quiet-but-real issues.

• In long sessions, message normalization cost grew quadratically with the number of turns, causing multi-second stalls and slow resumes
• Worktree-isolated subagents could redirect Git into the shared checkout via git -C, --git-dir, or GIT_DIR/GIT_WORK_TREE, defeating the isolation
• A symlink planted at .claude could redirect workflow saves and scheduled-task writes outside the project
• Compound Bash commands with redirects tucked inside && lists or negations could slip past permission checks
• The PowerShell tool's permission validation could be bypassed with invisible Unicode characters, and read-only commands on Windows could access network paths without a permission prompt
• Right after an OAuth token expired or rotated mid-session, auto mode misclassified "HTTP 401" errors as command denials

In short, there were small cracks in both the performance foundation and the security boundary.

What changes

This release fixes all of that. The quadratic growth in normalization cost that slowed down long sessions is gone, so stalls and resumes should be smoother. The worktree-isolation escape, the .claude symlink write escape, and the Bash/PowerShell permission-check bypasses are all closed too.

On the feature side, there's a new sandbox.filesystem.disabled setting — it lets you turn off filesystem isolation alone while keeping network egress control in place.

Dive Deep

A bunch of smaller-but-useful fixes landed too.

Background sessions & worktrees

• Fixed resumed background agent sessions reverting to the default agent — the agent's prompt and tool restrictions are now restored
• Fixed worktree sessions landing in another project's leftover worktree when the working directory didn't match the selected project
• Fixed background sessions whose worktree has no git repository being undeletable
• Fixed background subagents getting cancelled when a high-priority message arrives during their startup window

Usability & UI

• Fixed AskUserQuestion telling Claude to continue even when a free-text answer asked it to wait or explain first
• Fixed Claude Code on the web re-asking the same question and dropping the answer after a session sat idle for a few minutes
• Fixed @-mentions silently attaching nothing after file-modifying hooks, vim dot-repeat of c-operators and paste, statusline running twice on resume, and resume-picker hangs on failure
• Fixed dialogs in fullscreen mode stretching past their panel's right edge, the /config settings list clipping its footer hint, and the transcript-mode (Ctrl+O) footer wrapping on terminals narrower than 104 columns

Everything else

• Fixed claude daemon stop --any potentially terminating an unrelated process via a stale legacy daemon lockfile
• Fixed the Prometheus metrics endpoint (OTEL_METRICS_EXPORTER=prometheus) emitting invalid # UNIT lines
• Fixed skills and commands changed during a session not appearing in the slash menu until restart
• /rewind no longer restores or deletes files through symlinks or hard links, and reports how many paths it skipped

Wrap-up

• Fixed the quadratic message-normalization cost bug that slowed down long sessions
• Closed several loopholes around worktree isolation, symlinks, and Bash/PowerShell permission checks
• Added sandbox.filesystem.disabled to disable filesystem isolation alone while keeping network controls
• Plus a pile of smaller background-session, worktree, and UI fixes

If you lean on Claude Code for long sessions, worktrees, or background agents, this release is worth grabbing for both the performance and security fixes!