2.1.10 (2.1.10)

Claude Code 2.1.10 (released 2026-01-16) introduces the Setup hook event type, a new lifecycle phase that fires before SessionStart and enables repository initialization, CI bootstrapping, and scheduled maintenance workflows.

Epistemic status: changelog-derived and partially runtime-verified. Features marked UNTESTED in the source were not runtime-confirmed; claims about those features are derived from the changelog only.

What changed

The headline addition is a new hook event: Setup. It fires on three CLI triggers: --init, --init-only, and --maintenance. The hook input payload includes a trigger field ("init" or "maintenance"), a session_id, and the standard cwd and transcript_path fields.

The --init-only flag is the automation-oriented variant: Claude runs the Setup hooks and exits without starting a session. This makes it suitable for CI steps or bootstrapping scripts where no interactive session is wanted.

Secondary changes in 2.1.10 are bug fixes and UX polish: a heredoc template crash on expressions like ${index + 1} was fixed, keystroke capture was improved, and file suggestions were surfaced as attachments. VSCode install-count and trust-warning additions were also shipped. The non-Setup features were not runtime-verified in the battle-test run; they are changelog-derived.

What the tests found

Two features reached PASS status during the 2026-01-16 battle-test run.

Setup hook (PASS). Three invocation forms were confirmed working:

echo "hi" | claude --init -p          # Setup fires, then SessionStart, session continues
claude --init-only                     # Setup fires, process exits; no session
echo "run diagnostics" | claude --maintenance -p  # trigger: "maintenance"

A session-aware initialization workflow was validated: a Setup hook creates a /tmp/claude-sessions/{session_id}/ directory, and SessionStart hooks can read from that shared state in the same run.

Heredoc fix (PASS). Template literals containing ${index + 1} no longer crash.

One notable limitation surfaced: --init-only passes trigger: "init" in the hook payload, identical to --init. A hook cannot distinguish between the two modes from the payload alone; external state tracking is required.

"hook input gives you session_id even in --init-only mode. a session id for a session that doesn't exist... so it's more like 'execution id' than 'session id' in the init-only case."

Why it matters

Setup completes the hook lifecycle surface. Before 2.1.10, hooks covered SessionStart, PreToolUse, PostToolUse, and SubagentStop. Setup adds a phase that precedes all of those, giving automation authors a guaranteed pre-session entry point for environment validation, dependency installation, and config generation.

The --init-only pattern in particular is a job-runner primitive: claude --init-only || exit 1 as a CI preflight step requires no interactive session and exits with a meaningful status code.

Caveats

--init, --init-only, and --maintenance are not listed in claude --help as of 2.1.11. They function as documented here but carry undocumented-flag risk: behavior may change without deprecation notice. Five features from this release (OAuth URL copy, keystroke capture, file-attachment UX, and two VSCode items) remain UNTESTED in the battle-test record; treat changelog descriptions of those as unverified.