Added after our earlier coverage. The original source date is shown below; this is not a new announcement today.

What happened

Anthropic’s October 1 guide introduces JavaScript or TypeScript mods for Claude Code 2.1.287 and later. They can respond to session events and customize supported interface elements.

iNC / Analysis

Why it matters

The opportunity is to fit an agent to a team’s review process rather than forcing every team into one workflow. The corresponding question is who maintains these extensions as the host changes. Treat a mod as software to review, version and test; a convenient interface feature is not evidence of an effective security control.

What to watch

Watch compatibility across updates and test whether custom behaviour survives realistic coding sessions.

Sources & verification

Source links are not a count of independent confirmations.

01
Claude developer guidePrimary source · claude.dev · Oct 1, 2026
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