Breaking

Anthropic Seeks Feedback on Unreleased Claude Code Function Hooks

September 3, 2026 at 21:27 EDT

Software Dev & Coding
AI Agents

Anthropic is circulating an unreleased Claude Code design called Function Hooks that would let plugins intercept tools, UI, and policy with in-process TypeScript functions. The feature has not shipped; the company says community response will likely decide whether it does.

Sep 3, 2026 · Anthropic

Function Hooks, still unreleased

Claude Code may gain in-process TypeScript plugins that wrap tools, UI, and admin policy. Community feedback will likely decide whether the design ships.

Spawn tax vs in-process dispatch

~90 ms

1 Python subprocess hook (Windows floor 86–99 ms)

~1.9 s

21 serial PreToolUse hooks at that spawn floor

50us p99

In-process Bun dispatch in the internal prototype (~1,800x vs a ~90 ms spawn)

Takeaway: Process creation, not hook logic, is what made today’s pipeline unusable for one heavy Windows install. Fifty microseconds is dispatch, not the work a hook still does.

Existing transports in the architecture note: command, prompt, agent, http

Placements per event: before, after, during, instead, modifying

Demo videos (4 basic, 3 advanced, 2 case studies)

How a function hook would run

1. Register
TypeScript module exports register(on)

→

2. Event on $
Engine or plugin calls $.tool.call / $.ui.render

→

3. Nested next()
Earlier plugins wrap later ones

→

4. Result
Deny, rewrite, draw, or continue

What developers want

Mechanical capability locks on $, MCP and non-MCP tool.call, secret redaction before the model, Desktop masking for screen share, and a * audit log that downstream plugins cannot peel off.

What is still open

Unhandled errors may fail open and skip plugins. Command-hook interleaving, the full $ surface, timeouts in a next() chain, and non-TypeScript migration are not settled. The feature is not in the product.

Ship gate

Feedback first. Demos run on real binaries, including local Claude Code Desktop. Other surfaces and a release are still to be decided.

Continue reading

The rest of this article is for AI News Blitz readers. Choose an option below to keep reading.