Group of 6 Use it now
Plugins and hooks gain renamed filesystem actions, new capabilities for settings/env/session usage, stricter validation, and a new terminal UI system
What
- The plugin capability actions
fs.readFile,fs.writeFile, andfs.listDirare renamed tofs.read,fs.write, andfs.list(including the underlying IPC event name). - Plugins and hooks gain four new capabilities:
session.usage(read session usage stats),settings.read(read merged settings from a named source), andenv.get/env.set(read and write environment variables) — all fully wired with permission checks and handlers. - New validation guards these and other hook APIs: a hook's
on('event')matcher can't be a nested object matched against a primitive;next(e)handlers forenv.get/env.setcan only change the value's data, not other fields; andui.messagecalls can't rewrite fields likesurface,component,requestId,element, ormodule(onlydatamay change), and are rejected if their serialized data is too deeply nested or too large. - A large new subsystem lets plugins mount custom terminal UI elements ("Clients") declared via a
surfacefield inhooks.json. It handles rendering, mounting/unmounting, resizing, mouse and keyboard input, hover/focus state, a row-budget that can reject renders pushing a dialog over its row limit, and message dispatch between the plugin and its UI.
Why Together these give plugins and hooks a broader, more capable API — access to environment variables, settings, and session usage, plus the ability to draw real interactive terminal UI — while the renamed, more consistent action names and new validation keep that expanded surface from letting a plugin corrupt data it shouldn't touch or send oversized payloads.
Names in the bundlesurface
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Added since
A small documentation edit on TypeScript SDK V2 session API (removed) touched a line naming surface after this was published.
V2 was an experimental session API that removed the need for async generators and yield coordination. Instead of managing generator state across turns, each turn was a separate `send()`/`stream()` cycle. The API surface reduced to creating…agent-sdk/typescript-v2-preview see the edit
Confirmed since
Anthropic's documentation has since written up surface, on List Events.
When set, this event was cross-posted from a subagent's thread to surface its custom tool use on the primary thread's stream. Empty on the thread's own events. Echo this on a `user.custom_tool_result` event to route the result back.api/beta/sessions/events/list see the edit
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agrees
Anthropic's documentation has since written up surface, on List Events.