A new SDK CLI flag makes the process wait for an initialize request over stdin before starting.
The Claude Agent SDK CLI has a new --await-initialize flag that makes the process block at startup and read the first stdin line as an initialize control request, applying its launch-scoped fields (currently plugins) the same way --plugin-dir/--plugin-dir-no-mcp would. It requires --input-format=stream-json, cannot be combined with --sdk-url, and only applies when stdin isn't a TTY. Startup fails with a descriptive error if the first line isn't valid JSON, isn't an initialize request, or never arrives before the wait times out.
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.
Trying the plugin with `--plugin-dir` tells you it can work. To find out how often Claude actually reaches for it and gets the right result, run it against a set of test prompts with [`claude plugin eval`](/docs/en/plugin-evals). Each prom…plugins see the edit
* Edits to a plugin you loaded with [`--plugin-dir`](/docs/en/plugins#test-your-plugins-locally) while you develop itdiscover-plugins see the edit
Anthropic's documentation has since written up --plugin-dir, on Discover and install prebuilt plugins through marketplaces.