A hidden --proactivity option and a matching session control request

What

Claude Code is gaining a proactivity level, a setting for how much Claude does on its own. It has three levels, ask, default and proactive; the --proactivity startup entry lists what each one does and what turns the feature off.

• A new --proactivity <level> command-line option sets the level at startup. It is hidden from claude --help, because the check that would show it always says no in this build, but it is read if you type it.
• When Claude Code starts a remote session (one running on Anthropic's servers) while a level is set, it sends that level to the new session as a set_proactivity_level control request, a message that changes a setting in a running session. The request sets offer_bypass to false, so it can never move the remote session into bypass permissions mode.
• A separate proactivity attachment, a note Claude reads in the conversation, is also built, except for bare forks.
• The part of Claude Code that routes requests for a cloud-hosted session refuses set_proactivity_level and replies that it is not available there yet.

Why

The option is missing from help but works when typed, and the level it sets can change how freely Claude commits and pushes and which permission mode the session starts in.