You'll noticeTier: how much it should matter to you
2Useful: my rating, 1 to 5
1Signal: worth watching, 1 to 5
HooksArea: what it touches
ImprovementsKind: in v2.1.299,
ImprovementsSection of the release
Unclear It is not clear which kinds of hook changes lead to the "Prompt not sent" message.
What
When you submit a prompt, UserPromptSubmit hooks can look at it and change it. A hook is a command of your own that Claude Code runs at set moments. The prompt now carries the slash command's name and arguments through to those hooks.
There is also a new message: "Prompt not sent: ... changed it, and Claude Code has no place to put the change." It appears when a change cannot be applied to the prompt.
Why
UserPromptSubmit hooks that rewrite slash commands may behave differently than before.
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.
Confirmed sinceAnthropic's documentation has since written up UserPromptSubmit, on Intercept and control agent behavior with hooks.* `UserPromptSubmit` and [`UserPromptExpansion`](/docs/en/hooks#userpromptexpansion): Claude Code blocks the prompt with a message naming the hook and the timeout, and the session continues. Before v2.1.208, Claude Code ended the query wit…agent-sdk/hookssee the edit
How sure we are
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubtIt is not clear which kinds of hook changes lead to the "Prompt not sent" message.
Anthropic's documentation agreesAnthropic's documentation has since written up UserPromptSubmit, on Intercept and control agent behavior with hooks.
Anthropic's release notes agreeFixed Edit and Retry in Cowork and claude.ai cloud sessions failing on a message stopped while its UserPromptSubmit or mod prompt.submit…
