DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.
Plan mode exit now shows more detailed handoff messaging: "I'm sending this plan to Ultraplan to be refined remotely. Let me know it's been handed off and that a web link will appear here in a moment" instead of the terse "Plan being refined via Ultraplan — please wait for the result."
Evidence
Plan handoff message (search for "I'm sending this plan to Ultraplan") — Gt7
Strings lifted out of the shipped bundle, so the claim above can be checked against them.