Every update to an Artifact is a new version at the same link. The history is kept, and you can hold readers on an earlier version.
Every update is a version
When your agent changes an Artifact, or you edit a Markdown Artifact in the browser, the result is a new version. The link does not change. Earlier versions are not overwritten; they stay in the history.
Update the migration plan with the new cutover date.
The agent publishes the whole page again, and the new version becomes the one readers see. An update that left readers on the old page would not be an update, so a new version always moves readers forward, even if you had held them on an earlier one.
History
From the Artifact's title menu, Version history lists every version, newest first: who made it and when, with a check beside the one on screen. Choose any row to look at that version. The row readers get is marked Published when it is not the newest one, the one case worth saying out loud.
Someone reading an Artifact while a newer version is published sees a small notice offering to load it, and can keep reading the version they opened. A Markdown document updates in place unless the reader is in the middle of writing a comment or editing.
A comment thread records which version it was left on, and when the agent resolves a thread after an update, the thread shows which version resolved it. See comments.
Holding readers on an earlier version
Readers get the newest version by default. If you want them on an earlier one, open Share from the title menu and choose Show readers an earlier version. Pick the version, and that is the one everyone who opens the link gets until you change it or until the next edit, which shows readers the newest version again.
You can also ask for it:
Keep readers on the version from Monday until I say otherwise.
Buyers and versions
A person who bought an Artifact keeps what they paid for. They can open the version that was published when they bought it and every version published since, and their own Version history lists those. A version that was never published is a draft, and a buyer never sees it. See Selling.