Graphite uses “versions” of a pull request to keep track of the history of a PR. On first submit, a PR is v1 and is incremented each time a PR is updated and submitted through gt submit.

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Switch between PR versions

By default, the pull request page shows you a “diff” between v1 (the initial submitted state of the PR) and vN, where N is the latest version of the PR. You can toggle between the version you’re currently viewing by clicking the versions dropdown and choosing a version for the “right” and “left” sides of the diff.

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”Hide reviewed changes”

In the event that a pull request is updated after you’ve already reviewed it, you’ll see a banner prompting you to hide reviewed changes.
Clicking hide reviewed changes automatically changes your view so you see a comparison between the last reviewed version and the latest version of the pull request.