Not quite forced registration: it can be dismissed by clicking the "x" in the corner (cropped out of this screenshot -- EDIT: There might not be a way to dismiss it in all of the variants; see comment below).
Also, it's part of an A/B test and is not universal.
More information:
https://www.reddit.com/live/x3ckzbsj6myw/updates/be54fb90-32...