How does a 'quasi-tenured' hire work in practice? I'm posting to help out a friend. The operational parameters are US + research university + computer science, so I'm looking for information primarily in that context, though the question is not computer science-specific.

He's tenured at one university and applying to another place. The latter has a funny kind of tenure option. In addition to regular tenured hires, they can make a rapid hiring decision based on just a small number of letters (say 3-4) into a quasi-tenured position. When this happens, after the person joins they go through a proper tenure review. So in principle, you could be hired to a "tenured" position but then later find you don't have tenure after all.

It seems to be neither the traditional "enter with tenure" model nor "enter with abbreviated tenure clock" model, but some new thing entirely. Someone I spoke to said this is increasingly common, and he'd heard of other departments that did this too. I have never heard of it before and find it rather strange.

Do you know of departments that do this? How does it work in practice?
I don't see how this is really different from hiring somebody with a very short (i.e. one year) tenure clock.  The difference probably has more to do with the hiring institution's internal rules than anything else.

We had a senior hire with a one year clock a while back.  It wasn't labeled as "quasi-tenure," but that was basically how it worked.  You don't give somebody a one year clock unless you are overwhelmingly sure that the person is going to get tenure.  And that seems to be what this position is offering; the hire will start without tenure, but the expectation is that they will be fully tenured in short order.