Citing multiple sources, Mary Jo Foley reports that Microsoft has quietly canceled plans to add Sets to Windows 10.

As you may recall, Microsoft announced Sets in late 2017, and originally planned to release this feature—which would have added a tabs-based shell around application windows—as part of a 2018 version of Windows 10. But after briefly testing Sets, Microsoft pulled it from pre-release Windows 10 builds and hasn’t since mentioned it in any official capacity. We know that it will not be included in Windows 10 version 1903, which was recently completed, because it was never tested as part of that release.

But this past week, Sets fans were given a bit of hope when a Microsoft senior program manager said on Twitter that “adding tabs is high on [Microsoft’s] to-do list” despite Sets not being included in Windows 10 version 1903. I speculated at the time that the delay had to do with Microsoft’s transitioning of its Edge web browser to the Google Chromium code base: Sets was based on the tabs functionality in classic Edge, and since Microsoft is dropping that product, it would need to start over.

That bit of speculation has been confirmed: Foley’s sources say that the Edge transition to Chromium “helped finalize the decision to [cancel] Sets.” It just would have been too time-consuming to reimplement the feature using Chromium.

As to whether Sets—or something like Sets—will ever come to Windows 10, Foley is less positive.

“Windows 10’s ‘Sets’ feature is gone and not expected to return,” she writes. As bad, “the feature generally wasn’t well received or understood” anyway, indicating that a system-wide Sets replacement is unlikely.

In the good news department, Sets-like tabbed user interfaces do appear to be coming to future versions of File Explorer, Windows 10’s file management app, and to the Windows 10 console applications. That should satisfy the most common needs for Sets-like functionality, and avoid the issues that mainstream users might have had with tabs popping up all over Windows.

RIP, Sets. Like so many Microsoft ideas, it seemed like you had a future. And then you didn’t.