Tim Sweeney doesn't like Windows 10 or Microsoft's Universal Windows Platform, the common development platform that allows developers to create software that can run on Windows on PCs, phones, tablets, HoloLens, and the Xbox. In March he published an op-ed in The Guardian saying that UWP "can, should, must, and will die" because, he claimed, Microsoft could use UWP to create a walled garden, with UWP games not available through competing stores such as Steam. Still apparently concerned with the health of the PC gaming industry, Sweeney is now claiming, through an interview with the print-only Edge magazine, that Microsoft will use Windows updates to kill Steam.

Sweeney's complaints about UWP were technically off-base. His issues are based on the assumption that all UWP apps had to be individually vetted by Microsoft and could only be delivered by the Windows Store. This was somewhat true in Windows 8—apps built using the WinRT platform (the predecessor branding to UWP) could not be trivially sideloaded, as the ability was officially restricted to enterprise users only. But it's not true in Windows 10. Sideloading is enabled by default in Windows 10, and any third-party store could download and install UWP-based games in much the same way as they already do for software that uses the Win32 API.

Sweeney's Steam concerns are once again driven by UWP:

There are two programming interfaces for Windows, and every app has to choose one of them. Every Steam app—every PC game for the past few decades—has used Win32. It's been both responsible for the vibrant software market we have now, but also for malware. Any program can be a virus. Universal Windows Platform is seen as an antidote to that. It's sandboxed—much more locked down. The risk here is that, if Microsoft convinces everybody to use UWP, then they phase out Win32 apps. If they can succeed in doing that then it's a small leap to forcing all apps and games to be distributed through the Windows Store. Once we reach that point, the PC has become a closed platform. It won't be that one day they flip a switch that will break your Steam library—what they're trying to do is a series of sneaky maneuvers. They make it more and more inconvenient to use the old apps, and, simultaneously, they try to become the only source for the new ones.

As before, it's worth remembering that UWPs are not tied to the Windows Store. Anyone can produce a UWP that installs and runs on Windows without having to use the Windows Store at all. Even if Microsoft were to remove Win32 somehow, this would not be equivalent to forcing the use of the Windows Store.

On the one hand, it's certainly possible to imagine a future world in which at least some PC users need never use anything other than UWPs. For a PC primarily used for mail, Web browsing, and a little light gaming, UWPs can handle this job. This is not a problem in itself. Some people today don't need anything more capable than an iPad, so of course there will be a certain audience for whom UWPs apps (with or without sideloading) are sufficient to handle their computing needs.

But, on the other hand, this is neglecting to consider some important details. For example, UWP is built on Win32. It is a fairly large subset of Win32, and it runs in a sandboxed environment, but there's no clear path for Microsoft to completely strip Win32 from Windows without also removing UWP. Similarly, core applications currently depend on Win32: this includes things like Windows' own Explorer shell, as well as critical applications such as the full Office suite. This makes ditching Win32 even more untenable; Microsoft would have to get all of its own software off Win32 first, and that's not going to happen for many years.

On the gripping hand is a vast array of Win32 software that isn't going away any time soon. This includes major applications such as Adobe Photoshop and all manner of custom, line-of-business applications. This enormous legacy of software is a key part of Windows' value proposition: 64-bit Windows today will run almost any 32-bit Windows application (going back to Windows NT 3.1 in 1993). 32-bit Windows today will run almost any 16- or 32-bit Windows application and a substantial number of DOS applications dating back further still. The big reason that Windows is what it is, and Microsoft hasn't gotten rid of weird quirks such as drive letters, is precisely so that these applications continue to work. They're not discardable relics; they're why Windows is used on more than a billion computers.

Microsoft has even been down this road before. Windows RT, the version of Windows 8 and 8.1 for ARM processors, included a near-complete Win32 API, but it locked that API away; only applications developed and digitally signed by Microsoft could use it. Third-party applications all had to use WinRT, making the systems running Windows RT functionally equivalent to "Windows but without Win32." They bombed, hard. Windows without Win32 means Windows without Win32 applications, and the market for Windows without Win32 applications is very limited indeed.

Sweeney appears to be betting that Microsoft will make the same costly mistake again. While a richer UWP ecosystem will certainly make ditching Win32 more palatable, especially for those with simple needs, the notion that Microsoft will willingly break compatibility with a million or more extant Win32 applications is ridiculous. Indeed, the company is, if anything, working in the opposite direction: Project Centennial makes it possible for developers to use the Windows Store to sell and service their existing Win32 applications without having to rewrite them to use UWP.

Xbox chief Phil Spencer even recognizes how core this backwards compatibility is to gaming. Back when rumors of an updated Xbox first started circulating, Spencer said that any hypothetical upgrade or replacement would "effectively feel a little bit more like we see on PC, where I can still go back and run my old Doom and Quake games that I used to play years ago, but I can still see the best 4K games come out and my library is always with me." This compatibility is a virtue, and the still-mysterious next generation Xbox system Project Scorpio will boast full compatibility with the Xbox One and Xbox One S.

More extraordinarily, Sweeney believes that Microsoft will somehow sabotage Steam to drive gamers away:

Slowly, over the next five years, they will force-patch Windows 10 to make Steam progressively worse and more broken. They'll never completely break it, but [Microsoft] will continue to break it until, in five years, people are so fed up that Steam is buggy that the Windows Store seems like an ideal alternative. That's exactly what they did to their previous competitors in other areas. Now they're doing it to Steam. It’s only just starting to become visible. Microsoft might not be competent enough to succeed with their plan, but they're certainly trying.

If this were Wikipedia, both the "that's exactly what they did" and "they're certainly trying" claims would be adorned "citation needed." Evidence of Microsoft doing such a thing is decidedly thin on the ground. Perhaps Sweeney is thinking back to beta versions of Windows 3.1, which issued warnings when used in conjunction with DR-DOS, Digital Research's competitor to Microsoft's MS-DOS.

It's true that Steam is somewhat reckless as a Win32 application. Steam plays fast and loose with file permissions so that a Steam client can update itself, download games, and download patches without requiring Administrator rights. One could perhaps imagine Microsoft doing something, eventually, to crack down on this behavior. If so, Valve would have to change Steam accordingly. But breaking Steam in some kind of incremental patch-by-patch way to drive users away is a non-starter for much the same reason that ditching Win32 is a non-starter. Steam is a Win32 application, and Win32 applications represent a major part of the Windows value proposition. Microsoft can no more start breaking Win32 apps in weird, secretive ways than it can scrap Win32 entirely. If Win32 stops working properly, Windows stops working properly.

Sweeney's fixation with Windows 10 and gaming in particular is peculiar. Gaming is an important part of the Windows platform, but it's a small factor when compared to the hold the company has on the corporate desktop market. The very idea that Microsoft would jeopardize Windows in business situations by breaking Win32 just to kill off Steam is extraordinary.