Microsoft officials officially acknowledged the existence of the rumored Windows 8.1 with Bing version of the product in a blog post on May 23.
Word of the existence of Windows 8.1 with Bing first leaked a few months ago. The new SKU sets Bing as the default search engine, though users are allowed to change that on devices with the SKU is installed.
Tipsters have told me and others that this Windows 8.1 with Bing SKU is the one that Microsoft is making available to OEMs either for free or a substantially reduced rate. I'm not sure whether this is the only Windows 8.1 SKU that Microsoft is making available for free to its OEMs, but it may be. Officials have said previously that Windows is now available for free for Windows Phone and Windows tablet makers building devices with screen sizes under nine inches.
Windows 8.1 with Bing is one piece of Microsoft's experimentation with how to monetize Windows. Microsoft already has thrown a lot of software and services in for free with Windows 8, so it needs to find ways to make money in a world where the pressure to drop OS licensing fees is increasing.
The Windows 8.1 with Bing SKU will be available only preloaded on OEM devices, Microsoft officials said. It's not available for purchase as a standalone SKU. Some of the devices running this SKU, "in particular tablets, will also come with Office or a one-year subscription to Office 365," according to Microsoft's blog post.
Microsoft disclosed the existence of the new SKU in preparation for new Windows devices that will debut at the Computex show in Taipei in a couple of weeks.