Build 10049 was also the month's second update to Windows 10's preview, released less than two weeks after the first. Microsoft has vowed to pick up the pace of Windows 10 updates.
The preview refresh was almost exclusively about the new browser. "This build is pretty much all about Project Spartan," said Gabriel Aul, engineering general manager for Microsoft's operating system group, in a blog post.
Spartan relies on a new browser rendering engine, dubbed "Edge," a streamlined version of Microsoft's 18-year-old Trident engine, which will continue to power IE11. Windows 10 will also include IE11 as a backward-compatible browser primarily for enterprises. IT administrators will be able to set IE11 as the default browser within their organizations via group policy settings.
Last week, Microsoft announced that, contrary to previous statements, it would separate the two browsers, with only Spartan using Edge and only IE11 relying on Trident.
Spartan, which for now is available only to Windows 10 testers on PCs, larger tablets and 2-in-1s -- including the Surface Pro 3 -- will be seeded to smartphones and smaller tablets in a future release for those devices.
The new browser sports a minimalist user interface (UI) somewhat reminiscent of Google's Chrome, integrates Microsoft's Cortana personal assistant, and offers annotation tools -- with more forthcoming -- for page markup and later retrieval or sharing.
In a separate blog post Monday, Windows design chief Joe Belfiore noted that Project Spartan would be "regularly updated ... along with the rest of Windows 10," implying that the final browser, whatever its moniker, would also receive frequent feature enhancements, not only the monthly security patches that Microsoft has long provided IE.
Belfiore's comment likely means Microsoft will ship feature additions and improvements for Spartan on a schedule similar to its two biggest rivals, Chrome and Mozilla's Firefox, which are upgraded every six to eight weeks. Spartan -- and the continued availability of IE11 as a "legacy" browser -- will also let Microsoft change its longstanding browser support policy.
Chrome and Firefox are patched only in their latest versions, requiring users to keep pace or risk running a vulnerable application. Microsoft could mimic that practice with Spartan, telling customers that they need to run the latest update to receive patches, and point the change resistant -- businesses in most cases -- to IE11.
IE11 will continue to receive security updates on Windows 7, Windows 8.1 and Windows 10. Unless Microsoft changes its support policies for Windows 10, it will patch IE11 for at least a decade after that OS's official release. However, Microsoft is not expected to update IE11 with enhancements or new features.
Build 10049 can be downloaded via Windows Update on devices running Windows 10 Technical Preview.