Microsoft's new browser for Windows 10, codenamed "Spartan," will be getting extensions, company officials confirmed during a Twitter chat on January 27.
In an #AskIE chat on Twitter, IE team members confirmed what had been rumored: Extensions are coming to IE.
"Yes. We're working on a plan for extensions for a future update to Project Spartan," tweeted the @IEDevChat team on Twitter.
There has been talk among various sources (including some of my own) that Microsoft is seeking ways to enable Google Chrome extensions to work on Spartan. All that the team said today was that they are "still building our plan for extensions."
Spartan is the replacement for both the Desktop and "Modern"/Windows Store versions of Internet Explorer. It will be able to run on Windows 10 Desktop and Mobile and will work with touch, keyboards and mice.
Microsoft also plans to continue to offer Internet Explorer for users of certain Windows 10 versions who need IE 11 for legacy purposes. Spartan uses a forked version of Microsoft's Trident rendering engine, known as EdgeHTML.dll. (IE11 in the Windows 10 Desktop preview uses that same engine.) Microsoft is not using WebKit as its Spartan rendering engine, as some developers had hoped.
There's a good Smashing Magazine article on the rendering engine in Spartan, written by Jacob Rossi, a Microsoft Web Platform engineer, with lots more technical details.
Spartan is not yet part of the Windows 10 Desktop preview builds. It also is not slated to be part of the first Windows 10 Mobile preview, due out in February. It will be added to both previews some time in the coming months, Microsoft officials said.
Update: Microsoft has only committed to bringing Spartan to Windows 10 so far, but the IE team said it will watch whether there's demand for it on Windows 7 and then decide what to do. I've heard the team could ultimately bring Spartan to some non-Windows platforms, but have no information on how or when that might happen.