From the official Microsoft blog:
We have released the first drop of a fully 64-bit version of Office 2016 for Mac to the Insider Fast channel! The update number is 15.25 (160630). I do encourage Insider Fast users to install this update and give it a test. We want to know about any problems you encounter as soon as possible, so that we can make sure we address them before the official release.
My original take on this was amazement that a 64-bit Office was just now emerging in beta. After all, the ability to produce 64-bit apps has been around since OS X 10.4 Tiger, which shipped in 2005.
But this Office team has had to overcome some significant hurdles to bring this new product to life. So many hurdles, that it might be more appropriate to be amazed that they were able to accomplish what turned out to be a Herculean task.
For starters, since Tiger, Microsoft Office for Mac has had a series of major product releases: Office 2004, Office 2008, Office 2011, not to mention updates and side releases (like Outlook). All that work was done while making the transition from CodeWarrior to Xcode, PPC to Intel, gcc to clang, moving from Carbon to Cocoa, not to mention dealing with the emergence of a brand spanking new platform in iOS.
Props to the Office for Mac team for their dedication in bringing this new version to life. And note to self: Don’t be so amazed that something so difficult took so long. The best things do.