Outlook, Excel, Word, PowerPoint, and OneNote have all adopted the 64-bit runtime environment to enable better performance and "new innovative features." 64-bit support has previously been available to Microsoft's "Office Insider" beta testers but is rolling out to all users today.
Microsoft Office users who do not use add-ins will be unaffected by the change, while those who do will need to update their add-ins to 64-bit versions as add-in developers release the necessary updates. All add-in developers have had several months to make the updates thanks to the beta testing period, so the transition should be seamless for most end users.
Apple's Mac operating system has supported 64-bit applications for many years, but prior to 2016, Microsoft continued to offer 32-bit Office for Mac apps.
Microsoft Office for Mac is available through an Office 365 subscription or as a standalone purchase from the Microsoft website. Office 365 costs a minimum of $69.99 per year while the standalone version of Office 2016 for Mac is priced at $149.99.