Office 365 is changing its build numbers to a five-digit format
In June, 2018, Microsoft Office 365 is changing its build numbers from a four-digit to a five-digit format. This change is shown in the following table.
To locate the build number of an Office installation, start an Office application, select File > Account, and then look under About <ProgramName>.
How does this affect me?
If you're an information worker, this change shouldn't affect you. You will see this change only in the Backstage build version number. This change will not affect the functionality of any application.
If you're an IT Professional or an ISV, this change shouldn’t affect any of your manageability tools if those tools have no hardcoded logic that expects to find four-digit build numbers. This expectation also applies to any line-of-business (LOB) applications that may rely on logic that detects build version numbers.
The major version number in Office binary files remains 16.0. Therefore, this change doesn’t affect registry hive locations or file folder locations.