Apple on Tuesday seeded the third developer beta of macOS Sierra 10.12.6. Macs already on the developer beta can update through the Mac App Store. Registered developers can also access the update through the Apple Developer Connection.
Apple hasn’t announced any new features in the developer seeds of macOS Sierra 10.12.6, and it is most likely a maintenance release. Any remaining macOS Sierra releases are most likely to be maintenance and/or security-focused as the company ramps up to macOS High Sierra this fall.