Unlike previous versions, cumulative updates do not use the rollup infrastructure. Instead, under the new Exchange servicing model, "cumulative updates are actually full builds of the product, meaning that when you want to deploy a new server, you simply use the latest cumulative update build available and do not necessarily need to apply additional Exchange Server updates," the team explained in a new blog post with instructions for installing CU1.
The final build number for CU1 is 15.0.620.29. "CU1 is the minimum version of Exchange 2013 required for on-premises coexistence with supported legacy Exchange Server versions," according to the team.
Among the new features in CU1 are:
Addition of an address-book-policy routing agent
The ability of groups to manage groups
Access to public-folder favorites through Outlook Web App
Enhancements to the Exchange Admin Center, including unified-messaging management
According to a blog post by the team, Exchange 2013 RTM CU1 will support the Exchange Server 2013 Management Pack for System Center Operations Manager (SCOM) -- a management pack that will be available at an unspecified later date. This management pack is supported on SCOM 2007 R2 and SCOM 2012.