With Windows 8, Microsoft has introduced versioning rather than service pack updates as the key approach for being on latest build.  The requirements to be on latest build for update support will be similar to what is required for being on latest service packs



QUOTE: Windows 8 customers will have two years to move to Windows 8.1 after the General Availability of the Windows 8.1 update to continue to remain supported under Windows 8 lifecycle. With the availability of Windows 8.1 Enterprise Preview, it is time to start planning your deployment  – and there are deployment tools and guidance available to help make these updates seamless for customers.