Little by little various OEMs are beginning to test out Marshmallow on their devices. So far only a handful of devices, namely nexus devices, actually have official Marshmallow builds. Sony has just started the rollout of a Marshmallow beta test program. The beta will be available for Xperia Z2, Z3 and Z3 Compact users in countries to include Italy, Netherlands, and Spain. Part of the Beta program is to crowd source the search for bugs in the software. As bugs are squashed Sony will be closer to releasing Marshmallow to the rest of the user base.
via Xperia Blog