Thanks, I double-checked the release notes and discovered the key section below, which was counter-intuitive at first.
OS:
The base OS version for FreeNAS 9.10 is now FreeBSD 10.3-RC3,
bringing in a huge number of OS-related bug fixes, performance
improvements and new features (new drivers, new CPU chipset support,
USB 3.0, etc) and basic support for hosting virtual machines with
bhyve.