Prior to the beta2 release version of the Samba 4 software, the project was mainly investing the new
NTVFS file server daemon . However, the first stable release of Samba 4 used the old and very stable
smbd daemon to act as the default file server for the brand new version of Samba 4.0.0.
The release notes, dated December 11, 2012, state that the project will still support and provide continued development on the new
NTVFS file server to guarantee support to the users who are exploring this new daemon already (for example, the early adopters of the Samba 4 alpha releases).
The new NT-FSA architecture is planned to be the default architecture in the future as it is architected to match the requirements of the new Active Directory Domain Controller model. So, the
smbd daemon should be replaced as the default Samba's file server in the long term  (presently,
smbd is still the recommended file server).