"Officially" is a loaded term, since the FBI doesn't make public announcements about these things. If anything, I would take Sessions' recusal as an indirect admission that there WAS an investigation underway.
Heck -- I've suspected that Rudy Giuliani was nowhere to be found among the senior cabinet appointments in the new administration, and has almost completely disappeared from public view since January, because of the likelihood that his own security consulting firm had been retained by the Trump transition to team to investigate the matter on their own.
True. But I doubt they could keep that secret this long. We’ll see.