Although O'Brien hasn't yet publicly declared the starter, he acknowledged during a Thursday night radio show that the team was well aware of who will line up under center on Saturday. O'Brien had hoped each quarterback could avoid the limelight if he held off on making the announcement public.
"The team knows," he said on the weekly "Penn State Football Show." "That's all that matters."
Hackenberg, ESPN's top-rated passer of the 2013 class, beat out junior college quarterback Tyler Ferguson for the job. Ferguson enrolled in January and held an early edge in preseason camp. But by Week 2, O'Brien said the battle was too close to call.
Regardless, O'Brien said both first-year quarterbacks will see time Saturday.
"The guy who's the starter is going to play the majority of the snaps," he said. "But I think it's important when you have two young guys -- it's a totally different situation from last year -- is that whoever the backup is needs to get his feet wet a little bit."
Hackenberg will become just the third true freshman since 1910 to start at quarterback for the Nittany Lions. Shorty Miller was the first in 1910, and Rob Bolden made his debut in 2010.
As a senior in high school, Hackenberg led Fork Union (Va.) Military Academy to the state title game, where it lost to Liberty Christian 35-14. He finished the season completing 54 percent of his passes and throwing for 2,144 yards, 24 touchdowns and 9 interceptions.