The main claim of this article is that Autzen Stadium will be expanded in the future. It claims that Oregon athletic director Rob Mullens has stated, “I don't know that we'll go into it with expansion as a goal necessarily…We will go into it with, in the modern expansion experience, what other premium options do we need to offer? What other amenities do we need to put into Autzen Stadium to make sure that we are meeting the expectations of the fans?”
When I search this quote online, it appears on reliable sources again, such as Sports Illustrated. So, one can assume Mullens did in fact say this statement.
The Eugene Science Center website says that UO does plan to construct a new indoor practice field next to the stadium. https://eugenesciencecenter.org/uo-football-expansion/
However, there is no evidence of UO actually expanding the stadium itself.
So, the only concrete evidence of an expansion lies in Mullen’s quote. He said himself that expansion isn’t necessarily a goal. Overall, the claim that “Autzen Stadium will be expanded if Oregon stays in the Big 10” is misleading and likely misinformation.