Is Pfizer Doing Gain of Function Research on Coronaviruses?

Pfizer came out with a rebuttal that was like, we have never done this kind of research on these vaccines. Well, they said it wasn't gain a function that they said they were doing. They said that they sometimes do certain research to make sure that the antiviral properties work. And then they were like, this is research that's required by US regulators for all antivirals. So they might not be lying when they say they haven't done any gain a function or a directed evolution research because that's actually not the claim that the guy made.