Other than Ford pardoning Nixon, I can't recall one quite on this level. Usually, there's a ton of pardons that would either not have been politically popular, or are obvious quid-pro-quo (Trump was the master of this last one), but a preemptive one for a large group isn't one I think we've seen before.

Biden pardoning his family is unprecedented, makes Clinton's pardon of Marc Rich trivial, blatant case of quid pro quo