401-k Plan Merger

Company B was acquired by Company A and is adopting their plan effective 1/1/2025.  Company B has a discretionary match with a vesting schedule while company A is a safe harbor match plan with no vesting on the safe harbor or profit sharing.  Is it permissible to make everyone at Company B 100 vested with their funds that currently are not 100% vested?  I know going forward there would be no vesting but what about the funds that are currently forfeitable?

I think you should check exactly when those "forfeitable" amounts are supposed to be forfeited.  If that date hasn't occurred, then your amendment could then fully vest those previously not-yet-vested amounts.  I'd be more concerned if you tried to un-do forfeitures processed before the effective date of the change.

Where the company is going to amend vesting to accelerate everything to 100%, the vesting should be able to be amended either prospectively or retroactively.  Most of the issues regarding amending vesting come up when vesting is simply changed (e.g., 6-year graded to 3-year cliff, then have to give the better of to certain folks).  But these issues do not come up when you accelerate to full vesting.  Of course, this is assuming there aren't any shenanigans like firing all the NHCEs and then vesting all the retained HCEs.

Just my thoughts so DO NOT take my ramblings as advice.