I have always been troubled ever since I started receiving RSUs that the IRS doesn't already have access to the cost basis for vested RSUs, and I'm baffled that you wouldn't want them to have that information.
Fair point. I'd be somewhat comfortable with sharing that information earlier than they strictly require it.
But I think a better solution to the very real problem you've identified would be for your stock plan administrator to hold that information and transmit it to the IRS as basis information just like your retail broker now transmits basis for closed positions on a 1099-B, but only transmit it in the year the closing transaction happens.
If I vest RSUs this year and sell them in 2026, the IRS needs to know that basis in 2026, but they don't need to know it now (other than as it is already included in W-2 boxes 1 and 14, but that's only a dollar figure, not a per-share basis figure).
