Don’t see this online yet to link to. CNN just reported that Biden has been sent a letter from GSA and CC’d to Mark Meadows that the transition can begin.
Little short item from AP
Federal agency ascertains Biden 'apparent winner' of election, clears way for start of transition from Trump.
update
Trump being “reasonable” (for him)
here is link to CNN story
First on CNN: GSA tells Biden that transition can formally begin