Doing a bit of number crunching.... Based on the Associated Press predictions... 270 college votes needed to (just) win. With Arizona (marginal but being called for Biden), Biden appears to have 238 votes in the bag. If he can win Nevada, Wisconsin and Michigan - which is plausible - that gives him another 32 votes, so exactly 270. Not exactly a comfortable win, and I don't know what the chances are of it getting screwed if - say - an electoral college voter doesn't show up or votes the wrong way. If Biden can also win one of Georgia or Pennsylvania (possible but not at all certain) or North Carolina (looking unlikely) then he's won comfortably.
That's a fairly good summary.
It's also got me wondering why some betting companies installed Trump as the favourite a few hours ago and have now started reverting back. They either saw him wrongly declare victory and jumped the gun which would be strange, or they have no idea of the process and in particular the postal voting situation. It's not like they haven't had time to swot up on it.