Oscar news is coming bit by bit, although calling this 'news' might be a little bit too generous. '4-3-3 Esportes' in Brazil are reporting that the 20-year-old will sign with Chelsea on Friday:
Oscar vai para Londres para não voltar mais. Essa será a sua nova cidade a partir de agora. O meia irá assinar contrato de cinco anos com o Chelsea em Manchester até a sexta-feira.
Roughly translated, that goes along the lines of 'Oscar will not come home from the Olympics. Instead, he'll sign a five year contract with Chelsea. The piece later goes on to claim that the deal is indeed for 25M, which fits what we've heard earlier. It's not entirely clear whether this is reliable information -- last week, Oscar himself claimed that he wasn't making a decision until after the Olympics, but that was a weird statement to make with a medical confirmed and Internacional essentially confirming that a transfer fee had been agreed, so it's not completely out of the question that this report is true.
All in all, I would expect a five year deal, and having it signed on Friday sounds reasonable enough, but still, don't expect an announcement for a while. I suspect this will end up looking a lot like Barcelona's Jordi Alba transfer, where everyone knows it's done well in advance and we all just sit around and wait for someone to confirm it.