It was reported last week, but it's apparently become official now and will go into effect as soon as next week.
So, the NPB team sets the posting fee in advance and it can go up as high as $20 million. Then MLB teams submit bids and all teams that bid the value that the NPB team set can negotiate with the player.
For example, Masahiro Tanaka's team will set the posting fee at $20 million and all 30 teams can then submit a bid. All the teams who submit bids of $20 million will get to negotiate with Tanaka.
Assuming the Cubs aren't idiots, they will bid $20 million and take it from there. They probably don't end up signing him and the amount he gets could be absurdly high due to the new system, but they have to at least bid the maximum amount here.