Remedy's Sam Lake announced on the Quantum Break Facebook page that the game has gone gold. This means the game has been approved and certified and that production of discs can commence. Of course, this likely means that Remedy are tinkering with things and figuring out issues that couldn't be solved in time, but that may be sorted with a day one patch (which is almost a given these days).
Anyway, this means there is no risk for any further delays and we'll see the game launch on April 5th both on PC (Windows 10 exclusive) and Xbox One.