That was a fixed price contract for the new planes. Boeing will have to eat any cost overruns. Their CEO has Already been complaining about it.

The days of cost plus contracting with companies like Boeing are essentially gone luckily. Now that the practice is decently well known by the public, it can't just be hidden as a cost of private sector business anymore like they used to claim.

A decently large reason for that is SpaceX's dramatically cheaper space launch costs, even with iterative design principles resulting in a lot of "waste" designs and products being destroyed or never used. Their contracts were fixed prices through NASA commercial programs so they never received contracts cost plus the way companies like Boeing did, so they actually optimized to minimize their costs. They proved in the real world that cost plus wasn't necessary for those contracts at all, and Boeing has been one of the worst hit by that.