BO states that seven and nine engines versions f New Glenn will continue to work concurrently to cover different needs.
Wouldn't it be more logical to keep only the nine-engine version, to be used (even partially refueled if necessary) with different upper stages? Why keep two different production lines open?
The engines should be the same.
The first stage is different (looks like only the aft section, strakes, and a few more rings to extend the tanks), but it is reusable, so they should not need to produce them like sausages.
The second stage is currently not reusable, but it seems to be easy and cheap to build. A few more rings to extend the tanks, and a thrust structure that holds 4 engines + piping, and that should be it.
The fairing is different (could they also fly the same?), but it will be reusable, so production isn't that critical.
Software should be the same, but with different values.
The pad looks overbuilt for the New Glenn as it is, so that should not need any changes. They are not showing the erector behind the 9x4, so maybe that will be different?
In the end, the 9x4 doesn't seem revolutionary but evolutionary, so there should be much commonality. Also, while they are working on it, they have something to fly and learn from.