What is inside the Technic Powered Up XL motor?
I was curious about this, and TLG was willing to provide me with one of these motors, so I opened it up. I was able to get the outer shell off by cutting down the 4 tabs on the outside. This motor does not appear to be meant to be opened and put back together. These tabs hold it together very firmly and I wasn't able to move them out of the way without damaging them. The motor does not stay together properly without them.

The light bluish gray front can also be removed from the motor to reveal the internals.

We can see that it uses a double set of planetary gears that are very similar to the PF XL motor.

We can see an additional chip under the drive axle that is not present in PF motors. I believe that this is a rotary encoder to allow the motor to rotate in fixed increments.

There is a black ring around the red drive axle that is magnetic.

For comparison, here is an image from another teardown of the PF XL motor:

We can see that the internal motor and gearing is roughly the same, but the PF version does not include the rotary encoder.