The operating system on the Librem5 will be upgradeable. That is one of our main goals: you are allowed to run whatever you want because the phone belongs to you.
On that side, we’re going to adhere to the requirements set by the FSF, as we’re striving for their Respects Your Freedom certification. The negotiations are still ongoing, and as far as I can tell, there’s nothing that’s designed especially to prevent updates in the current batch.
The modem may support FOTA, which is a tricky aspect because some people may not want that, and because it may be outside the control of the phone or its operating system.