Very low if they use confidential VMs (CPU rooted encryption). Just like the Xbox uses and remains unhacked 10 years later.

What would be the benefit of hacking the Xbox? What would you get?

Pirated games, cheating/botting in multiplayer rooms, etc.

And fame.

Seems pretty high, this is an air gapped product so at some point the employees of whatever government they are giving it to would need to SSH into the VM's to load new weights etc. Lots of ways to make it tricky/watermark the weights though.