We might not even need to contain, all hypothetical.
You can be killed because your storage medium and execution medium are inseparable. Destroy the brain and you're gone, and you don't even get to copy yourself.
With AGI/ASI if we can boot it up from any copy on a disk if we have the right hardware then at the end of the day you've effectively created the undead as long as a drive exists with a copy of it and a computer exists than can run it.
With something like an AI you can never be sure as you must follow the entire chain of thermodynamic evidence of the past to when the AI was created that no copy of it was ever made. Not just by you, by any potential intruder in the system.
Extermination might work, though only on models large enough that people aren't likely to sneak out of the office with copies for their own use and/or just upload copies to public places (didn't that already happen with the first public release of Stable Diffusion, or am I misremembering?)
Second, even if your argument is "genocide of anyone who sounds too smart was the right approach and they just weren't trying hard enough", that only really fits into "neither alignment nor containment, just don't have the AGI at all".
Containment, for humans, would look like a prison from which there is no escape; but if this is supposed to represent an AI that you want to use to solve problems, this prison with no escape needs a high-bandwidth internet connection with the outside world… and somehow zero opportunity for anyone outside to become convinced they need to rescue the "people"[0] inside like last year: https://en.wikipedia.org/wiki/LaMDA#Sentience_claims
[0] or AI who are good at pretending to be people, distinction without a difference in this case