"Ice Nine" is a fictional assassination device that makes you turn into ice after consuming ice (?) https://en.m.wikipedia.org/wiki/Ice-nine
"Ice IX" (ice nine) is Ice III at a low enough temperature and high enough pressure to be proton-ordered https://en.m.wikipedia.org/wiki/Phases_of_ice#Known_phases
So here, Sam Altman is stating a death threat.
If we're seriously entertaining this off-handed remark as a measure of Altman's true character, it means not only would be willing willing to murder an adversary, but he'd be willing to risk all humanity to do it.
What I take away from this remark is that Altman is a nerd, and I look forward to seeing a shaky cell-phone video of him reciting one of the calypsos of Bokonon while dressed as a cultist at a SciFi convention.
Oh okay, I didn't really grok that implication from my brief scan of the wiki page. Didn't realize it was a cascading all-water-into-Ice-Nine thing.