Спгс с оригинального обсуждения:
Well there are two questions there, one is whether SCP-3125 counts as Apollyon and the other is whether I should list it as such in the writeup.
As I understand it, "Apollyon" means "completely uncontainable, and will 100% certainly wipe out all of humanity no matter what we do". I think SCP-3125 falls marginally short of this definition. As related in this document, there is at least one method by which it is believed that SCP-3125 could theoretically be stopped. Additionally, the existence of the SCP-3125 "inverted containment unit" itself indicates that there are ways to keep SCP-3125 out of your universe. It's an extremely bleak outlook, but it's a long way short of hopeless.
The other angle is whether, in-universe, the term "Apollyon" would be used here, even if it were appropriate. I think it wouldn't, for a simple reason: the Apollyon classification is a confession of defeat. And at the time of writing, the Antimemetics Division was dying, but not defeated. To call SCP-3125 "Apollyon" would alter SCP-3125's perception among the Antimemetics Division for the worse, elevate SCP-3125's power, harm Division morale and decrease the chance of ever containing SCP-3125. Writing "Keter" instead of "Apollyon" could, in fact, be viewed as a tiny act of defiance and confidence.
To be honest I can see this being a legitimate in-universe reason for the Foundation (outside the Antimemetics Division, the Foundation in general) to have coined the "Apollyon" classification and then thought better of it and retired it. You can imagine an email circulating, saying: "'Apollyon' is a confession of defeat, and the Foundation is not a suitable working environment for defeatists." I may even write that Tale.