> "The singularity is a specific belief that we will achieve AGI
That is one version of it, but not the only one. "John von Neumann is the first person known to have discussed a "singularity" in technological progress.[14][15] Stanislaw Ulam reported in 1958 that an earlier discussion with von Neumann "centered on the accelerating progress of technology and changes in human life, which gives the appearance of approaching some essential singularity in the history of the race beyond which human affairs, as we know them, could not continue""[1]. A time when people before it, would be unable to predict what came after it because it was so different. (And which I argue in another comment[2] is not a specific cutoff time, but a trend over history of the future being increasingly hard to predict over shorter and shorter timeframes).
Apart from AGI, or Von Neuman accelerationism, I also understand it as augmenting human intelligence: "once we become cyborgs and enhance our abilities, nobody can predict what comes next"; or artificial 'life' - "if we make self-replicating nano-machines (that can have Darwinian natural selection?), all bets about the future are off"; or "once we can simulate human brains in a machine, even if we can't understand how they work, we can run tons of them at high speeds".
> and usher in a golden age. (Either for itself or us. That part's a bit under contention, from my understanding.)
Arguably, we have built weakly-superhuman entities, in the form of companies. Collectively they can solve problems that individual humans can't, live longer than humans, deploy and exploit more resources over larger areas and longer timelines than humans, and have shown a tendency to burn through workers and ruin the environment that keeps us alive even while supposedly guided by human intelligence. I don't have very much hope that a non-human AGI would be more aligned with our interests than companies made up of us are.