Sam Altman said it himself. He seems like a reasonable source.
If you're familiar with other fields of AI, adding more and more layers to ResNet was the hotness for awhile, but the trick stopped working after awhile.
Altman didn't really say that. Reading what he actually said rather than a headline, He was alluding to economical walls. He didn't say anything about diminishing returns on scaling. And if anything, the chief scientist, Ilya thinks there's a lot left to squeeze.
Sure Sam Altman, the lying CEO of a tech company (they all do) should be listened to on this matter but not on the part where he thinks AGI within reach using his approach. Selective hearing.
It is possible they've reached some 80/20 point and he is pretty honest about how much more extendable the current approach really is.
Would explain going to congress and asking for regulation (of their not-quite-there-yet competitors who they want a regulatory moat against).