Catabolite repression is caused by glucose, not maltose, and our worts are primarily maltose. However, maltose is converted to glucose (but not in the presence of glucose), so if the rate of that conversion is high enough maybe it could trigger the Crabtree effect. Maybe conversion is so fast that even 100% maltose will still trigger it in brewing strains? Typical brewing strains are likely to more maltase than standard lab strains, which typically come from bread making. This is good to keep in mind with any published research.
The Crabtree threshold will also be dependent on the expression of various enzymes that will tend to push it toward the TCA cycle instead of fermentation. So it seems to me the threshold can be strain dependent even within brewing strains.
Anyway, I don't have access to the primary research (and it's in Polish), but it was reported by DeDeken (1966)
that Slonimski (1956) puts the level of glucose at 6 mM. That's ~1g/l, or 1.0004. Also in 1956 Ephrussi et al
reported that 3% glucose (SG = 1.012) triggers the Crabtree effect.
As far as I know, we still don't understand exactly what causes the catabolite repression, meaning what pathway does the level of glucose trigger that causes aerobic fermentation. But for what it's worth, standard lab yeast growth media uses 2% glucose (SG = 1.008). I asked my PI years ago why 2% and if that avoided the Crabtree effect. He didn't know what I was talking about, just shrugged and said that's what is standard.