The plateau doesn't have to be perfectly flat, but it's not a straight line upward anymore either (kind of like our work on transistors, where we've kind of hit the bounds of speed in clock cycles but are improving on miniaturization and power efficiency)
It took 6 years to solve ARC-AGI 1, 1 year to solve ARC-AGI 2 and 6 months to solve ARC-AGI 3.