Source is KeplerL2, who is generally considered a reliable source for insider hardware info, particularly on AMD GPU hardware and AMD SoC for consoles.
Previously I would have personally estimated Steam Deck 2 to release mid 2026-early 2027, but the recent info about an upcoming Steam Machine made me think that maybe I should push back that estimate.
Of course even if we assume this is reliable insider info, a lot can change in couple years, so things can definitely change.
I don’t know who those “we” people are but benchmarks have repeatedly shown that in low wattage situations the performance difference between Deck and the newer handhelds is negligible, so this prediction is hardly a surprise IMO.