So no, they are not foldable today - the headline submitted to HN is total clickbait.
"Over the next three years, Airbus will design, build and flight test full scale wing extensions."
... doesn't look like there's any folding being tested here, just the resulting wing shape to see what the benefits might. Full scale foldable wings would be years off.
The goal is longer, thinner wings than usual. Long and thin wings are far more efficient—think gliders and the U2. But beyond a certain width, those wings become incompatible with existing airports and other facilities for handling commercial aircraft. So the idea is to mount folding extensions that are extended for flight, but likely fold when being hangered or navigating taxiways.
It was hard enough to convince a few dozen of the world's largest airports to make the alterations needed to accommodate the A380's wings. Demanding similar changes at the thousands of smaller airports where A320-class planes land would be a non-starter.
E.g. for the 777X it fits in Category E. Without folding tips it would be in Category F. Less gates can accommodate Category F.
https://skybrary.aero/articles/icao-aerodrome-reference-code
That's a meaningful improvement but not that big. Perhaps the limits to this kind of technology are ~50% fuel gain? https://www.technologyreview.com/2013/01/24/180345/hybrid-wi...
We've got AI, but I'm still waiting on exponential technological gains. So far I've mostly gotten exponential enshittification of my google experience. Is AI going to unlock the detonation engine and bring down the cost of my plane ticket? https://www.technologyreview.com/2012/11/23/181486/exploding...
I've flown on the A321LR a few times, and it's always crazy to think about that tiny plane cruising over the Atlantic without stops.
I can't say for certain, but I believe Boeing may have explored this concept at some point. The idea would be to equip aircraft with mechanically extendable wingtips that could expand outward by several meters during flight and retract while on the ground.
The primary challenge is that most airport gates cannot accommodate aircraft with a significantly larger wingspan. Retractable wingtips would allow the aircraft to benefit from the improved aerodynamic efficiency and fuel savings of a longer wing in flight, while still fitting within existing gate infrastructure during boarding, deplaning, and parking.
My guess is that they will be folded after landing, and unfolded prior to takeoff, as other planes with foldable wings do, so that they can continue to fit in standard spaces in the parking/gate areas.