They call for 0W20.
That's right in the heart of the oil consumption class action lawsuit that was filed against Subaru. Subaru extended the warranty to 100k in response.
There are 2 oil lights. A low oil level light, and a low oil pressure light (the older cars only had pressure, and interestingly the first few years of FB engined Foresters, most Forester owners just drove them until they blew up, whereas Impreza and Leg/OBK owners got the warning light). The level light comes on kind of prematurely, as the engine is usually less than a quart low. But this prevents catastrophic damage.
My mom bought her 2012 Impreza with about 20k miles on it, it's over 200k, now. It has a salvage title, so was not eligible for a free engine, so she keeps a quart of oil in the trunk, and a funnel tucked in next to the battery. I just found out this week that she's down to ~750 miles per quart, so I advised her to switch to synthetic 5W30. She has seen a P0420 a couple times, so the cat is probably not happy with the hundred + quarts of oil that has gone through it,