What This Means
The 400 tier is Interior - GTY only, so the cabin is basic. But the itinerary quality is strong enough to make the region usable immediately if the goal is destination first. At 600, Alaska is still the top region in the best results, and at 800 the region gains Balcony - GTY inventory.
If you want Alaska with a balcony, 800 is the more practical floor. If you just want Alaska on the certificate, 400 is enough.