GTA V is rather technologically interesting. Normally in a game, the scenery shadows are "baked" (non movable, time effecient), and the interactive objects like the player and vehicles have dynamic shadows (rendered real time, performance cost) that are rendered.

Does anyone have any ideas on how gta v might have done its shadows? The day/night cycling makes all the shadows look very dynamic. But I have hard time believing this is just conventional shadow rendering, especially given the age of the hardware that it runs on. What kind of tricks might they do to make all the shadows/lighting seem dynamic?

Shadows on current gen hardware are pretty boring. There's plenty of aliasing visible here and I suspect it's little more than a refinement of techniques from IV. Four cascades, probably some basic filtering (E/VSM?), and maybe some misc things to stitch up between cascades and stuff like that. I sincerely doubt it's any more complex than that. There's just nowhere to go on the hardware they're using.

Yep, they just did a good job in setting up the cascade distances, as the last cascades is IMMENSE. Which is really nice to see for an open world game, lack of terrain shadows in other such always bothered me. GTAV is a very nice demonstration of how you set up things can be as important as how clever you're new shadow trick is. They get a lot of mileage out of a few shadow cascades, most likely 10bit HDR, and their planar reflections.

The big thing I want to know about is what they're doing for non planar reflections. All the buildings have shifting reflections on their glass, and they look quite low res but at least somewhat accurate, including time of day changes. Sure they can apply the skydome as an environment map for the sky, but I wonder how the reflect buildings, which appears to happen well enough that I didn't really notice anything wrong with it.

The big thing I want to know about is what they're doing for non planar reflections. All the buildings have shifting reflections on their glass, and they look quite low res but at least somewhat accurate, including time of day changes. Sure they can apply the skydome as an environment map for the sky, but I wonder how the reflect buildings, which appears to happen well enough that I didn't really notice anything wrong with it.

They've probably got a boatload of low pre-rendered environment probes. You can get away with a lot for reflections and I haven't seen any reason to think it's more complex than that.

Entirely possible, but disappointing if so.