Instagram will now display photos at a higher resolution inside its mobile apps. Previously displayed at a resolution of 640x640, Instagram will soon show users their photos at 1080x1080. The rollout is currently in progress and seems to be limited, for the moment, to the Android and iPhone apps, with no mention being made of the web interface or the beta app on Windows Phone.
From Instagram co-founder Mike Krieger:
This change means that images will generally be displayed at a resolution much closer to that of the original image. As Instagram is currently rolling out higher resolution display and storage, it might take some time for higher-quality images to show up in your feed.
Source: Mike Krieger