Manual:$wgMaxAnimatedGifArea

Details
Force thumbnailing of animated GIFs above this size to a single frame instead of an animated thumbnail.

As of MW 1.17 this limit is checked against the total size of all frames in the animation. It is kept equal to $wgMaxImageArea, which is 12.5 million pixels or 3500x3500. In previous versions this was set to 1 megapixel (1000x1000).