I'm importing 3D models with pixel-art style textures on them. Godot is automatically using a lossy form of compression on them when the textures are saved out during the import process. Is there any way to specify that the textures need to use a lossless compression?

You have to export with glTF + binary + bin, then you can modify the textures in Godot.

cybereality Okay, so this is something I have to do manually after the import for each image that's been imported.

Yeah, in import, but no I actually confused the question because you mentioned pixel art style, so beyond the import setting for compression which is in asset import settings the mipmapping/filtering is a per texture slot property in materials/shaders.

You can click on every image in the assets window (by shift/control click) or filter by jpg/png and then do them all at once.