What a GIF file actually is
GIF dates to 1987 and stores at most 256 colours from a palette, compressed losslessly with LZW. Transparency is a single on/off flag on one palette entry rather than a real alpha channel, which is why GIF edges against a coloured background look jagged.
GIFs come from the reaction-image corner of the internet, from old web assets, and from screen recorders that default to it. Anything animated and low-colour that has been passed around for years is probably still a GIF.
What you get from WebP
WebP output uses lossy compression with a quality control, but unlike JPEG it can keep an alpha channel at the same time — one format for photographs and for graphics with transparency.
Every current browser reads WebP; Safari joined in version 14 in 2020, which was the last real holdout. Desktop applications are patchier, so it is a format to publish in rather than to archive in.
What changes when you convert GIF to WebP
This is where the file size actually drops. A GIF stores its image without discarding anything, and WebP's lossy mode decides what the eye will not miss — typically landing 25–35% below a JPEG of matching quality, and keeping the alpha channel while it does so, which JPEG cannot. The catch is not visual but practical: WebP is a format to publish in, and a poor choice for anything you are handing to someone else's desktop software.
Transparency technically survives, but it improves on the way. GIF has no alpha channel — just one palette entry flagged as transparent — which is why GIF cut-outs have hard, jagged edges. WebP stores a full 8-bit alpha, so anything you composite afterwards can have genuinely smooth edges, even though the original's jaggedness is baked in.
Only the first frame survives. GIF is the one source here that can be animated, and WebP output is a still image, so an animated GIF converts to its opening frame. The upside for static GIFs is real: escaping the 256-colour palette removes the banding, and the file usually gets smaller at the same time.