Does GitHub have banners?

No. GitHub profiles only have an avatar, so only the avatar is offered.

Does it work for organizations?

Yes. Org avatars work the same as user avatars.

What size is the avatar?

Full resolution as stored on GitHub's avatar CDN.

GitHub Avatar Downloader

How to download GitHub profile pictures

Paste a GitHub profile URL or octocat into the field above and press Grab. The original avatar is fetched directly from the source. Download saves the file with a clean filename. Open shows it in a new tab if you'd rather view first.

Questions

Does GitHub have banners?: No. GitHub profiles only have an avatar, so only the avatar is offered.
Does it work for organizations?: Yes. Org avatars work the same as user avatars.
What size is the avatar?: Full resolution as stored on GitHub's avatar CDN.

Other platforms

grab. also handles Bluesky, YouTube, X / Twitter, TikTok, Reddit, Mastodon, Ko-fi, Buy Me a Coffee, Discord (User), Discord (Server), Spotify (Artist), Spotify (User).