Git.io is a URL shortening website that GitHub created in 2011 for redirecting to GitHub domains like github.com and github.io. What began as an experiment was only lightly documented and thus not heavily used.
Today, git.io is increasingly being used for malicious purposes. At GitHub, we want to end that activity, focus on building great developer tools, and cede URL shortening to companies and teams who provide it as a core offering. There are many URL shortening services available today that have more capabilities than git.io.
For these reasons, we have disallowed new link creation on git.io. Existing URLs will continue to be accessible, but we encourage using one of the many URL shortening services that are available, instead of git.io, as we will be deprecating the tool in the future. This allows us to concentrate on what we’re able to make and keep great.