GitHub Pages supports two Markdown processors: kramdown and GitHub's own extended CommonMark processer, which is used to render GitHub Flavored Markdown throughout GitHub.

Github Pages is a sweet service that builds your Jekyll site for you when you commit changes to a Github repo. If you were using redcarpet and Pygments, you now should switch to Kramdown and Rouge to stay updated with the recommended Markdown filter and syntax highlighter supported by Github Pages.

Switch from redcarpet to kramdown, the new Github Pages default