A Jekyll plugin to expose a `jekyll_version` Liquid template tag which returns the Jekyll version number

jekyll_version.rb

module Jekyll
  class JekyllVersionTag < Liquid::Tag

    def initialize(tag_name, text, tokens)
      super
      @text = text
    end

    def render(context)
      Jekyll::VERSION
    end
  end
end

Liquid::Template.register_tag('jekyll_version', Jekyll::JekyllVersionTag)

To use this, drop this file into your _plugins/ folder and use {% jekyll_version %} in your template where you want to access it.