To find out what version we are of Git or Mercurial we are running at any time, scroll to the footer of any page and click on Version info. Bitbucket generally keeps up to date with recent versions of Git and Mercurial.
Neither Git nor Mercurial have introduced changes that would cause backwards compatibility issues. However, we still recommend staying up to date with Git and Mercurial in your local environment.
If you encounter any issues with Git or Mercurial interacting with the website, first, ensure your environment is up to date. If that doesn't resolve the issue, then open a support request to support.atlassian.com. Be sure to include the specific version and any detailed error messages you may have received.