What is the difference between the two Google JS client CDN's?
A) <script src="https://apis.google.com/js/api:client.js"></script> versus B) <script src="https://apis.google.com/js/client.js"></script> The only differnence being the api: before client.js . CDN A is used in the Google Sign-In for Websites docs in the Building a button with a custom graphic section. CDN B is used almost in the Google API Client Library for JavaScript (Beta) docs . They both appear to work interchangeably. Short answer: there is no difference Long answer: The Google JS client CDN is a bit weird because the actual JS you get is dynamically created based on the file name you