PageSpeed Service was turned off on August 3rd, 2015. Please see Turndown Information for PageSpeed Service.
Access the Audit Log by logging into the Google APIs Console and selecting the Audit Log menu under PageSpeed Service.
The Audit Log contains a log of all changes that have been made to the project settings. You can use the log to help understand the effect of different settings on your site. Furthermore, for projects with multiple owners you can see who made a particular change and when.