The best way to review the complete history is to check the Changelog on our official API documentation. Modifications to our API (including additions and deprecations) are added here by date.
Additions
The best way to be alerted of new changes (and any disruption in our service) is to subscribe to our status page. This will add you to our quarterly newsletter, which recaps the changes and best practices regarding the API.
Deprecations
Deprecated items are usually announced early via email to our clients with a future deprecation date, multiple months ahead of the actual changes. This allows our API users ample time to move away from whatever data or feature is being deprecated.