You operate a recommendation API for retail customers and must preserve stability when making backward-incompatible changes. Which API-versioning strategy should you follow?

Incrementing the API version number for every backward-incompatible change (e.g., v1, v2) is the standard and most robust strategy. This allows clients to continue using the older, compatible version while new clients or those ready to adapt can migrate to the new version. This preserves stability and gives customers control over when they adopt changes. Notifying customers via email is a communication strategy, not a versioning strategy, and doesn't prevent breakage. Automating documentation is good practice but doesn't solve backward incompatibility. Appending 'DEPRECATED' and reusing the version number would force all clients to immediately update or break, which defeats the purpose of maintaining stability during incompatible changes.