How to Answer: "How do you approach API versioning, deprecation, and backwards compatibility?"

“My primary rule is to avoid breaking changes whenever possible by treating API contracts as additive. When breaking schema alterations are unavoidable, I prefer URI path versioning (`/v2/`) or explicit header versioning depending on client capabilities. For deprecations, I implement a structured sunset policy: returning standardized `Sunset` and `Deprecation` HTTP headers, logging caller telemetry to identify unmigrated clients, sending proactive notifications to partners, and maintaining older endpoints throughout a clear 6-to-12 month support lifecycle before decommission.”

“I ensure backward compatibility by making new fields optional and avoiding deleting or renaming existing response attributes. When major updates require new versions, I update our API documentation, add deprecation notices to older endpoints, and log API client traffic so we can reach out directly to developers using deprecated routes before turning them off.”

“I keep APIs backward-compatible by adding new properties rather than altering old ones. When an API version needs to be retired, I follow the team's versioning guideline, adding deprecation logs and giving clients enough time to update their requests.”