When evolving APIs, maintain backward compatibility to prevent breaking changes for existing consumers. Key approaches: 1. **Retain removed members with obsolete attributes**: When removing or replacing public methods, mark the original as obsolete but maintain its functionality. ```csharp // Old method [EditorBrowsable(EditorBrowsableState.Never)] [Obsolete("Use UpdateAsync(WaitUntil, ConnectorPatch) instead")] public virtual Response Update(ConnectorPatch patch, CancellationToken cancellationToken = default) { // Call the new implementation return UpdateAsync(WaitUntil.Completed, patch, cancellationToken).EnsureCompleted(); } // New method public virtual ArmOperation Update(WaitUntil waitUntil, ConnectorPatch patch, CancellationToken cancellationToken = default) ``` 2. **Handle constructor parameter changes**: When a required parameter becomes optional, keep a constructor overload that accepts the previously required parameter: ```csharp // Old constructor required publisherId public MarketplaceDetails(string planId, string offerId, string publisherId) : this(planId, offerId) { PublisherId = publisherId; } // New constructor makes publisherId optional public MarketplaceDetails(string planId, string offerId) { } ``` 3. **Add code-gen attributes for serialization**: When properties are removed from models, use code generation attributes to maintain serialization compatibility: ```csharp [CodeGenSerialization(nameof(BlockResponseCode), "blockResponseCode")] public partial class DnsSecurityRuleAction { [EditorBrowsable(EditorBrowsableState.Never)] public BlockResponseCode? BlockResponseCode { get; set; } } ``` These approaches ensure that existing code continues to work while allowing APIs to evolve with improved designs.