The ObsoleteAttribute has existed in C# since the beginning to indicate that a feature is deprecated.
C# 12.0 introduces the ExperimentalAttribute to signal that a feature is experimental and therefore subject to change and emits similar compiler warnings.
Code
C#
[Experimental("MyAdvancedConnections")]
public Connection StartConnection(ConnectionSpecification specification) => new Connection(specification);
#pragma warning disable MyAdvancedConnections
var connection = StartConnection(specification);C#
/// <summary>
/// Warning: This feature is experimental and may change in future versions.
/// </summary>
public Connection StartConnection(ConnectionSpecification specification) => new Connection(specification);
var connection = StartConnection(specification);