see on GitHub

Session: How to Get Entity Change-Vector

The change-vector reflects the cluster wide point in time where something happened. It includes the unique database ID, node identifier, and the Etag of the document in the specific node. When a document is downloaded from the server, it contains various metadata information e.g. ID or current change-vector. Current change-vector is stored within the metadata in session and is available for each entity using the GetChangeVectorFor method from the Advanced session operations.

Syntax

string GetChangeVectorFor<T>(T instance);
Parameters
instance T Instance of an entity for which an Etag will be returned.
Return Value
string Returns the current change-vector for an entity. Throws an exception if the instance is not tracked by the session.

Example

Employee employee = session.Load<Employee>("employees/1-A");
string changeVector = session.Advanced.GetChangeVectorFor(employee);