Is object assignment in .NET atomic?

AtomicAssignment.cs

class AtomicAssignment
{
    static object o;
    
    static AtomicAssignment() => o = new object();
    
    public static Update()
    {
       //is the assignment atomic? or is something like Interlocked.Exchange necessary?
       o = new object();
    }
    
    public static Read()
    {
       //if the assignment in Update() is atomic then this should be thread safe
       //we will get a valid reference to an object
       object refCopy = o;
    }
}