DRIVERS-2503 : The connectionId in the hello (or legacy hello) response can be an int32 , double , or int64 . Many drivers assume an int32 , which may result in connectionId truncation or connection failure. Drivers should ensure that the server's connectionId (and the client connectionId for consistency) is expressed as a numeric type capable of holding an int64 . NOTE: If the client and server connectionId fields are part of the driver's public API, you may have to add new int64 connectionId fields and deprecate the existing int32 fields. On the next major version bump, the deprecated int32 fields should be removed.