DRIVERS-1916: This ticket does two things: It clarifies that if the "hello" command is used (as opposed to "isMaster") it must be sent using OP_MSG Because the previous version of the spec already required that if a versioned API is specified, "hello" must be used, it is made explicit that this also means OP_MSG must be used. Drivers must ensure that their connection handshake uses both OP_MSG and "hello" if a versioned API is specified. For an example of what your connection process should look like after this change, take a look at the Python implementation in the handshake spec.