Flight Crew Air Transport Pilot (ATP)
Flight Crew Total 5314; Flight Crew Type 985
Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict
Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Airspace Structure; Human Factors
I was the PM. I was on the interphone talking to the FAs in the back about new routing which would add on flight time. ATC had re-cleared us to fly towards the west and then in on the [VOR] instead of the [STAR] due to weather. While on the phone; I started to hear a frantic call from ATC to DESCEND IMMEDIATELY to FL380. I hung up; and then there was second call. By this time; the Captain had already disconnected the autopilot and begun to descend manually in FLCH (Flight Level Change) down to FL380. I then told ATC we were. She then became very apologetic saying that all of the planes being rerouted created confusion and she had left us (or the other plane) at the wrong altitude. She asked if the nature of our descent caused any onboard injuries; which I said it did not. (It was not a violent descent.) We received a TA for the other traffic; but not an RA. When they passed overhead; they were about 900 ft. above. Before we descended; we were both at FL390 on a converging course. The controller was once again very apologetic and obviously alarmed at their error. The Captain wanted us to file this report given the situation; even though we did not technically respond to an RA. We continued on without any other issues.
B757 First Officer reported that during a reroute for weather their aircraft was on a converging course with another aircraft.