No they are not. The V4 design in drawings do not have the MCS charger cord or handle. They use the existing Tesla handle and V3 type cord. If it is as you say, all the new SC planned to use V4 would be incompatible with ALL current Tesla vehicles except the semi. Why would they build 12 stall chargers with passenger vehicle size back in spaces for Semis?Elon clearly stated that the CT will use the MW charger.
The new V4 chargers are the MW chargers. You need to go back review the Semi presentation.
Like Rocky pointed out, it’s about the 1000V and MW architecture and necessarily the charging standard.
Assuming the same power capacity of V3 but changing to 1000V architecture means V4 chargers get 625kw top end charging rate vs 250kw of V3. This would require no change in current wiring because the current draw would remain the same. It would allow the Cybertruck battery to be up to 2.5x larger (200kwh) and still charge in the same amount of time as a MY/M3. They have done the same thing with SR vs LR vehicles. LR has 50% larger battery (82 vs 55) but 50% faster charging (48A vs 32A and 250kw vs 150kw) so charging times are roughly the same. This looks to carry over with the CT.