Red Bull releases Carlos Sainz and severs ties, Carlos is free to join Renault.
Carlos Sainz criticized Red Bull and Toro Rosso over the past several weeks, concerned about his future career. Red Bull is reluctant to replace any of their top drivers, but at the same time would not release Toro Rosso drivers to move to other teams.
In the end, it doesn't make sense to keep a driver who is not happy with the team and with the progress, so they decided to let him go. Currently, Renault chief Cyril Abiteboul is negotiation with Dr Helmut Marko about the terms required to get Carlos to Renault. It is said they will need to raise $8 milion for the transfer.
...which means Jolyon Palmer will be replaced, and reportedly Carlos Sainz will drive the Renault at the Hungarian GP, if the deal comes through.