Marko: Vettel had get-out clause
Red Bull advisor Helmut Marko has revealed that Sebastian Vettel had a get-out clause in his contract with allowed him to leave the team at the end of the season and pave the way for his apparent switch to Ferrari.
Source: http://www1.skysports.com/news/24182/9502143/sebastian-vettel-had-red-bull-contract-get-out-clause-for-2015-says-helmut-marko