Tesla CEO and founder Elon Musk on Friday announced via Twitter and the company blog that the drivetrain warranty for the 85 kWh Model S has been extended, giving it an eight-year, infinite-mile warranty to match that of the battery pack. This new warranty arrangement applies retroactively to every Model S ever produced, too, meaning it benefits both existing and new owners. Originally, the Model S carried a four-year, 50,000-mile limited warranty that could be extended to 8 years and 100,000 miles for an additional $4,000 fee. Musk says in his blog post detailing the move that “[i]n hindsight, this should have been [Tesla’s] policy from the beginning of the Model S program,” as the company’s warranty should reflect its belief in the improved reliability of its electric engines vs. their gasoline-powered equivalents.