Jarvis signed an 8 year contract extension that has a phantom 9th year attached, where Jarvis will receive a bonus payment of deferred money through the deal. This means Jarvis' annual salary cap hit is lower, and the 9th year payment doesn't count against the salary cap - it's only out of ownership's pocket. The best part is, there's no limit to the amount of deferred salary, or how long the deferred payments can last.
This is obviously a contract strategy that the Oilers are likely looking into already, and may want to propose towards Leon Draisaitl. It would be a major financial commitment for life from Oilers ownership, but for some of the best players in franchise history - it will be well worth it for the annual payments until they're senior citizens.