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Players typically have three option years, but those who have accrued less than five full seasons (including both the Major and Minors) are eligible for a fourth if their three options have been exhausted already. For the purposes of this rule, spending at least 90 days on an active Major League or Minor League roster during a given season counts as one full season. Players also earn a full season if they spend at least 30 days on an active Major League or Minor League roster AND their active-roster and injured-list time amounts to at least 90 days in a given season.
I'm assuming that since Peralta was active for 90 days this season, it counts as 5 full years.
Anyway, all the Yankees beat writers said he couldn't be send down.