It's not very common at all. This particular offseason has been a bit insane in that lots of players that are pretty darn good but not necessarily all-time greats are getting longer contracts. Part of this is just an unusually robust free agent market, but part of it is that some teams realized that since the luxury tax (kind of an informal salary cap) calculations factor in the average annual value of a deal, spreading the deal out longer than the player will be good or useful might actually be a net gain on the team because they can be really good for most of the player's deal and then hopefully replace them with homegrown, cheap talent on the back end of the deal.

Before this year, basically the longest deals given out were 10 year deals, and those would only go to guy who were on a hall of fame trajectory and very, very young. But now, in this offseason, it's been a bit of an arms race, in part because the Mets are just throwing absolutely obscene amounts of money at some of the best players on the market. Last year the Mets set an all time MLB payroll high with something like $230M or so. This year, the Mets payroll is over $400M with luxury tax penalties.

The Correa situation is also a bit odd because Correa already had a 13 year deal lined up with a different team, and then yesterday they delayed their announcement of the signing due to "awaiting test results" with no further information. The Mets had made a late push to sign Correa only hours before he signed that deal with the Giants, and then all of a sudden in the middle of the night we find out that Correa's deal with the Giants is gone and the Mets swooped in with this offer. VERY rarely do you see deals like this fall apart, and for the Mets to already have a new deal in place before most people even knew the old deal fell apart is completely nuts.

The Mets are just turning the entire sport on its head. And it's great for fans and players.