NFL Network's Ian Rapoport provided the specifics:
Ian Rapoport @RapSheet
The #Bengals are signing star DT Geno Atkins to a 4-year extension worth $65.3M, source said. He gets $25.5M in first year. More than half of the deal ($37.5M) paid in first 2 years. $16.3M yearly average is highest yearly average signed by a 30+ year old non-QB in NFL history.
Rapoport also reported the Bengals signed defensive end Carlos Dunlap to a three-year, $45 million extension.
The 30-year-old remains one of the NFL's best interior pass-rushers. He finished the 2017 season with nine sacks in 16 games. Since the Bengals selected him in the fourth round of the 2010 draft, Atkins has recorded 61 total sacks, which is third among defensive tackles, per Pro Football Reference.
He sat second on Bleacher Report's NFL1000 year-end rankings of the top defensive tackles.
"An excellent pass-rusher using a devastating bull rush to put offensive lines on skates, Atkins has push-pull and club-swim moves as potent counters," NFL1000 scout Brandon Thorn wrote. "He takes good angles with solid foot quickness and closing burst to disrupt and finish plays behind the line of scrimmage."
The Athletic's Ross Tucker noted the timing of Atkins' extension:
Pro Football Talk's Mike Florio reported Sunday the Los Angeles Rams and Aaron Donald are working on a contract that would "make [Donald] the highest-paid defensive player in NFL history." Donald's deal will likely have an impact on extensions for elite defensive tackles going forward.
By getting Atkins' future secured now, Cincinnati likely saved itself some money before Donald resets the market.