General manager Reggie McKenzie said last week Jackson was next in line on the Raiders for a new deal.
A third-round draft pick in 2014 out of Mississippi State, Jackson had one year remaining on his rookie contract. The extension takes him through the 2022 season. The Raiders plan on moving to Las Vegas by 2020.
Jackson's extension is worth up to $56 million and includes $26 million in guaranteed money, sources told Anderson and Schefter.
The Raiders had more than $33.3 million in salary cap space before last week's $125 million extension for quarterback Derek Carr, and his salary cap number for 2017 was expected to be $15 million, which would bring the team's cap number down to about $18 million.
Jackson's cap number is not yet known, and the Raiders have yet to sign any of their top three draft picks, including first-rounder Gareon Conley, who has yet to hear if he will face charges after being accused of sexual assault before the draft.
In Jackson, the Raiders locked up a key part of their oft-dominant offensive line, which last season was a top-five unit in the NFL, according to Pro Football Focus. It also includes Pro Bowlers in left tackle Donald Penn, left guard Kelechi Osemele (also an All-Pro) and center Rodney Hudson.
The Raiders had the highest cap value on their offensive line last season ($37 million) and gave up an NFL-low 18 sacks, according to ESPN Stats & Information.
After two seasons at left guard, the 25-year-old Jackson switched to right guard in 2017 with the arrival of Osemele, and he did not appear to miss a beat.
Up next for the Raiders is defensive player of the year Khalil Mack, though the All-Pro edge rusher already had his fifth-year option, as a first-round pick in 2014, picked up by Oakland earlier this offseason, tying him to the team through at least 2018.
Sources told Schefter that Mack would have to wait until 2018 to get his extension because his deal is expected to be too big to fit under the cap this season.
No extension is expected to be in line for him until next offseason, when Pro Bowl receiver Amari Cooper will also be eligible for an extension.
But as a first-round pick in 2015, Cooper could also potentially be in line for a fifth-year option.