Ahh, gotcha Smitty. Open Passan’s tweet in the article you linked. He provides an addendum shortly afterwards that says there is no option.
Better yet, here it is:
Addendum to this: Sources tell @JesseRogersESPN that Lester's deal with the Nationals is indeed a straight one-year deal without an option. @Ken_Rosenthal and @jon_greenberg first linked Lester to Washington.
— Jeff Passan (@JeffPassan) January 19, 2021