The 48-year-old woman, known only by the pseudonym Heidrun Anschlag, was freed two days ago and returned to Russia while her 53 year-old husband, known as Andreas, remains in detention, the DPA news agency and Focus magazine reported.
The man was jailed in July 2013 for six and a half years and his wife for five and a half years by the higher regional court in the southwestern city of Stuttgart.
The pair were planted in former West Germany from 1988 by the Soviet Union's KGB secret service and later worked for its successor the SVR, the court heard.
The couple obtained NATO and EU political and military secrets, focussed especially on the relationship of NATO and the EU with Eastern European and Central Asian countries.
In true Cold War style, documents were left under trees and at other prearranged spots to be picked up by operatives at the Russian consulate general in Bonn, the capital of what was then West Germany.
The pair had posed as Austrian citizens who were born and grew up in South America and were living what prosecutors called a "middle class existence" as a cover for their clandestine activities.
Andreas was ostensibly an ordinary worker in the auto industry, living with housewife Heidrun.
According to Focus, the premature release could have been made as part of an exchange of agents between Russia and Germany.
Shortly after they were handed their prison sentences last year, a report emerged that Moscow wanted to exchange the married couple for at least one convict jailed in Russia on charges of spying for the West.
Such spy exchanges, familiar from the Cold War era and John le Carre novels, already have a precedent in post-Soviet Russian history.
In 2010, Russia and the United States agreed a sensational spy swap of 10 Russian "sleeper" agents caught in the United States for four men convicted in Russia of spying for the West.
The 10 Russian spies -- including the glamorous female agent Anna Chapman -- were brought back to Moscow and subsequently personally welcomed by Putin.