Prosecutors said they were given 20-year jail terms after the journalist’s family decided to pardon them.
However, his fiancée said the ruling made “a complete mockery of justice”.
Khashoggi, a prominent critic of the Saudi government, was killed inside the kingdom’s consulate in the Turkish city of Istanbul by a team of Saudi agents.
The Saudi government said the journalist was killed in a “rogue operation” and the following year Saudi prosecutors put 11 unnamed individuals on trial.
The trial was dismissed at the time as “the antithesis of justice” by UN Special Rapporteur Agnes Callamard, who concluded that Khashoggi was “the victim of a deliberate, premeditated execution” for which the Saudi state was responsible.
Ms Callamard said there was credible evidence that high-level officials, including Saudi Crown Prince Mohammed bin Salman, were individually liable.
The prince denied involvement, although two former aides are being tried in absentia in Turkey on the charge of instigating the premeditated murder of Khashoggi. Eighteen other Saudis are accused by Turkey of carrying out the killing.
How did Jamal Khashoggi die?
The 59-year-old journalist, who went into self-imposed exile in the US in 2017, was last seen entering the Saudi consulate on 2 October 2018 to obtain papers he needed to marry his Turkish fiancée, Hatice Cengiz.
After listening to purported audio recordings of conversations inside the consulate made by Turkish intelligence, Ms Callamard concluded that Khashoggi was “brutally slain” that day.
The Saudi public prosecution concluded that the murder was not pre-meditated.
It said the killing was ordered by the head of a “negotiations team” sent to Istanbul to bring Khashoggi back to the kingdom “by means of persuasion” or, if that failed, “by force”.
The journalist was forcibly restrained after a struggle and injected with a large amount of a drug, resulting in an overdose that led to his death, according to the prosecution. His body was then dismembered and handed over to a local “collaborator” outside the consulate. The remains were never found.
Turkish prosecutors concluded that Khashoggi was suffocated almost as soon as he entered the consulate, and that his body was destroyed.
In December 2019, the Riyadh Criminal Court sentenced five people to death for “committing and directly participating in the murder of the victim”. Three others were handed prison sentences totalling 24 years for “covering up this crime and violating the law”.
Three people were found not guilty, including Saudi Arabia’s former deputy intelligence chief, Ahmad Asiri.
Saud al-Qahtani, a former senior adviser to Crown Prince Mohammed, was investigated by the Saudi public prosecution but not charged.
Why were the sentences changed?
This May, Khashoggi’s son Salah announced that he and his brothers were “pardoning those who killed our father, seeking reward from God almighty”, accepting the contention that the murder was not premeditated.
That paved the way under Saudi law for a reprieve for the five facing execution.
On Monday, the Saudi public prosecution announced that the Riyadh Criminal Court had sentenced five of those convicted in January to 20 years in prison, and that the three others had received sentences of between seven and 10 years.
It said the verdicts were final and that the criminal trial was now closed.
“The Saudi authorities are closing the case without the world knowing the truth of who is responsible for Jamal’s murder. Who planned it, who ordered it, where is his body? These are the most basic and important questions that remain totally unanswered.”
Ms Callamard welcomed the fact that the death sentences had been commuted, but said the verdicts could not be allowed to “whitewash what happened”.
“The Saudi prosecutor performed one more act today in this parody of justice. But these verdicts carry no legal or moral legitimacy. They came at the end of a process which was neither fair, nor just, or transparent,” she tweeted.
Ms Callamard said Crown Prince Mohammed “remained well protected against any kind of meaningful scrutiny” and again called on the US intelligence services to release their reported assessment that he ordered the killing of Khashoggi.