Julian Assange is set to face his first US extradition hearing in London, with the case likely to boil down to the WikiLeaks founder's motivations and whether he acted as a journalist or a computer hacker.

The Australian's appearance via video link at Westminster Crown Court on Thursday will likely be a procedural formality but new details about the US case against him could be revealed.

The US Justice Department has charged the 47-year-old, who was arrested inside Ecuador's embassy on April 11, with conspiracy to commit computer intrusion with former American army intelligence analyst Chelsea Manning in 2010.

On Tuesday WikiLeaks tweeted that Assange was separately due to be sentenced at Southwark Crown Court on Wednesday for violating his bail conditions as he sought refuge in the Ecuadorian embassy in London in 2012.

But the organisation also said Assange's lawyers had not been able to confirm the sentencing time. His sentencing had earlier been set for May 22.

The US has already had difficulty in building its extradition case, with Manning refusing to testify about Assange before a grand jury. She has been jailed for her refusal.

The crux of the US accusation is that Assange tried to help Manning hack a password on a Pentagon computer system nine years ago.

The Justice Department alleges that cracking the code would have made it harder for authorities to identify Manning as Assange's source for more than 750,000 classified military and diplomatic documents that were published by WikiLeaks.

"Cracking the password would have allowed Manning to log on to the computers under a username that did not belong to her. Such a deceptive measure would have made it more difficult for investigators to determine the source of the illegal disclosures," the indictment says.

The US Attorney's Office alleges Assange told Manning he had tried to crack the password but "had no luck yet".

Glen Greenwald and Micah Lee of the online news outlet The Intercept claim that Assange was merely trying to maintain Manning's anonymity, as any journalist would.

"Assange was not trying to hack into new document files to which Manning had no access, but rather trying to help Manning avoid detection as a source. For that reason, the precedent that this case would set would be a devastating blow to investigative journalists and press freedom everywhere," they wrote.

So Assange's motivation for trying to help Manning is likely to be central to the US case - whether he was trying to protect his source's identity or trying to help Manning hack into the system to access new, previously inaccessible data.

The debate about whether Assange is a journalist or a hacker has been swirling around the WikiLeaks founder for more than a decade.

If Assange is considered a journalist, granting his extradition would set a historic legal precedent.

"This precedent means that any journalist can be extradited for prosecution in the United States for having published truthful information about the United States," his lawyer Jennifer Robinson has said.

But extraditing Assange as a hacker would also create a sensation in British courts, which have recently protected two high-profile hackers from US extradition.

Lauri Love, a friend of Assange, and Gary McKinnon were set to be extradited for allegedly hacking US military networks but recently had UK courts rule in their favour.

Love's legal team included Assange's lawyer Ms Robinson.

Somewhat muffled by the louder debate about US extradition is the pressing matter of a potential extradition application from Sweden, which has been wanting to question Assange about an allegation of rape lodged in 2010.

Three other cases, that also involve a second woman, were dropped in 2015 after the statute of limitations ran out.

Sweden is still yet to lodge a fresh extradition request but women's groups have been piling pressure on British Home Secretary Sajid Javid to prioritise any Swedish application.

Sarah Green, co-director of End Violence Against Women, called the downplaying of the sex accusations against Assange "undignified".

"This is serious - the harm rape does, even the impact it has when people dangle it around in the news as though it's a trivial part of the story," she told The Guardian last week

Amid debate about motivations and precedents, the cacophony of commentary and a potential jurisdictional tug of war, Assange himself will probably just be hoping his next judge is slightly less strident than his last.

District Judge Michael Snow, in finding him guilty of breaching bail in early April, labelled him "a narcissist who cannot see beyond his own self interest".