Updated, 4/11/19, 7:44am PT: The U.S. Department of Justice announced that it has charged Julian Assange with "conspiracy to commit computer intrusion for agreeing to break a password to a classified U.S. government computer." The department also confirmed that Assange was arrested "pursuant to the U.S./UK Extradition Treaty" and that he will be extradited to the United States. Assange is accused of working with Chelsea Manning in 2010 to crack a password stored on a Department of Defense computer so Manning could provide WikiLeaks with classified documents. The charge carries a maximum penalty of five years in prison, but the DoJ noted that maximum penalties are rarely applied.
Original article, 4/11/19, 6:06am PT:
The Metropolitan Police Service (MPS) announced today that it arrested WikiLeaks founder Julian Assange, who has lived in the Ecuadorian embassy in London since 2012, following Ecuador's withdrawal of his political asylum. MPS said in its announcement that Assange was "taken into custody at a central London police station where he will remain, before being presented before Westminster Magistrates' Court as soon as is possible."
MPS said it was invited into the embassy by Ecuador's ambassador to the United Kingdom. That hardly comes as a surprise: Reuters reported in October 2018 that Assange filed a "lawsuit challenging the Ecuadorean government requiring him to pay for medical bills [and] phone calls and clean up after his pet cat." The report also said that officials "complained of Assange riding a skateboard in the halls, of playing soccer on the grounds, and behaving aggressively with security personnel." Assange said the requirements and complaints were meant to force him to leave the embassy.
It turns out that Ecuador didn't need to find roundabout ways to get Assange to leave--it just had to withdraw his political asylum and let British police arrest him. That's exactly what happened today, with MPS arresting Assange in accordance with a warrant issued by the Westminster Magistrates' Court in June 2012. We should note at the start that the warrant had nothing to do with Assange's connection to WikiLeaks, at least not directly. (His supporters will inevitably argue that any legal action against Assange is motivated by his publication of top-secret documents.)
Rather, the warrant was issued because shacking up in the Ecuadorian embassy violated the terms of Assange's bail. He originally sought refuge in the embassy because he feared that British police would extradite him to Sweden on sexual assault charges--which have since been dropped--and that he would then be extradited to the United States for his involvement with WikiLeaks. There is some basis to those fears: The New York Times reported in November 2018 that the U.S. had secretly filed charges against Assange; it's not clear with what exactly he has been charged.
Yet the original sexual assault investigation, Ecuador's withdrawal of Assange's political asylum, and today's arrest haven't been directly linked to the charges in the U.S. Nor have the governments of Ecuador, the UK, or Sweden indicated that they would extradite Assange to the U.S. as part of this years-long back-and-forth. We won't know if this arrest was truly just standard procedure or if it was part of a multinational conspiracy to get Assange to the U.S. until he has his day in court. That couldn't happen while he was safe in the embassy; now it can.
WikiLeaks, for its part, attempted to rally its supporters on Twitter by saying that "Ecuador has illegally [sic] terminated Assange political asylum in violation of international law." It also linked to the Defend WikiLeaks web page, which purports to explain how the prosecution of Assange threatens U.S. journalism, and which also features a legal defense fund to which supporters of Assange and/or WikiLeaks can donate.