This is just now being picked up by commenters and news outlets. No time yet to read the opinion but the early accounts say that the DC Court of Appeals by 2-1 approved Flynn's petition for a writ of mandamus.
Per The Hill:
"In this case, the district court’s actions will result in specific harms to the exercise of the Executive Branch’s exclusive prosecutorial power," Judge Neomi Rao, who was appointed to the circuit court by President Trump, wrote in the majority opinion.
"If evidence comes to light calling into question the integrity or purpose of an underlying criminal investigation, the Executive Branch must have the authority to decide that further prosecution is not in the interest of justice," Rao added.
The ruling itself was a total no-brainer, only made close by the political foofaraw surrounding the Flynn case. Henderson was never going to allow Sullivan to trample established law, but the in-your-face nature of his arguments obviously convinced Henderson that Sullivan could not be trusted further than he could be thrown--so, no leeway granted. This will end up being a HUGE black eye for Team Mueller, Chris Wray's FBI, and the Fake News Media's Russia Hoax--because there is much more to follow, more evidence to be made public.
As important as anything else, Michael Flynn is now free to speak his mind and tell his story. That, too, will be huge as we head into the campaign season and as the Radical Left--proxies for the Dems--seek to turn the country upside down.
Per Undercover Huber--the victory for Flynn is "only partial." That's a tongue in cheek joke on his part. The "partial" part is that Sullivan wasn't kicked off the case--so Sullivan gets to dismiss it as ordered:
The ruling is only “partially” for @GenFlynn, as the appeals court ordered:
—Sullivan to dismiss the case
—Gleeson’s appointment as “amicus” immediately “vacated”. Bye Felicia!
—However they declined to grant the request to kick Judge Sullivan off the case immediately
Gleeson and Sullivan get the back of the Court's hand--Sullivan for ignoring "black letter law" and Gleeson essentially for being a jerk (that's a code word on a family oriented blog). The Court noted Gleeson's idiotic brief relied on "news stories, tweets, and other facts outside the record" as part of his "irregular and searching scrutiny" to encourage Sullivan to trespass on "a core aspect of the Executive's charging authority."
UPDATE 1: Jonathan Turley reminds us of an article he wrote back in May. Turley is too polite to say so but the article reveals the corruption of our legal establishment in the context of the Flynn case. Read it in light of what we now know about Gorsuch--first paragraph:
The Los Angeles Times has posted a column by UCLA Law Professor and former U.S. Attorney under Bill Clinton, Harry Litman. The column  captures just how disconnected legal analysis has become in the Trump era. Litman in the column admits, to his credit, that the precedent overwhelmingly opposes a denial of motion to dismiss. However, Litman then encourages U.S. District Judge Emmet G. Sullivan to use the hearing to “make trouble” for the Justice Department — a goal disconnected from the inescapable legal precedent (and thus the judicial obligations) presented by the motion. There is a word for using hearing to gratuitously “make trouble” for the Executive Branch: judicial activism. I have previously written about the need to dismiss the Flynn case and criticized those who dismiss new evidence of wrongdoing by the prosecutors.
Brett L. Tolman
He’s not wrong
Bernard B. Kerik
CONGRATS @GenFlynn—DC Circuit Court slaps Judge Sullivan – do your job and dismiss, DC Court to John Gleeson - you’re an asshole and out of order! twitter.com/tolmanbrett/st…
Maria Bartiromo: So do you think this goes all the way up to the top, to President Obama?
Sidney Powell: Absolutely.
UPDATE 4: Don Surber:
Appellate Judge Neomi Rao, writing for the majority, tore Judge Sullivan a new one.
She wrote the case is “about whether, after the government has explained why a prosecution is no longer in the public interest, the district judge may prolong the prosecution by appointing an amicus, encouraging public participation, and probing the government’s motives.
"On that, both the Constitution and cases are clear: He may not."
Doesn't get any clearer than that.