Update 2: A spokesperson for DC confirmed for Newsarama Soule's work on DC's Red Lanterns and Swamp Thing will continue until March 2015.
Update: Soule typed up a post on his personal blog to explain the status of his current work and why he took the exclusive contract with Marvel Comics late Tuesday evening.
”Signing a contract is a business decision,” he started off, explaining why he wouldn’t talk about the ins and outs of the contract itself. However, he did talk about the change and how he’ll come off the DC series. “The decision to work with Marvel for a while isn’t any sort of denigration of DC. I had a fantastic time there, I was treated extremely well, I have strong positive feelings about all of my editors and the DC universe of characters, and I look forward to hopefully working with them at some point down the road,” Soule said. “Both Marvel and DC were extremely gracious about working with me to make sure that I could complete my runs on DC titles the way I originally intended. So, you’ll see my work on Red Lanterns as part of the big Godhead event, you’ll see me ending my run on Superman / Wonder Woman the way I wanted to, and Swamp Thing will continue under my pen for a little while as well.” So, it seems his runs on Red Lanterns and Swamp Thing won’t simply end on a “2 of 4” issue in the middle of a story.
As for Letter 44, it “isn’t going anywhere,” and Soule is “on that one until it’s done, which won’t be for a while yet.”
As to why he took the deal, partially it was to even things out, as he was writing eight titles a month while still working full time as a practicing lawyer.
Original Story: In a new interview/preview about this week's Death of Wolverine #1, USA Today reports writer Charles Soule has recently signed an exclusive contract with Marvel Comics. Soule, who previously wrote Superman/Wonder Woman for DC and is listed at the writer of Red Lanterns and Swamp Thing as of their respective November on-sale issues, will presumably be leaving those series soon.
In addition to the weekly Death of Wolverine with artist Steve McNiven, the prolific Soule also writes (despite being a practicing New York attorney) Inhuman and She-Hulk for Marvel. It remains to be seen if the writer can/will continue his Oni series Letter 44 under the terms of his Marvel exclusive, but in recent years many exclusives at DC and Marvel have allowed creators to continue to work on creator-owned and small press projects.