According to Variety, Nu Image and Millennium Films have struck a deal with a pair of Chinese companies to produce The Expendables 4. The plan is to shoot next year for a release some time in 2017, likely in the summer given that every film has been released during that time. The budget is expected to be around $100M, which would be the franchise's highest.
There's no director or writer yet but you can bet Sylvester Stallone will start tweeting about it soon and the circus can begin. Every time there's a new Expendables film people start speculating about who will be the newest action hero to sign on. There are always one or two really big additions, like Wesley Snipes and Ronda Rousey last time, so don't be surprised if rumors start swirling. Hulk Hogan has thrown his hat into the ring but given his recent scandals that's probably not happening. We'll also probably see Stallone push to make this next film R-rated rather than PG-13 since that didn't work out so well before.