On the Twitch blog the company stated, “Our goal at Twitch is to create a safe, welcoming, inclusive community platform where everyone can feel comfortable and have fun. Previously, we made game-specific decisions about which games would and would not be available for broadcast – sometimes due to overtly sexual content, sometimes due to gratuitous violence. This is unsustainable and unclear, generating only further confusion among Twitch broadcasters. We would like to make this policy as transparent as possible. Simply put, AO games are not welcome on Twitch.”
ESRB ratings only apply to games sold in North America, but the company’s new policy extends to versions of AO-rated games in all territories. “Generally, if the US version is rated for Adults Only (18+) or has an equivalent rating in your territory, you should not broadcast that game on Twitch. Games rated 18+ by other rating systems are fine to stream, so long as they are not rated AO by the ESRB, and they don’t violate the standard language of our RoC and ToS,” confirmed the company.
Twitch has a small list of prohibited games that you can see here.