Sonic the Hedgehog Extended Edition is a hack in progress by Cinossu of Sonic the Hedgehog on the Sega Mega Drive/Genesis. In this version of the game, instead of new or fully edited zones, all the original zones are kept intact with minor editing to the acts. Instead, this hack extends the game beyond its original capabilities, including a zone map with warp rings to each act (much like in Sonic Advance 3), saving via SRAM slots (like in Sonic the Hedgehog 3), obtainable upgrades such as the Spin Dash and Super PeelOut (like in the Megaman X series) as well as a new type of ring, emerald, and special stage to add to the mix.

While work has not been shown on the hack for a while publicly, a lot of work goes on in private. This is mostly Cinossu either restarting the entire thing from scratch (currently on the 5th restart since conception), or constantly adding and refining new features and ideas. The latest restart is most likely the last one, however, as the disassembly is now so modular that the various chunks can be restarted rather than the entire hack.