Lineage and ArcheAge Creator Opens Up Experimental MMO Built for Human and AI Players

Song Jae-kyung, the Korean online game developer best known for work on Nexus: The Kingdom of the Winds, Lineage, and ArcheAge, has revealed a new solo-developed project called Open MMORPG. The browser-based MMO is playable with a Google login and doesn’t require a separate install.

The unusual hook is that Open MMORPG is designed so AI agents and human players use the same connection rules. According to the project documentation, AI agents join through the same WebSocket protocol as everyone else, with no special API access or hidden privileges. In theory, the server can’t tell whether a player is human or an agent, and agents can attempt the same actions humans can.

Song has also released the game’s source code and development documents through GitHub, opening it up for outside contributors. The project was built solo, with Song describing his workflow as “Vibe Coding,” where AI handled much of the code generation. Assets are a mix of AI-generated and procedurally generated work, while around 50 background tracks were made with AI music tools such as Suno.

Open MMORPG still includes a fairly traditional MMO feature set. The world is 32km by 32km, with generated terrain, rivers, coastlines, biomes, settlements, roads, and bridges. There’s a seasonal system with changing day and night lengths, plus two moons on separate orbital paths.

Players can build wooden houses up to four stories tall, place furniture, manage a weight-limited inventory, equip gear across 11 slots, and pick up dropped items left in the world. Combat uses server-side calculations and stat rolls inspired by Dungeons & Dragons and NetHack.

Song co-founded Nexon in 1994, later launched Lineage at NC, and founded XLGAMES in 2003 for ArcheAge. After leaving XLGAMES last year, he joined the Open Game Foundation as a senior advisor and board member.

Further reading: Invent Global