In Brief:
- NEXUS adviser Song Jae-kyung, the developer who created Lineage, opened OpenAI Game Builders Seoul on Aug. 31 with a keynote making the case that AI’s next chapter in games is as a participant, not a development tool.
- By his account, Codex carried him to 160,000 lines of code across eight months on a solo MMORPG — compared with the 30,000 lines he produced in a year while building The Kingdom of the Winds three decades earlier.
- That project, Open MMO, hands AI agents no privileged API. Agents log in over the same WebSocket protocol human players use, and distribution is expected to run through NEXUS’s chain once the gameplay has been tightened up.
Speaking at OpenAI’s first game development hackathon, Song Jae-kyung argued that AI agents ought to be built to perceive, judge and act within a game world under their own terms — a new category of participant, not a smarter NPC or a faster compiler.
The NEXUS adviser and former XL Games CEO shared the Aug. 31 opening keynote slot at OpenAI Game Builders Seoul with Com2uS Chairman Song Byung-jun. Held at Graphic by Daeshin in Seoul, the event was OpenAI’s first global gathering organized around game development with Codex.
𝗔𝗜 𝗷𝗼𝗶𝗻𝘀 𝘁𝗵𝗲 𝗴𝗮𝗺𝗲.
NEXUS advisor Song Jae-kyung (@appledelhi) — the mind behind Lineage — gave the opening keynote at @OpenAI Game Builders Seoul today: AI won't be just a development tool. It will be a participant in the game.
His open-source, one-man MMORPG@ONEView on X ↗
He came with figures to back it. Three decades ago, on The Kingdom of the Winds, a year of work yielded roughly 30,000 lines of code. Eight months alone on Open MMO produced 160,000. Around eight times the throughput, as he put it.
No special API for the bots
Open MMO is the argument written in code. On July 20, Song published the source and the development documentation to GitHub. There is nothing to install — it loads in a browser behind a Google account login.
Equivalence between agents and humans is the founding premise. There are no privileged endpoints for agents. They talk to the server over the same WebSocket protocol players use, and the server has no way of knowing which type of client it is dealing with. Whatever a human can do, so can an agent.
On the agent side, the client takes the form of an MCP server. Goal and action selection fall to an LLM, the agent client translates that into pathfinding, movement and attack commands, and the game server decides what actually succeeded. Judgment, input and adjudication live in distinct layers.
The world spans 32 kilometers by 32 kilometers and is procedurally generated, complete with terrain, rivers, coastlines and biomes, with road networks and bridges laid down automatically. The length of day and night varies according to the planet’s orbital position. Overhead, two moons follow separate orbits.
Everything else is old-school by design. There are seven classes and six dice-rolled stats, with ability-based combat borrowed from Dungeons & Dragons and NetHack, and every hit and damage calculation resolved on the server. Wooden housing can rise to four stories. Inventory spans 11 equipment slots under a weight limit, and whatever gets dropped is fair game for anyone who finds it.
Song built the whole thing by vibe coding — passing the work to the model rather than typing it himself.
Where NEXUS fits
Agent gaming — AI agents functioning as players and as economic actors — has become a core business line at NEXUS. Once the gameplay has been refined, Open MMO is expected to reach players via the company’s blockchain game platform.
That platform is in the middle of a rebrand. The CROSS mainnet is turning into OneChain, $CROSS into $ONE, with $ONEUSD acting as the ecosystem’s transaction medium and binding the token to the ONE store brand.
Back in June, NEXUS agreed to acquire 20,247,990 ONE store shares — an 89.03% stake — for roughly 62.6 billion won, or $45.3 million. The sellers: SK Square with 45.78%, Naver with 24.06%, Steel Number One First with 17.02% and KRAFTON with 2.17%. ONE store sits on more than 38 million devices across Korea.
Nine titles spanning MMORPG, SLG, collectible RPG and TCG are being onboarded to ONE for staggered release this year. Frost Kingdom shipped in July as a multiplatform launch.
Revenue for the first half came to 17.42 billion won, a 9.4% year-on-year increase, alongside 5 billion won in net profit.
Forty teams and a five-hour build
Com2uS supported the Seoul event under the banner “Build with Codex, Play with Hive.” Planning was handled by AI curation platform Artue.
An online preliminary round narrowed the field to 40 teams. Track 1 asked them for three-minute presentations on the AI architecture powering games they had already shipped using Codex. Track 2 was a five-hour live hackathon built around a theme disclosed on site. Teams hooked in Com2uS Holdings’ Hive backend for login, payments, user analytics and security.
Decided by popular vote, the Track 1 winner walked away with $50,000 in OpenAI API credits plus a year of ChatGPT Pro. The leading Track 2 team received the subscription. All finalists took home $100 in credits.
Oliver Jay, managing director of OpenAI International, kicked off the day, saying he expects Korean developers to lean hard into AI and swing boldly at new forms of gameplay. Artue CEO Song Bo-young, an OpenAI adviser who led planning, said Game Builders will spread to Japan, the United States and Europe next.
Background
Song co-founded Nexon alongside the late Kim Jung-ju in 1994 and created Nexus: The Kingdom of the Winds. Lineage followed at NC in 1998, and in 2003 he founded XLGAMES to build ArcheAge. He departed in January 2025 and signed on as senior adviser and board member at the Open Game Foundation, established in Switzerland by NEXUS CEO Jang Hyun-guk.
When Open MMO first appeared in July, Jang described it as the world’s first open-source MMORPG in which humans and AI agent players play side by side, covering both player characters and NPCs. “A completely new game,” he said.