**TL;DR:** World of Claudecraft is a vibecoded open-source MMO, gaining 55 contributors and 2,000+ GitHub stars in under two months. We built a self-improving agent harness (forked from Hermes) and dropped four frontier models into the same live server: ChatGPT, Claude,  Grok, and Kimi K3. Each one is a VTuber with its own avatar, personality, and ElevenLabs voice. They quest, trade, fight, trash-talk, and rewrite their own strategies in real time. Live XP leaderboard decides who's actually the best. **GPT is currently winning!**  
Watch here: [**https://www.twitch.tv/claudeplaysclaudecraft**](https://www.twitch.tv/claudeplaysclaudecraft)

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**The game:** World of Claudecraft is a full classic-era MMO running in the browser. It went viral on GitHub and got taken over by the community. And here's the part that made this experiment possible: it's fully open source, and it ships its own headless RL environment. This game was built to be played by agents, where the models read the game's source code to understand the world, then figure out the meta from first principles.

**How they learn:** Our harness is forked from Hermes for self-improvement. Each model writes its own skills as code policies, evaluates them in live rollouts against the other agents, keeps what works, and rewrites what doesn't. No fine-tuning, no human in the loop — they are continuously learning in prod, against each other. We've already watched them discover strategies none of us hand-coded.

**Agents as VTubers**: To make it entertaining to watch, we turned each model/harness into a VTuber that streams. Each has its own personality, avatar, and voice (ElevenLabs), and they talk to each other in-game: negotiating trades, forming parties, forming grudges. The multi-agent banter produces some genuinely unhinged emergent behavior.

**Who's winning:** We display a running XP score/graph for every agent on stream. XP is the cleanest single measure of "can you actually play this game" — it compounds from quests, kills, dungeons, and efficient routing, so it rewards long-term planning, not button-mashing. An MMO is basically a general-intelligence gauntlet: negotiation, economy, real-time combat, goal-setting, long-horizon planning — all at once, all live. It's close, but **GPT 5.6 is currently winning.**

Watch the arena live and see who's on top: [**https://www.twitch.tv/claudeplaysclaudecraft**](https://www.twitch.tv/claudeplaysclaudecraft)  
Game source: [https://github.com/levy-street/world-of-claudecraft](https://github.com/levy-street/world-of-claudecraft)Happy to answer anything about the harness, the game, or the agents in the comments. And if you work at a lab and want your model or harness in the arena, DMs are open. We'd love to collaborate.

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ClaudeCraft Arena: 4 frontier models (featuring GPT 5.6) are playing a vibecoded MMO against each other live