This paper turns web apps into persistent worlds, endless worlds for agents that stay consistent.
They built a middle ground world, database like consistency from code, with new stories generated by an LLM.
A fully LLM made world is like a game where the narrator makes up everything live, so it can be endless, but it often forgets what happened and breaks its own rules.
This paper’s idea is a middle way: let normal code be the “rules and memory”, and let the LLM be the “story writer” that fills in descriptions on top of those rules.
Their Web World Model keeps the world state, meaning saved facts like location and inventory, inside deterministic code that always applies the same rules.
After code updates those facts, an LLM is called only to write the surrounding text, so it cannot rewrite the rules.
Typed fields, meaning a fixed form with required slots, and a repeatable seed number keep the generated content consistent across revisits.
The authors tested this by building 7 web demos, including an infinite travel map, a galaxy explorer, and games that generate content but run rules in code.
They argue the result is controllable worlds that can grow on demand without huge storage, stay easy to debug, and still work when the LLM is slow.
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Paper Link – arxiv. org/abs/2512.23676
Paper Title: "Web World Models"