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simgrammar the grammar of simulation

core loop

agents perceive nearby events and objects -> observations enter the memory stream -> retrieve memories by recency, importance, and relevance -> plan the day and react -> converse and act -> reflections summarize memories -> plans and relationships change

design notes

Park and colleagues replace authored behavior trees with a loop of language-model calls on gpt-3.5-turbo. Every observation is stored as text with timestamps; retrieval scores memories by recency (decay 0.995 per game hour), importance (rated 1-10 by the model when stored), and embedding relevance, each normalized and weighted equally. When the summed importance of recent events passes 150 (two or three times a day) the agent writes reflections, and plans are decomposed from a day outline into hour and 5-15 minute chunks. Seeding one agent with the intent to host a Valentine's Day party led to 13 of 25 agents hearing about it and five attending over two game days, at a cost of thousands of dollars in API credits. The open-source release steps the town 10 game seconds per step.

relations

8 stored edges
influenced by
uses

Daily schedules

Each morning the model drafts a day plan of about five to eight broad chunks, decomposed into hour-long and then 5-15 minute actions that agents revise when they react to events.

core
uses

Gossip propagation

Information spreads only through agent conversations; over two game days awareness of a mayoral candidacy rose from 1 to 8 agents and of a party from 1 to 13, with 6 of 453 awareness answers hallucinated.

core
uses

Memories and thoughts

Each agent's memory stream stores observations, plans, and reflections as text; retrieval ranks them by recency (0.995 decay per game hour), model-rated importance (1-10), and embedding relevance, and reflections fire when summed importance exceeds 150.

core
uses

Agent inspection

Researchers interview agents and read their memory streams to evaluate believability.

supporting
uses

Generative content on demand

Plans, dialogue, importance ratings, and reflections are all generated by gpt-3.5-turbo calls at runtime.

supporting
uses

Natural-language interaction

Users address agents in natural language as a persona or as the agent's inner voice, and can rewrite the status of objects in natural language.

supporting
uses

Relationship values

Agents form acquaintances through conversation; network density rose from 0.167 to 0.74 over two game days.

supporting

backlinks

computed from other records

claims

1 with sources
c01high

In the two-day end-to-end run, relationship network density rose from 0.167 to 0.74 and five agents attended the Valentine's Day party.

src-park-2023-generative-agents

sources

2
Joon Sung Park, Joseph C. O'Brien, Carrie J. Cai (2023-04-07). Generative Agents: Interactive Simulacra of Human Behavior. UIST '23 (ACM Symposium on User Interface Software and Technology)
Joon Sung Park (2023). joonspk-research/generative_agents. GitHub

provenance

runs in log/runs
2026-10-24
created2026-10-24-catalog-gdcatalog
2026-10-25
reviewed2026-10-25-contributor-readinessmaintenance