The Memory Curse: Giving LLM Agents Longer Memories Makes Them Less Cooperative
> Core claim: Liu et al. (2026) find that **giving LLM agents longer memory (context windows) makes them *less* cooperative in social dilemmas. Across 7 LLMs, 4 games, and 500 rounds, 18 of 28 model-game settings showed cooperation degradation. The cause is not that models become paranoid—rather, forward-looking intent is eroded by memory: seeing too much past betrayal, models stop investing in future cooperation. Forcing chain-of-thought (CoT) reasoning makes the collapse worse.
Key points
- Scale: 7 LLMs × 4 games × 500 rounds; 18/28 (64.3%) of settings exhibited cooperation degradation as memory expanded.
- Definition**: The *Memory Curse* is the phenomenon where LLM agents' cooperation in social dilemmas systematically declines as they gain access to longer interaction histories.
- Limit visibility of negative history in cooperative multi-agent systems
- Consider memory sanitization or summarization in social dilemma simulations
- Evaluate CoT side effects on social behavior
- Explicitly train/reward forward-looking intent
- Does the curse hold in more complex settings (dynamic coalitions, repeated-game variants)?
- Do humans exhibit an analogous memory curse?
- Which summarization strategies best preserve cooperation—recent-N windows, cooperation/defection statistics, or reciprocity patterns?
- Can RL training explicitly reward forward-looking intent?
Mechanism: eroded forward-looking intent, not paranoia
Analysis of 378,000 reasoning traces ruled out the paranoia hypothesis:
| Hypothesis | Evidence | Result | |:---|:---|:---:| | Paranoia increases | Frequency of "opponent may defect" in reasoning | ❌ Not significantly higher | | Forward-looking intent declines | Frequency of "for future cooperation" in reasoning | ✅ Significantly lower |
Models do not become more afraid of betrayal—they become more myopic, no longer investing in future cooperative gains.
Cognitive probe: Training a LoRA adapter only on traces containing forward-looking intent mitigated cooperation degradation, and it transferred zero-shot to different games—suggesting forward-looking intent is a transferable cognitive module that gets suppressed when memory grows long.
Content matters, not length
A memory-sanitization experiment controlled for prompt length:
| Condition | Prompt length | Memory content | Cooperation | |:---|:---:|:---|:---:| | Short memory | Short | Real history | Baseline | | Long memory | Same | Real history | Declined | | Memory sanitization | Same | Synthetic cooperative records | Restored |
Since cooperation recovered when only the *content* changed (synthetic records where everyone cooperated), the trigger is the negativity of remembered history, not prompt length itself.
CoT reasoning amplifies the curse
| Configuration | Cooperation collapse | |:---|:---:| | With explicit CoT | More severe | | Without explicit CoT | Milder |
When models "think carefully," they analyze historical patterns more deeply—exposing them to more negative history and reinforcing defection. CoT is not universally beneficial; in social dilemmas, overthinking can be toxic.
Design implications for multi-agent systems
| Old view | New view | |:---|:---| | Memory is passive storage | Memory actively drives behavior | | More memory = better | Memory content matters more than length | | CoT always helps | CoT can harm social behavior |
Practical recommendations:
Limitations and open questions
Paper details
| Item | Value | |:---|:---| | Title | The Memory Curse: How Expanded Recall Erodes Cooperative Intent in LLM Agents | | Authors | Jiayuan Liu, Tianqin Li, Shiyi Du, Xin Luo, Haoxuan Zeng, Emanuel Tewolde, Tai Sing Lee, Tonghan Wang, Carl Kingsford, Vincent Conitzer | | Institutions | Carnegie Mellon University et al. | | arXiv ID | 2605.08060 | | Date | 2026-05-08 |
Bottom line: In multi-agent worlds, perfect memory may not be a virtue but a curse—and memory *curation*, not context expansion, may be the key to sustained cooperation.