PlugMem: A Task-Agnostic Plugin Memory Module for LLM Agents

AuthorsKe Yang, Zixi Chen, Xuan He et al.

2026

TL;DR

PLUGMEM uses a knowledge-centric memory graph over propositions and prescriptions to deliver up to 1.4e-1 bits per token on HotpotQA, far higher than retrieval baselines.

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THE PROBLEM

Task-agnostic agents drown in raw memory and low task-relevance

Existing long-term memory for LLM agents is either task-specific and non-transferable, or task-agnostic but less effective due to low task-relevance and context explosion from raw memory retrieval.

Vanilla retrieval-based systems that store all past interactions as raw text chunks suffer from unbounded memory growth, high computational cost, and degraded decision-making when deployed in complex environments.

HOW IT WORKS

PLUGMEM — Knowledge-centric memory graphs from episodic traces

PLUGMEM combines a Structuring Module, Retrieval Module, and Reasoning Module to transform episodic trajectories into semantic and procedural knowledge stored in a unified memory graph.

You can think of PLUGMEM like a brain with a hippocampus that turns raw experiences into compact facts and workflows, then a librarian that fetches only the shelves relevant to the current question.

By operating over propositional and prescriptive knowledge units instead of raw trajectories, PLUGMEM enables retrieval and reasoning that a plain context window cannot, achieving much higher information density per memory token.

DIAGRAM

Abstraction-aware retrieval over semantic and procedural memory graphs

This diagram shows how PLUGMEM retrieves task-relevant propositions and prescriptions via multi-hop abstraction-specific traversal over semantic and procedural graphs.

DIAGRAM

Unified evaluation pipeline and ablation design for PLUGMEM

This diagram shows how PLUGMEM is evaluated across LongMemEval, HotpotQA, and WebArena with ablations on structuring, retrieval, and reasoning.

PROCESS

How PLUGMEM Handles a Long-term Decision Episode

  1. 01

    Structuring Module

    PLUGMEM uses the Structuring Module to standardize episodic traces into tuples and extract semantic propositions and procedural prescriptions linked into memory graphs.

  2. 02

    Semantic Memory

    PLUGMEM builds the semantic graph by turning propositions and concepts into nodes with embeddings and provenance edges to episodic memory.

  3. 03

    Procedural Memory

    PLUGMEM segments trajectories by subgoal similarity, induces intent prescription pairs, and stores them in the procedural graph with return scores.

  4. 04

    Retrieval Module

    PLUGMEM runs the Retrieval Module to perform abstraction-aware multi-hop retrieval over semantic and procedural graphs before the Reasoning Module condenses results for the base agent.

KEY CONTRIBUTIONS

Key Contributions

  • 01

    Design principles

    PLUGMEM formalizes cognitively motivated principles for task-agnostic memory, separating episodic, semantic, and procedural memory via the Structuring Module and knowledge-centric graphs.

  • 02

    Evaluation framework

    PLUGMEM introduces an information-theoretic measure of memory utility and efficiency, reporting global memory information density up to 1.4e-1 bits per token on HotpotQA.

  • 03

    General memory module

    PLUGMEM provides a plugin memory system with Structuring, Retrieval, and Reasoning Modules, evaluated unchanged on LongMemEval, HotpotQA, and WebArena with higher information density than baselines.

RESULTS

By the Numbers

EM

61.4

+9.7 EM over Vanilla Retrieval on HotpotQA

F1

74.1

+11.4 F1 vs Vanilla Retrieval on HotpotQA

Info. Density

1.4e-1 bits per token

about 11.7x higher than Vanilla Retrieval at 1.2e-2 on HotpotQA

#TokAvg.

81.6 tokens

about 8.1x fewer tokens than Vanilla Retrieval at 659.2 on HotpotQA

On HotpotQA, which tests multi-hop knowledge retrieval and reasoning, PLUGMEM delivers 61.4 EM and 74.1 F1 with only 81.6 memory tokens, showing that knowledge-centric memory graphs can provide much higher decision-relevant information per token than retrieval baselines.

BENCHMARK

By the Numbers

On HotpotQA, which tests multi-hop knowledge retrieval and reasoning, PLUGMEM delivers 61.4 EM and 74.1 F1 with only 81.6 memory tokens, showing that knowledge-centric memory graphs can provide much higher decision-relevant information per token than retrieval baselines.

BENCHMARK

Results on HotpotQA

EM on HotpotQA for PLUGMEM and key memory baselines.

BENCHMARK

Results on LongMemEval

Accuracy on LongMemEval for PLUGMEM and representative baselines.

KEY INSIGHT

The Counterintuitive Finding

PLUGMEM reaches 61.4 EM and 74.1 F1 on HotpotQA with only 81.6 memory tokens, while Vanilla Retrieval needs 659.2 tokens for 51.7 EM and 62.7 F1.

This is surprising because task-agnostic memory modules are usually assumed to trade effectiveness for generality, yet PLUGMEM beats task-specific designs like RAPTOR and HippoRAG2 in information density.

WHY IT MATTERS

What this unlocks for the field

PLUGMEM shows that agents can share a single plugin memory that abstracts episodic traces into reusable knowledge, then retrieve it efficiently across heterogeneous tasks.

Builders can now attach PLUGMEM to new agents and benchmarks without redesigning memory, gaining long-term semantic and procedural recall without exploding context windows.

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