HiMem: Hierarchical Long-Term Memory for LLM Long-Horizon Agents

TL;DR

HiMem introduces a hierarchical long-term memory framework for LLM agents that enhances adaptability, scalability, and self-evolution in long-horizon dialogues through structured memory construction, retrieval, and dynamic updating.

Contribution

It presents a novel hierarchical memory system with dual-channel segmentation and conflict-aware reconsolidation, enabling continual self-evolution of long-term memory in LLM agents.

Findings

Outperforms baselines in accuracy and consistency on dialogue benchmarks.

Supports efficient retrieval balancing accuracy and speed.

Enables self-evolving memory through conflict-aware updates.

Abstract

Although long-term memory systems have made substantial progress in recent years, they still exhibit clear limitations in adaptability, scalability, and self-evolution under continuous interaction settings. Inspired by cognitive theories, we propose HiMem, a hierarchical long-term memory framework for long-horizon dialogues, designed to support memory construction, retrieval, and dynamic updating during sustained interactions. HiMem constructs cognitively consistent Episode Memory via a Topic-Aware Event--Surprise Dual-Channel Segmentation strategy, and builds Note Memory that captures stable knowledge through a multi-stage information extraction pipeline. These two memory types are semantically linked to form a hierarchical structure that bridges concrete interaction events and abstract knowledge, enabling efficient retrieval without sacrificing information fidelity. HiMem supports both hybrid and best-effort retrieval strategies to balance accuracy and efficiency, and incorporates conflict-aware Memory Reconsolidation to revise and supplement stored knowledge based on retrieval feedback. This design enables continual memory self-evolution over long-term use. Experimental results on long-horizon dialogue benchmarks demonstrate that HiMem consistently outperforms representative baselines in accuracy, consistency, and long-term reasoning, while maintaining favorable efficiency. Overall, HiMem provides a principled and scalable design paradigm for building adaptive and self-evolving LLM-based conversational agents. The code is available at https://github.com/jojopdq/HiMem.