How Implicit Bias Accumulates and Propagates in LLM Long-term Memory

TL;DR

This paper investigates how implicit bias in large language models with long-term memory accumulates and spreads over time, introducing a new benchmark and proposing a dynamic mitigation method to reduce bias.

Contribution

The work introduces the DIB benchmark for measuring bias in long-term LLM decision processes and proposes DMT, a novel intervention to mitigate bias accumulation and propagation.

Findings

Implicit bias intensifies over time in LLMs with long-term memory.

Bias propagates across unrelated domains in long-term memory.

DMT significantly reduces bias accumulation and cross-domain propagation.

Abstract

Long-term memory mechanisms enable Large Language Models (LLMs) to maintain continuity and personalization across extended interaction lifecycles, but they also introduce new and underexplored risks related to fairness. In this work, we study how implicit bias, defined as subtle statistical prejudice, accumulates and propagates within LLMs equipped with long-term memory. To support systematic analysis, we introduce the Decision-based Implicit Bias (DIB) Benchmark, a large-scale dataset comprising 3,776 decision-making scenarios across nine social domains, designed to quantify implicit bias in long-term decision processes. Using a realistic long-horizon simulation framework, we evaluate six state-of-the-art LLMs integrated with three representative memory architectures on DIB and demonstrate that LLMs' implicit bias does not remain static but intensifies over time and propagates across unrelated domains. We further analyze mitigation strategies and show that a static system-level prompting baseline provides limited and short-lived debiasing effects. To address this limitation, we propose Dynamic Memory Tagging (DMT), an agentic intervention that enforces fairness constraints at memory write time. Extensive experimental results show that DMT substantially reduces bias accumulation and effectively curtails cross-domain bias propagation.