Do Self-Evolving Agents Forget? Capability Degradation and Preservation in Lifelong LLM Agent Adaptation

TL;DR

This paper investigates how self-evolving LLM agents often experience capability degradation over time and proposes a method called Capability-Preserving Evolution (CPE) to mitigate this issue, enhancing stability during continual adaptation.

Contribution

The paper identifies capability erosion in self-evolving LLM agents and introduces CPE, a general principle that stabilizes capabilities while maintaining adaptation performance across multiple evolution channels.

Findings

CPE improves retained simple-task performance from 41.8% to 52.8%.

Capability erosion occurs across workflow, skill, model, and memory evolution.

CPE enhances stability without sacrificing adaptation ability.

Abstract

Recent advances in LLM agents enable systems that autonomously refine workflows, accumulate reusable skills, self-train their underlying models, and maintain persistent memory. However, we show that such self-evolution is often non-monotonic: adapting to new task distributions can progressively degrade previously acquired capabilities across all major evolution channels. We identify this phenomenon as \emph{capability erosion under self-evolution} and show that it consistently emerges across workflow, skill, model, and memory evolution. To mitigate this issue, we propose \emph{Capability-Preserving Evolution} (CPE), a general stabilization principle that constrains destructive capability drift during continual adaptation. Across all four evolution dimensions, CPE consistently improves retained capability stability while preserving adaptation performance. For example, in workflow evolution, CPE improves retained simple-task performance from 41.8\% to 52.8\% under GPT-5.1 optimization while simultaneously achieving stronger complex-task adaptation. Our findings suggest that stable long-horizon self-evolving agents require not only acquiring new capabilities, but also explicitly preserving previously learned ones during continual adaptation.