Knowledge editing for large language models typically treats a fact update as a replacement in which a new object overwrites the old. Many real-world facts, however, evolve through sequences: the same subject–relation pair maps to different objects across disjoint intervals, each correct within its validity window. Existing temporal-editing benchmarks probe latest-value or explicit-time recall, so they cannot determine whether an edited model retains a coherent timeline. We introduce TKE-Bench, a diagnostic benchmark that operationalizes temporal accessibility along three reasoning-oriented axes with paraphrased variants. On TKE-Bench, all evaluated editing baselines collapse on chronologically structured queries, revealing catastrophic temporal interference (CTI). We trace CTI to a geometric property implicit in locate-and-edit methods: mid-layer subject-token keys are nearly collinear across time slices of the same subject, so stacked updates write along one direction and the latest edit overwrites every earlier value. Building on this, we propose ChronoExpert, a temporal mixture-of-experts that stores each time slice in an independent lightweight expert and activates only the matching one at inference, leaving the base model otherwise untouched. Across multiple LLM backbones, ChronoExpert consistently outperforms the strongest editing baselines and stays robust as chains grow longer.

Large language models have achieved strong single-turn language understanding and generation abilities, but long-term agent applications require models to handle dynamic interaction history beyond an isolated inference call. Existing agent memory systems address this need through external storage and retrieval and have achieved promising results. However, many existing frameworks rely on full storage or highly structured memory representations, which can increase cost and noise while disrupting event coherence. Inspired by cognitive views of event organization and adaptive forgetting, we introduce ECO-Mem, an event-centric organization framework for visibility-controlled long-term memory. ECO-Mem segments dialogue into source-linked event episodes and connects them through typed event relations, representing memory as linked events rather than isolated facts. It implements forgetting as non-destructive visibility control instead of destructive deletion. At query time, it traverses the event-relation graph to identify relevant hidden support and reactivates it only when the source evidence confirms the query context. Experiments on LoCoMo and RealTalk validate ECO-Mem’s effectiveness and efficiency for long-term agent memory.