MemArena: An Ego-Centric Benchmark for On-Device Agentic Personal Memory Assistants at Scale

Edge-deployed personal memory assistants must handle private interpersonal conversations on-device with open-weight models. Yet, existing memory benchmarks often under-test the combination of activity-dense interaction, ego-centric perspective, and coherent multi-session worlds. MemArena fills these gaps with a single-world conversational benchmark built with its MASim agent simulator, for 50 agents over 15 days (10.3M dialog-text tokens, 24.1K text-only ego-observed tokens/agent/day). With the interaction history, it co-generates ground truth over six recall, reasoning, and trustworthiness evaluation dimensions. We evaluate five open-weight readers with Vanilla context, BM25-RAG, Oracle retrieval, Memobase, and MemSearch as memory backends. Three results stand out: (1) Memory-backend choice matters more for content accuracy: At Qwen3-8B, moving from Memobase to MemSearch gains +22.1/+21.2 pp, whereas scaling the reader to Qwen3-32B-AWQ gains at most +3.5/+4.4 pp under either backend. (2) Permission-aware access fails in two distinct modes: Oracle leaks heavily, while the other backends fail to surface the protected fact. (3) Search latency bites only at small readers: on a Spark GB10 edge node, memory-search adds a moderate and fixed 87/8/51 ms (BM25-RAG/Memobase/MemSearch) that composes a small part of TTFT for most reader-backend combinations. We release code, the MASim simulator, and the MemArena-L benchmark at https://github.com/dereksodo/MemArena-Bench.