RAG is so back! Another paper showing that plain RAG keeps winning the agent memory comparison. They show that many dedicated memory systems score below naive retrieval over the raw history on LongMemEval, PersonaMem, and MINT-Eval, while costing much more. They split a memory system's value into two parts. Memory benefit counts questions it answers that RAG misses. Memory tax counts questions RAG answers that the memory system gets wrong. Why does the tax appear? Building memory rewrites…