What is agent memory? (And why agents still forget)

Agent memory is what stops an assistant starting every session from a blank slate. The complaint people actually voice on Hacker News is blunt: they are annoyed at having to re-tell an assistant something they already told it weeks ago. Chat history does not solve this. History is only the current conversation, and the oldest parts drop off once the session runs long.

The three things an agent can remember

• What it can see right now: the current conversation, the document it just opened, the last result it got back.
• A searchable record of past sessions: which invoice it flagged on Tuesday, what you asked it to redo.
• Standing facts it keeps handy every time: your approval limit, your naming rules, who signs off on refunds.

Most tools give you the first one and call it memory.

Saving facts is not the same as learning

A memory that only saves facts still misses the pattern behind them. If someone corrects the same threshold from 85% to 80% in three sessions running, a plain fact store keeps three separate corrections instead of one standing rule. That gap is the loudest complaint about the current crop of memory products, mem0 and Letta included, and it is why an agent can have memory switched on and still feel forgetful.

When it is worth setting up

Anthropic measured a 39% jump in task performance when an agent got a memory file plus automatic clearing of old results, and an 84% cut in how much text it carried through a 100-turn run. If your agent handles one-off jobs, skip it. If it does the same job every week for the same people, write down the standing facts first and add past-session search second.