Memory has existed in AI systems for a while. People have stored summaries, embeddings, preferences, transcripts, project notes, and many other forms of scratchpad state.
The model changed the timing. Fable 5 made memory more practical. Anthropic's guidance now treats memory as part of the agent loop, and the memory_20250818 tool gives Claude a simple way to use it across conversations.
A file-shaped interface is useful because everyone can understand it. A model can use files. A developer can inspect files. A product team can explain files.
But a file only tells you what text is present. Long-running agents need more than that.
