Agent memory is the question of where, and in what format, to keep information that must outlive a conversation. The context window disappears when a session ends and cannot grow without limit. Until the first half of 2026 the closest thing to a standard answer was vector databases and knowledge graphs; this year, keeping memory in a single folder of Markdown files has taken hold. People can read and edit it, git keeps its history, and search ends with grep.
The path from Karpathy's LLM wiki gist to Google Cloud's Open Knowledge Format v0.1 and to v0.2, which adds trust signals; the line between what the specification actually defines (one required field, type) and what tools and the community claim; and the Brain Layer architecture that ties memory, search, citation and knowledge-graph reasoning together.