Episodic Memory
Episodic memory is memory of specific events tied to time and context — "what happened when, where, and with whom." The term comes from cognitive science (Tulving, 1972) and is contrasted with semantic memory (general facts) and procedural memory (how-to skills). In LLM agents, episodic memory typically takes the form of an event log of past interactions, often stored with timestamps and retrievable by time, entity, or semantic similarity. Letta's recall storage and mem0's session-scoped memories serve this layer; in custom architectures it usually lives in a database table or vector store of full turn-by-turn records.
Example
A personal-assistant agent that can answer "what did I ask you about the budget last Tuesday?" is querying episodic memory — retrieving the specific event ("Tuesday's budget conversation") rather than a synthesized fact. The retrieval pattern is usually a semantic search over the event log filtered by date range, with the matched events injected into the agent's working memory before the next response.
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