Memory Tier Architecture

Agent memory is not a single store. It is a tiered architecture, each tier optimized for a different access pattern and retention requirement. Tier one: working memory. The current context window — the active conversation, the current task, the immediate inputs. Fast access, zero persistence. Tier two: session memory. Key decisions, artifacts, and context from the current work session. Persists for the duration of the session. Lost when the session ends unless explicitly promoted. Tier three: episodic memory. Significant events, completed tasks, and their outcomes. Persists across sessions. Indexed by timestamp and context. Tier four: semantic memory. Distilled knowledge — facts, patterns, and learned preferences extracted from episodic memory. Persists indefinitely. Indexed by concept.

The critical design decision is the promotion mechanism — how does information move from a lower tier to a higher tier? Working memory is ephemeral by default. If a decision in working memory should persist as episodic memory, something must trigger the promotion. The trigger can be explicit (the agent or user marks it for retention) or implicit (the system promotes any decision with consequences above a threshold).

1. 1. Define Tier Boundaries Specify what belongs in each tier: working memory (current task context), session memory (this session's decisions), episodic memory (significant events with timestamps), semantic memory (distilled knowledge). Every piece of information belongs to exactly one tier.
2. 2. Design Promotion Triggers Define what causes information to move from a lower tier to a higher tier. Decision outcomes, error patterns, stakeholder preferences, and task completions are common promotion triggers. Not everything should be promoted — retention is selective.
3. 3. Set Retention Policies Episodic memory decays — oldest memories are summarized and compressed after 90 days. Semantic memory persists but is verified quarterly. Working memory is cleared at task completion. Session memory is cleared at session end unless promoted.