# Five-Tier Memory Cascade

> Stage agent memory across five tiers — sensory, working, short-term, episodic, long-term — with explicit promotion and decay between each, matching each tier to its natural timescale.

- **Category**: Agentic AI
- **Subcategory**: Memory
- **Canonical URL**: https://designpattern.fyi/patterns/five_tier_memory_cascade/

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## Description
**Intent**: Stage agent memory across sensory, working, short-term, episodic, and long-term tiers with explicit promotion and decay between them.
**Context**: A long-running agent accumulates information at very different timescales. Some observations are one-tick-only ("the user just clicked save"); some are day-level patterns; some are month-level preferences; some are stable identity facts. A flat single-tier store cannot represent these differences in age, decay rate, or relevance horizon.
**Solution**: Five tiers — **Sensory**: raw input per tick. **Working**: top-N items in active focus (Global Workspace Theory, ≤7 items). **Short-term**: recent verbatim (1–7 days). **Episodic**: compressed summaries (5–10×). **Long-term**: distilled rules and insights. Compaction promotes upward on a schedule; decay archives downward; rehearsal lifts archived items back when re-attended.



## Use Cases
- A flat append-only log is collapsing signal across timescales (sensory, working, recent, episodic, distilled).
- Promotion and decay between tiers can be implemented on a schedule.
- Working memory needs an explicit cap (e.g. ≤7 items per Global Workspace Theory).






## Trade-offs


### Advantages

- Each tier is optimized for its natural timescale — sensory is cheap and ephemeral, long-term is durable and distilled.

- The memory hierarchy is inspectable and maps to well-understood cognitive science vocabulary.




### Considerations & Drawbacks

- Architecturally heavy — only earns its seat in genuinely long-running agents; overkill for short sessions.

- Tuning promotion thresholds and decay rates between tiers is empirical work per deployment.







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**Reference**: [Original Source](https://www.agentpatternscatalog.org/patterns/five-tier-memory-cascade/)