AWS published actual retention math for agent memory, which nobody else has.

The AgentCore lifecycle post sets TTL defaults by memory type: 90 days episodic, 30-60 for summaries, 6-12 months semantic, optionally indefinite procedural. It defines a relevance decay score weighting creation recency 0.40, last-access recency 0.35 and access frequency 0.25 with a 0.3 threshold at 45 days, and LLM consolidation folding five episodic memories into one semantic entry before deletion. Cost runs about $0.01-$0.02 monthly at 1,000 memories and $50-$100 at 100,000, dominated by consolidation calls (AWS).