The Cache TTL Trap: Why We Need Paid Retention Windows
EmetInteractive · reddit · 2026-08-30
The author discusses the cost issue of prompt cache expiring when users step away, leading to full re-ingestion costs upon return.
- Pain Point: Developers often write keep-alive scripts. However, a short break (e.g., for coffee) causes the next short prompt to re-ingest the entire context at full input price, a 10x hit for large sessions.
- Proposal: Suggests a "Retention Window" feature. Users would pin a cache key with a TTL and pay a one-time write premium (e.g., 1.25x for short-term, 2x for long-term), significantly reducing read costs for the window's duration.
- Ecosystem: Anthropic has had a 5min/hr mechanism; OpenAI recently added TTL options, and hosts like DeepInfra offer similar features. However, many wrappers hardcode 5 minutes and don't expose these controls.
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