Is Implicit Caching Prompt Retention?

Implicit caching in large language models (LLMs) refers to the automatic storage of key and value tensors, which represent intermediate activations, to enhance computational efficiency without explicit user control. This process, particularly when employing SSD storage, allows providers to handle more concurrent sessions by skipping prompt prefill, thus saving computational resources and costs. While Google views implicit caching as data retention, most providers and OpenRouter consider it a performance optimization, not a true retention mechanism, as the cached data is ephemeral and not aligned with raw tokens or user data. OpenRouter monitors and documents endpoint practices to ensure compliance with Zero Data Retention (ZDR) standards, emphasizing transparency and allowing users to configure routing based on their preferences or concerns. Despite the potential for a sophisticated actor to theoretically recover information from caches, the data is typically encrypted and not retained in a meaningful or operational way, aligning with the ZDR principles for protecting user data.

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