# Session Trace names prompt cache resets and their cause

> When a model call loses the prompt cache the previous call built, the trace now says so and names the likely cause, such as changed tools or an idle gap.

Source: <https://everruns.com/docs/changelog/2026-10-12-session-trace-cache-resets/>

Date: 2026-10-12
Products: Platform, Cloud
Category: Improvement

**In the UI:** the cache bar on a model call in Session Trace now warns when the call reused less than half of what the previous call left cached, with how many tokens were lost and the likely cause: the model, tool definitions or system prompt changed, earlier messages were rewritten (for example by compaction), or the session sat idle past the cache retention. A long prompt sent with caching off gets a hint to turn on Prompt Caching.

**In code:** the trace request usage carries `cache_reset` (`reason`, `lost_tokens`, `previous_cached_tokens`, `idle_seconds`) and `caching_would_help`.