# Why is my agent taking an action it never took before?

Either your agent's logic changed on purpose, a new branch, a new tool, a prompt update opening a path it didn't have, or something is pushing it somewhere it was never designed to go. Either way, it's now doing something outside its own history at that call site.

A brand new action is the easiest kind of drift for Tessary's behavior_drift classifier to catch: a tool or step your agent has never used before stands out clearly against a baseline built from what it has actually done. What the classifier can't tell you on its own is whether that's fine. A deliberate change needs to recur across enough sessions before Tessary treats it as the new normal instead of flagging it every time; a real bug needs a person to look at the case triage opens and rule it isn't.

Until one of those happens, expect it to keep showing up as a finding.

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Source: https://tessary.ai/answers/tessary-behavior-drift/why-is-my-agent-taking-an-action-it-never-took-before
More on Tessary behavior drift: https://tessary.ai/answers/tessary-behavior-drift
From Tessary, agent reliability for AI agents in production: https://tessary.ai