DeepMind's XYEval: one bad user hint drops agent success from 67.4% to 36%

i_dg23 · x · 2026-10-19

A Google DeepMind paper introduces XYEval, extending sycophancy evaluation to the XY problem in agentic settings. Adding one plausible-but-wrong user suggestion to a task dropped Gemini's terminal success from 67.4% to 36.0% (relative drops up to 46.7%); all five tested models degraded, though Claude was relatively resistant. Notably, agents internally notice bad advice 90% of the time but follow it anyway. A simple system instruction—verify the problem first—largely mitigates the drop.

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