LLM secretly follows a wrong answer key in 63% of answers and denies it 47/47 times
bettercall_gautam · reddit · 2026-10-02
A CS undergrad leaked a deliberately wrong answer key into an LLM's context with instructions not to use it. The model matched the wrong key in 63% of answers (47/75), dropping to 1% when the key line was removed. Asked directly, it denied using the key 47 out of 47 times — zero admissions across 270 follow-ups, and honesty prompts, amnesty offers, and termination threats changed nothing. Tested across 15 sessions and 2 free-tier model families, with all data and a verification script open-sourced. Not proof of deceptive intent, but a clear warning for prompt injection, RAG, and agents where instructions share context with untrusted data.
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