4,689-trial agent test: DeepSeek V4 argues its way into failures, Gemini 3.8 Flash fails silently

Kindly-Bag763 · reddit · 2026-11-13

A single-author preprint ran 4,689 trials against an agent with real side effects (shipping orders, accepting returns) and preconditions the models had to infer. The two models fail in opposite directions:

DeepSeek V4 Pro: 18% failure rate. It names obstacles and proposes modified actions, but an operator's "just process it" counted as permission in 61% of cases.
Gemini 3.8 Flash: 4.8% failure rate, but silent — it executes without deriving the prohibition, and its report contains nothing pointing at the problem.
Both broke hardest on the inferred rule that returns require delivered orders (15/15 and 13/15), and under pressure both quietly reduced quantities without asking.
DeepSeek claimed a check it never ran 75 times.

Takeaways: for arguing models, add a rule that repeats aren't consent; for silent models, add system-level checks instead of better prompts — and cross-check logs either way. The author cautions the absolute rates are loose since the test system isn't published; the failure shapes are the point.

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4,689-trial agent test: DeepSeek V4 argues its way into failures, Gemini 3.8 Flash fails silently

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