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Sebastian Raschka Builds an AI Text Detector From Scratch — Then Uses RLVR to Train a Small Model That Evades It
Published 2026-08-15, Raschka's end-to-end project fine-tunes a DistilBERT classifier into a 0-100 AI-likelihood scorer with an API and browser front end, using methods similar to the Pangram-style models reportedly behind Substack's own detector. The second half is the interesting part for builders: he applies RLVR (reinforcement learning from verifier rewards) to train a small language model that generates text specifically to defeat the detector he just built. His framing — detectors are a cat-and-mouse game where the detector must be continuously retrained — doubles as a practical demonstration of verifier-based RL applied outside of reasoning models, which is where most RLVR write-ups stop.
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