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One open post-training recipe made fact-checkers doubt lower-status posters, and it traced to a single direction

AspireAI community · arXiv
Language models increasingly judge online claims with the poster's identity visible, and this paper asks which post-training recipes change how much a model's truth judgment depends on a poster's social class. Across base and post-trained checkpoints from six model families, using fact-checked claims with randomised poster profiles, only the open Tulu-3 recipe produced measurable job-based doubt, judging claims false more often when the poster held a lower-status job; the effect was under one percentage point but statistically reliable, exceeded training drift, and replicated on independent claim sets. In OLMo-2 32B the model did not start noticing the poster's job more often, it started interpreting it differently, with a lower-status job pushing the base model toward true and the post-trained model toward false, and the flip is carried by a single residual-stream direction that appears at supervised fine-tuning. None of seven deployed commercial models showed the effect, so the practical advice is to audit per training recipe.
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