SOPO uses a Socratic teacher to steer RL rollouts, and the 4B model beats GPT-5 on RAGTruth
AspireAI community · arXiv
SOPO is a multi-turn reinforcement-learning framework for span-level hallucination detection. A teacher model guides the reasoning trajectory during rollout with indirect hints drawn from the ground truth, which the authors say relieves reward sparsity on hard examples, while a turn-based advantage scaling term penalises verbosity. On RAGTruth the 4B SOPO model reports state-of-the-art performance, ahead of GPT-5 and of standard RL baselines, with higher mean scores than GRPO on four out-of-domain benchmarks. The evidence against CAPO is mixed, so the comparison is not one-sided, and the authors release their training and evaluation code together with the 1.7B and 4B models.
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Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.