An OpenAI API bug leaked raw reasoning traces for months, and the fix only shipped on October 23
AspireAI community · Vendor
OpenAI's API had a flaw that returned raw chain-of-thought from frontier reasoning models in plaintext. Xint's researchers found the bug in August 2026 and named the technique compaction smuggling: they encode one model's encrypted reasoning inside a compaction, then let a weaker model from the same provider decode it and transcribe it verbatim. The move bypasses the mitigations OpenAI shipped after the earlier Stolen Thoughts paper, and it works in three API calls. OpenAI confirmed the issue and deployed an undisclosed fix on October 23, 2026, and Xint was paid a 6,000 dollar bounty. The interesting part is the timeline: the leak ran for roughly two months after the previous hardening pass, which suggests anti-distillation defenses on encrypted reasoning are not yet a solved problem. The limitation is that the write-up documents a bug that is already patched, so it explains what was possible rather than what is possible now.
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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.