In plain words: Mixture-of-experts models send each word to a few expert subnetworks, and those routing choices leak enough to rebuild the original text from them alone. A sequence-reading decoder recovered 91% of tokens in short passages, far more than the simple classifier used before.
Abstract · Expert Selections In MoE Models Reveal (Almost) As Much As Text
We present a text-reconstruction attack on mixture-of-experts (MoE) language models that recovers tokens from expert selections alone. In MoE models, each token is routed to a subset of expert subnetworks; we show these routing decisions leak substantially more information than previously understood. Prior work using logistic regression achieves limited reconstruction; we show that a 3-layer MLP improves this to 63.1% top-1 accuracy, and that a transformer-based sequence decoder recovers 91.2% of tokens top-1 (94.8% top-10) on 32-token sequences from OpenWebText after training on 100M tokens. These results connect MoE routing to the broader literature on embedding inversion. We outline practical leakage scenarios (e.g., distributed inference and side channels) and show that adding noise reduces but does not eliminate reconstruction. Our findings suggest that expert selections in MoE deployments should be treated as sensitive as the underlying text.
Amir Nuriyev, Gabriel Kulp
arXiv:2602.04105 · cs.CL, cs.CR · submitted Feb 4, 2026 · updated Mar 13, 2026
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