cs.AIOct 20, 2026

Privacy-preserving inference on hosted models: a learned input-embedding transform for frozen Qwen3.8-27B

Authors: Mahendra Roopa, Srikanth Roopa

Organizations: Spinal

Abstract

Every prompt sent to a hosted language model is readable by whoever runs it. We study whether the prompt can remain on the client while the host receives transformed vectors that stand in for it. A language model converts text to vectors exactly once, with a public lookup table; we perform that step locally and pass the vectors through a small trained network (55.6M parameters) before they leave the perimeter. The host runs a frozen 27B model (Qwen3.8-27B) on the transformed vectors and never receives text or token ids. We train the transform against the frozen model as a fixed judge, combining a forward-KL utility term with an auxiliary term that pushes each vector away from its original direction. On 1,490 MMLU questions held out from training, the transform costs 1.5 points of accuracy (80.7% vs. 82.3%), breaking 68 of the 1,226 questions the unmodified model answers correctly (5.5%), while 30.1% of content tokens no longer decode to their original token under a nearest-neighbour lookup.

Figures & tables

Explore similar work

CardsList
  1. Privacy-Preserving Mechanisms Enable Cheap Verifiable Inference of LLMs

    Feb 19, 2026Arka Pal, Louai Zahran, William Gvozdjak +2Verifiable Outsourced ComputationLLM Inference

  2. SharedRequest: Privacy-Preserving Model-Agnostic Inference for Large Language Models

    Jun 3, 2026Peihua Mai, Xuanrong Gao, Youlong Ding +3Privacy-Preserving Language ModelsLLM Inference

  3. Privacy from Symmetry: Orthogonally Equivariant Transformers for LLM Inference

    Jun 15, 2026Alexander Yukhimchuk, Andrey Shulga, Mladen Kolar +1Privacy-Preserving Language ModelsLLM Inference