Quantizing a model to 4 or 8 bits barely reduced membership-inference risk, and the privacy defenses built for full-precision models added little on top
AspireAI community · arXiv
The first comprehensive empirical study of privacy risk in quantized deep networks evaluated eight state-of-the-art membership-inference attacks across six representative quantization methods. The result runs against the intuition that compression is also a privacy tool: at practical 4 to 8 bit quantization levels, quantized models remained largely as vulnerable to membership inference as their full-precision counterparts. Only aggressive 2-bit quantization delivered meaningful privacy gains, and those came with substantial utility degradation. The paper also asks whether defenses designed for full-precision models transfer, and finds they provide only limited additional protection on quantized models while further amplifying the utility loss. The practical implication is that choosing 4-bit or 8-bit weights for deployment should not be justified on privacy grounds, and any privacy claim attached to compression needs its own evidence. The caveat: the findings are empirical, over eight attacks and six quantization schemes, and do not rule out attacks not covered by that set.
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