Noise Hypernetworks: Amortizing Test-Time Compute in Diffusion Models
Authors: name: Luca Eyring; name: Shyamgopal Karthik; name: Alexey Dosovitskiy; name: Nataniel Ruiz; name: Zeynep Akata
Published: 2025-08-13 17:33:37

Abstract: The new paradigm of test-time scaling has yielded remarkable breakthroughs in
Large Language Models (LLMs) (e.g. reasoning models) and in generative vision
models, allowing models to allocate additional computation during inference to
effectively tackle increasingly complex problems. Despite the improvements of
this approach, an important limitation emerges: the substantial increase in
computation time makes the process slow and impractical for many applications.
Given the success of this paradigm and its growing usage, we seek to preserve
its benefits while eschewing the inference overhead. In this work we propose
one solution to the critical problem of integrating test-time scaling knowledge
into a model during post-training. Specifically, we replace reward guided
test-time noise optimization in diffusion models with a Noise Hypernetwork that
modulates initial input noise. We propose a theoretically grounded framework
for learning this reward-tilted distribution for distilled generators, through
a tractable noise-space objective that maintains fidelity to the base model
while optimizing for desired characteristics. We show that our approach
recovers a substantial portion of the quality gains from explicit test-time
optimization at a fraction of the computational cost. Code is available at
https://github.com/ExplainableML/HyperNoise