SpiralFovea: Input-Adaptive Foveated Tokenization as a Third Lever of Resource-Adaptive Inference

Most adaptive-inference techniques for foundation models change what the model does — early exit, MoE routing, KV-cache compression, dynamic attention sparsity. The input that hits the backbone, however, remains a fixed-grid tokenisation indifferent to image content. We argue that this is a missed lever. We present SpiralFovea, a parameter-free, input-adaptive tokeniser in which token identity, location, scale, and count are all functions of local visual entropy and selection completes before any backbone parameter is queried. Around content-driven hotspot anchors, multi-scale spiral rings produce ≤ 78 patches that replace the standard 196-patch ViT grid at the input stage. Across four canonical fine-grained benchmarks SpiralFovea yields +1.7–2.1 pp accuracy with a 60% reduction in input tokens, a 84% reduction in self-attention FLOPs at every transformer layer, and 18–29% throughput gains over the matched static tokenisation baseline. A controlled ablation on CUB-200-2011 Genus across four backbones reveals a clean diagnostic: the gain magnitude tracks inversely with the strength of the backbone’s whole-image positional prior, isolating self-supervised foundation models as the regime where input-adaptive tokenisation is most valuable.