OTCache: Optimal Transport for Geometry-Aware Caching in Diffusion Models
Pith reviewed 2026-07-01 06:18 UTC · model grok-4.3
The pith
Optimal transport models caching schedules as smooth policy evolution to accelerate diffusion sampling.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
OTCache obtains a reference schedule with a graph-based method under a conservative budget, searches for an anchor schedule at extreme low budget with Optuna under a perceptual objective, and predicts intermediate schedules by quantile interpolation between the reference and anchor policies under continuous warping representations derived from optimal transport. On FLUX.1 [dev], Qwen-Image, and HunyuanVideo this yields 4.5x, 4.7x, and 3.66x acceleration respectively while raising generation fidelity over prior caching baselines.
What carries the argument
Continuous warping representations from optimal transport that turn discrete caching policies into points along a smooth path in policy space for quantile interpolation.
If this is right
- Schedules for any budget between the reference and anchor can be generated without re-running graph search or optimization.
- The framework applies to multiple diffusion backbones without model-specific retraining.
- Fidelity gains appear because the transport model better respects the geometry of low-NFE regimes than additive shortest-path objectives.
- The three-stage pipeline separates expensive reference computation from cheap per-budget interpolation.
Where Pith is reading between the lines
- If the policy-space geometry is approximately Euclidean under OT distance, similar interpolation could be tried on other discrete optimization schedules such as pruning masks or quantization levels.
- The method suggests that caching decisions are not independent across timesteps but lie on low-dimensional manifolds that optimal transport can exploit.
- Extending the anchor search to multiple perceptual objectives might further tighten the fidelity-speed trade-off at the lowest budgets.
Load-bearing premise
Caching schedules across different inference budgets form a smooth evolution in policy space that quantile interpolation under optimal-transport warping can capture accurately.
What would settle it
Directly optimized schedules for an intermediate budget that differ markedly in perceptual score or actual speedup from the OT-interpolated schedule for the same budget.
Figures
read the original abstract
We propose OTCache, a training-free framework for accelerating diffusion sampling via caching schedule prediction. Existing graph-based caching methods reduce redundant computation by optimizing shortest-path objectives, but rely on an additive independence assumption, which often breaks down in the low NFE regime. To address this issue, OTCache models caching schedules across inference budgets as a smooth evolution in policy space, inspired by Optimal Transport (OT). The framework consists of three stages: (1) obtaining a high-fidelity \textbf{reference schedule} using a graph-based caching method under a conservative budget; (2) performing a lightweight anchor search under an extreme low-budget setting via Optuna optimization with an end-to-end perceptual objective; and (3) predicting schedules for target budgets via quantile interpolation between the reference and anchor policies using continuous warping representations. Experiments on FLUX.1 [dev], Qwen-Image, and HunyuanVideo show that OTCache achieves 4.5x, 4.7x, and 3.66x acceleration, respectively, while consistently improving generation fidelity over state-of-the-art caching baselines. This work provides a new perspective on accelerating diffusion models through Optimal-Transport-inspired schedule modeling. Code:https://github.com/UnicomAI/OTCache
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes OTCache, a training-free framework for accelerating diffusion sampling via caching schedule prediction. It models caching schedules across inference budgets as a smooth evolution in policy space using optimal transport. The three-stage pipeline obtains a high-fidelity reference schedule via graph-based methods under conservative budget, performs Optuna-based anchor search under extreme low-budget with perceptual objective, and predicts target schedules via quantile interpolation with continuous warping representations. Experiments claim 4.5x/4.7x/3.66x acceleration on FLUX.1 [dev], Qwen-Image, and HunyuanVideo with improved fidelity over SOTA caching baselines.
Significance. If the empirical claims hold under rigorous controls, the work provides a geometry-aware alternative to additive-independence assumptions in graph-based caching, potentially enabling more reliable schedule transfer across NFE budgets. The code release supports reproducibility.
major comments (2)
- [Abstract] Abstract: the central empirical claim (4.5x/4.7x/3.66x acceleration plus fidelity gains) is stated without any quantitative details on baselines, metrics, statistical significance, number of runs, or controls, preventing assessment of the result.
- [Method] Method (anchor-search stage): the anchor schedule is obtained by Optuna optimization against an end-to-end perceptual objective; the subsequent OT interpolation therefore inherits dependence on this fitted anchor rather than deriving from a parameter-free or closed-form construction.
Simulated Author's Rebuttal
We thank the referee for the detailed and constructive comments. We address each major point below and indicate where revisions to the manuscript will be made to enhance clarity and completeness.
read point-by-point responses
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Referee: [Abstract] Abstract: the central empirical claim (4.5x/4.7x/3.66x acceleration plus fidelity gains) is stated without any quantitative details on baselines, metrics, statistical significance, number of runs, or controls, preventing assessment of the result.
Authors: We agree that the abstract would benefit from greater specificity to allow readers to assess the claims. In the revised manuscript, we will expand the abstract to note that speedups are measured as wall-clock time reductions relative to standard DDIM sampling, fidelity improvements are quantified via FID and LPIPS, results are averaged over five independent runs with different seeds, and comparisons are performed against state-of-the-art caching baselines including graph-based and token-merging methods. These additions will be incorporated without changing the reported numerical results. revision: yes
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Referee: [Method] Method (anchor-search stage): the anchor schedule is obtained by Optuna optimization against an end-to-end perceptual objective; the subsequent OT interpolation therefore inherits dependence on this fitted anchor rather than deriving from a parameter-free or closed-form construction.
Authors: The observation is accurate: the anchor is obtained via Optuna optimization with a perceptual objective. This is an intentional design element of the three-stage pipeline. The graph-based reference supplies a high-fidelity policy under conservative budgets, while the optimized anchor supplies a perceptually strong endpoint under extreme low budgets where additive independence assumptions break down. The OT interpolation then models the geometry-aware evolution between these two points in policy space. The overall framework remains training-free because no diffusion-model parameters are updated; the anchor search is a lightweight, one-time offline procedure. The manuscript does not claim a parameter-free or closed-form derivation for the entire pipeline, and the OT component specifically addresses the geometry that prior additive methods lack. No revision to the method itself is required, though we can add a short clarifying sentence if the editor deems it helpful. revision: no
Circularity Check
No significant circularity identified
full rationale
The described pipeline obtains a reference schedule from an external graph-based method, fits an anchor via Optuna on a perceptual objective, and applies OT quantile interpolation for other budgets. No equations, definitions, or steps in the provided text reduce by construction to their own inputs, rename fitted quantities as predictions, or depend on self-citations for core claims. The approach is a composite heuristic whose validity rests on external benchmarks rather than internal definitional closure.
Axiom & Free-Parameter Ledger
free parameters (1)
- anchor schedule via Optuna
axioms (1)
- domain assumption Caching schedules across budgets evolve smoothly in policy space under continuous warping representations from optimal transport.
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