From optimizing pixels to choosing samples
Every earlier paradigm treats the synthetic set as a variable to optimize. A pretrained diffusion model changes the question. The model can already produce realistic, high-resolution images of each class, so condensation becomes a matter of choosing where in its distribution to spend a small budget, and of steering sampling there. Minimax Diffusion and D4M brought this view to ImageNet-scale benchmarks in 2024. By 2026 it was the family with the most activity, and the most visible arguments.
It inherits from two earlier generative ideas, each of which fixed one problem and kept another:
- Optimizing GAN latents (IT-GAN, GLaD) fixed cross-architecture generalization. GLaD’s own ablation shows the benefit comes from constraining synthesis to a structured generator manifold at all; generators trained on unrelated data, or even randomly initialized, keep most of it. But it still paid the full cost of a matching objective through the generator.
- Storing a generator (DiM, D2M) made redeploying at a new budget nearly free, but stayed at 128×128 and trained its generator on the target data.
Diffusion sampling removed the scale ceiling. It gave up optimizing each sample for training utility, and much of the family’s later history is about recovering that without paying for it.
How the family developed: each fix exposed the next problem
- Fine-tune or pick prototypes (2024). Minimax fine-tunes a DiT with representativeness and diversity terms. D4M clusters latent prototypes of a Stable Diffusion model.
- Guide without training (2025). MGD³ discovers modes and guides sampling toward distinct ones, with no fine-tuning. D3HR inverts the dataset into the Gaussian domain with DDIM and samples representative latents there. CaO₂ fixes mismatches between generation and the evaluation objective. IGD guides by the influence a sample would have on training.
- The guidance itself is questioned (2026). ManifoldGD shows that Euclidean mode guidance pushes samples off the data manifold, and projects guidance onto its local tangent space. CoDA transplants guidance methods between backbones and argues their success rests on a diffusion model already trained on the target dataset. It then gets comparable ImageNet-1K results from an off-the-shelf SDXL model steered toward a density-discovered “core” of each class. DAP reads representativeness directly from the frozen backbone’s own features.
- From samples to sets (2026). Even good per-sample guidance produces redundant sets: learnability-guided diffusion measures 80–90% overlap between successively generated increments and builds the set as a curriculum instead. DMGD adds optimal-transport matching over the whole set. IMS3 names the underlying tension: a model trained for likelihood over-represents dense regions and under-covers the class boundaries a classifier needs.
- New generators. HIERAMP uses a visual autoregressive model’s coarse-to-fine scales as separate control points. Path-guided flow matching samples in 32 steps rather than 50 and reports 78% mode coverage against MGD³’s 30%. Neither has yet been compared head-to-head with the strongest training-free diffusion methods.
What the numbers support
Under a matched soft-label protocol, the evidence is consistent. D4M, IGD, D3HR, MGD³ and CaO₂ each beat RDED and SRe2L on ImageNet-1K in their own tables. The 2026 methods cluster tightly. At 50 IPC with ResNet-18 students and teacher relabeling, pushforward quantization and DAP report 62.7%, EVLF on MGD³ 61.9%, DMGD 61.4%, VLCP 60.5% and CoDA 60.4%. That band also contains the best decoupled methods, and it sits a few points above random real images trained with the same kind of relabeling (58.1% in Hard truths about soft labels). At this scale, with a teacher relabeling every crop, the choice between paradigms moves accuracy by a few points at most.
Under hard labels the picture changes. H-GLaD strips soft labels from both sides at very low budgets and finds GAN-latent optimization far ahead of Minimax and D4M (ImageNette, 1 IPC: 45.4% vs 22.8% vs 15.2%). On ImageNet-1K with hard labels, a diversity-aware coreset beats every diffusion method tested (Do distilled sets outperform coresets?). The reversal is ImageNette, where diffusion synthesis beats coresets even with hard labels. Diffusion-based condensation clearly produces better sets than naive generation. Whether its images beat carefully selected real ones at scale is not yet shown.
Open problems specific to this family
- Whose prior is it? Most strong results still use a generator pretrained on the target domain. CoDA shows one way around this for ImageNet, but no method has yet removed fine-tuning, target-domain pre-training and per-sample redundancy at once, with a head-to-head comparison.
- Likelihood is not utility. Sampling concentrates where the density is high; classifiers need coverage near boundaries. Set-level objectives are the current answer, and they reintroduce training loops.
- Cost accounting. Sampling is cheap, but a diffusion model trained on ImageNet cost thousands of accelerator-days, and synthesis time grows with the budget, unlike selection.
- Evaluation. Nearly every ImageNet-1K headline uses teacher relabeling. Hard-label numbers are rare and, where they exist, less favorable. See Evaluation.