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Remix-DiT: Mixing Diffusion Transformers for Multi-Expert Denoising
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Remix-DiT crafts N diffusion-transformer denoising experts for different timestep intervals by softmax-mixing K<N learnable basis DiT models, so inference cost matches a standard DiT.
Problem
Multi-expert denoising for diffusion transformers improves quality but training N independent experts is costly, and the number of experts and timestep partition are hand-chosen heuristics.
Approach
Learn K basis DiT models and per-expert softmax mixing coefficients over timesteps so that N experts are weighted averages of the bases; the mixed expert has the architecture of a plain DiT, and the coefficients learn an adaptive timestep partition. A one-hot prior regularizer breaks symmetry when initializing from a pretrained DiT.
Key results
- Remix-B-4-20 (100K fine-tune from DiT-B/2) reaches FID 9.02 vs 9.31 for continual training and 9.28 for 8x multi-expert baseline, at the same 23.04 GFLOPs per step.
- Remix-S-4-20 improves FID from 26.05 (continual training) to 22.84 with IS 69.23 at 6.07 GFLOPs per step.
- Remix-L-4-20 achieves FID 3.22 vs 3.73 for DiT-L/2-1M, with IS 207.54.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Mix 4 basis models into 20 experts for 100k fine-tuning steps | DiT-L/2-1M · ImageNet 256×256, cfg=1.5 | FID: 3.41 -> 3.22 | Helped |
| Mix 4 basis models into 20 experts for 100k fine-tuning steps | DiT-B/2-1M · ImageNet 256×256, cfg=1.5 | FID: 9.28 -> 9.02 | Helped |
| Mix 4 basis models into 20 experts for 100k fine-tuning steps | DiT-S/2-2M · ImageNet 256×256, cfg=1.5 | FID: 25.00 -> 22.84 | Helped |
| Replace one-hot mixing with learnable softmax mixing (ablation) | Remix-S-4-20 · ImageNet 256×256, 10K samples | FID-10K: 32.00 -> 31.11 | Helped |
| Replace unconstrained raw coefficients with softmax-normalized mixing (ablation) | Remix-S-4-20 · ImageNet 256×256, 10K samples | FID-10K: 31.46 -> 31.11 | Helped |
| Use layer-wise local rather than globally shared mixing coefficients (ablation) | Remix-S-4-20 · ImageNet 256×256, 10K samples | FID-10K: 31.11 -> 31.21 | Hurt |
| Use 4 rather than 20 experts (ablation) | Remix-S with 4 basis models · ImageNet 256×256, 10K samples | FID-10K: 31.11 -> 31.77 | Hurt |
| Use 8 rather than 20 experts (ablation) | Remix-S with 4 basis models · ImageNet 256×256, 10K samples | FID-10K: 31.11 -> 31.60 | Hurt |
| Increase the number of experts from 20 to 100 (ablation) | Remix-S with 4 basis models · ImageNet 256×256, 10K samples | FID-10K: 31.11 -> 31.48 | Hurt |
| Increase the number of experts from 20 to 1000 (ablation) | Remix-S with 4 basis models · ImageNet 256×256, 10K samples | FID-10K: 31.11 -> 35.60 | Hurt |
| Reduce the number of basis models from 4 to 2 (ablation) | Remix-S-4-20 · ImageNet 256×256, 10K samples | FID-10K: 31.11 -> 31.67 | Hurt |
| Increase the number of basis models from 4 to 8 (ablation) | Remix-S-4-20 · ImageNet 256×256, 10K samples | FID-10K: 31.11 -> 32.05 | Hurt |
Surprising findings
- Raw (unconstrained) mixing coefficients performed worse than softmax-constrained mixing because negative coefficients made learning harder.
- Increasing the number of experts beyond 20 (to 100 or 1000) did not consistently help; 1000 experts degraded FID to 35.60 for DiT-S.
Limitations
- Only one expert is activated per forward/backward pass, so gradients to mixing coefficients are sparse and need momentum updates.
- Evaluated only on ImageNet 256x256 class-conditional generation with DiT backbones; no error bars reported.
- Extra GPU memory is needed to store basis models, and training is somewhat slower.
Experimental setup
Datasets: ImageNet
Benchmarks: ImageNet 256x256
Metrics: FID IS Precision Recall GFLOPs per step steps per second GPU memory latency
Baselines: DiT-S/2 DiT-B/2 DiT-L/2 Multi-expert 8x denoisers (continual training baseline) DiT continual training
Builds on: DiT E-Diff MEME Multi-expert denoising
Closest papers by meaning
- High-Fidelity Diffusion-Based Image Editing (AAAI 2024 · similarity 0.91)
- Denoising Diffusion Bridge Models (ICLR 2024 · similarity 0.90)
- DEFT: Efficient Fine-tuning of Diffusion Models by Learning the Generalised $h$-transform (NeurIPS 2024 · similarity 0.90)
- ALTER: All-in-One Layer Pruning and Temporal Expert Routing for Efficient Diffusion Generation (NeurIPS 2025 · similarity 0.90)
- FlexiDiT: Your Diffusion Transformer Can Easily Generate High-Quality Samples with Less Compute (CVPR 2025 · similarity 0.90)
- Decouple-Then-Merge: Finetune Diffusion Models as Multi-Task Learning (CVPR 2025 · similarity 0.89)
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