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Dynamic Mixture of Experts: An Auto-Tuning Approach for Efficient Transformer Models
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Proposes DynMoE, which uses a top-any sigmoid-threshold gating with per-expert thresholds and an adaptive process that adds and removes experts during training, removing the need to tune the number of experts and top-k.
Problem
Sparse Mixture of Experts performance depends heavily on hyper-parameters (number of experts K and top-k), making tuning costly; existing fixes either need extra hyperparameters (top-p) or dense warm-up.
Approach
Treat gating as multi-label classification: each token independently activates any subset of experts via cosine similarity against learnable per-expert thresholds (sign function with straight-through gradient), while experts are added when tokens activate none and removed when unused; a diversity-and-simplicity auxiliary loss encourages sparsity.
Key results
- On the vision-language setup with StableLM-1.6B, DynMoE-LLaVA (avg k=1.25, 1.75B activated) matches or exceeds MoE-LLaVA (k=2, 2.06B) on most benchmarks, e.g., MMB 63.2 vs 60.2 and VizWiz 40.6 vs 36.2.
- On GLUE with BERT-large, DynMoE averages 81.64 across COLA, MRPC, QNLI, MNLI, and RTE, within the range of the best fixed MoE settings (81.26 to 81.77).
- On ImageNet pretraining with ViT-S, DynMoE-B (k=1.25) reaches 68.5% Acc@1 versus 67.3% for DeepSpeed-MoE top-2.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use dynamic expert count and top-any gating instead of fixed top-k MoE | BERT-large MoE · GLUE average | score: 81.77 -> 81.64 | No clear effect |
| Use dynamic expert count and top-any gating instead of fixed top-2 routing | MoE-LLaVA with StableLM-1.6B · VQA-v2 | score: 76.7 -> 77.4 | Helped |
| Use dynamic expert count and top-any gating instead of fixed top-2 routing | MoE-LLaVA with Qwen-1.8B · VQA-v2 | score: 76.2 -> 76.4 | No clear effect |
| Use dynamic expert count and top-any gating instead of fixed top-2 routing | MoE-LLaVA with Phi-2-2.7B · VQA-v2 | score: 77.6 -> 77.9 | Helped |
| Add load-balance loss (ablation) | DynMoE with StableLM-1.6B · VQA-v2 | score: 77.4 -> 77.1 | Hurt |
| Add efficiency loss on top of load-balance loss (ablation) | DynMoE with StableLM-1.6B · VQA-v2 | score: 77.1 -> 77.1 | No clear effect |
| Weight expert-output averaging by gating scores (ablation) | DynMoE-LLaVA with StableLM-1.6B · VQA-v2 | score: 77.4 -> 73.9 | Hurt |
| Weight expert-output averaging by gating scores (ablation) | DynMoE-LLaVA with StableLM-1.6B · MME | score: 1300.9 -> 1176.8 | Hurt |
| Initialize new experts by averaging existing expert parameters (ablation) | DynMoE with ViT-S · TinyImageNet fine-tuning, E20 | accuracy: 86.70 -> 86.75 | Helped |
| Initialize new experts by weighted averaging existing expert parameters (ablation) | DynMoE with ViT-S · CIFAR-10 pretraining, epoch 500 | accuracy: 83.57 -> 82.01 | Hurt |
| Initialize new experts from the most frequently activated expert (ablation) | DynMoE with ViT-S · CIFAR-10 pretraining, epoch 500 | accuracy: 83.57 -> 80.58 | Hurt |
Surprising findings
- Weighting expert outputs by gating scores instead of plain averaging drops VQAv2 from 77.4 to 73.9 and MMBench from 63.2 to 52.1.
- In the vision-language experiments, the trained DynMoE model with Qwen-1.8B is roughly on par with MoE-LLaVA rather than clearly better.
Limitations
- The adaptive process and top-any gating are not efficient in the current implementation (routing overhead, no CUDA kernels).
- Gains over well-tuned MoE baselines are often within random fluctuation; some vision and language results are comparable rather than superior.
- Maximum number of experts is capped (16 for vision and language, 4 for vision-language), and all experts occupy GPU memory.
Experimental setup
Datasets: GLUE DomainBed PACS VLCS OfficeHome DomainNet ImageNet CIFAR-10 Tiny-ImageNet LLaVA-Finetuning
Benchmarks: GLUE DomainBed VQA-v2 GQA VisWiz ScienceQA-IMG TextVQA POPE MME MMBench LLaVA-Bench (in-the-Wild) MM-Vet
Metrics: accuracy activated parameters throughput latency FLOPs memory
Baselines: GMoE MoE-LLaVA top-p gating DeepSpeed-MoE LLaVA-1.5
Builds on: GMoE MoE-LLaVA MoEfication GShard auxiliary loss
Closest papers by meaning
- FuseMoE: Mixture-of-Experts Transformers for Fleximodal Fusion (NeurIPS 2024 · similarity 0.87)
- SwitchHead: Accelerating Transformers with Mixture-of-Experts Attention (NeurIPS 2024 · similarity 0.86)
- Exploiting Activation Sparsity with Dense to Dynamic-k Mixture-of-Experts Conversion (NeurIPS 2024 · similarity 0.86)
- Monet: Mixture of Monosemantic Experts for Transformers (ICLR 2025 · similarity 0.85)
- Mixture-of-Control: State-Aware Fine-Tuning for Transformer-based Models (NeurIPS 2026 · similarity 0.85)
- FourierMoE: Fourier Mixture-of-Experts Adaptation of Large Language Models (NeurIPS 2026 · similarity 0.85)
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