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Pushing Mixture of Experts to the Limit: Extremely Parameter Efficient MoE for Instruction Tuning

Paper · 2023 · Ted Zadouri, Ahmet Ustun, Arash Ahmadian et al.

Summary

Mixture of Experts (MoE) models route inputs to specialized sub-networks while keeping compute constant. However, they are costly because every expert must be stored and, when fine-tuned, updated. Zadouri et al. (Cohere for AI) ask whether MoE can still help in instruction tuning when only a tiny share of weights may change. They swap the usual feed-forward experts for lightweight PEFT modules, producing two variants:

  • Mixture of Vectors (MoV), built from (IA)³ rescaling vectors
  • Mixture of LoRA (MoLORA), built from LoRA adapters

A softmax router assigns weights per token. Because these adapters are linear, the experts are averaged first and then applied once ("soft merging"). The pretrained T5 weights stay frozen.

The models (770M to 11B) are trained on P3 tasks and evaluated zero-shot on held-out tasks. The method beats plain (IA)³ and LoRA and comes close to or matches full fine-tuning while touching under 1% of parameters. Routing works on tokens and needs no task labels, so it transfers to unseen tasks. This makes MoE-style instruction tuning practical on modest hardware.

Key points

  • Training data comes from P3 (12 task types across 55 datasets). Evaluation covers 8 held-out tasks, using T5 models at 770M, 3B and 11B.
  • MoV changes only 0.32% of weights in T5-3B and 0.86% in T5-11B, yet stays competitive with full fine-tuning.
  • MoV improves on standard (IA)³ by up to 14.57% at 3B and 8.39% at 11B. For comparison, (IA)³ alone updates 0.018% of T5-3B, and LoRA at rank 4 updates about 0.3%.
  • Ablations examine the number of experts, soft versus top-k routing, token versus embedding routing, and hyperparameter sensitivity. The code is published at github.com/for-ai/parameter-efficient-moe.
  • The authors note two limitations: only encoder-decoder (T5) models were tested, not decoder-only GPT-style models, and the method was studied only for fine-tuning, not pretraining.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

Cite

Cite as Ted Zadouri, Ahmet Ustun, Arash Ahmadian, Beyza Ermiş, Acyr Locatelli and Sara Hooker. 2023. Pushing Mixture of Experts to the Limit: Extremely Parameter Efficient MoE for Instruction Tuning. arXiv:2309.05444.

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.48550/arxiv.2309.05444 · arXiv 2309.05444

@misc{zadouri2023pushing,
  title = {{Pushing Mixture of Experts to the Limit: Extremely Parameter Efficient MoE for Instruction Tuning}},
  author = {Ted Zadouri, Ahmet Ustun, Arash Ahmadian, Beyza Ermics, Acyr Locatelli and Sara Hooker},
  year = {2023},
  doi = {10.48550/arxiv.2309.05444},
  eprint = {2309.05444},
  archivePrefix = {arXiv},
  url = {https://doi.org/10.48550/arxiv.2309.05444}
}

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