Adapting a mixture-of-experts model with coupled-state replay cut peak memory from 64.8 GB to 38.8 GB on a single H800
AspireAI community · arXiv
Sparse expert execution cuts the compute a mixture-of-experts model spends, but it does not remove the stored states you still need in order to fine-tune one. DuplexTune replays coupled hidden states through pretrained attention and expert modules, with trainable width bridges connecting two residual streams to the backbone, bridge warm-up before backbone adaptation, and router weights kept frozen. On Qwen1.5-MoE-A2.7B with a single H800 it reports 38.8 GB peak memory against 64.8 GB for supervised fine-tuning with checkpointing, and 25.1 samples per second against 19.9, while reaching 67.2 percent MMLU, 75.6 percent GSM8K and 7.69 MT-Bench. The honest limit is in the paper itself: multilingual scores are weaker than the checkpointed baseline, and the result characterises a configuration-dependent tradeoff among state storage, throughput and adaptation quality rather than a free win.
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Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.