The first masked diffusion model pretrained from scratch on text, images and audio at once
AspireAI community · Apple Machine Learning Research (NeurIPS)
Discrete diffusion models are a credible alternative to autoregressive language models, but prior work initialized and finetuned a base unimodal model for bi-modal generation rather than pretraining across modalities properly. This work introduces the first tri-modal masked diffusion model pretrained from scratch on text, image-text and audio-text data, and systematically analyses multimodal scaling laws, modality mixing ratios, noise schedules and batch-size effects while providing optimized inference sampling defaults. The batch-size analysis yields an SDE-based reparameterization that decouples the physical batch size (chosen for GPU saturation and wall-clock time) from the logical batch size (chosen for gradient variance), removing the need to tune an optimal batch size as prior work required. A preliminary model at 3B parameters and 6.4T tokens shows strong results on text generation, text-to-image and text-to-speech. It is a preliminary model, not a released checkpoint.
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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.