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NVLM: Open Frontier-Class Multimodal LLMs
· NVIDIA · 2024-09 · arXiv:2409.11402
Why it matters
Compares decoder-only and cross-attention multimodal designs head to head and ships a hybrid. Useful to this atlas as evidence for when the cross-attention pattern stopped being the default rather than as a claim that it failed.
What this paper does
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By late 2024 two incompatible templates for connecting vision to an LLM were both in wide use: decoder-only designs (e.g., LLaVA) that unroll image patch tokens and feed them through the LLM's own self-attention alongside text, and cross-attention designs (e.g., Flamingo) that keep the LLM's self-attention text-only and inject visual information through separate cross-attention layers. No systematic head-to-head comparison of the two under matched conditions existed alongside a production-grade open model release.
The problem
Which of the two dominant multimodal LLM architectures, decoder-only or cross-attention, is actually better, and can a single design get the strengths of both, in particular avoiding the widely observed degradation of text-only capability after multimodal training.
The idea
Run decoder-only and cross-attention architectures side by side under matched training, characterize each one's strengths and weaknesses, and then build a hybrid, NVLM-H, that routes a low-resolution thumbnail of the image through the LLM's self-attention (for joint multimodal reasoning) while routing the dynamic set of high-resolution tiles through gated cross-attention (for efficiency and fine detail), combined with a 1-D tile-tagging scheme for dynamic high-resolution tiling.
How it works
NVLM-D (decoder-only) unrolls all image tile tokens and feeds them through the LLM's self-attention. NVLM-X (cross-attention) uses a Perceiver-style resampler and gated cross-attention layers injected into the LLM, with the LLM itself optionally frozen. NVLM-H combines both: thumbnail tokens go through self-attention with text tokens, while the dynamic number of high-resolution tiles go through gated cross-attention. The 1-D tile-tagging design adds a flat sequence of tags (tile_1, tile_2, ..., tile_global) marking each tile, compared against no tag, a 2-D grid tag, and 2-D bounding-box tags. All variants are trained with a high-quality curated text-only dataset mixed into multimodal training specifically to preserve text-only performance, plus multimodal math and reasoning data. Weights are released for NVLM-D-72B.
Evidence
Tile-tag ablation (NVLM-D, Yi-34B, Table 1): OCRBench 622 with no dynamic high-res, 728 with dynamic high-res and no tag, 806 with the 1-D tag (best), versus 787 (2-D grid) and 791 (2-D bbox); MMMU validation rises from 50.9 to 52.0 with the 1-D tag. Architecture comparison: NVLM-D reaches the family's best OCRBench (853) but has lower training throughput (28.8 samples/sec vs NVLM-X's 50.6, a 76% gap) because it unrolls all tile tokens through self-attention; NVLM-X is more training-efficient but its vision-language performance drops when the LLM is frozen (54.4 vs 57.4 MMMU for 72B), and its Perceiver resampler disrupts spatial relationships between patches, hurting OCR. NVLM-H gets the family's best MMMU validation (60.2) and best MathVista (66.6) at intermediate throughput (36.2 samples/sec). On text-only benchmarks, multimodal training improved the Qwen2-72B-Instruct backbone's average score by +4.3 (NVLM-D), +2.5 (NVLM-X), +2.7 (NVLM-H) over the 79.8 text-only baseline, versus reported degradations of -6.3 to -6.9 points in LLaVA-OneVision-72B, InternVL-2-Llama3-76B, and VILA-1.5 40B.
Limitations
The paper concedes that high-resolution designs that boost OCR performance sometimes reduce accuracy on reasoning benchmarks like MMMU relative to low-resolution counterparts. It notes training splits of several benchmarks (ChartQA, DocVQA, VQAv2, TextVQA, AI2D) are included in its SFT data mixture, so those evaluations are not zero-shot. Ablation studies were run on smaller 34B models under limited compute, without careful checkpoint selection or hyperparameter tuning, so ablation conclusions may not transfer cleanly to the 72B models. It is also unclear whether proprietary competitor models were evaluated zero-shot or fine-tuned.
Why it matters
The paper does not declare cross-attention obsolete; instead it finds a genuine trade-off (cross-attention is more training-efficient and helps preserve text-only performance under a frozen LLM, but decoder-only self-attention gives stronger OCR and reasoning when data quality is handled well) and resolves it with a hybrid rather than picking a winner. As evidence for when cross-attention stopped being the default, this paper shows that by late 2024 a leading lab treated decoder-only as strong enough to be the headline variant (NVLM-D gets the best standalone OCR score and is the one whose weights were released) while still finding cross-attention useful enough to keep in a hybrid, i.e., cross-attention was demoted to a component rather than eliminated.
Abstract, in the authors' own words
We introduce NVLM 1.0, a family of frontier-class multimodal large language models (LLMs) that achieve state-of-the-art results on vision-language tasks, rivaling the leading proprietary models (e.g., GPT-4o) and open-access models (e.g., Llama 3-V 405B and InternVL 2). Remarkably, NVLM 1.0 shows improved text-only performance over its LLM backbone after multimodal training. In terms of model design, we perform a comprehensive comparison between decoder-only multimodal LLMs (e.g., LLaVA) and cross-attention-based models (e.g., Flamingo). Based on the strengths and weaknesses of both approaches, we propose a novel architecture that enhances both training efficiency and multimodal reasoning capabilities. Furthermore, we introduce a 1-D tile-tagging design for tile-based dynamic high-resolution images, which significantly boosts performance on multimodal reasoning and OCR-related tasks. Regarding training data, we meticulously curate and provide detailed information on our multimodal pretraining and supervised fine-tuning datasets. Our findings indicate that dataset quality and task diversity are more important than scale, even during the pretraining phase, across all architectures. Notably, we develop production-grade multimodality for the NVLM-1.0 models, enabling them to excel in vision-language tasks while maintaining and even improving text-only performance compared to their LLM backbones. To achieve this, we craft and integrate a high-quality text-only dataset into multimodal training, alongside a substantial amount of multimodal math and reasoning data, leading to enhanced math and coding capabilities across modalities. To advance research in the field, we release the model weights at https://huggingface.co/nvidia/NVLM-D-72B and will open-source the training code for the community soon.
Research line
Method note — the shared flow-matching interpolation
Every flow-matching / rectified-flow paper in this atlas trains toward a straight-line path between a noise sample x₀ and a data sample x₁:
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