Scaling Vision Transformers to 22 Billion Parameters (ViT 22B)

Trains Vision Transformer models at 22 billion parameters using advanced distributed training techniques including gradient checkpointing, activation recomputation, and optimized communication patterns across multi-GPU clusters. The architecture decomposes the transformer stack into memory-efficient stages, enabling training on hardware that would otherwise exceed VRAM constraints through careful orchestration of forward/backward passes and intermediate activation management.

Converts raw images into sequences of patch embeddings by dividing images into fixed-size patches (typically 16×16 pixels), projecting each patch through a learned linear layer, and adding learnable 2D positional embeddings that encode absolute spatial position. This tokenization enables transformer architectures to process images as sequences while preserving spatial structure through explicit position encoding rather than implicit convolution-based inductive biases.

Extracts image features at multiple spatial resolutions by applying transformer blocks at progressively downsampled feature maps, creating a feature pyramid where early layers capture fine-grained details and deeper layers capture semantic information. This is implemented through selective patch merging (combining adjacent patches) at specific depths, reducing sequence length and enabling efficient multi-scale attention computation without explicit pooling operations.

Implements efficient attention mechanisms that approximate full quadratic attention with linear or near-linear complexity in sequence length, enabling ViT to process high-resolution images without prohibitive memory costs. Uses techniques such as local window attention (attending only to nearby patches), sparse attention patterns (attending to a fixed subset of patches), or kernel-based approximations (replacing softmax attention with kernel methods) to reduce the O(n²) memory and compute requirements of standard multi-head attention.

Trains vision transformers using contrastive objectives that align image embeddings with text descriptions or other modalities, pulling embeddings of matching image-text pairs together while pushing apart non-matching pairs. This is implemented through dual-encoder architectures where image and text encoders produce embeddings in a shared space, with contrastive loss computed over batches using techniques like in-batch negatives or momentum contrast to improve gradient signal.

Compresses 22B parameter vision transformers into smaller student models by training students to match teacher model outputs and intermediate representations, using techniques like response-based distillation (matching final logits), feature-based distillation (matching intermediate layer activations), and relation-based distillation (matching attention patterns). This enables deployment of models with 10-50x fewer parameters while retaining 90-95% of teacher accuracy.

Trains 22B parameter models using a combination of float16 (half-precision) and float32 (full-precision) computations, where matrix multiplications and activations use float16 for speed and memory efficiency, while loss computation and gradient updates use float32 for numerical stability. Implements automatic loss scaling that dynamically adjusts gradient scale factors to prevent gradient underflow in float16 while avoiding overflow, enabling stable training without manual tuning.

Extracts and visualizes attention patterns from transformer layers to understand which image regions the model attends to when making predictions. Implements techniques for aggregating attention across multiple heads and layers, projecting attention weights back to image space, and generating saliency maps that highlight important regions. Enables both post-hoc analysis of trained models and real-time attention visualization during inference.