AI & Machine Learning

The mathematics of neural network pruning has been studied since the 1980s, when Yann LeCun demonstrated that optimal brain damage could remove redundant weights without harming performance. Yet for decades, pruning remained a niche technique—the computational savings rarely justified the engineering effort. Large Language Models changed everything. A 70-billion parameter model requires approximately 140 GB of memory just to store weights in FP16. At 50% sparsity, that drops to 70 GB—but only if your inference engine can efficiently skip the zero weights. The potential savings are measured in hundreds of thousands of dollars per deployment. The question is no longer whether to prune, but how to do it without destroying the model’s capabilities. ...

The Transformer architecture revolutionized machine learning with its attention mechanism, enabling models to capture dependencies across entire sequences. Yet despite their dominance, Transformers suffer from a fundamental limitation: they have amnesia. Every token beyond the context window vanishes into oblivion, and even within that window, the quadratic complexity of attention makes scaling prohibitively expensive. In December 2024, Google Research introduced Titans, a new family of architectures that fundamentally rethinks how neural networks handle memory. The breakthrough isn’t just another efficiency trick—it’s a paradigm shift that treats memory itself as a learnable neural network, updated in real-time during inference through gradient descent on a surprise-based objective. ...

The smartphone in your pocket has more computing power than the entire NASA control room that guided Apollo 11 to the Moon. Yet until 2024, running a useful language model entirely on that device seemed like science fiction. The revolution that made it possible wasn’t a single breakthrough—it was a cascade of engineering innovations that fundamentally rethought how neural networks run on constrained hardware. The Memory Bandwidth Abyss The first and most brutal constraint facing on-device LLMs isn’t compute—it’s data movement. When you run a 7-billion parameter model on an H100 GPU, you’re working with memory bandwidth of 3.35 TB/s. A flagship smartphone in 2026? You get 50-90 GB/s through its LPDDR5X memory. That’s a 30-50x gap, and it dominates every architectural decision. ...

When GPT-4 was released in 2023, rumors suggested it contained over 1.7 trillion parameters. Training such a model requires approximately 25,000 A100 GPUs running for months—a feat that would be impossible without sophisticated distributed training systems. The challenge isn’t merely computational; it’s fundamentally a memory problem. A single 80GB A100 GPU can barely hold a 40B parameter model during training, let alone a trillion-parameter behemoth. This is the story of how systems researchers cracked the memory wall through a decade of innovations in data parallelism, ZeRO, tensor parallelism, and pipeline parallelism. ...

The fundamental flaw in large language model security isn’t a missing authentication layer or an unpatched vulnerability—it’s the absence of a trust boundary. When you ask ChatGPT to summarize a document, the model treats every token in that document with the same authority as your original instruction. This architectural decision, while enabling remarkable flexibility, creates an attack surface that traditional security frameworks cannot address. In February 2025, Anthropic invited 183 security researchers to break their Constitutional Classifiers system. After 3,000+ hours of attempted jailbreaks, one researcher finally succeeded—using a combination of cipher encodings, role-play scenarios, and keyword substitution to bypass safety guardrails and extract detailed chemical weapons information. The attack required six days of continuous effort, but it worked. This incident illuminates both the sophistication of modern LLM attacks and the inadequacy of current defenses. ...

The race for larger context windows has defined LLM development for years. From GPT-4’s 128K tokens to Gemini’s 1M and beyond, the assumption has been simple: more context equals better performance. But a January 2026 paper from MIT CSAIL challenges this assumption entirely. Recursive Language Models (RLMs) don’t expand the context window—they render it irrelevant by treating prompts as external environments that models can programmatically explore, decompose, and recursively process. ...

Every transformer you’ve ever used treats every token with the same computational respect. Whether processing “the” or untangling complex mathematical reasoning, the model devotes identical FLOPs to each position in the sequence. This uniform allocation isn’t a design choice—it’s a constraint baked into the transformer architecture from its inception. In April 2024, researchers from Google DeepMind, McGill University, and Mila demonstrated that this constraint is not only unnecessary but actively wasteful. Their proposed Mixture-of-Depths (MoD) framework reveals a startling truth: transformers can learn to dynamically allocate compute across tokens, achieving 50% faster inference with equivalent performance. ...

The long-context problem has haunted transformer architectures since their inception. While self-attention’s $O(n^2)$ complexity is well-known, the real tragedy lies deeper: even modern RNNs like Mamba, despite their linear complexity, plateau after 16K tokens. They simply cannot compress enough information into their fixed-size hidden states. What if the hidden state wasn’t a fixed-size bottleneck, but a model that could grow in capacity through learning—even at test time? This is the radical proposition of Test-Time Training (TTT), introduced by Stanford researchers in July 2024 and extended to production-ready systems by NVIDIA and Stanford in December 2025. The results are striking: TTT-Linear matches Transformer performance while maintaining RNN efficiency, and the latest TTT-E2E achieves 2.7x faster inference than full attention at 128K context length. ...

When you ask ChatGPT about your company’s internal documents, it hallucinates. When you ask about events after its training cutoff, it fabricates. These aren’t bugs—they’re fundamental limitations of parametric knowledge encoded in model weights. Retrieval-Augmented Generation (RAG) emerged as the solution, but naive implementations fail spectacularly. This deep dive explores how to architect RAG systems that actually work. The Knowledge Encoding Problem Large Language Models encode knowledge in two ways: parametric (weights) and non-parametric (external data). Parametric knowledge is fast but frozen at training time, prone to hallucination, and impossible to update without retraining. Non-parametric knowledge—RAG’s domain—solves all three problems at the cost of latency and complexity. ...

The Open LLM Leaderboard tells a surprising story: many top-performing models aren’t trained at all. They’re merged. A 7B parameter model, created by strategically blending weights from existing fine-tuned models, can outperform models 10x its size. This isn’t alchemy—it’s mathematics. Model merging represents a paradigm shift in how we think about model development. Instead of investing millions in GPU hours for training, practitioners are discovering that the collective intelligence embedded in existing open-source models can be combined to create something greater than the sum of its parts. The technique requires no gradients, no backward passes, and no training data. Just arithmetic operations on weight tensors. ...

The sequential nature of autoregressive language models creates a fundamental bottleneck: generating each token requires a full forward pass through billions of parameters. A 70B parameter model processing a single token must load roughly 140GB of weights from memory (FP16), and memory bandwidth—not compute—becomes the limiting factor. This is why a 70B model might generate only 20-30 tokens per second on an H100, despite the GPU being capable of orders of magnitude more computation. ...