LLM Architecture

For years, the next-token prediction (NTP) paradigm has been the unquestioned foundation of large language model training. Given a sequence of tokens $x_{1:t}$, the model learns to maximize $P(x_{t+1} | x_{1:t})$. Simple, elegant, and remarkably effective—until you realize the fundamental inefficiency baked into this approach. The problem is that transformers spend the same computational budget predicting filler words (“the”, “and”, “is”) as they do on information-carrying tokens (“quantum”, “entanglement”, “superposition”). Research from Apple and EPFL reveals that over 50% of English text consists of function words—linguistic glue that carries minimal semantic weight. Yet models trained on NTP treat every token with equal reverence, creating a massive computational inefficiency. ...

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. ...

Every time you increase a Transformer’s context window from 4K to 128K tokens, you’re asking the attention mechanism to compute a matrix 1,024 times larger. The O(n²) complexity isn’t a bug—it’s fundamental to how self-attention works. Every token must attend to every other token, creating a quadratic relationship that makes long-context models prohibitively expensive. Mamba, introduced by Albert Gu and Tri Dao in December 2023, doesn’t just optimize around this constraint. It eliminates it entirely, replacing attention with selective state space models that scale linearly O(n) while matching Transformer quality. A Mamba-3B model outperforms Transformers of the same size and matches Transformers twice its size. The key insight? Making the model’s memory mechanism input-dependent—letting it choose what to remember and what to forget. ...

When DeepSeek-V3 was released in December 2024, it achieved something remarkable: a 671-billion-parameter model that activates only 37 billion parameters per token. This isn’t a magic trick—it’s the power of Mixture of Experts (MoE), an architectural paradigm that has quietly become the backbone of nearly every frontier large language model. The math is compelling. A dense 671B model would require approximately 1,342 TFLOPs per token during inference. DeepSeek-V3 achieves comparable performance with roughly 74 TFLOPs—an 18x reduction in compute. This isn’t incremental optimization; it’s a fundamental rethinking of how neural networks scale. ...