Open Models: Architecture Walkthroughs

You built a GPT-2 Small from scratch in Lesson 04. Frontier open models in 2026 are the same family with five or six concrete changes. RMSNorm instead of LayerNorm. SwiGLU instead of GELU. RoPE instead of learned positions. GQA or MLA instead of full MHA. Mixture-of-Experts at scale. The math you already know covers 95% of them. This lesson reads Llama 3, DeepSeek-V3, Mixtral, Qwen, and Gemma side by side and names the exact line where each architecture diverges.