11-868 spends only two lectures on the model itself. L06 breaks the Transformer into embeddings, multi-head attention, FFN, LayerNorm, and residuals; L07 uses T5, LLaMA, and GPT-3 to show what modern LLMs changed. For a systems engineer the point is to remember the shapes: GPT-3 175B has 96 layers, d_model 12288, a 2048-token context, and trained on 300B tokens; LLaMA 65B has 80 layers, d_model 8192, and trained on 1.4T tokens. Those numbers set the workload for every acceleration, parallelism, and serving lecture that follows.
Hung-Yu Kao's Fall 2025 W8 slides walk from GPT-1 to GPT-3, explain how the Sparse Transformer behind GPT-3 cuts attention cost, and then use InstructGPT to show the gap between continuing text and following instructions. The maximum likelihood objective can't tell a fabricated fact from a slightly wrong synonym, so three extra stages are added: SFT learns how humans write, a reward model learns how humans grade, and PPO optimizes against that grade while a KL penalty keeps the model from drifting too far. The lecture closes with Llama-2: separate safety and helpfulness reward models, context distillation, and GQA for faster inference.
'Open-source' in AI doesn't mean what it means in software. MIT and Apache 2.0 let you do almost anything; the Llama License requires a separate deal above 700M MAU; old Gemma terms let Google change rules unilaterally (Gemma 4 switched to Apache 2.0). This guide maps what you can and can't do by license type.
Nous Research doesn't pretrain — they fine-tune and do RL. Hermes 4 scores 96.3% on MATH-500, NousCoder-14B improves Qwen3-14B's coding ability by 7% using only 24K training samples. But the real moat is Hermes Agent: 236K GitHub stars, #19 globally, 3,000 contributors.
Llama is Meta's open-source LLM family, with the largest enterprise deployment footprint and the most mature ecosystem. Llama 4 Scout (10M context) and Maverick (17B active / 400B total MoE) are the current open multimodal benchmarks, but Meta pivoted to closed-source Muse Spark in April 2026—Llama 4 is likely the last major open Llama, and its license is not truly open (Llama 4 Community License, separate license required above 700M MAU).
The main on-device LLMs in 2026 are Gemma 3n, Qwen 3.5 Small, Llama 3.2, Phi-4-mini, Ministral 3, and SmolLM3. Sub-3B quantized models can hit 30-50 tokens/sec on phones with 8GB RAM, but RAM, thermal throttling, and context window remain hard constraints.
2026 Q1 saw a full-blown open-source model explosion: on the LLM front, GLM-5, Kimi K2.5, and Qwen3.5 caught up with closed-source models; Embedding and Reranker are dominated by Qwen3 and BGE; speech has Voxtral TTS and Whisper V3; image has FLUX.2; and video has Wan 2.2 rivaling Sora. This is the complete navigation map.