Everyone wants to understand large language models right now, and most of the content chasing that demand is shallow, so it is worth knowing that the deep version has existed for years and is free. CS224n is Stanford's natural language processing course, run for a long stretch by Christopher Manning, who is one of the people the field was partly built by, and that lineage shows in how the material is framed. It does not start at transformers, which is the right call. It starts at word vectors, has you sit with word2vec and GloVe until the idea of meaning as geometry actually lands, then moves through neural networks for language, recurrent models, and the machine translation problem that motivated attention in the first place.
By the time the transformer arrives you understand the problem it was invented to solve, so self attention feels like an answer rather than a magic trick, and that is the difference between this and a weekend crash course. The later lectures carry you into pretraining, the family of large language models, and the questions around their behaviour and limits, so it has stayed close to the research frontier rather than ageing into a historical artifact. The assignments are the part people skip and should not, because writing your own implementation of word vectors and then a transformer is what converts a vague mental picture into real understanding. My caveats are the usual ones for a Stanford course.
It assumes you arrive already comfortable in Python and NumPy with at least a working sense of neural networks, and it moves quickly, so a single lecture can quietly imply a long weekend of coding to keep up. There is also no certificate or formal feedback unless you are enrolled, so the discipline to actually finish the assignments has to come from you. I still recommend it above almost anything else for this topic. Pair the YouTube lectures with the posted notes and assignments, go at your own pace, and you end up understanding language models at a level that makes the rest of the current hype easy to see through.