This is the course I find myself recommending most often to people who can already program, and it is striking that the answer to what is the best AI course is so frequently something that costs nothing. CS50 AI sits on top of the wider CS50 reputation, and it earns it. Instead of teaching you to paste prompts or call a single library function, it walks you through the actual machinery of the field, search algorithms, knowledge representation and logic, probability and uncertainty, optimisation, then machine learning and neural networks, and finally a taste of natural language processing, and you implement each of these yourself in Python. That last part is the whole point.
The projects are not gentle, you build things like a minimax game player, a system that reasons under uncertainty, and small learning models, and the moment where your own code finally behaves correctly is where the understanding actually lands. The lectures are clear and well made in the way CS50 always is, and because you are auditing for free, the only thing you would ever pay for is the verified certificate, which I would treat as optional unless you specifically want it for a CV or LinkedIn. I want to be straight about who this is not for, though. You need to be comfortable writing Python before you arrive, because this course teaches AI, not programming from zero, and if your coding is shaky you will spend your energy fighting syntax instead of learning the concepts.
The problem sets can also be genuinely hard, and people regularly underestimate the weekly time, so going in expecting a relaxing watch-and-learn experience is a mistake. It also leans toward the foundations rather than the newest generative tooling, so it will make you understand how these systems think without being a tutorial on the latest model of the month, which I consider a strength but is worth knowing if shiny new tools are all you came for. And as with anything self-paced and free, the lack of a hard deadline is the real enemy, so set your own schedule and treat it like a real commitment. Do that, and you come out the other side with something most courses simply do not give you, an actual mental model of how AI works rather than a memorised list of steps.