Is ImageNet 1k a subset of ImageNet 22k
Yes, the full ImageNet is a superset of the 1k version (see Benchmarking Neural Network Robustness to Common Corruptions and Perturbations). The 1k synsets (a.k.a. classes) corresponding to the 1k version are also present in the full 22k version. So there are 21841 classes in total, 1000 of them are exactly the same as in the 1k version (and images are exactly the same), and the other 20841 can be treated as OOD to the 1k version dataset (at least they are treated so in one of the papers by Hendrycks et al, Using Self-Supervised Learning Can Improve Model Robustness and Uncertainty.