I vote for lemmurs instead

I have to go with lemmurs :)

So python standard library lists?

You mean numpy arrays? I think the most efficient way to store them is via np.save. You could try creating a new directory and store all of your arrays there with clever file naming to retrieve the dictionary structure later.

Alternatively if you are up to trying to use pytorch you can convert the arrays to tensors and use torch.save to save the entire dictionary in one file. Installing pytorch just for this might be a bit overkill as it is a >1GB installation tho.