I've also found Pydantic to be a valuable library to use.
However, it does have a strongly opinionated approach to casting that can sometimes yield non-obvious results. This behavior is documented and I would suggest new potential adopters of the library to explore this casting/coerce feature in the context of your product/app requirements.
For the most part, it's not an huge issue, but I've run into a few surprising cases. For example, sys.maxint, 0, '-7', 'inf', float('-inf') are all valid datetime formats.