The following FX pages are 404.
Based on a comment from the source it seems they are intentionally not shows, since they are prototypes:
Prototype features are not available as part of binary distributions like PyPI or Conda (except maybe behind run-time flags). To test these features we would, depending on the feature, recommend building from master or using the nightly wheelss that are made available on pytorch.org.
These are intentionally left out of the pytorch.org/tutorials build and will not show up on the website.