We have currently an issue with stac_fastapi 2.4 in Python 3.10 conda environment due to the recent introduction on `ciso8601` as a dependency: see https://github.com/stac-utils/stac-fastapi/pull/368 What about having this dependency optional? ciso8601 is a C dependency, so a bit trickier to be installed and it's only an optimisation.