Hi @Erikmeier ,
The current PyMC3 releases have very specific requirements for the Theano backend. Your problem is likely because the installed versions are not compatible with each other.
We recently updated the installation instructions: Installation Guide (MacOS) · pymc-devs/pymc3 Wiki · GitHub
The latest 3.11.0 release prints some warnings that you can ignore. We’ll release 3.11.1 in the next few days to fix this.