I'm interested in tinkering with the AI in Civ 5. I know there are XML files that can adjust the AI's strategies, but are there other easily moddable AI components? The XML files contain comments that reference some CPP files, are those available to end users or are those comments just aimed at internals?
The Civ 5 SDK has been released, which should include the source code for the core game library, including all of the AI code (including those files referenced in the XML comments). You should be able to change the AI to any extent you like, even going so far as to rewrite it completely if you so desired. Have fun! :)
EDIT: My apologies, but it seems I was a bit premature. It was my understanding that the sources would be included in the SDK as they were for Civ 4. Further inspection of the SDK reveals that those sources are not included. I suspect the sources will be made available eventually, and that they were excluded from the initial SDK release in order to get something into the hands of anxious mod creators. It's possible that Firaxis reconsidered their SDK strategy and decided not to release the sources at all, but I imagine that would invite quite a backlash from the community. I guess we'll just have to wait and see.