Just started to get my head around behavior trees, and how they might be implemented. I have also come across alot of references to BTs being very similiar to HTN planners. I think i understand(ish) how GOAP works but HTNs have elluded me. What is the gist of the difference between HTN and BT? I know one is planner and one is not. But their structure really seems similiar, but how is a HTN traversed differently that makes it a planner?

Please forgive my ignorance.

A HTN is actually searched ahead of the current behavior, so it's not just a best-first search it goes the full tree if necessary. You'll need backtracking to implement an HTN planner, and the result will be a list of actions that are not executed by the planner, but passed back for you to execute yourself.

Look into SHOP, it's a well documented HTN planner with source code.

Alex
AiGameDev.com