The free version doesn't support response caching, only the enterprise one. If you reach any kind of scale it's a one-way ticket to enterprise, or a complete rewrite, at least last I checked.
I too wish hasura supported query caching in OSS. Not sure if you need to rewrite exactly, though. You could put something like GraphCDN in front of it or write your own cache layer that works similar to GraphCDN.
