How many known actual use cases are there for this header anyway? (I.e. API modules which take inputs that might be too long for a GET request?) The documentation only mentions parse; looking through the API sandbox, I think compare might potentially qualify as well. Given that this whole feature is just a performance optimization, I think I could live with hard-coding a check for just those two API modules, and add the header unconditionally for them, but not for query etc.