Originally Posted by link2

It's the API that the Heathrow website (and presumably the mobile app as well) uses to fetch flight information. Interestingly, the response contains a lot of information that the website and app choose not to display! Including the actual stand information and whether it's provisional or confirmed. And it works for arrivals as well.

I assume the wayfinder, that HAL API, and BA's internal tools ultimately use the same underlying data source.