It doesn't make any sense for a company to ship "dog food" publicly to developer partners. In fact, the decision to make an API public is critical to get right

It doesn't make any sense for a company to ship "dog food" publicly to developer partners. In fact, the decision to make an API public is critical to get right and should not be taken lightly. Making a mistake in private APIs creates some burden within Apple as revisions are made, but this is to be expected from pre-release software. Making a mistake in public APIs erodes the trust of partners that invested time and money in the platform, and it leads to subpar user experiences.