I don't like this because a lot of us put validation logic in Model#save and use the signals to trigger the search indexer, and so forth. This behavior is definitely going to catch some people off guard and it's bound to lead to serious bugs.

I understand why they don't call Model#save for every object, but I think they should have introduced something like Model#validate which is called before every save (including the new bulk inserts) so you still get a place to put custom validation logic that you know will get called the moment something is placed in the database. So now inserts are faster but at the expense of correctness. I'm not convinced that's a good trade off.

Oh, and for some reason bulk updates are completely missing, even though it seems natural to add bulk_insert and bulk_update at the same time.