https://www.polygon.com/2018/7/24/17608100/lucky-pokemon-not-released-announcement-pokemon-go

A new type of Pokémon — Lucky Pokémon — were announced for Pokémon Go yesterday. They were first hinted at in a picture tweeted by the official Pokémon Go account, then revealed further in patch notes, a blog post and even in-game notifications. But for all the information rolled out about the new feature, Niantic forgot to mention one thing: Lucky Pokémon aren’t actually in the game yet.

Though there’s no indication in the announcements about when Lucky Pokémon were supposed to go live, the information made many players think that they were currently available in the game.