Chapter 2 of Toby Fox's Deltarune surprise launches on PC for free today
In a status update posted in September of 2020, Toby Fox stated that future chapters will likely not take as long as chapter 2 has. After releasing chapter 1, most of that development time was spent on finishing a detailed outline of the rest of the chapters, filling out the rest of his team, and trying to find a better engine to make the following chapters in other than GameMaker, which was used to develop the first chapter (before ultimately deciding to continue using GameMaker). As of right now, however, no solid details have been given on when to expect future chapters.
Official Deltarune website