“In 2016 Microchip/Atmel announced a completely new range of chips designed to replace their older ATmega and ATtiny ranges. The new ATtiny chips started with the 1-series ATtiny417 and ATtiny817, followed in 2018 by a lower cost series called the 0-series. The range now consists of a total of 25 parts.
Until recently these new chips were not accessible to users of the Arduino IDE, because no Arduino core existed for them, and you couldn’t program them using the existing ISP programmers. That changed a couple of months ago when Spence Konde released a megaTinyCore  for the new range, taking advantage of the work that Arduino have done to support their new ATmega4809-based boards.
This article gives an introduction to the new ATtiny parts, and explains how you can now program them from the Arduino IDE.”