On October 21, miHoYo announced Genshin Impact (PC, PS4, Mobile, soon on Switch, PS5) will be entering its first maintenance on October 22, from 0800 JST to 1200 JST. In ET, this means on October 21, from 1900 ET to 2300 ET. (Click here for a table with other time zones). The announcement was made through the Japanese Genshin Impact Twitter:

The statement wasn't shared in English yet as usual. However, this should hold true for all servers. Long story short, there are two main Genshin servers, the Chinese one, and the Global one. With the Global server being subdivided into "America", "Europe", "Asia", and "TW + HK + MO" servers. Meaning if a server maintenance was announced in Japan, server maintenance will be happening on all of global server, at the same time. It's possible the maintenance time for each server might turn out different though. Update: The maintenance was announced in English, on the same times.

miHoYo explained the maintenance is to provide a better gaming experience, and to fix some bugs. The developers also advised players to logout from the game before maintenance starts. Or else your game progress might not save properly.

Japanese (stylized) online games and gacha games always distribute compensation for maintenance, and Genshin Impact is no exception: miHoYo announced 240 Primogems will be distributed to all players within 5 hours after maintenance ends. The Primogems will be sent via in-game mail, and you'll have 30 days to claim them. Note however that only accounts who reached Adventurer Rank 5 before the maintenance will get the Primogems.

miHoYo also explained the compensation will always be 60 Primogems for each hour of maintenance. For example, if a ten hours maintenance ever happens, we'll get 600 Primogems. miHoYo also explained the amount won't change even if a maintenance ends earlier than scheduled.

Online games usually have weekly maintenance or so, Genshin Impact didn't have a single down time since launch, this October maintenance is the first one. PSO2 most notably has its weekly maintenance on Wednesday. This gave birth to hashtags such as  #メンテの日なのでssを貼る / "It's maintenance day so let's share screenshots" on Jp Twitter. Genshin Impact is making waves in Japan right now, assuming the game keeps its popularity in the coming months, players will probably start a similar hashtag.

Be sure to check our guide on the Klee banner. miHoYo is currently considering adding key bindings to Genshin Impact. Lisa’s seiyuu Rie Tanaka sometimes streams the game too on YouTube. Genshin Impact Version 1.1 is expected to launch on November 11 with a new event. Version 1.2 is expected to launch on December 23, and will add another event and the new Dragonspine area. Version 1.3 is scheduled for February 2021. You can read in detail about each update here and here.