Estimated time (UTC+8): 2021/02/03 ~ 2021/02/17 15:59:59
Xiao will be released through the new event wish. Getting a five star when you summon on this banner will have a 50% chance of it being Xiao. Through the game's pity system, if your last five star that you got was not the banner character, the next 5 star is guaranteed to be the banner character. Diona, Beidou, and Xinyan's rates have also been increased!
Xiao will be getting his own story quest called "Alatus Chapter". It will be available on Feb 10th when the lantern rite event starts.
Keqing will also be getting her own event wish called "Dance of Lanterns", as well as her own story quest. Estimated to be released around February 17. Presumably released at the same time as her event wish.
Is Xiao good?
His kit is made for a damage dealer, with little to no supporting ability. His attacks are fast, and possibly spammable, potentially making it very strong since it has no cooldown, similar to Ganyu's charge attack playstyle. The big downside is that he relies on his elemental burst for the damage increase, and to convert his normal attacks into Anemo, which can be an issue if your team isn't good at generating enough energy.
If you already have a good standard main DPS artifact set of 2 piece gladiator, then building him will be easy since you only need to add in 2 Viridescent Venerer. Being an Anemo element, he can also make good use out of 4 piece Viridescent Venerer to reduce enemy's elemental resistances. This will be good if you can combo him with characters like Xingqiu or Fischl since they don't need to stay on the field to help deal damage.
Should you pull?
Since he's mainly made to be a damage dealer, consider pulling for him if your team is in need of one. Being an Anemo element can mean that his damage will be somewhat consistent since there are only a few enemies that are resistant to Anemo, but he won't be as good as other elements when it comes to breaking elemental shields, so you will need to have teammates that can compliment him for those situations, as well as generating some energy for him. If you already have 2 teams for Spiral Abyss and are not lacking in damage, then going for Xiao might not be good for you because he won't be adding much.
Xiao or Ganyu
Both Ganyu and Xiao are made to be damage dealers, just through different ways. Ganyu deals a lot of damage through her bow charge shot, but this can be somewhat tricky to play with since you can miss your shot, or be easily interrupted by attacks. Meanwhile, Xiao is a lot easier to use. His attacks are fast, and he's quite mobile, which can help with getting in and out of combat.
The other big difference between the two are their elements. Ganyu's Cryo element means that she has access to Cryo elemental reactions, including "Melt" for increased damage. On the other hand, Xiao can ONLY do "Swirl" reactions, which is not that good on its own. However, being able to Swirl means that he can use Viridescent Venerer artifact set for -40% elemental reduction to enemies, but only for elements that's not Anemo or Geo. This means that he won't be increasing his own damage, but his teammates' damage.