Die Welt seem pretty confident that it's a done deal. Unless we're planning to gazump Dortmund. https://www.welt.de/sport/fussball/bundesliga/article176827328/BVB-Werder-Bremens-Thomas-Delaney-vor-dem-Wechsel-zu-Borussia-Dortmund.html
Nothing official as yet. Reports in Germany suggesting it will be announced on Friday. This Dortmund fansite thinks he's a bit overpriced too https://www.fearthewall.com/2018/5/30/17409852/report-bvb-will-sign-thomas-delaney
Perhaps most importantly we can offer a greater chance of playing regularly. There's a lot of competition in the Dortmund midfield (Reus, Gotze, Weigl, Sahin, Kagawa, Mahmoud).