http://buy.guildwars2.com/store/gw2/....buyguildwars2
No official word on how long the sale will last but if you've been dying to try it out, here's your chance!
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Here's the official - sale is through May 11th.
https://www.guildwars2.com/en/news/save-50-percent-on-guildwars2-from-now-until-may11/