I just brewed a batch of this and I tasted a sample before I pitched the yeast and it was extremely bitter. Will this mellow out as the beer ages?
I did use the biab method and put the in tettnanger hops once I pulled the grain bag.
In my experience, the wort always tastes considerably more bitter before fermentation than the finished beer does. A fair amount of the bitter hop resins usually get spit out of the fermenter with the blow-off, or stick to the sides of the fermenter in that ugly greenish-brown krausen ring. Also, some of these bitter resins and hop acids actually adhere to the cell walls of yeast cells, so you lose some bitterness in that way as well.
Don't worry, IPA wort is supposed to taste bitter. It will mellow quite a bit once fermentation is complete.