There are rumors that it might be released during the 1st Qtr of 2018, source: https://www.reddit.com/r/Bitcoin/comments/7e909x/should_we_expect_antminer_s11_in_the_early_2018/

Yet, we can't rely on those as most rumors fail to predict the real outcome. I keep visiting Bitmain site for any news or updates so that I will be included in the list of early birds that will purchase upon its release. Well, my money is sleeping for ages and couldn't purchase an S9 since S11 is coming. I'm just hoping that it will be released sooner than expected.