Usually, earnings pre-announcements are done if they are going be be significantly different (good or bad, but most times good) that the results expected by analysts who report on that stock. We should then expect that the 3Q results are about what AGNC analysts expected ($1.09 per share, according to Earnings Whispers). If, however, there is a surprise in that number, it would be on the down side.
Given the market environment, just meeting expectations could trigger a small sell-off in AGNC stock. I don't expect that mood to change until we near Thanksgiving (11/22 this year). Then, we should see a rise in AGNC share price until XD date in December (date has not yet been announced).