There hasn't yet been a formal announcement, but HBO GO is indeed available for the Fire TV Stick through the dongle's app store.
HBO GO originally hit the Fire TV back in December, but users of its smaller sibling, the Fire TV Stick, were left out of the party with a promise that the service would hit the streaming dongle sometime in the spring.
If you'd like to try the app out on your Fire TV Stick, you should be able to snag it from the device's app store now. However, do keep in mind that HBO GO does require an active cable subscription from a participating provider to use.
