Last August we reported on the 'Faraway Islands' GPU which was meant to be the Radeon R9 400 series but it looks like this is known as 'Arctic Islands'. You might have guessed from the word 'arctic' that AMD is looking to keep the R9 400 series cooler, with improved power efficiency, better aligning them with NVIDIA's Maxwell-based GeForce GTX 900 series GPUs.
Then in November we reported that the Radeon R9 490X (and any GPU close to it in the R9 400 series) could feature over 1TB/sec memory bandwidth, thanks to HBM. The latest rumors are pointing to Arctic Islands being baked onto the 20nm process, which should see the GPUs running much cooler than the R9 290X which runs quite hot, especially compared to a GTX 980.
When can we expect AMD to begin shipping the Radeon R9 400 series? Well, we are to expect the R9 300 series in Q2 2015 of this year (sometime between April and June) so we shouldn't see the R9 400 series until at least the second half of 2016.