Official answer from Asus support

"4 Gb soldered on the notebook and 1 expansion slot.
There are tested modules:
DDR3L 1600 SO-D 2G 204P HYNIX/HMT425S6AFR6A-PB
DDR3L 1600 SO-D 4G 204P HYNIX/HMT451S6BFR8A-PB
DDR3L 1600 SO-D 4G 204P SAMSUNG/M471B5173DB0-YK0
DDR3L 1600 SO-D 4G 204P KINGSTON/ASU16D3LS1KFG/4G
DDR3L 1600 SO-D 8G 204P SAMSUNG/M471B1G73DB0-YK0