Basically, 1g stall speed in EAS stays constant. Higher up, because of compressibility, IAS is slightly higher than EAS, so IAS stall speed is a little higher. Additionally, at very high altitude Mach effects come in at EAS as low as the 1g stall speed, reducing available CLmax and further raising the 1g stall speed.

See the buffet boundary charts in the notes.

Whatever EAS and IAS/CAS are doing, the higher you go the greater TAS you get for any EAS or IAS.