NT is an improved model of the Block 1, while Block 2 is pretty much a new missile. That’s what the MBDA website says. It says the new contract is for “Aster Block 1 NT”, which it describes as “a new version of the Aster 30 Block 1 missile, referred to as Aster B1 NT”. It also says the contract “also covers the modernization of the current SAMP/T system to provide enhanced capabilities particularly against ballistic missiles.”
Press release.