From Test-Scratch-Wiki
Yes, you can still upload projects to the Scratch Website which are created in Scratch 1.4 or older, and will also be compatible with Scratch 2.0. However, projects created in Scratch 2.0 will not work in 1.4 as 2.0 has many features 1.4 does not support.
For users willing to convert a 2.0 project into a 1.4 project (SB2 to SB), they can use a program which is explained here.
