Decompress a tar.xz file using all cores

I have 37 GiB File which was created by tar + xz. I have a server with 6 cores, so for maximum compression speed I want to use all my 6 cores using this command

XZ_OPT='-T0 -9 –memory=75%' tar -cJf mydir.tar.xz mydir

And it was pretty fast. What can I do to make decompress using all the cores?

tar -xvf mydir.tar.xz 

Uses only 1 core for decompression

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