In this competition, and in similar competitions, the size of the binary used to decompress is taken into account. If you wanted to use a dictionary, you would

In this competition, and in similar competitions, the size of the binary used to decompress is taken into account. If you wanted to use a dictionary, you would need to pay for it in binary size. In this competition, the file must be self-decompressing. Dictionaries are powerful tools when compressing small data. But once the data is large enough they stop mattering so much. See the dictionary compression section of https://engineering.fb.com/core-data/zstandard/ https://engineering.fb.com/core-data/zstandard/.