This is very cool, thanks for sharing! From the readme (https://bellard.org/nncp/readme-gpt2tc.txt), the program benchmarks very comparably to CMIX, which is the top algorithm on the Large Text Compression Benchmark (http://mattmahoney.net/dc/text.html). I'm guessing that any GPT implementation would be ineligible for the benchmark because of its file size but impressive nonetheless.