[einpoklum]

While it is possible they throw it all away:

1. If a third-party does their link-shortening, which gets the program text, then - it doesn't matter how nice they are. And if that party is Google then, well...

2. The language you quoted still allows them to keep effectively all information through mining aspects of it rather than keeping the entire code as a stretch of plain text.

3. If GodBolt or its servers are subject to US law, then there might be National Security Letters which compel it to pass information on to the US government, and keep that secret. And this is not a conspiracy theory, this what Snowden has exposed about Google, Apple, Microsoft, Yahoo etc.

So - I respect and like the GodBolt'ers, but you don't have a good guarantee of your data being kept private.