For the benefit of people who don't follow such things attentively: /y18.svg has been /y18.gif for — at least 16 years, as a lower bound [0]. Some have filed bug reports [1] about it. The old one was rasterized and slightly fuzzy when zoomed.

[0] https://hn.algolia.com/?query=y18.gif&type=all

[1] https://news.ycombinator.com/item?id=21544141 ("Can whoever is in charge of HN's site design convert this to an SVG image?" 'octosphere, 3 years ago)