Spez (Huffman) wrote the original LISP version of reddit.

From wikipedia:

During spring break of his senior year at UVA, Huffman and college roommate Alexis Ohanian[1] drove to Boston, Massachusetts, to attend a lecture[6] delivered by programmer-entrepreneur Paul Graham.[1][7] Huffman and Ohanian talked with Graham after the lecture and he invited them to apply to his startup incubator Y Combinator.[1] Huffman came up with their original idea, My Mobile Menu,[7] which was intended to allow users to order food by SMS.[1][7] The idea was rejected, but Graham asked Huffman and Ohanian to meet him in Boston to pitch another idea for a start-up; it was at this brainstorming session that the idea for what Graham called the "front page of the Internet" was created.[1] Huffman and Ohanian were accepted in Y Combinator's first class.[1][7] Huffman coded the entire site in Lisp.[8][9] He and Ohanian launched Reddit in June 2005, funded by Y Combinator.[5][10]

The site’s audience grew rapidly in its first few months, and by August 2005, Huffman noticed their habitual user-base had grown so large that he no longer needed to fill the front page with content himself.[8][11][12] At 23, Huffman and Ohanian sold Reddit to Condé Nast on October 31, 2006, for a reported $10 million to $20 million.[1][13] Huffman remained with Reddit until 2009, when he left his role as acting CEO.

Swarz came around in "fall 2005"

In early fall of 2005, Swartz worked with his fellow co-founders of another nascent Y-Combinator firm Reddit, to rewrite Reddit's Lisp codebase using Python and web.py

So according to that, it was launched in LISP in June 2005 and then Swartz re-wrote the whole thing in python in early fall 2005. So it sounds like reddit's LISP version was only operational for a couple of months in total! So basically the entirety of it's existence is from Swartz's code