reddit/reddit — comment on commit a7bcdaa25ff34eff8b6e96ddc48ae777c733c4d7
File:  line 0
By spladug:

This ups the maximum from 30K characters to 40K. Note, this affects subreddits that are set to accept self posts only. Mixed content subreddits use the same limit for self posts as comments do: 10K characters.