Jagex launched a hardcore mode for Old School RuneScape today across PC, iOS, and Android. In hardcore, players get one life. Death triggers a choice: fully reset progress to level 1, or transfer the character to the main game and keep all items considered "kept on death" items. All other items are lost upon death.
The mode works like other realms in OSRS. Future content and updates apply to hardcore characters the same way they do in the standard game.
World of Warcraft: Classic added a similar hardcore mode in 2023. Those servers have been "a massive hit among the Classic community," and the mode is coming to World of Warcraft: Forever after its November 4 launch, though not immediately at release.