Deadlock is an upcoming third-person shooter and multiplayer online battle arena (MOBA) game developed and published by Valve. It is set in an alternate urban fantasy New York in the early 20th century, featuring battles between two teams of six heroes trying to destroy each other's "Patron" gods as part of an occult ritual. Initially known as Neon Prime, Deadlock was leaked to the public in May 2024, and its Steam page was published in August. It has since remained an invite-only closed alpha, reaching a concurrent player count of over 170,000 in September 2024.

Deadlock is a third-person shooter and MOBA game, featuring two teams with six players each that battle each other. In each match, the twelve players control characters who split across three lanes (formerly four lanes) in a large map. To win, one team has to advance their "troopers", a category of non-player characters (NPCs) who fight alongside players, towards the enemy "patron", a possessed effigy, by defeating the other's team troopers and players who respawn in waves. Before defeating the patron, a team has to take down "guardians" and "walkers", entities which are located on the lanes and protect the patron. Its style of gameplay has been described as a mix of Overwatch, Dota 2, and Team Fortress 2.

Throughout the game, a player can heal and retreat to their base. Additionally, they can unlock items which can be bought in a shop using "souls" as a currency, such as items which increase the player's damage output, defense, and healing. It features various movement mechanics, including sliding and double jumping, and players can also travel through the lanes via zip lines and fans. Initially, there were 20 characters available to play, but this has since increased to 38.

The Street Brawl game mode features two teams of four players being limited to only one lane, and item purchases being disabled. Street Brawl is divided into several rounds; with each round players are offered to choose between three randomly given items that sometimes include unique ones, unavailable in the classical game mode (including "enhanced" versions of normal items).

Deadlock is being developed by Valve in the Source 2 video game engine. Its development allegedly started in 2018. References to its internal code name Citadel were first discovered in the code for Dota 2 in 2019, and it was speculated at the time to be an entry in the Half-Life series due to sharing its name with the final area of Half-Life 2. In October 2022, Valve registered a trademark for Neon Prime; video game journalists suggested that it could be a new video game from the developer.

Duncan Drummond, co-creator and designer of Risk of Rain 2, is a gameplay designer on Deadlock, and its movement systems and design choices have been noted as similar to the Risk of Rain sequel. Dota 2 director IceFrog has also contributed, and was speculated by a data miner to also be Deadlock's lead. Further details were reported from the same data miner in 2023, who speculated that it was an installment in the Dota series and "a sci-fi-oriented third-person 'MOBA-lite' that looks like Overwatch mixed with Team Fortress 2 mixed with Dota 2". He added that there was an external playtest of the game during the same period. In August 2024, an anonymous Valve developer shared early footage of Deadlock.

Deadlock was leaked to the public in May 2024 by playtesters, revealing that Neon Prime was its previous name and that it evolved from a sci-fi oriented to a fantasy/steampunk art style. Gameplay details were also leaked, suggesting it to be a third-person shooter taking place in a "modern steampunk European city". A data miner revealed that there were hundreds of playtesters by this point. In late May, Valve trademarked Deadlock. Valve published the Steam page for the game in August 2024, with it being invite-only. Its description read that it was in early development "with lots of temporary art and experimental gameplay", and the page featured a teaser image and a short trailer. Upon publishing the Steam page, developers removed the non-disclosure agreement (NDA) dialog box. Before its Steam page was published, Deadlock had a concurrent player count of 20,000. By September 2024, it reached a peak concurrent player count of more than 170,000.

Since Deadlock was officially announced in August 2024, Valve has worked on adding anti-cheat detection. In February 2025, Valve published an update in which it lowered the number of lanes from four to three. Later in May 2025, Valve published an update in which the shop and items saw changes. In August, the game's visual style was overhauled and 6 new characters were added one by one through an in-game vote. In January 2026, the Old Gods, New Blood update was released, adding a vote for six new characters, two items, and the Street Brawl mode.