From Halopedia, the Halo wiki
Halo Online was to be a multiplayer-focused Halo game developed by Saber Interactive and Innova Systems in collaboration with 343 Industries. It was officially announced in March 25, 2015, with a closed Alpha test that started on April 21, 2015 in Russia only. On December 28, 2015, a closed Beta test was suspended and on August 24, 2016, cancellation of the game in its current form was announced.
Halo Online takes place shortly after the events of Halo 3 around January 28, 2555. The game is set on a secret UNSC space installation called Anvil, where SPARTAN-IV and Sangheili soldiers train together in simulated war exercises to sharpen their battle skills and test experimental technology.
Halo Online was to include "classic weapons and vehicles" from the Halo franchise, including the Hornet and the energy sword. Several new weapons were also to be implemented into the game. Fan favorite multiplayer maps were to return, along with several new maps—one of which was set in a Russian town. Halo Online would have been optimized for keyboard and mouse controls. Online matches could handle up to sixteen players, with four players being required for a match.
Players were to be able to customize their loadouts, including armor, weapons and abilities. There were several variants of each weapon available for modification. Each weapon featured variants with increased damage, accuracy, and rate of fire. Unlike most of Halo games, players would not be able to change their armor pieces individually, only as a whole set.
Similar to Halo 5: Guardians there was an ending animation for a match. Though in Halo Online it featured only the top three players rather than the entire team.
In Halo Online three professions were available to the player: Assault, Sharpshooter, and Tactical. These professions dictated the player's starting equipment, such as primary weapon and armor
Halo Online featured a number of multiplayer maps, some original to the game and others remakes or direct ports of maps from other Halo games.
Halo 3 Maps
These maps were direct ports of Halo 3 multiplayer maps, albeit renamed.
There were two player models which players could choose from, the standard SPARTAN model or an Elite model. Each model had several armor sets. Each armor set had different effects on gameplay, such as an increased motion tracker range or melee damage boost.
On April 6, 2015 the Halo Online closed Alpha test started, and a special armor was given to people who played on that day during the Alpha to signify they were there day one. The Closed Alpha's servers were only active for small hours during the day. All players' stats and progress, were wiped after the closed alpha finished on September 11, 2015
On September 30, 2015 the closed beta started, and on December 28, 2015, the closed Beta test was suspended. The developers said that they encountered serious problems during the development of Halo Online, and with 343 Industries' counsel they decided to suspend testing and "send the game to a serious revision" for several months. Because of that, for people who bought the exclusive premium Beta tester kits, there was a compensation offer.
On October 9, 2015 a developer took an image of an upcoming update that had the user in an Armory on Anvil Station.
On March 24, 2016 it was announced that testing was to resume, and that an exact date, and detailed information about development would be announced on the official Halo Online VK account at a later date.
2015 build scrapped
On August 24, 2016 Innova Systems announced that Microsoft Studios still had not made a decision on the project's fate, and the game would never be released in its current form, making the project's fate uncertain. Therefore the publisher is shutting down the game's website and the page on social network vk.com. The community manager of Halo Online stated that "such project most likely won't ever exist at all, but only time will show", answering the question if the game is suspended indefinitely.
During the Halo Online closed testing, a group of modders were able to mod the game and began to work on "ElDewrito", a fan-attempt to bring the classic Halo experience to the PC platform by modding the game to play like the original release of Halo 3. In April 2018, version 0.6 of the mod released to widespread community acclaim, reaching 12,000 concurrent players. Four days following the release of ElDewrito 0.6, the members of the team were contacted by 343 Industries including Frank O'Connor, whereupon they were asked to pause development of the mod, and were not given an official cease and desist or DMCA takedown. An official statement was given by 343 Industries the same day, explaining that the mod was taken down due to legal requirements to protect Microsoft intellectual property.
Despite this, 343 Industries retained communications for the team, expressing their admiration for ElDewrito's success and informing that the interest in Halo on PC had "lit a spark" for the company. While Halo: The Master Chief Collection had been intended for a release on PC eventually, the ElDewrito project was responsible for giving 343 the "kick in the pants" needed to begin development of the PC port of Master Chief Collection when they did. In March 2019, the Master Chief Collection was announced for a release on Steam and Windows, with the ElDewrito team working alongside 343 in an advisory role to help bring the Master Chief Collection experience to the PC platform.
An announcement trailer was revealed in March 26, 2015 on YouTube, showing the first in-game gameplay of Halo: Online, displaying the return of some weapons of Halo 3 and the introduction of new armors.
Press Conference (March 26th 2015)
On March 26, 2015 a press conference about Halo Online happened. At this press conference there were holographic pyramids with several renders of Halo Online content were in them.
An story trailer was released around December 29, 2015 on the official Halo Online site. The trailer went though the story elements leading up to the training the Spartans and Elites on Anvil Station on January 28, 2555. The story trailer can be found here.