Gamerscore

Gamerscore is an awarded point system awarded as part of the Achievements system of Xbox 360, Xbox One and Xbox One X games, alongside other Xbox LIVE-connected services such as Windows. Every achievement unlocked in a game awards the player with a gamerscore value, set by the developer, with the player's sum gamerscore total then shown on their Xbox LIVE profile. The amount of points awarded for a given achievement varies depending on how many achievements are in a game, and the difficulty.

Halo games that award Gamerscore
All Halo titles released since the launch of the Xbox 360 have awarded Gamerscore. By default, games launching on Xbox have a total of 1,000 gamerscore to unlock, though Downloadable content released for Halo games typically comes bundled with some exclusive achievements to unlock that raise the gamerscore total.

Halo 2 for Windows Vista
While the original Halo 2 game did not support achievements due to its launch on the original Xbox console, its 2007 PC port did, supporting 41 achievements worth 1,000 Gamerscore.

Halo 3
Halo 3 was the first Halo game on console to award gamerscore, shipping with 1,000 gamerscore unlockable at launch across 49 achievements. The Legendary and Mythic Map Packs later added an additional 750 Gamerscore, bringing the total to 1,750. Notably, Halo 3 is the only Halo game with in-game rewards tied to unlocks; unlocking 750 gamerscore unlocks the shoulders of the Security in-game armor permutation, while reaching 1,000 unlocks the Security helmet and the Katana body armor.

The Legendary Map Pack shipped with seven achievements worth 250 gamerscore, while the Mythic map packs featured twenty three achivements worth 500 gamerscore - notably, the Vidmaster Challenges featured were worth 0GS.

Halo Wars
Halo Wars shipped with 50 achievements worth 1,000GS. The Strategic Options Pack and Historic Battle map pack each add four achievements worth 100GS, bringing up the total Gamerscore unlockable for Halo Wars to 1,200.

Halo 3: ODST
Halo 3: ODST shipped with 47 achievements worth 1,000GS. No DLC was created for Halo 3: ODST, though the game did ship with the Halo 3: Mythic disc, granting access to all Halo 3 multiplayer gamerscore. Unike Halo 3, the Vidmaster Challenges in Halo 3: ODST are worth 25GS each.

Halo: Reach
Halo: Reach shipped with 49 achievements worth 1,000GS. The Noble Map Pack added an additional seven achievements worth 250GS, followed by the Defiant Map Pack featuring six achievements worth 200GS, bringing the total to 1,450GS. The later release of the Anniversary Map Pack added a final seven achievements worth 250GS, making the total gamerscore available to unlock in Halo: Reach 1,700GS.

Halo: Combat Evolved Anniversary
Halo: Combat Evolved Anniversary launched as a remake of Halo: Combat Evolved, and added 44 achievements worth 1,000GS to the original game - which did not support achievements on its original launch in 2001. Alongside the 1,000 GS available for the Anniversary singleplayer, Anniversary also saw the launch of the aforementioned Anniversary Map Pack for Halo: Reach, making an additional 250GS available to unlock for that game.

Halo 4
Halo 4 launched with 49 achievements worth 1,000GS. The Crimson, Majestic, Castle and Champions Bundle DLCs each added 250GS to this total, bringing Halo 4 to a total of 2,000 unlockable gamerscore - the highest amount available in a single Halo title at the time.

Halo: Spartan Assault
Halo: Spartan Assault launched on several different platforms, each with varying achievement values and unlockable achievements. The game's launch for Windows 8 and Windows Phone devices had a total of 20 achievements available for 200 Gamerscore on each, with five additional achievements worth 50GS later added in a title update for a total of 250 unlockable gamerscore. On Xbox 360, the game features 28 achievements worth 400 gamerscore while the Xbox One version features the same achievements as the Xbox 360 edition, with two additional exclusive achievements, for a total of 30 achievements and 1,000GS.

Playing Halo: Spartan Assault across all platforms allows the player to unlock 108 achievements worth 1,900 gamerscore.

Halo: The Master Chief Collection
Released in 2014, Halo: The Master Chief Collection launched as a collection of Halo: Combat Evolved Anniversary, Halo 2: Anniversary, Halo 3 and Halo 4 on one disc and suitably had a massive achievement count to match - moreso than any other title on Xbox LIVE. Prior to launch day, the game had 400 achievements worth 4,000 Gamerscore, though a day-one patch added an additional 50 achievements and 500 gamerscore to the collection, for a total of 4,500 followed by another patch in early 2015 adding an additional 500 gamerscore and 50 achievements. In spring 2015, the release of Halo 3: ODST's campaign in the collection added an additional 100 achievements worth 1,000 gamerscore. The release of Halo: Reach to the collection in 2019 brought the total count for Halo: The Master Chief Collection to 7,000 gamerscore across 700 achivements. A full breakdown of gamerscore values per-game in the collection can be seen below;
 * Halo: Combat Evolved Anniversary - 915 gamerscore.
 * Halo 2: Anniversary - 1,420 Gamerscore.
 * Halo 3 - 805 Gamerscore.
 * Halo 3: ODST - 990 Gamerscore.
 * Halo 4 - 865 Gamerscore.
 * Halo: Reach - 1,000 Gamerscore.
 * Cross-game achievements - 1,000 Gamerscore.

Halo: Spartan Strike
Halo: Spartan Strike launched exclusively for Windows 8 and Windows Phone, containing 20 achievements worth 200 Gamerscore.

Halo 5: Guardians and Halo 5: Forge
Halo 5: Guardians launched with 65 achievements worth 1,000GS. The release of the Warzone Firefight update added an additional eight achivements worth 250GS.

The launch of Halo 5: Forge on Windows 10 allows players to unlock 22 exclusive achievements worth 1,000GS.

Halo Wars 2
Halo Wars 2 launched with 60 achievements worth 1,000GS. Each of the six DLC leaders released for the game added a respective three achievements worth 30GS, bringing the total to 1,180GS. The Halo Wars 2: Operation: SPEARBREAKER expansion additionally awards 40GS across five achievements, while Halo Wars 2: Awakening the Nightmare adds 410 Gamerscore, bringing a final total for Halo Wars 2 to 1750GS.