In late 2006, eagle-eyed Halo fans noticed several Bungie employees on Xbox Live playing something called "Pimps at Sea", the code name for Halo 3's alpha build.

Hi ferrex!

Shortly after, gameplay footage leaked onto YouTube. In typical leak quality.

Until recently, this particular phase of H3 development was shrouded in mystery. Then early in 2022, twitter user landaire showed off new footage of the build, confirming it was out there.

Now as a special Christmas present, Landaire has finally released the build. Anyone can check it out. The Project Sunrise Team (responsible for reviving OG 360 H3 Matchmaking functionality) has even revived the MM for the Alpha.

There's a lot to unpack, but a few highlights are:
-A cut "Leaning" mechanic, as seen in many stealth games.
-A cut missile launcher, which likely evolved into the missile pod in the final game.
-The use of several H2 models/SFX showing off the development process.

I goes a lot deeper than that, and many people are still searching through the build, but here's a good overview of the game so far: