A confirmation and a codename.
“Over the past few days, footage has recently made the rounds of an exploratory Xbox 360 project we worked on several years ago, known as “Haggar.” Since then, we’ve received a lot of great feedback from the community. Haggar was something we prototyped with our friends at Mega Bloks that focused on the elements of action, exploration and user creativity found within the Halo universe. Haggar had a lot of fun ideas and invention behind it, but ultimately didn’t progress beyond the early prototyping levels that are shown in the recent video. This is just one example of several similar projects we have evaluated throughout the years – a process that we continue exploring on an ongoing basis,” said Ross in the forum post.
So long story short: yes, it existed, and it does not now.
The project, which was in the testing phases sometime in 2013, was allegedly being designed for the Xbox 360, despite the Xbox One releasing later that year. The game’s developer, n-Space, has a long history of making spin-off games for licensed franchises for the Nintendo DS, but recently released an original project in 2015’s Sword Coast Legends.