https://wccftech.com/halo-5-halo-mcc-halo-4-pc-test/

343 Industries’ most recent Halo installment, Halo 5: Guardians, won’t be added to Halo: The Master Chief Collection, the developer has reaffirmed.

343 Industries already said as much last year when it pointed out that the team’s plan was to bring over Halo: MCC and Halo Reach to PC, and in a new blog post on the official Halo Waypoint, the Halo developer reaffirmed that the Halo 5 won’t be added to the collection at this point. This applies to both the Xbox One and PC versions of The Master Chief Collection.