- Paris IV is attacked. Staff Sergeant Avery Johnson gets an encounter with max dosage of radiation after using a box of Plasma grenades and becomes diagnosed with Boren's Syndrome, which in the future will save his life from Flood infection on Installation 04 and onward. However, the Borens' Syndrome story involving Johnson is a hoax, based on the account described on page 122 of the Halo Graphic Novel.
- The 2549 edition of the Civilian Warthog is probably released, although it could have been late in 2548.
- The Covenant recall their standard Type-25 Wraith model to update its design, fitting a Type-52 Directed Energy Support Weapon on a ring mount.
- Some time during this year, the SPARTAN-II Program was announced to the public, and any Spartan who dies is to be listed as ether MIA or WIA, to give the illusion that Spartans never die in accordance with the Office of Naval Intelligence Directive 930.
- September 9: Second Battle of Arcadia. The Covenant glasses Arcadia.
- November 7: Cortana is created from Dr. Catherine Halsey's flash-cloned brain.
- December 15: A mandatory psychiatric reevaluation for the members of Noble Team takes place. Jun-A266 is noted as having "an unhealthy emotional detachment in regards to the consequences of his actions".
- The date of Cortana's creation could be a reference to John-117. She was created in November on the 7th, or 117, the month being 11, and the day being 7.