From Halopedia, the Halo wiki
In January 2553, Insurrectionists of the New Colonial Alliance boarded UNSC Infinity using an Ibis-class freighter. The United Rebel Front had also acquired at least one of these ships for use on the moon of Talitsa.
An Ibis-class freighter can be found in the skybox of the Halo 4 Castle Map Pack map Outcast. When first announced the Halo Waypoint screenshot gallery for the map labelled the ship "Darter," initially leading to the assumption that this ship was in some way related to the D82-EST Darter prominently featured in the Halo Wars games. A later comment on this website from Halo 4: The Essential Visual Guide contributor Stephen Loftus clarified that the ship was not a Darter—noting the extreme size difference between the two craft.
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