According to an embodiment, an apparatus comprises a fiber-breakout transition configured to break out optical fiber sets from a first end of an optical fiber cable. The fiber-breakout transition comprises a first channel configured to receive an end segment of the optical fiber cable. The fiber-breakout transition further comprises a plurality of second channels. Each of the plurality of second channels is configured to receive and mechanically attach a buildup tube for holding one or more optical fibers. The transition has an interior cavity connecting the first channel to the plurality of second channels. Some of the channels have cross-sections whose diameters increase in a stepped manner with distance away from the interior cavity of the transition.