In September 2010, SBS Transit announced the purchase of 300 Citaro (Mk II or facelift version) units while SMB136C was still on its one-year trial. The SBS Transit Citaros first began revenue service on Route 28 on 1 June 2011, and they now represent the spiritual replacement of the older O405s which were fully retired just days before.

The modular nature of the Citaro meant that production orders for both SBS Transit and SMRT Buses were rolled out from the same factory and to a degree share common features, such as the bodywork and the driver's dashboard. These buses utilize BlueTec 5, the selective catalytic reduction (SCR) technology by Mercedes-Benz requiring the use of AdBlue, to meet the Euro V emission standards.

SBS Transit units also received the OM906hLA engine (6,374cc), but opted for the Voith D854.5 4-gear automatic transmission and Lawo HighLED EDS (which offered higher resolution LED display) with Luminator USA ODK 4 controller (predecessor of Lawo TOUCH-Control). The interior is fully low-floor and its air-conditioning was supplied by Konvekta. Both operators have also customized their interior fixtures to a certain extent in order to blend in with their existing WAB fleet and corporate identity.

Satisfied with the performance of the Citaros, SBS Transit in July 2012 placed an additional order of 450 similar units. Deliveries for this batch is expected to begin from January 2013 onwards. A third order for 250 more Citaros was placed by SBS Transit on 1 July 2014.