Several divisions of Austro-Hungarian ethnic troops (i.e. slavs, czechs, etc.) were present during the Ludendorff Offensive in the Spring of 1918. Before then the AH army was largely confined to "fighting" the Russians and Italians with sporadic assistance from the Germans. Once the Bolsheviks took over in November 1917 and the treaty of Brest-Litovsk was signed, the Austrians were able to send some troops west for the final push for Paris but most of the army was still fighting in the Balkans, specifically Romania, into 1918. Before that there were some regiments sent north when the Germans were in dire straits and needed immediate support, things like heavy artillery that was so important to trench warfare but less useful on the more mobile eastern front, but nothing much in the grand scheme of things as the Germans didn't value the AH troops very highly.