Coupled simulation, also known as co-simulation,
has been proposed to provide more information to a task scheduler by simulating at runtime the Quality of Service (QoS) arising from a scheduling action. To do so, co-simulation algorithms run the simulation assuming a static set of arrival time series, restricting the diversity of the traffic scenarios. To ensure the co-simulator can provide valuable and representative results, we present an online adaptive arrival forecasting framework that contains a change-point detection module and a probabilistic transformer model to couple co-simulators with arrival series forecasting. The framework can also update the prediction model to adapt to dynamic environments. Our experiments show that our online adaptive forecasting framework has lower forecasting errors than established prediction models, such as autoregressive processes, and lower on real-world traces the co-simulator prediction error by up to 27% on average response time and 39% on average service-level agreement (SLA) violation.