It's not over budget, but the plans have been changed since that map (which is from January 2019) to stay within the allocated budget. It's due to be completed between 2023-2024. The Taff Valley lines (through Pontypridd) will be completed first, with the tram-trains expected to be running on those lines by mid-2023, and the Rhymney Valley and Coryton lines are expected to be completed in 2024.Mind you, every infrastructure project is really!
They're usually all late, bits missing as it's gone overbudget so they've had to remove some things to keep costs down!
Just out of interest, when is this project expected to be complete and how much overbudget is it?