Victorian taxpayers have been forced to pump an extra $1.37 billion into Melbourne's Metro Tunnel project to get it built by 2025 after the state government agreed to a 50-50 settlement on long-running design and cost disputes.

The Cross Yarra Partnership, which includes contractors Lendlease, John Holland and Bouygues, and is building twin rail tunnels and five new underground stations, will also put in $1.37 billion to pay for the cost of design changes, labour, materials and equipment needed to finish the $11 billion project on time, bringing total cost increases to $2.74 billion.