The new operators of Wales and Borders rail services have taken over the running of the franchise.
French-Spanish joint venture KeolisAmey promises to eventually replace all trains, at a cost of £800m.
There is also £738m to electrify the South Wales valleys lines, add more services and launch the new South Wales Metro over the next 15 years.
It marks an end to the troubled tenure for Arriva Trains Wales, criticised for overcrowding on commuter services.
This is the first time the Welsh Government has had control over the £5bn franchise, which will be overseen by Transport for Wales (TfW), promising to transform rail travel over the next 15 years.
It comes as the public is taking more journeys by train, with passenger numbers forecast to continue rising.
KeolisAmey has been given targets on punctuality and overcrowding - with potential financial penalties - and faces a cap on its profits.
But most of the biggest promised changes will not happen for at least a couple of years.
"From day one, we'll see changes come in quite gradually," said TfW chief executive James Price.
"We'll see branding beginning to change, staff uniforms will look different - and over the coming months you'll see new services introduced.
"Then the next 12 to 18 months, the beginnings of the new rolling stock will come into play."
source: BBC News