It said the first new fleet between the Scottish capital and King’s Cross in London for nearly 30 years will provide 100 more seats per train, extra legroom and more low fares.
The trains will initially take over one service a day in each direction on the route, starting with the southbound 5.40am Flying Scotsman.
These will increase to eight between the cities by the end of September.
For the first time, the same type of trains will be able to run on all these lines because Azumas can run using diesel as well as electric power.
This will enable them to continue on non-electrified tracks north of Edinburgh to Dundee and Aberdeen, and north of Dunblane to Perth, Dundee and Inverness.
From December 2021, Edinburgh-London trains every two hours will be speeded up by some 20 minutes to four hours. The trains can do 140mph but are limited by the line’s 125mph limit.
The fastest stretches north and west of Edinburgh are 100mph, but most sections are slower.
Passengers were impressed on a preview run between Edinburgh and Berwick-upon-Tweed, but said staff must ensure everything worked.
John Mayhew, director of the Association for the Protection of Rural Scotland, said: “Hopefully, the new trains will be more reliable, which should improve punctuality.
“But spending hundreds of millions on new rolling stock will be wasted if staff don’t clean the toilets regularly and ensure a working water supply. The seats felt firmer than the old ones, but that doesn’t bother me as I quite like a firm seat – the test will be whether they are comfortable for four to five hours.”
Paul Tetlaw, rail spokesman for sustainable transport campaigners Transform Scotland, said: “We’re confident Azuma will make a critical contribution to driving the switch from air to rail.”
But he called for more Scottish electrification to cut emissions and match the £3 billion spent on dualling the A9.
A spokesman for the Scottish Government’s Transport Scotland agency said: “Electrification of Scotland’s railway network is a key component of our commitment to improving rail services and tackling climate change. We are working with Network Rail to identify the next scheme.”