However the final figure will not be known for weeks.

The Gungahlin to Civic line will finally open to the public on Saturday after more than 1000 days of construction.

Canberra Metro has missed out on millions of dollars in availability payments after the contracted completion date of December 21 came and went.

But Chief Minister Andrew Barr said the government would make the $375 million capital contribution within a business day or so of operations getting under way.

"That will see us pay down a significant part of the debt and then we make the equivalent of mortgage payments I guess over the intervening period that cover the rest of the capital as well as the operations maintenance," Mr Barr said.

However the overall construction figure is expected to be lower than the $707 million set out in the project's business case. That figure had been revised down from a previous estimate of $783 million.

Asked whether the delayed start had helped bring the project in under budget, Transport Minister Meegan Fitzharris said: "Not really".

"One, I think the market has changed since then so we're very mindful of that," she said.

"We [also] had a really good team who selected a really good bid. It was a very competitive process and they gave us a very competitive price and they've been able to deliver on that so the team has managed the project well in close partnerships with Canberra Metro."

Transport Canberra director general Emma Thomas said the cost of the project had been managed well.

"It wasn't obviously in a place where we could have launched it in December, but that being said, we had always projected in our business case that it would be sometime in 2019, so the fact that things had pushed into that was something that we could understand and accept," Ms Thomas said.

Ms Fitzharris said the transparency and engagement was "without a doubt" greater on the light rail project than any other in Canberra's history, and better than most other projects around the country.

She said a review would be released within six weeks that would have firmer figures on how the project performed.

But Mr Barr said the government's expectations had been "exceeded" in terms of the transformation of the Northbourne corridor.

"We have obviously anticipated that the publicly owned, the government held, sites would transform but the rate at which the private sector have responded has probably exceeded our expectations. We thought it would happen eventually but it's happened a bit quicker than we thought," he said.

"It's not the first time the Northbourne corridor has changed. It has already in my lifetime, so when I first came to Canberra it had gone through a replanting of the trees that were cut down in this round ... so it is an avenue that has seen change over the last 100 years and this is its next evolution."

Ms Fitzharris said the light rail itself was of an exceptional quality.

"We've got lots of other institutions that are about being a world class city but we didn't have a good public transport network and we now have a world class public transport network," she said.

Transport Canberra deputy director general Duncan Edghill said the public-private partnership with Canberra Metro had performed well.

"The PPP model has done two things. One, it's meant that Canberra Metro who have done this before are the ones who are managing that risk, and they are better placed to manage that risk," Mr Edghill said.

"And then the second thing it's done is it has provided the commercial framework where everyone has an appropriate incentive to deliver the project not only safely but as promptly as they can while minimising disruption to the ACT community. So for stage one, I think PPP was absolutely the right decision."

However Mr Edghill said the procurement for the second stage of the project could work differently.

"I think the way that we approach it from a procurement and delivery process might be a bit different to the way we delivered for stage one. I think, particularly getting light rail around Parliament House and then down Adelaide Avenue, it means there will be a lot more design and perhaps more early works that happen, before we get the Commonwealth planning approval, that allows the rest of the project to continue."

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