"The Spark consortium, led by Milan-based WeBuild (formerly Salini Impregilo), submitted a bid that pitched extending the project’s twin three-lane tunnels, according to multiple sources" writes The Age.

https://www.theage.com.au/national/victoria/state-s-favoured-bidder-proposes-longer-north-east-link-tunnel-20210624-p58419.html

An independent advisory committee had already concluded more than a year ago, that the six-kilometre tunnels must be extended to curb the impact on residents.