The announcement will be made alongside a further announcement about skills training and employment, including new "skills hubs" in Christchurch for trades training.
The official youth wage was abolished in 2008, but the current system does provide for 16- and 17-year-olds in their first jobs to be paid $10.80 an hour for up to three months or 200 hours, as well as those doing 60 credits or more as a training course.
Announcing the policy last year, Mr Key had said the lower wage would give many youth "a much-needed foot in the door" and encourage employers to take on youth, rather than more experienced workers.
But Labour argued that it would instead send young workers over to Australia where the pay was higher.
The latest Household Labour Force Survey showed 61,700 15- to 24-year-olds were unemployed - up from 41,100 four years ago.
The Youth Wage comes on top of a package of wage subsidies of up to $21,000 a year for employers who take on high-risk youth, such as former prisoners.
The Starting Out Wage
Paying 80 per cent of the minimum wage to:
* 16- to 17-year-olds for first six months with a new employer.
* 18- to 19-year-olds going to work after six months on a benefit.* 16- to 19-year-olds doing more than 40 credits a year on a training course.