Lifetime Isas will launch on Thursday - but many major high street banks have ruled out immediately offering one.
The accounts, also known as Lisas, can be opened by people aged between 18 and 39 to save for their first home, or their retirement, in the same pot.
They can put away up to £4,000 each year and receive a Government bonus of up to £1,000 a year on their contributions until they turn 50.
Funds can be withdrawn tax-free to buy a first home or saved for later in life.
The total amount savers can put into an Isa in a year will also increase on Thursday from £15,240 to £20,000 - as the new tax year starts.
While some providers have confirmed their plans to launch Lisas, many major high street names have said they are reviewing their position.
Hargreaves Lansdown and Nutmeg have both said they will launch Lisas on Thursday. Skipton Building Society will offer a Lisa from June and will give further details closer to launch.
Several providers have said they are still considering their plans or have no plans to offer a lifetime Isa.
Lloyds Banking Group said in a statement: " We are a long-standing advocate of the simplicity of Isa wrappers and the tax benefits are valued by investment and savings customers.
"Whilst we will not have a Lisa on the launch date, we will continue to continue to review our product range plans and the role of Lisa within that."
A Barclays spokeswoman said: "We are continuing to review the recently-issued final lifetime Isa rules and guidance, and therefore will not be launching a lifetime Isa in April."
An RBS/NatWest spokesman said: " At this time we will not be offering the lifetime Isa but continue to offer our help to buy: Isa and a range of savings and investment options."
Santander said: "At this point in time Santander has no plans to launch the lifetime Isa.
"We have an extensive range of Isas already available and we will continue to keep our position under review."
HSBC said: "We are continuing to work through the details of the product."
Nationwide Building Society has said it has no plans to offer a Lifetime Isa product.
Nationwide said: "As a major savings provider, our members have many and diverse needs, and we need to be assured that such products are simple for them to understand.
"We will always look at each new product as it arises and evolves in the interest of all our members."
Over their lifetime, people saving into a lifetime Isa could potentially get a maximum bonus of £32,000.
Savings can be used to buy a first home or used for other purposes after the saver reaches 60.
Generally, savers withdrawing their money early for reasons other than buying their first home face withdrawal charges.
Lifetime Isas were unveiled during the Budget in March 2016 by the then chancellor George Osborne.
Some experts have raised concerns that some savers may ditch their workplace pension, which gives them the benefit of employer contributions and tax relief, in favour of saving into a lifetime Isa.
The Treasury has said it expects the market to continue to grow, with more providers coming on board as products are developed.