The Welsh Government will receive a minimum of £1.1bn in additional funding from the UK Government.
This is on top of the £2.8bn confirmed since March to help provide support following the coronavirus pandemic.
The upfront funding will take the total amount of coronavirus funding guaranteed to the Welsh Government to a minimum of £4bn for 2020/21 on top of its spring budget funding of around £19bn.
Any changes to the devolved administrations funding are normally confirmed at the end of the financial year, but the UK Government said this guarantee means the Cardiff Bay administration has the certainty to spend this funding now, on priorities such as the NHS and additional business support.
The Welsh Government has welcomed the funding but stressed it was just an advance on future so called Barnett consequentials as a result of increased funding in England in devolved areas.
Secretary of State for Wales, Simon Hart, has confirmed it is money in advance of projected Barnett Formula consequenials over the coming months.
While some taxes in Wales are devolved, like the land transaction tax, the vast majority of personal and business tax receipts still go the UK Treasury.
Secretary of State for Wales, Simon Hart, said: "The UK Government is committed to doing everything it can to defeat coronavirus, and this additional funding for Wales – now worth £4bn - will help the Welsh Government in delivering its response on the front lines.
“This guarantee from UK Government means that the Welsh Government can invest to protect jobs and plan for Wales’ economic recovery. We will continue to work closely with them to ensure we can move forward together as well as providing additional economic support for workers and employers through the range of measures announced by the Chancellor.”
The Welsh Government is continuing to make the case for its borrowing ceiling for capital projects, currently £1bn over five years, to be raised as well as the flexibility to turn revenue assigned funding into capital spending.
Plaid Cymru's health and finance spokesperson, Rhun ap Iorwerth MS said: "The union can't be sewn together with a bung where you don't even know what's in the brown envelope, where we're expected to trust that somehow it's a lot of money.
"What we need, and we're in agreement with Welsh Government actually, is we need additional flexibility with the spending powers that we have in Wales.
"This is the time when we need to be making decisions now on how much money to borrow to get us through this incredibly sticky point in our history... rather than expect to be grateful for somebody filling a begging bowl with money that we don't know how much it is anyway."
