Representatives from Community, Unite and GMB union began talks at the Tata-owned Port Talbot steelworks in south Wales.
"We are seeking a positive future for the UK business and during discussions with the trade unions we made substantial assurances to achieve this," a Tata Steel statement said.
While the details of the deal are yet to be confirmed, unions had insisted on maintaining the site's two blast furnaces in talks with management last week.
The Tata Group employs more than 4,000 at Port Talbot alone, and hundreds more at other sites across the UK at Trostre and Shotton, Corby, Hartlepool and at sites in the West Midlands.
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If the plan is agreed, it could see investment in the Welsh site in return for concessions on staff terms and conditions and would mean job security for thousands of workers, according to UK media reports.
Central to the plan is the retention of both of Port Talbot's blast furnaces, which turn iron ore and coke into molten iron.
One was due to stop production in 2018 but unions have been fighting to keep it open.
Earlier this year, Tata Steel announced all of its plants across the UK would be put for sale. But in July the sale came to a halt.
Meanwhile, Tata Steel and workers' union leaders have been in talks over the existing final salary British Steel Pension.
The next defined contribution into the scheme of 60 million pounds is due next March.
The Welsh government said it is committed to providing Tata with a 60-million-pound funding package, as long as it maintains existing primary steelmaking capacity over the long-term.
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