Two designs called Granite Web and Winter Garden will go head-to-head to win the competition to transform Aberdeen's Union Terrace Gardens.
An international contest was held to find a design for the high-profile £140m City Garden Project, which saw six teams shortlisted.
The teams behind the two favourite designs have now been asked to clarify the costs and viability.
A decision on the winning design is expected to be made in January.
BBC Scotland revealed one of the two favoured designs earlier this month.
Malcolm Reading, of Malcolm Reading Consultants - the organiser of the international design competition, said: "The jury was faced with six designs of exceptional and consummate design quality.
"The jury's unanimous decision at this stage is that further clarification work should be done by two design teams."
John Stewart, chairman of the City Garden Project management board, added: "The complexity of the project and the importance of the development to the people of Aberdeen deserve further consideration.
"We are confident that either scheme can provide a world-class solution and further exploration of these two designs will enable us to select the right design for Aberdeen."
A decision on a possible referendum is expected in December.
Aberdeen oil services tycoon Sir Ian Wood has pledged £50m of his own money for the City Garden Project.
During a previous public consultation process, 55% of those who took part said they did not support the new development.
However, councillors backed taking the plans to the next stage.
If the project proceeds, Aberdeen City Council believes construction could be finished by 2016.