No details of the ownership structure were disclosed, but delegates told Reuters that China would likely take a 25-30 percent stake in the bank, and India was likely to be the second-largest shareholder.
China's share in the $100 billion lender would be less than 30 percent, an Asian delegate told Reuters. A second delegate said India's share would be between 10 and 15 percent. Both spoke on condition of anonymity.
In all, Asian countries are expected to own between 72 and 75 percent of the bank, while European and other nations will own the rest.
Another delegate said each country representative would take the proposals back to their governments for a final decision.
Some were skeptical of the timeline for the bank to start running, as each member will need to obtain cabinet and legislative approvals at home.
"It is uncertain if we can start from early next year," said one of the delegates.
"China hopes that members will get such approvals by year-end and the operations start from the next year. But I wonder if it is possible, given domestic political situations in each country."
A total of 57 countries have joined AIIB as its prospective founding members, throwing together countries as diverse as Iran, Israel, Britain and Laos.
The United States and Japan have stayed out of the institution, seen as a rival to the U.S.-dominated World Bank and Japan-led Asian Development Bank, citing concerns about transparency and governance, although Tokyo for one is keeping its options open.