The company confirmed it would formally announce a shrunken version of its 4.8-inch flagship phone at the event Thursday, the Los Angeles Times reported.
The mini version with a smaller, 4-inch screen will launch first in Europe, J.K. Shin, Samsung's head of mobile communications, said.
"There's a lot of demand for a 4-inch screen device in Europe," Shin told The Verge website. "Some call it an entry-level device, but we call it 'mini.'"
While larger displays are selling points for Android smartphones, giving them screen-size bragging rights over the new iPhone 5 with its 4-inch screen, there is ongoing demand for more-compact devices.
The Galaxy S3 has been a sales success for Samsung since it launched in late May, and in August it beat out the iPhone 4S as the top-selling phone in the United States, the Times reported.