"Squid Game" is a fictional drama from South Korea in which contestants who are desperately in need of money play deadly children's games to win cash prizes.
Seong Gi-hun, the main protagonist of "Squid Game," is a divorced gambler who entered the contest for the big money.
Hwang also teased new characters and developments in the second season.
"The man in the suit with ddakji might be back," he wrote, referring to the mysterious salesman who recruits desperate players to the game show.
The letter also said viewers will be introduced to Cheol-su, the "boyfriend" of the show's infamous animatronic doll, Young-hee.
Netflix told CNN in October that "Squid Game" was the biggest-ever series at launch" for the company. It is the platform's first-ever Korean series to reach No. 1 in the United States, attracting 1.65 billion hours of viewing in the 28 days following its release.
"It took 12 years to bring the first season of Squid Game to life last year," Hwang said in the letter. "But it took 12 days for Squid Game to become the most popular series ever."
Hwang had confirmed last year that he would make a second season of the show.
"There's been so much demand, love and attention for a season two," he said. "So I feel I have no choice but to make a season two."