Tancock clocked 24.50 seconds to win gold ahead of Camille Lacourt of France, who took silver in 24.57, while Gerhard Zandberg of South Africa claimed the bronze in 24.66.
"I’m going to go back and go through the footage and sit down with my coach Ben Titley and go through how I can improve and how I can make it better and stronger next year," said Tancock.
"Obviously there is no 50m in the Olympics it is going to be 100m so that is what I’m going back to do. I’ve got a couple of weeks off and then I’m off on the road to London.
"My focus has been and will always be the 100m and a by-product of that is the 50m and I’ve got the easy speed and I’ve got the attributes to be fast and to go out strong.
"I need to convert that in the training I do to go out in an easy speed and bring it back as well."
China's Sun broke Hackett's decade-old record to take gold and stake his claim to succeed the Australian as king of long-distance swimming.
The 19-year-old Sun clocked 14:34.14 seconds after a blistering final 100 metres to eclipse the 14:34.56 the now retired Hackett set in Fukuoka in 2001.
It had been the longest-standing record still on the books following a glut of records at the last world championships in Rome in 2009 when swimmers wearing the now banned polyurethane swimsuits set 43 records.
Canada's Ryan Cochrane took the silver in 14:44.46, while Hungary's Gergo Kis won bronze in 14:45.66.
"The coach told me before the race to focus on the gold medal and not to worry about breaking the world record," Sun said.
"It's not surprising, I had thought about it (breaking the record) before," he added in reference to the 14:35.43 he achieved at the Asian Games last year.
The gangly Sun, who had also won the 800m freestyle in Shanghai, controlled the race from start to finish.
While Cochrane kept within a body length of the 19-year-old Chinese for the first half, he was unable to stay with him after that and Sun kicked away.
Sun had looked unlikely to break Hackett's record as he was slipping consistently outside the world record split times until the final 300 metres when he noticeably accelerated his pace.
He was more than two seconds outside Hackett's time when he heard the bell at 1400 metres but somehow found the energy to produce an amazing 25.94 over the final length of the pool at the Oriental Sports Centre to break the record.
The USA celebrated the final day of the championships with four more gold medals.
They won the men's 4x100m medley relay in a time of 3:32.06, taking full advantage of France's surprise failure to qualify from their heat for the final. Australia took silver in 3:32.36 while Germany claimed the bronze in 3:32.60.
The 26-year-old clocked four minutes, 7.13 seconds to win gold, his fifth of the championships, ahead of compatriot Tyler Clary, who took silver in 4:11.17, while Japan's Yuya Horihata claimed the bronze in 4:11.98.
Hardy clocked 30.19 to win gold ahead of Yuliya Efimova of Russia who took silver in 30.49, while Soni claimed the bronze in 30.58. Soni had won the 100 and 200 breaststroke titles earlier.
"I can't believe I've got a silver medal," said Miley.
"This is the closest thing to the Olympics, so to get on that podium is unbelievable and a reward for all the hard work and training.
"I was hanging on for dear life at the end and my legs couldn't take any more."