The joint ride-hailing system is still being built and Tan did not give an indication of when it might be operational.
But time is of the essence. Uber has set its sights ever more firmly on the Asian market - as recently as Wednesday, Uber received almost $2 billion in funding from Chinese investors - and has far more money to play with.
Collectively, Didi Kuaidi, GrabTaxi, Lyft and Ola have raised more than $7 billion in funding, while as of December, Uber had attracted $62.5 billion.
But for Tan, taxis are as much personal as they are business.
His grandfather was a taxi driver and his family runs an auto business that has franchises for several car brands, including Nissan and Subaru, in Malaysia. When he is not running his start-up, the 33-year-old Harvard Business School graduate occasionally drives a taxi.
"Well, [more] specifically a [ride-hailing] car," he said. "I have recently signed up as a GrabHitch [a car-pooling service from GrabTaxi] driver to pool for others."
Tan says the time he spent working in the family business - he quit in 2012 to start GrabTaxi - taught him how to work with governments, as well as with people of different nationalities and cultures, and instilled in him the "need of getting my hands dirty as a driver."
GrabTaxi has raised about $700 million in funding so far, from notable names such as Singapore's Temasek, China's Didi Kuaidi, Japan's Softbank, and Silicon Valley-based GGV Capital.