Originally Posted by
germatory
According to the Changi Airport website, with link and screenshot below, you need to clear immigration according to your departure terminal.
Cathay's service desk at T4 Row 6 essentially told me the same thing when I asked about entering airside at T1 instead of T4.
I don't know how strictly the Airport enforces this policy.
https://www.changiairport.com/en/faq.html
I think this is poorly worded with a glaring grammatical error and untrue.
"In If you would like to travel to travel to other terminals, they are connected in the public areas... "
If you really cannot depart from other terminals, it does not make sense to write instructions to transfer landside where they will be denied immigration at another terminal.
btw, Singapore airlines has flights & checkin counters from both T2 & T3 and you can check-in and enter at any terminal. However T4 has security just before/after immigration compared to security at the gate so i think that causes some hassle to travel from T4->(T1-3)