Istanbul Airport, in Istanbul, Turkey.

What is the difference between IST and LTFM?

IST is the IATA code, used commercially — tickets, timetables, luggage tags. LTFM is the ICAO code, used operationally by pilots and air traffic control, and assigned geographically by region.

Is IST the same as SAW?

No. SAW is sabiha Gökçen, on the Asian side, used heavily by low-cost carriers.

What airport is IST?

IST is

Istanbul Airport

Istanbul, Turkey

Why the code is IST

ISTanbul. The code moved to the new airport when the old one closed.

The airport authority or a contemporaneous record states this directly.

The airport

IATA code: IST
ICAO code: LTFM
Airport: Istanbul Airport
City: Istanbul, Turkey
Opened: 2018
Code origin: Documented

The entire operation moved from Atatürk to the new field in a single 45-hour window in April 2019, one of the largest airport relocations ever attempted; the last aircraft to leave Atatürk flew the short hop to the new airport carrying the airport code sign. Atatürk kept the ICAO code LTBA and now handles cargo and government flights.

Codes it used to have

Code	Until	What happened
IST	—	The code transferred from Atatürk Airport, which held it until 2019, rather than being newly assigned.

Codes people book by mistake

Code	What it actually is
SAW	Sabiha Gökçen, on the Asian side, used heavily by low-cost carriers.

The other code, LTFM

Every airport has two codes. The three-letter IATA code, IST, is the one on your boarding pass and your luggage tag, and it is assigned for commercial use. The four-letter ICAO code, LTFM, is the one pilots and controllers use, and it is assigned geographically: the first letter or two identify the region, so every airport in the same part of the world shares a prefix. That is why LTFM looks nothing like IST.

Common questions

What airport is IST?: Istanbul Airport, in Istanbul, Turkey.
Why is Istanbul's airport called IST?: ISTanbul. The code moved to the new airport when the old one closed.
What is the difference between IST and LTFM?: IST is the IATA code, used commercially — tickets, timetables, luggage tags. LTFM is the ICAO code, used operationally by pilots and air traffic control, and assigned geographically by region.
Is IST the same as SAW?: No. SAW is sabiha Gökçen, on the Asian side, used heavily by low-cost carriers.

Turkey Capital, area, population and currency
The flag of Turkey Colours, symbols and lookalikes
Airport codes in Turkey 1 here

Sources

OurAirports — OurAirports (Public domain)

How these figures are compiled and checked