4O

4O or 4-O may refer to: Quarto (4° or 4o), a format of a book 4 Degrees and Beyond International Climate Conference, 2009 Quaternary sector of the economy (4o Sector) Air Montenegro (IATA code: 4O), the flag carrier of Montenegro Interjet (former IATA code: 4O), a former Mexican airline 2007 Rally d'Italia Sardegna (4º Supermag Rally Italia Sardinia) GPT-4o, a large language model developed by OpenAI

==See also== Fourth (disambiguation) (4º) 4° (disambiguation) O4 (disambiguation) 40