A heterodimeric protein complex that possesses 1-phosphatidylinositol-4-phosphate 3-kinase activity; comprises a catalytic Class IB phosphoinositide 3-kinase (PI3K) subunit of 110-120 kDa and an associated regulatory subunit that is larger than, and unrelated to, the p85 proteins present in class IA complexes. Class I PI3Ks phosphorylate phosphatidylinositol [PI], phosphatidylinositol-4-phosphate [PI(4)P] and phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2] and are divided into subclasses A and B according to the type of adaptor subunit with which they associate. Class IB PI3Ks are stimulated by G-proteins and do not interact with the SH2-domain containing adaptors that bind to Class IA PI3Ks.