Updated project metadata. Mass spectrometry‐based in vitro kinase screens play an essential role in the discovery of kinase substrates, however, many suffer from biological and technical noise or necessitate genetically‐altered enzymecofactor systems. We describe a method that combines stable γ‐[18O2]‐ATP with classical in vitro kinase assays within a contemporary quantitative proteomic workflow. Our approach improved detection of known substrates of the non‐receptor tyrosine kinase ABL1; and identified potential, new in vitro substrates.