Monthly grids are available (L3). You will find below NetCDF files, one per month, per instrument. See IASI_Flux_and_Temperature.pdf (Data Manager Plan OPIDoR).
Metop-A data are available from January 2008 til December 2017.
Metop-B data are available starting January 2013.
Metop-C data are available starting January 2020.