A report for the progress of this Work Package (WP) was made in month 6: D2.1 - Report on the first alpha release of the I/O library, ready for WP4. We recall in this section the key points of the developed library. The objective of the TREX Input/Output (TREXIO) library is to facilitate inter-operability between codes in the field of quantum chemistry, primarily focused on enabling the communication of data between the flagship codes of the Targeting REal chemical accuracy at the eXascale (TREX) Center of Excellence (CoE): Neci, GammCor, Quantum Package, QMC=Chem, Champ, TurboRVB. In the long term, we expect this library to be also adopted by codes outside of the CoE. Data is read from or written to files in which the electronic wave function, reduced density matrices, integrals, etc. are stored, and an Application Programming Interface (API) is provided to store and retrieve the data in the files. To maximize the portability of the library, the source code is written in the C99 language, and it is released under the BSD-3 clause license.