The CHEOPS workshop IV will be held 13-16 July, 2021, some 15 months after the beginning of CHEOPS science operations. The workshop will be the occasion for the planetary science community at large to discuss and share the first main results of CHEOPS in different fields, from the planetary internal structure to atmospheric characterization, etc. Participants are invited to propose contributed talks and posters on all scientific aspects linked to CHEOPS, including CHEOPS based-results as well as proposals for future observations and synergies with other facilities.