• Participant must have ongoing participation in an etavopivat parent study for treatment of sickle cell disease (SCD) or thalassaemia and have completed at least a treatment period of the parent study.

• Participant must have derived clinical benefit from treatment with etavopivat, as determined by the investigator.

• Any participant with dose reduction or temporary discontinuation will need to be successfully rechallenged to the full dose of etavopivat before transferring.

• Participants on hydroxyurea (HU), crizanlizumab or l-glutamine oral powder (Endari®) treatment at the time of consent may be eligible if they have been on a stable dose in the parent study as defined at the investigator's discretion. Necessary adjustments related to weight or age are accepted. Participants with temporary dose reductions or pauses due to medical reasons may still be considered to have a stable dose, as determined by the investigator, who will assess the impact of these adjustments based on clinical context and the participant's overall health status.