Upper panels: peak hydrogen envelope mass fraction at the end of accretion, before any mass loss, shown in colour for the slow, medium, and fast host star rotators. The time when 90% of the envelope mass is lost due to solar XUV radiation is shown in white contour lines in Myr. Lower panels: atomic composition of the outgassed atmospheres of the slow, medium and fast rotator simulations at 300 Myr. Values of R/O < 1 (blue) indicate an atmosphere with free oxygen, a value of R/O= 1 (green) imply sufficient oxygen to oxidise H to H₂O and C to CO₂, and values of R/O > 1 (red) indicate reducing conditions (see definition of R/O in Equation (8)). The white contour lines in the lower panels show a value of R/O = 1.3. The patch of R/O = 0 present for the slow rotator is due to the perseverance of the envelope for those high planetary masses even after 300 Myr, with the magma ocean still providing a significant pressure of free oxygen.