And when they don't, like Gurgeh in Player of Games, it's specifically pointed out as an eccentricity on their part. He gets lightly teased for being cis.

Edit: found the quote

'There's something very I don't know; primitive, perhaps, about you, Gurgeh. You've never changed sex, have you?' He shook his head. 'Or slept with a man?' Another shake. 'I thought so ,' Yay said. 'You're strange, Gurgeh.' She drained her glass.