Effective altruism is based on the core belief that all people count equally. We unequivocally condemn Nick Bostrom’s recklessly flawed and reprehensible words. We reject this unacceptable racist language, and the callous discussion of ideas that can and have harmed Black people. It is fundamentally inconsistent with our mission of building an inclusive and welcoming community.
— The Centre for Effective Altruism
First sentence of the apology says "I have caught wind that somebody has been digging through the archives of the Extropians listserv with a view towards finding embarrassing materials to disseminate about people." So it seems like he is trying to get ahead of a public disclosure by someone else.