Astral Codex Ten (ACX)

Astral Codex Ten (ACX) is a blog written by Scott Alexander Siskind under the pen name Scott Alexander. It launched on January 21, 2021 on Substack as the direct successor to Slate Star Codex (SSC), which had been running since March 2013 on Blogger. SSC was taken down in June 2020 after a New York Times privacy incident but the intellectual project continued uninterrupted with ACX on Substack. The blog covers reasoning, science, psychiatry, medicine, ethics, genetics, AI, economics, and politics. It describes its focus as exploring the concept of 'rta,' a Sanskrit word related to rationality, truth, and harmony. The blog is a central venue for the rationalist and effective altruism communities, drawing hundreds of thousands of subscribers, though all important content is and always will be free. Paid subscriptions at $10/month (or $2.50/month for those with financial hardship) provide access to subscriber-only threads, AMAs, and draft posts, and help fund Scott Alexander's psychiatric work providing low-cost care to uninsured patients. ACX is also the home of ACX Grants, a recurring small-grants program Scott Alexander began in November 2021 with an initial pool of $250,000, which grew to $1.3 million in the first round after outside funders joined. Grants typically range from $5,000 to $100,000, with occasional larger awards. The program is administered through Manifund, which handles logistics and fiscal infrastructure. The 2025 round expected approximately $1 million in total funding ($200,000 from Alexander personally, and ~$800,000 from outside donors), and awarded 42 grants from 654 applications across areas including global health, biotechnology, AI safety, scientific integrity, and policy. Alexander has stated he can sustain approximately five more grant rounds at current contribution levels, after which outside donors would need to carry the program.