SITUATION EXPLAINED: OpenAI's ad business hit $1 billion annualized. • ChatGPT Ads reached a billion in annualized run rate after starting US testing earlier this year • From today, advertisers across India, Europe, the Middle East, and North Africa can buy directly through OpenAI's Ads Manager, and advertisers outside the US are a growing share • Ads run on the free tier and on ChatGPT Go, the $8 plan aimed at markets where $200 a month isn't viable • eMarketer's Nate Elliott called it…