tl;dr: Pangram's Chrome extension analyzed over 1 million social media posts and found that 25% of longform content (250+ words) is fully AI-generated, with LinkedIn accounting for two-thirds of all flagged AI content and over 40% of its longform posts. X/Twitter had the highest combined AI rate at nearly 47% when including mixed human/AI writing, while Reddit stayed low overall (4.4%) due to mostly human-written replies—though top-level Reddit posts were 5x more likely to be AI than comments.