An analysis of Substack newsletters suggests that most of the platform’s biggest writers are still publishing human-made work, even as AI-generated posts become more visible in some of its most analytical categories. The finding comes after a viral March 2025 post on Substack purporting to show a debate between Elon Musk and Keanu Reeves drew tens of thousands of likes and reposts despite never taking place at all; the piece was generated entirely by AI. The episode has become emblematic of a wider unease about synthetic writing spreading through online publishing.

To gauge the scale of the problem, the writer behind the analysis used Pangram, an AI-detection tool that says it can identify machine-written text even after attempts to disguise it, and examined the 10 most recent posts from the top 25 Substack Bestsellers in each category. Pangram says its detector has been independently verified and is available through a browser extension as well as an API. The resulting picture was more mixed than alarmist: roughly two-thirds of the 575 newsletters reviewed showed no detectable AI content in their recent archives, according to the analysis.

Where AI writing did appear, it was concentrated in categories built around explanation, analysis and argument. Technology showed the highest proportion, with 28 per cent of writing in top newsletters judged to be fully or partially AI-generated. Philosophy and health followed, at 23 per cent and 22 per cent respectively, while culture stood at 13 per cent. By contrast, sports, food and drink, and music registered far lower levels. The pattern suggests readers may be more accepting of machine assistance in information-heavy niches than in areas that depend more heavily on voice, taste and personal judgement.

The analysis also found that AI use tends to be all or nothing. Rather than lightly editing a few drafts, some newsletters appear to be running almost entirely on automation, with several publishing posts that were assessed as 100 per cent AI-generated. A small number of big operators distorted the overall figures: just 29 publications accounted for half of all majority-AI posts, while one AI-heavy News newsletter made up 35 per cent of the category’s majority-AI content. Similar outliers in culture and world politics had an outsized effect on the averages.

There are limits to the data. Some newsletters place key material behind paywalls, so only free preview text could be scanned, and Pangram requires at least 50 words before it will make a call, with a bias towards “Human” when uncertain. Even so, the findings echo a separate Wired analysis that estimated about 10 per cent of Substack’s top newsletters publish AI-generated or AI-assisted material. Taken together, the evidence points to a platform that is still broadly human-led, but increasingly shaped at the margins by high-volume AI publishing.

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Source: Noah Wire Services