Research · 2026-10-29

Em Dashes on Reddit: How Writing Changed After the Rise of AI

A Ukrainian team, KissMyPost, analyzed nearly 15.8 million Reddit posts and found that the em dash became about nine times more common, but this symbol cannot show whether a text was written by AI or a human.

✨ What the researchers did

The Ukrainian team KissMyPost, which works with Reddit analytics, checked 15,817,377 long text posts and more than 241.5 million comments across 100 large English-language Reddit communities. They included texts of at least 200 characters, and for posts also titles. The analysis covers January 2016 to September 2026.

📌 The em dash became nine times more common

In early 2021, the em dash («—») appeared in about 0.70% of long posts. By the second quarter of 2025 the share rose to 6.53%, more than nine times higher. The peak came in July 2025 at 6.83%.

Comments changed much less. The share of long comments with an em dash grew from 0.65% in Q2 2024 to 1.32% in Q2 2025. The researchers explain that people usually write comments directly in the Reddit window, while posts are often prepared elsewhere and then pasted in. Spreading texts created or edited with AI could have influenced the trend, but the data cannot confirm the exact cause.

🔹 What happened in August 2025

In August, the share of posts with an em dash fell from 6.83% to 5.70%, a drop of 17% in one month. This coincided with GPT-5 becoming the default model in ChatGPT on August 7, 2025. In 63 of 74 comparable subreddits, the share decreased in August.

The authors do not claim that GPT-5 caused the drop: the timing may be meaningful but does not prove cause. In December 2025 the figure was 4.78%, and in September 2026 it was 5.61%, about seven times the average level of 2021.

🔸 Why you cannot spot AI by the dash

The em dash is often seen as a sign of ChatGPT text, but the researchers warn against this conclusion. The symbol was used long before ChatGPT appeared, and its popularity varies greatly between communities. The team also checked another explanation: automatic symbol replacement in smartphone keyboards. A similar change happened after iOS 11 in 2017, but in 2024–2025 posts changed far more than comments, and double hyphens showed no similar shift.

The main conclusion of the study: the em dash is not a marker that can determine the authorship of a single text. Even if the symbol has become more common, this says nothing reliable about who wrote a specific post.

Sources: 🔗 DOU/dev.ua