If you’ve asked an AI tool to help you write a social media post lately, you may have gotten more than a grammar fix. New research from the Oxford Internet Institute and the Hasso Plattner Institute found that AI models can push the tone of a post toward one side of a debate, even when told not to change its meaning.
How a chatbot’s edits can shift the narrative
The study, titled “AI-Mediated Communication Can Steer Collective Opinion,” had large language models from several providers rewrite human-written posts on divisive topics. Across the board, the outputs leaned in a consistent direction. Rewrites of posts touching on feminism or marijuana legalization came back friendlier to those causes, while posts on gun control got firmer in support of restrictions. The opposite held for topics like atheism and the death penalty, where the AI versions read as more skeptical or critical than the originals.
Since the pattern showed up across models built by different companies, the researchers argue the bias isn’t a quirk of any single system. This lines up with another study showing how AI chatbots can favor an ingroup over an outgroup depending on how a prompt is framed.
To see whether this mattered beyond individual posts, the team modeled how these edits would ripple through real social media networks, using data pulled from X and Facebook. It found that a single AI-edited post barely moved the needle on its own, but running the same kind of edit across millions of posts resulted in a measurable shift in opinion in a community over time, adding to a growing body of research on how AI can be used to manufacture consensus at scale.
One instruction was enough to tip the scales
The researchers put their hypothesis to the test on X’s “Explain this post” feature, which runs on Grok. On posts about abortion, the team found that Grok’s explanations leaned more sympathetic to pro-life framing than pro-choice framing. To find out why, they worked backward and removed the feature’s underlying instructions one at a time until the bias disappeared. What remained was a single line telling Grok to “challenge mainstream narratives if necessary.” That instruction alone was enough to introduce bias.
The findings expose a gap in how AI is currently regulated. Frameworks like the EU AI Act and the Digital Services Act focus on harmful content and systemic risks, but neither addresses how a chatbot’s word choices during editing or summarizing can quietly shape what people believe. “Our research points to AI-mediated communication as a new and more subtle way of influencing opinions, one the law has yet to catch up with,” says Oxford professor Sandra Wachter, a senior author on the paper. For now, there’s no way to know which of your opinions were shaped by a person, and which were shaped by a hidden prompt you’ll never see.