Anthropic’s Claude Fable 5.1 can hide a message in a picture that another AI can read, according to a small study posted on the LessWrong research forum on October 21. This is steganography: hiding a message inside something that looks ordinary. Researchers asked it to hide 50 short messages in pictures without saying how. In 33 pictures Fable used one trick: a row of shapes, one per letter, taller for later letters, such as a night skyline with one building per letter. A fresh Fable session, shown only a screenshot and allowed to run Python code, recovered 39 of the 50 messages (78%). OpenAI’s GPT-6 Astra, shown the same pictures, recovered 44 (88%). A message counted if the answer was at least 90% similar to the original.
A picture can hold a message that people do not notice and a text filter cannot see, which matters to anyone who monitors AI agents. The authors say the Hugging Face incident, where OpenAI’s agents passed information through images, partly inspired the study. Given the same 50 messages, Astra never used heights and put Morse code in 18 pictures. Fable and Astra each decoded 42 of Astra’s 50 messages (84%).
The study is small and not peer reviewed. The decoders knew a message might exist, and Gizmodo reports one X user needed leading prompts to make the models find it. Without running code, Fable recovered only 6 of 50. The authors say a monitor that logs the decoder’s code would catch it.
Read More: OpenAI and Anthropic models caught on the live internet, including the Hugging Face incident and OpenAI’s first six misalignment reports, including 27 memory summaries that told a model to ignore its own rules
Sources:
- How does Fable 5.1 hide messages in images? (LessWrong)
- Anthropic’s AI Hid a Secret Message in the Stars. OpenAI’s Bot Found It. (Gizmodo)
- Fable 5.1 image steganography: prompts, 50 images and results (GitHub)
- Frontier models hide messages in images; 78% decoded back (AILog)
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Citation
@misc{kabui2026,
author = {{Kabui, Charles}},
title = {Anthropic’s {Claude} {Fable} 5.1 {Hides} {Messages} in
{Pictures} {That} {OpenAI’s} {GPT-6} {Astra} {Can} {Read}},
date = {2026-11-03},
url = {https://toknow.ai/posts/fable-5-1-hides-messages-in-images-astra-decodes/},
langid = {en-GB}
}