# Show HN: Semantic Overlays – an NX bit for LLM prompt injection (live demo)

> Source: <https://semantic-overlays.vercel.app/>
> Published: 2026-09-01 17:40:13+00:00

I've built a new method for steering LLMs called Semantic Overlays, small trained adapters on a frozen model which change how its perceives a piece of its context. The most readily applicable usage is to mitigate prompt injection, and it lets us take a very-injectable Qwen-3.5-9B to SOTA scores on all the prompt injection benchmarks I could find. (They are only blackbox attacks, but I did NOT train on anything like them — whitebox attacks are out of scope for this paper)

I'm excited for you to play with the tech — see if YOU can break it! (let me know if you can)

Paper at [https://arxiv.org/abs/2608.23873](https://arxiv.org/abs/2608.23873) if you want to read more about it, code at [http://github.com/JoshuaSP/semantic-overlays](http://github.com/JoshuaSP/semantic-overlays), adapters at [http://huggingface.co/joshuapenman/semantic-overlays-adapter...](http://huggingface.co/joshuapenman/semantic-overlays-adapters)

Also [https://x.com/joshua_s_penman/status/2094823990472884389](https://x.com/joshua_s_penman/status/2094823990472884389) if you wanna watch a little video I made!

Comments URL: [https://news.ycombinator.com/item?id=49525220](https://news.ycombinator.com/item?id=49525220)

Points: 1

# Comments: 0