preprint · Open MIND · 2026

ADAPT: Hybrid Prompt Optimization for LLM Feature Visualization

João N. Cardoso, Arlindo L. Oliveira, Bruno Martins · 0 citations

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Summary AI-generated

TL;DR
Researchers have developed a new method called ADAPT that automatically generates text prompts to reveal what specific concepts or features Large Language Models are focusing on.
Problem
To understand how Large Language Models (LLMs) make decisions, researchers need to identify what concepts trigger specific internal activations. While searching through massive datasets for these triggers is expensive, existing automated text-generation methods often get stuck and fail to find the best activating prompts due to the discrete nature of language.
Method
The authors introduce ADAPT, a hybrid optimization method designed specifically to overcome these limitations. It first uses a structured search to find good starting prompts, and then refines them using an adaptive, gradient-guided mutation process to maximize the target activation.
Results
Evaluated on Sparse Autoencoder latents from the Gemma 2 2B model, ADAPT consistently outperformed existing prompt optimization techniques across different layers and feature types. The researchers also introduced new evaluation metrics based on real dataset statistics to ensure a rigorous and fair comparison.
Takeaways
Feature visualization for LLMs is highly achievable but requires optimization techniques specifically tailored to the challenges of text. ADAPT provides a robust framework for generating highly activating prompts, proving that targeted optimization is a viable alternative to costly dataset searches.
For industry
For businesses deploying AI, understanding why a model produces a specific output is crucial for safety, reliability, and compliance. ADAPT provides a tool to automatically probe and visualize the internal concepts of LLMs, making it easier to audit model behavior without scanning through terabytes of training data.
Why it matters
This research enhances AI transparency and safety by providing a reliable way to inspect the inner workings of complex language models. By making feature visualization practical, it paves the way for better alignment, bias detection, and debugging tools in real-world AI applications.

Abstract

Understanding what features are encoded by learned directions in LLM activation space requires identifying inputs that strongly activate them. Feature visualization, which optimizes inputs to maximally activate a target direction, offers an alternative to costly dataset search approaches, but remains underexplored for LLMs due to the discrete nature of text. Furthermore, existing prompt optimization techniques are poorly suited to this domain, which is highly prone to local minima. To overcome these limitations, we introduce ADAPT, a hybrid method combining beam search initialization with adaptive gradient-guided mutation, designed around these failure modes. We evaluate on Sparse Autoencoder latents from Gemma 2 2B, proposing metrics grounded in dataset activation statistics to enable rigorous comparison, and show that ADAPT consistently outperforms prior methods across layers and latent types. Our results establish that feature visualization for LLMs is tractable, but requires design assumptions tailored to the domain.

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