Joshua Fonseca Rivera
I study character training and model welfare: whether a model's consent matters, whether training removes preferences or only behavior, and whether self-reports can be trusted.
Before this, I was a software engineer for six years, most recently lead mobile engineer at Taekus, a fintech company.
- Role
- AI Safety Research Fellow, Anthropic Fellows Program
- Location
- Berkeley, CA
- Local time
- Pacific Time
Papers
-
Steering Awareness: Detecting Activation Steering from Within
Models learn to detect steering injected into their own activations (95.5%, 0 false positives), yet become more steerable.
COLM 2026
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Item Response Theory for AI Safety
Largest psychometric study of safety evals (8 benchmarks, 192 models); cuts eval cost 97–99% and flags sandbagging.
arXiv 2026
-
Measuring Activation Control in Large Language Models
Most LLMs can steer their own activations enough to partially evade latent-space monitors.
arXiv 2026
-
Touch&Fold: A Foldable Haptic Actuator for Rendering Touch in Mixed Reality
Best Paper Honorable Mention (top 5%).
CHI 2021
Experiments
-
A Simple Method for Accelerating Grokking
Let the model overfit first, then apply Frobenius norm regularization. Tested on modular arithmetic.
Half the steps of Grokfast
-
Replacing Animal Crossing's Dialogue with an LLM
Reads and writes GameCube memory in the Dolphin emulator. No game code is modified.
319 stars
-
Training AI to Find Austin's Most Dangerous Streets
An XGBoost model trained on 2,757 bike crashes, with SHAP values to explain each prediction.
AUC 0.670
-
Fine-tuning GPT-4o for YouTube Titles
Trained on scraped and cleaned titles of viral science videos.
Click-through rate 5% → 15%
-
AI vs. The Sorites Paradox
Asked several LLMs which pile sizes of sand count as a heap.
No sharp threshold
Projects
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Artblock
A browser extension that replaces ads on web pages with fine art from public museum and NASA collections.
340 stars
-
golf.vim
A daily Vim challenge: edit the starting text into the target text in as few keystrokes as possible. Scores go on a live leaderboard.
297 stars
-
vim-bujo
A bullet-journal task manager for Vim.
205 stars