Joris Postmus

Joris Postmus

AI Researcher & Developer

Amsterdam, Netherlands

About

I think AI is the most significant human invention of our time, and as someone in the field, I feel a real responsibility to help make sure it develops in ways that are genuinely good.

This is what originally got me into AI Safety. I previously co-founded AISIG, one of the largest student-led AI Safety organizations in the world, where I still serve on the advisory board. I also like to do research on making language models more interpretable and steerable, having published at NeurIPS on methods for controlling model behavior.

Over the years, I've noticed that the problems I care about most deeply seem to always trace back to deep human patterns. Growing disconnection and polarization, collapsing epistemics, an inability to coordinate even when the stakes are existential. I think a lot of this comes down to ego, self-deception, a fundamental disconnect from how our own minds actually work, and a prisoner's dilemma playing out at a global scale. I also think AI (if used properly), for the first time, gives us a real chance to actually help people grow past those patterns, epistemically, cognitively, spiritually, at a scale that was never possible before.

Given where my skills, personal interests, and sense of purpose point right now, that's what I want to focus on. I'm currently building AI-powered tools for personal and contemplative development at Waking Up, one of the largest meditation apps in the world. I've personally been using it for over five years, and the practice has deeply transformed how I think, experience, and relate to myself and others. I think we have a real chance to help millions, if not billions of people grow in ways that weren't possible before, to positively change the trajectory of our future across the board.

Experience

AI R&D – Present

Waking Up (Contractor)

Exploring how AI can best serve and advance the mission of making personal and contemplative development accessible to everyone.

Co-Founder & Co-Director, now Advisory Board – Present

AI Safety Initiative Groningen (AISIG)

Built one of the largest student-led AI Safety organizations in the world. Organized 20+ events, facilitated AI Safety courses for 60+ students, and supported research published at top-tier conferences.

Joris Postmus presenting on existential risk from AI to a packed lecture hall of over 100 students at the University of Groningen
Opening an AISIG event at the University of Groningen.
Co-Founder

MomentumAI

Helped European organizations deploy AI effectively, safely, and responsibly. Translated complex metrics on model safety and performance into clear, actionable insights.

Director of Engineering

Yara AI

First hire. Built an AI-powered self-improvement tool combining cutting-edge language models with clinical expertise. Full-stack development, AI safety engineering, and product design.

Teaching Assistant & Student Mentor

University of Groningen

TA for Introduction to Artificial Intelligence and Basic Scientific Skills. Mentored ~10 students per year through individual and group sessions. Separately selected as a Study Buddy, providing one-on-one academic coaching for students with ASD or ADHD under professional supervision.

Research

Steering Large Language Models using Conceptors: Improving Addition-Based Activation Engineering

NeurIPS 2024 · Workshop on Foundation Model Interventions

Joris Postmus, Steven Abreu · 17 citations

Visualization of conceptor steering vs. traditional additive steering for LLMs
Conceptor steering (bottom right) represents steering targets as ellipsoids rather than single points, enabling more precise and compositional model control.

A novel approach to controlling LLM behavior using conceptors as soft projection matrices. Instead of representing steering targets as single points in activation space, conceptors represent them as ellipsoids. This enables Boolean operations (AND, OR, NOT) over multiple steering objectives for compositional control, outperforming traditional methods across all tested tasks.

Additional papers submitted to NeurIPS 2025 and ICLR 2025, expanding this framework with more comprehensive compositional steering methodology.

Joris Postmus presenting his poster on conceptor steering for LLMs at the NeurIPS 2024 conference in Vancouver
Presenting at the MINT Workshop (Foundation Model Interventions), NeurIPS 2024, Vancouver.

Education

BSc Artificial Intelligence

University of Groningen · 2020–2024

Final grade: 8.3/10 · Thesis: 9.5/10 (Conceptor steering for LLMs)

BSc Computing Science

University of Groningen · 2022–2025

High School

Malvern Collegiate Institute, Toronto · 2016–2020

Gold medal in province-wide coding contest (Skills Ontario) · Highest mark in Computer Science · Avg. 96%

Building

I started programming when I was about ten, making video games to play with friends. That turned into web development, then software tools, then AI applications. It's always been my main creative outlet. Some of those early projects are still playable at jorispos.github.io.

Screenshots of video games and software projects built by Joris Postmus since age 10

Frequently Asked Questions

What is activation engineering?+

Activation engineering is a technique for steering the behavior of large language models by modifying their internal activations during inference. My research introduces conceptors as an improvement over traditional vector-based approaches, enabling more precise and compositional steering through Boolean operations (AND, OR, NOT) over multiple objectives.

What is AISIG?+

The AI Safety Initiative Groningen (AISIG) is one of the largest student-led AI Safety organizations in the world. I co-founded it in 2022 with the mission of raising awareness of AI risks, supporting research, and educating students through courses, workshops, and events. I currently serve on the advisory board.

What is conceptor steering for LLMs?+

Conceptor steering is a method I developed with Steven Abreu for controlling large language model behavior. Unlike traditional activation engineering that uses single vectors, conceptors represent steering targets as ellipsoids in high-dimensional activation space. This enables Boolean algebra over steering objectives for compositional control. The approach was published at the NeurIPS 2024 Workshop on Foundation Model Interventions.

Occasionally available for meaningful AI work. Feel free to get in touch.