The Test Set by Posit

Trevor Manz went from measuring plant apertures by hand in a wet lab to building the notebook that lets coding agents take the wheel. The creator of anywidget and founding engineer at marimo (marimo.io/pair) popped into The Test Set to spill on reactive notebooks, why marimo pair threw out every MCP tool but one, and what agents really want out of a data environment. This conversation also features a jacket bouncer, a hidden Python API, and Michael's slow-motion war with the word "marimo."
What's inside:
Cell order doesn't matter in a reactive Python notebook
Wet-lab pipettes and Harvard's visualization group, via Raspberry Pi
The problem with building beautiful tools nobody actually uses
The reason marimo pair deleted every agent tool but one
Code mode: the hidden API humans aren't supposed to touch
What happens when you ship the API your LLM hallucinated

Leilani Battle studies how software shapes what we see and believe. The University of Washington professor and co-director of the UW Interactive Data Lab talks with Michael, Hadley, and Wes about an experiment that manipulated people using nothing but loading speed, and why AI models don't seem to recommend charts the way the community that studies charts actually does. Other highlights: rationality's blind spots and a thorough disc golf origin story.
What's inside:
Loading spinners that quietly change what people find
AI models that don't recommend charts like humans do
The blurry line between databases and human factors
A behavior-change experiment for building fairer models
Rationality's role in producing unethical outcomes
Disc golf origin story
A vegan pancake recipe

Joe Cheng is the CTO of Posit and the creator of Shiny. He joins Michael and Hadley to talk about why he almost walked away from AI work entirely over ethics concerns and what it takes to lead a team that didn't necessarily choose you. Plus, why saying yes to everyone is a worse strategy than it sounds. Bonus: Hadley calls out Joe's people-pleasing in real time.
What's inside:
Joe's 2012 self-doubt spiral that accidentally created Shiny
Why Joe almost quit working on AI entirely
The "loaded guns" problem with releasing AI tools
Hadley's blunt leadership style vs. Joe's people-pleasing
Nobody actually wanted to make Joe CTO?
Joe's take on curiosity, duty, and fear as motivators

Caitlin Colgrove is the CTO of Hex, the data workspace for building and sharing data projects using SQL and Python that somehow counts a Sweetgreen chef as a power user. She joins Michael, Hadley, and Isabel to talk about what AI agents actually get wrong in data work (it's not the hallucinations, it's supreme overconfidence), why data teams aren't going anywhere, and how she thinks about building products for humans and agents at the same time.
What's inside
What Hex's Context Studio does, and why it's a data team's new job
More code is now written in Hex by agents than by humans
"My job is to vouch for the correctness of the answer" — redefining the data team
The vibe-coded CEO PR is coming for your data team (if it hasn’t already)
Soulsborne games as couple's therapy, aka, the Elden Ring co-op report

Alex Hillman built one of America's first co-working spaces, wrote a business book in tweets, and recently handed his inbox to a Claude Code agent — not to draft emails, but to notice when a friendship is going cold. In this episode, Alex, Michael, Wes, and Hadley dig into marketing for people who hate marketing, what 20 years of email reveals about your relationships, and why the hardest part of AI-assisted coding was always before you wrote a single line.
What's inside: 
Marketing is really just listening at scale
Building a 20-year relationship database from your sent folder
"Hot rod vs. plumbing" — the two kinds of software you build now
What early internet and the AI boom have in common
The case for reading 20-year-old engineering books with a coding agent
Karaoke philosophy as a framework for community building