The Test Set by Posit

Mike Bostock made D3 when the browser was still a joke. He built bl.ocks when people needed somewhere to share their work. Now he's building Observable — reactive notebooks with an AI that actually looks at what it made. In this episode: the three-GIF bar chart that launched 25 years of viz, why open source needs both intrinsic and extrinsic motivation, and why an agent that can't see its own output is likely to be confidently wrong.
What's Inside
The 1998 visualization library that could only make bar charts
Why D3 hit #3 on GitHub, and what killed the gallery
What spreadsheets got right that notebooks ignored for years
"The agent can lie with text, but not with code"
Why Observable scrapped canvases and went back to notebooks
The penguin dataset that exposes AI
Strength training, tennis mind games, and a resurrected Stanford game

Paige Bailey is a developer relations engineering lead at Google DeepMind. She's a geophysicist-turned-AI-engineer who was once told by her professors that building open-source libraries was a waste of time. We talk about her path from planetary science to TensorFlow, why statisticians have a hidden edge in the age of AI, and what it means to be a curious generalist when the cost of building software is approaching zero. Bonus: installing solar-powered silent-film birdhouses as street art in San Francisco.
What's inside
From planetary science to TensorFlow, before it was GPU-capable
Geophysicists as early GPU adopters
The professors who said open-source wasn’t “real science”
Building silent-film birdhouses as San Francisco street art
Hiding Gemini API tests inside whimsical side projects
The right-tool-for-the-job case for mixing AI models
Why “taste” is the skill that matters when code costs nothing

Vincent Warmerdam has been the first full-time hire at a startup, a spacey punster who accidentally got himself a job, a bartender at an Amsterdam comedy theater, and a Dutch bike tour guide — and he'll tell you all of it was career development. Now doing DevRel at Marimo, Vincent makes the case for reactive notebooks, Lego-brick widgets, and why "number go up" is not a data science strategy. Also: chickens die. The model doesn't know. This matters more than you think.
What's inside
How a spacey pun accidentally launched Vincent's career
Why Marimo's constraints make it better for LLMs, not just humans
The gorilla hiding in your dataset — and why the model missed it
Vibe coding vs. notebooks: three cells at a time as a discipline
Widgets as Lego bricks: reusable, composable, criminally underused
Cognitive debt, confirmation bias, and sycophantic data science
Why natural intelligence is still, actually, a pretty good idea

Benn Stancil built Mode Analytics, spent a decade in the data trenches, and now writes some of the sharpest, funniest essays in the data world. On The Test Set, he talks about the cultural shift from Nate Silver to Rick Rubin why AI might kill the analytics dashboard, and what happens when a thousand startups all build the same thing. Plus: boy bands as a model for collaboration, and why the best creative work starts with cheating.
What's inside: 
Why the modern data stack was basically big data 2.0
The cultural flip from Nate Silver to Rick Rubin
Gas Town, tar pits, and the AI startup zero-sum game
Software is becoming content, and that changes things
Benn's creative process: Lorde lyrics, Codenames, and cheating
The boy band as a model for small-team collaboration
BI is (mostly) dead, and vibes might replace SQL

dbt Labs CEO Tristan Handy drops into The Test Set to map the fault lines between the data science world and the enterprise data world — and explain why analytics engineers are basically pissed-off data analysts who decided to organize the bookshelf. We get into SQL's glow-up, the community magic of dbt Slack, what AI agents mean for data warehouses, and why everyone's building iOS apps with Claude now.
What's inside:
What analytics engineers *actually* do
SQL's journey from deeply unsexy to indispensable
How dbt turned source control into a source of truth
Building a tech community without the RTFM energy
AI agents on your data lake: permissions get personal
Will LLMs kill the open-source package ecosystem?
Edible gardening, welding dreams, and digital dysphoria