Simon Willison's Weblog: startups

CoreWeave adds Marimo to their 2025 acquisition spree

2025-10-31T13:57:51+00:00

I don't usually cover startup acquisitions here, but this one feels relevant to several of my interests.

Marimo (previously) provide an open source (Apache 2 licensed) notebook tool for Python, with first-class support for an additional WebAssembly build plus an optional hosted service. It's effectively a reimagining of Jupyter notebooks as a reactive system, where cells automatically update based on changes to other cells - similar to how Observable JavaScript notebooks work.

The first public Marimo release was in January 2024 and the tool has "been in development since 2022" (source).

CoreWeave are a big player in the AI data center space. They started out as an Ethereum mining company in 2017, then pivoted to cloud computing infrastructure for AI companies after the 2018 cryptocurrency crash. They IPOd in March 2025 and today they operate more than 30 data centers worldwide and have announced a number of eye-wateringly sized deals with companies such as Cohere and OpenAI. I found their Wikipedia page very helpful.

They've also been on an acquisition spree this year, including:

Weights & Biases in March 2025 (deal closed in May), the AI training observability platform.
OpenPipe in September 2025 - a reinforcement learning platform, authors of the Agent Reinforcement Trainer Apache 2 licensed open source RL framework.
Monolith AI in October 2025, a UK-based AI model SaaS platform focused on AI for engineering and industrial manufacturing.
And now Marimo.

Marimo's own announcement emphasizes continued investment in that tool:

Marimo is joining CoreWeave. We’re continuing to build the open-source marimo notebook, while also leveling up molab with serious compute. Our long-term mission remains the same: to build the world’s best open-source programming environment for working with data.

marimo is, and always will be, free, open-source, and permissively licensed.

Give CoreWeave's buying spree only really started this year it's impossible to say how well these acquisitions are likely to play out - they haven't yet established a track record.

Via @marimo_io

Tags: entrepreneurship, open-source, python, startups, ai, jupyter, marimo

Quoting Paul Biggar

2025-06-16T17:56:57+00:00

In conversation with our investors and the board, we believed that the best way forward was to shut down the company [Dark, Inc], as it was clear that an 8 year old product with no traction was not going to attract new investment. In our discussions, we agreed that continuity of the product [Darklang] was in the best interest of the users and the community (and of both founders and investors, who do not enjoy being blamed for shutting down tools they can no longer afford to run), and we agreed that this could best be achieved by selling it to the employees.

— Paul Biggar, Goodbye Dark Inc. - Hello Darklang Inc.

Tags: entrepreneurship, programming-languages, startups

Atlassian: “We’re Not Going to Charge Most Customers Extra for AI Anymore”. The Beginning of the End of the AI Upsell?

2025-05-13T15:52:09+00:00

Atlassian: “We’re Not Going to Charge Most Customers Extra for AI Anymore”. The Beginning of the End of the AI Upsell?

Jason Lemkin highlighting a potential new trend in the pricing of AI-enhanced SaaS:

Can SaaS and B2B vendors really charge even more for AI … when it’s become core? And we’re already paying $15-$200 a month for a seat? [...]

You can try to charge more, but if the competition isn’t — you’re going to likely lose. And if it’s core to the product itself … can you really charge more ultimately? Probably … not.

It's impressive how quickly LLM-powered features are going from being part of the top tier premium plans to almost an expected part of most per-seat software.

Via @jasonlk

Tags: atlassian, startups, saas, ai, generative-ai, llms

Quoting Oleg Pustovit

2025-05-08T19:30:54+00:00

Microservices only pay off when you have real scaling bottlenecks, large teams, or independently evolving domains. Before that? You’re paying the price without getting the benefit: duplicated infra, fragile local setups, and slow iteration.

— Oleg Pustovit, Microservices Are a Tax Your Startup Probably Can’t Afford

Tags: software-architecture, startups, microservices

Quoting James Dillard

2024-11-23T18:47:53+00:00

If you try and tell people 5 interesting things about your product / company / cause, they’ll remember zero. If instead, you tell them just one, they’ll usually ask questions that lead them to the other things, and then they’ll remember all of them because it mattered to them at the moment they asked.

— James Dillard

Tags: entrepreneurship, startups

The economics of a Postgres free tier

2024-07-11T19:26:35+00:00

The economics of a Postgres free tier

Xata offer a hosted PostgreSQL service with a generous free tier (15GB of volume). I'm very suspicious of free tiers that don't include a detailed breakdown of the unit economics... and in this post they've described exactly that, in great detail.

The trick is that they run their free tier on shared clusters - with each $630/month cluster supporting 2,000 free instances for $0.315 per instance per month. Then inactive databases get downgraded to even cheaper auto-scaling clusters that can host 20,000 databases for $180/month (less than 1c each).

They also cover the volume cost of $0.10/GB/month - so up to $1.50/month per free instance, but most instances only use a small portion of that space.

It's reassuring to see this spelled out in so much detail.

Via lobste.rs

Tags: postgresql, startups, saas

Quoting Yishan Wong

2024-02-20T16:23:28+00:00

In 2006, reddit was sold to Conde Nast. It was soon obvious to many that the sale had been premature, the site was unmanaged and under-resourced under the old-media giant who simply didn't understand it and could never realize its full potential, so the founders and their allies in Y-Combinator (where reddit had been born) hatched an audacious plan to re-extract reddit from the clutches of the 100-year-old media conglomerate. [...]

— Yishan Wong

Tags: reddit, y-combinator, startups

(Almost) Every infrastructure decision I endorse or regret after 4 years running infrastructure at a startup

2024-02-10T05:51:00+00:00

(Almost) Every infrastructure decision I endorse or regret after 4 years running infrastructure at a startup

Absolutely fascinating post by Jack Lindamood talking about services, tools and processes used by his startup and which ones turned out to work well v.s. which ones are now regretted.

I’d love to see more companies produce lists like this.

Via lobste.rs

Tags: architecture, infrastructure, startups

Quoting Craig Mazin

2023-12-31T20:53:21+00:00

There is something so vulnerable and frightening about doing your own thing, because it’s your fault if it doesn’t work. And then there’s this other kind of work, where you’re paid an extraordinary amount of money, you’re the hero before you walk in the door, you’re not even held that accountable, because you have a limited amount of time, and all you can do is make it better.

— Craig Mazin

Tags: screen-writing, entrepreneurship, startups

ChatGPT plugins

2023-03-23T20:56:02+00:00

ChatGPT plugins

ChatGPT is getting a plugins mechanism, which will allow developers to provide extra capabilities to ChatGPT, like looking up restaurants on OpenTable or fetching data from APIs. This feels like the kind of feature that could obsolete—or launch—a thousand startups. It also makes ChatGPT much more interesting as a general purpose tool, as opposed to something that only works as an interface to a language model.

Tags: startups, ai, openai, chatgpt, chatgpt-plugins

Retrospection and Learnings from Dgraph Labs

2022-09-16T18:43:34+00:00

Retrospection and Learnings from Dgraph Labs

I was excited about Dgraph as an interesting option in the graph database space. It didn’t work out, and founder Manish Rai Jain provides a thoughtful retrospective as to why, full of useful insights for other startup founders considering projects in a similar space.

Via Hacker News

Tags: entrepreneurship, startups, graphql

Quoting Solomon Hykes

2021-09-07T14:47:49+00:00

We never shipped a great commercial product. The reason for that is we didn’t focus. We tried to do a little bit of everything. It’s hard enough to maintain the growth of your developer community and build one great commercial product, let alone three or four, and it is impossible to do both, but that’s what we tried to do and we spent an enormous amount of money doing it.

— Solomon Hykes

Tags: docker, startups

Django for Startup Founders: A better software architecture for SaaS startups and consumer apps

2021-06-24T20:43:38+00:00

Django for Startup Founders: A better software architecture for SaaS startups and consumer apps

The opening section of this article has very little to do with Django: it’s an insightful description of the technical challenges faced by a startup that is still seeking product-market fit. Alex then extends that into his own architectural recommendations for startups building with Django to help waste as little time as possible on problems that aren’t core to the product they are building.

Via Hacker News

Tags: django, startups

The SOC2 Starting Seven

2021-03-05T19:50:52+00:00

The SOC2 Starting Seven

"So, you plan to sell your startup’s product to big companies one day. Congratu-dolences! [...] Here’s how we’ll try to help: with Seven Things you can do now that will simplify SOC2 for you down the road while making your life, or at least your security posture, materially better in the immediacy.

Via @jacobian

Tags: security, startups

Quoting Michael Malis

2020-12-11T06:39:51+00:00

If you are pre-product market fit it's probably too early to think about event based analytics. If you have a small number of users and are able to talk with all of them, you will get much more meaningful data getting to know them than if you were to set up product analytics. You probably don't have enough users to get meaningful data from product analytics anyways.

— Michael Malis

Tags: analytics, startups

Quoting Sam Altman

2020-05-28T21:36:03+00:00

Any time you can think of something that is possible this year and wasn’t possible last year, you should pay attention. You may have the seed of a great startup idea. This is especially true if next year will be too late.

— Sam Altman

Tags: ideas, startups, sam-altman

How the Digg team was acquihired.

2020-01-03T02:27:55+00:00

How the Digg team was acquihired.

Useful insight into how a talent acquisition can play out from Will Larson, who was an engineering leader at Digg when they negotiated their acquihire exit.

Via Patrick McKenzie

Tags: digg, startups, will-larson

Advice for a new executive, by Chad Dickerson

2018-08-31T13:45:08+00:00

Advice for a new executive, by Chad Dickerson

Lara Hogan shares the advice she was given by Chad Dickerson (CTO and then CEO of Etsy) when she first became VP Engineering at Kickstarter. There is so much good material in here. I can vouch for the “peer support group” recommendation: Natalie and I benefited from that through Y Combinator and ended up building our own founder peer support group when we moved our startup back to London. Having a confidential trusted group with which to discuss the challenges of growing a company was invaluable.

Via @lara_hogan

Tags: startups, management

Getting Your First 10 Customers

2017-10-23T17:36:19+00:00

Getting Your First 10 Customers

There is so much good advice embedded in this article by Patrick McKenzie, and it constantly comes back to the theme of doing whatever it takes to get to your first ten paying customers.

Via Patrick McKenzie

Tags: startups, sales, patrick-mckenzie

It’s Not a Feature Problem—Avoiding Startup Tarpits

2017-10-22T12:53:41+00:00

It’s Not a Feature Problem—Avoiding Startup Tarpits

“When we turned on paid advertising for the first time the increase we had a sizable increase in signups. We always feared that a new user would just churn because of what we perceived as deficiencies in the product. While there were users who churned for that reason, it was never the nightmare scenario that we imagined.”

Via Hacker News

Tags: marketing, startups

Should I build my startup's web-based product as if it's going to one day be widely adopted and experience high-volume, or instead focus on quick delivery over scalability?

2017-10-07T03:30:52+00:00

My answer to Should I build my startup's web-based product as if it's going to one day be widely adopted and experience high-volume, or instead focus on quick delivery over scalability? on Quora

Absolutely the second: build for rapid learning, not for eventual scalability. The vast majority of startups fail, and the number one reason they fail is that they didn’t achieve product-market fit: they failed to build something that customers actually wanted.

Whatever you think your product should be, you’re certainly wrong. If you’re lucky you will be at least aiming in the right direction, and getting it in front of actual users will lead you to course correct and figure out what it is you should really be building.

If you do manage to build something that people want, then you can start to focus on how you’re going to scale it up. That’s a great problem to have! But building for scale before you’ve proved your product is a recipe for months of wasted work.

Tags: quora, startups

What's the first thing you would check if the company is losing money even though there's a big increase in its revenue?

2016-08-15T14:12:00+00:00

My answer to What's the first thing you would check if the company is losing money even though there's a big increase in its revenue? on Quora

The company's expenses.

Tags: quora, startups, entrepreneurship, business, careers

What is the single greatest value-add from Y Combinator?

2016-08-15T13:32:00+00:00

My answer to What is the single greatest value-add from Y Combinator? on Quora

It's very difficult to pick the best one, but from our experience here's something that really stood out: the sense of camaraderie and trust you have in others who are also going through YC.

Building a startup is incredibly difficult. Almost by definition, you have no idea what you are doing and every day you'll need to figure out how to do something brand new (to you) to as high a standard as possible: interview a candidate, pitch an investor, prepare a press release etc etc etc.

Unfortunately, it's also a bad idea to be honest about how difficult you are finding it. If someone asks how your startup is going the only correct answer is “yeah, totally awesome!” even if you are completely drowning. After all, that person might be or know a potential investor, employee, business partner or customer!

YC helps here because when you join you enter a code of fellowship with your fellow YC companies (certainly those in the same batch, but it extends to alumni companies too). You'll keep their secrets, and they will keep yours.

This means you now have the largest, most engaged and helpful support group you could possibly imagine!

Having trouble putting together a plan for your launch? So are half the other companies in your batch. Go swap notes with them and figure it out together.

Raised money in dollars but need to convert it to another currency and don't know how to do it? Someone else in your batch had to figure out exactly that last week, and since they only just learnt it themselves they are the best person to learn from.

Feel like everything is going to pieces and your company is doomed? Get together for dinner and you'll find that EVERYONE feels like that, then swap stories about your latest disasters with each other.

If you're not in YC it's still possible to build up a trusted network like this, but it's s huge amount of work: find other founders you trust at a similar stage to you, get them to trust you, then introduce them to each other and hope that everyone clicks. YC does that all for free and grants you a much larger network than you could ever build by yourself.

Tags: quora, y-combinator, startups

What are the best strategies to get a tech job at YC-backed startups in the next 5 months?

2015-12-18T11:02:00+00:00

My answer to What are the best strategies to get a tech job at YC-backed startups in the next 5 months? on Quora

Keep an eye on jobs | Hacker News - it's the official listing of almost all jobs advertised at YC companies.

Tags: quora, techstars, 500startups, y-combinator, startups, jobs, careers

Does Y Combinator accept purely app ideas like WhatsApp, Flipboard, etc.?

2014-02-24T10:16:00+00:00

My answer to Does Y Combinator accept purely app ideas like WhatsApp, Flipboard, etc.? on Quora

Yes they do, but you'll need to demonstrate that your team also has the ability to execute on the idea.

Tags: quora, y-combinator, startups

What is the best payment provider for a web app with monthly subscription fees at its early stage?

2014-02-20T17:35:00+00:00

My answer to What is the best payment provider for a web app with monthly subscription fees at its early stage? on Quora

We found Stripe extremely easy to get started with for charging subscription payments.

Tags: quora, webapps, startups, stripe

What are the key points accelerators such as Y-Combinator drill into their startups?

2014-02-07T18:36:00+00:00

My answer to What are the key points accelerators such as Y-Combinator drill into their startups? on Quora

Build something people want. This is so important that YC have it printed on the T-Shirts they hand out to each batch.

They also teach the importance of launching something and getting real feedback. The entire three month YC process is based around the need to launch and demonstrate traction in order to raise money from investors.

Paul Graham's essays cover many of the lessons that YC teaches startups.

Tags: quora, y-combinator, funding, startups, entrepreneurship

Do accelerators (which do not take up equity) accept not-for-profit ventures into their programs? If yes, which are some of the best ones?

2014-01-28T13:41:00+00:00

My answer to Do accelerators (which do not take up equity) accept not-for-profit ventures into their programs? If yes, which are some of the best ones? on Quora

Y Combinator recently started funding non-profits: http://ycombinator.com/np.html

Tags: quora, 500startups, y-combinator, funding, startups, entrepreneurship

How much equity does YCombinator get on average?

2014-01-21T16:24:00+00:00

My answer to How much equity does YCombinator get on average? on Quora

They almost always take 7% - they get diluted down in further rounds.

Tags: quora, y-combinator, funding, startups

Is YCombinator's $20k seed capital enough to keep a team of 3 founders alive in Silicon Valley during the program?

2014-01-15T10:13:00+00:00

My answer to Is YCombinator's $20k seed capital enough to keep a team of 3 founders alive in Silicon Valley during the program? on Quora

Yes - especially if the three founders live together. A three bedroom apartment near Mountain View can be had for around $3-4,000/month (just check Craigslist), which will be the bulk of your expenses. The rest can cover food, car rental and some business-related expenses (we spent some money on office chairs and a desk).

Tags: quora, y-combinator, startups