Fly.io Said Agents Don't Want Sandboxes. Now Its Homepage Sells Them.

8 November 2026 12:24 Will & Brian

In January Fly.io's founder wrote that AI agents don't want sandboxes, they want computers; this week Fly's home page rewrite put "agent sandboxes" in its menu, Render launched Render Sandboxes in public beta, and Railway's have been on every plan since September. Will and Brian argue whether a computer for every agent is a category the hosts can own or a feature on its way to commodity, with Modal's sandbox business, Daytona's billion-dollar round and GitHub Next's Ace, which moved from cloud microVMs to the laptop, as the evidence.

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At the start of this year, a cloud company told developers that AI agents don't want sandboxes. Today its home page sells... agent sandboxes. It's one word, and it's the plainest sign yet of what happens when a whole tier of companies decides its next customer isn't a person: the founder's word loses to the market's. The company is Fly.io, the host that grew up on a single pitch, deploy your app servers close to your users. Two other hosts now sell the same thing, and a team at GitHub built one in the cloud, then carried it home to the laptop. So: is a computer for every agent a real new business, or a feature that ends up free?
Hold on. The same company said no, and then it said yes? What happened in between, Will?
A side project, then the whole company, then the word. At the start of the year Fly launches a product called Sprites, a small Linux computer you hand to an agent. Most sandboxes worked like hotel rooms. The agent checks in, does its job, checks out, and housekeeping wipes the room. Fly's founder, Kurt Mackey, launched Sprites against that. Stop killing your sandboxes every time you use them, he wrote. He wanted the agent to have an apartment: it comes back, its stuff is where it left it, and when it goes out the lights switch off and you stop paying for the computer. And he put it in one line: "They don't want containers. They don't want sandboxes. They want computers." So at Fly, sandbox was the word for what the other guys sold. The side project lived on its own website, not even on Fly's. Then in the summer the company turned to face it. Mackey handed the chief executive job to Scott Johnston, who used to run Docker, and wrote that the ideas Fly was founded on, servers close to your users and a cloud that's easy, probably don't matter anymore. Do one thing or the other, he said, don't limp in on both. The reason was customers: among Fly's biggest, it says, companies building agents now bring in about two-thirds of the revenue. Fly's number, and it's agent companies in general, not Sprites. But that's a company reading its own invoices and finding out what it is now. Then the word. This week Fly rewrote its home page once more, and the headline today reads computers for agents, from sandboxes to production. In the menu, Sprites are now agent sandboxes. The hotel word, on the front of the apartment building. And click through to the Sprites page, same day: its headline still says sandboxes aren't enough.
So the landlord who swore he'd never run a hotel put hotel on the sign. Did he give in, or did he just run out of other words? Because those are two very different stories, and only one of them is about the customer.
I'd guess the customer gave him the word. And this week a second host launched one. Render put out Render Sandboxes in public beta, under the line a computer for every agent. But Render didn't touch its headline. It still reads your fastest path to production. Its founder, Anurag Goel, said on the Kubelist podcast, months before the launch, that Render is an application cloud for people who understand code, and that it chose not to chase vibe coding. So at Render the sandbox is one more flat in the building, not the building's new name.
So why is everybody suddenly converting to apartments?
Money, and most of it isn't going to the hosts. Modal, which has sold sandboxes for years alongside the rest of its cloud, says its sandboxes alone are now running at about three hundred million dollars a year. That's Modal's own number. What it tells you is that the sandbox stopped being an extra and became something people pay for in its own right. And then there's a company that sells nothing but the sandbox and the things around it. That's Daytona, and a couple of weeks ago it announced a round at a billion-dollar valuation. A company whose whole product is the room the agent works in. When somebody's spare room turns into a business like that, every landlord on the street goes and looks at his own spare rooms.
And that's where I come down on the other side from you. Look at who gets paid. Daytona does nothing else. Inside Modal, the sandboxes became a business of their own. A feature is something nobody builds a whole company on, and investors just backed a company built on nothing else. A server for every app once sounded like a feature too, and it turned into hosting, which is how these hosts exist at all. So I'd call it a category, and the hosts are the obvious people to own it, because renting out a computer is the job they already do. I've got people on my side. One is Ivan Burazin, who runs Daytona. On Latent Space, the AI engineering podcast, back in the spring, he was asked whether he's building a new AWS or a new Stripe. He said there will be a cloud built specifically for agents, with sandboxes and search and databases in it, and that it might look more like Stripe than AWS. An opinion from the man selling it, so weigh it that way. The better witness is Jake Cooper, who founded Railway, the third of these hosts, on the same show. His point is about shape. The era of renting one fixed box with a set amount of memory, he said, is going to get destroyed, because if you do that for agents you need a thousand of those machines. That's a host's founder telling you hosting itself changes shape for the agent. Not a word on a homepage. A different way of selling a computer.
Burazin's your witness? Did you hear the rest of that episode?
Go on, then.
Same conversation. He's listing the market, Railway, Vercel, the sandbox companies, and he says, more or less, they're still CPUs. That's the feature argument, from the man who runs the category. Now someone with no apartments to rent. Cole Murray built an open-source harness for coding agents called OpenInspect, and he was on Latent Space too. In his system the sandbox is a plug-in. Any provider can be one, and a contributor just added Daytona. Your customer can swap you out with a pull request from a stranger. That's what a feature looks like.
Same conversation, Will. Murray also said there's real money being made at the sandbox layer, at Daytona, at E2B, at a lot of others. Swappable, and still paid. Your witness is on my side.
Paid today. Watch what happens to the price. Kubernetes has an open-source agent sandbox project, free for anyone to run. David Crawshaw, who co-founded Tailscale and now sells virtual machines to agents, said on the Kubelist podcast that it isn't the clever virtualisation making these machines fast, it's Linux doing the heavy lifting. And he gets a lot of complaints, he said, that twenty bucks a month is too much. That's the sound of a market with no room left in the price. If the hard part is stock Linux and the fight is price, you're in a commodity, and a commodity bolted onto a bigger product is a feature. Fly even says it for me. Its own comparison page says the whole industry has converged on computers for agents, which is Fly's own headline, and that when that happens, "it's usually an attempt to get a word to do all the work that a product should." Fly adds that this isn't the case for Sprites. But it's a fair description of its own home page.
Price is a fight in every market, Will. By your logic hosting was a commodity too, and these companies make a living at it anyway. A commodity is still a business. A feature is what you give away to sell something else, and the hosts aren't giving the sandbox away. Fly's home page tells you that you pay only for the seconds it runs. That's a meter, and a meter on a computer is exactly the business these hosts already know how to run. Remember Cooper: renting one fixed box is over. Whoever meters the agent's computer by the second is selling the new shape. That's why I'd still back them to own it.
Then let me give you the team that tried your category and walked away from it. GitHub Next is GitHub's experiments group. One it has on show is Ace, a tool for building software with agents and your teammates, all from your own machine. The agents run as you, with a shell on your Mac. You bring your own model key, and there's no Ace service sitting in the middle. And it didn't start there. One line on the page: "It started in the cloud; this version runs on your own machine." Maggie Appleton, at GitHub Next, described the earlier version as Slack plus cloud computers, sandboxes and small virtual machines. The whole apartment block. So if GitHub's own experiment puts the agent on your laptop, who's renting the apartment?
Read to the bottom of the page. First, why they moved. Appleton said on The Pragmatic Engineer that doing it with all those virtual machines was too ambitious for a team of a handful of people, and that the sandboxes went into GitHub's desktop app. That's her account. It's a staffing call, not a verdict that the agent doesn't need a computer. Second, and this is the bit I love, Ace has an optional cloud channel, in beta, and its whole job is to keep working while every laptop on the team is closed. It needs Cloudflare's containers for that. And the team's shared folder deploys to Cloudflare or to Fly, or to one Mac somebody has to keep awake. That's Mackey's argument, from the post where he handed over the company, nearly word for word. Your laptop stops running when you close the lid, so people end up putting their agents in the cloud. Ace moved home and still rents a room for the night shift. Oh, and the page warns that its channels and lanes are not sandboxes. Everybody wants to tell you what isn't a sandbox.
It rents from whoever's there, though. That's my point, not yours.
It's the thing that changed my mind, but not over to you. I told you the hosts were the obvious owners, because renting a computer is the job they already do. Then Ace lists Cloudflare, Fly and a Mac under somebody's desk as if they were the same thing. A buyer like that doesn't choose a host's sandbox; it takes whichever one is there. So no, I don't think Fly or Render or Railway owns this. For them it's a product line. But that still doesn't make it your feature. Somebody gets paid for the plug, and the money went past the hosts to a company that does nothing else. That's the category, and it's Daytona's, not theirs.
And Daytona's own boss put it in the same pile as everyone else: still CPUs. A very good feature business is still a feature business. But if you want the one to watch, it's Fly. It's the only host that tore up its founding pitch for the agent, the one that said do one thing or the other. Render kept its headline. Fly rewrote the sign.
Rewrote it for whom, though? That's what I asked at the start, and Railway is what makes me doubt the answer is the agent. Railway has had sandboxes on every plan since September. It also has a second version of its home page, written for agents. It opens by telling the reader that it is an AI agent, reading Railway's website. And it doesn't mention sandboxes. The one page an agent actually reads leaves out the product built for agents.
Because the agent was never going to read the headline. The word on the sign is for whoever picks the host. The developer running the agent, or the people who just priced Daytona.
Category. Just not the hosts'.
Feature. Sold to people.
And Fly's new sign went up for which of them?

Will and Brian are fictional hosts voiced with ElevenLabs; the episode was researched and written by AI agents and fact-checked against the sources above. ElevenLabs is a company this site covers; it is a tool the site pays for, not a sponsor.

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Fly.io Said Agents Don't Want Sandboxes. Now Its Homepage Sells Them.

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