I'm really excited about https://sprites.dev/ - it hits two of my favourite problems at once:

1. Developer environment sandboxes. This is a cheap and convenient way to run Claude Code / Codex CLI / etc in YOLO mode in a persistent sandboxed VM with a restricted blast radius if something goes wrong.

2. Sandbox API. Fly now have a product that lets me make a simple JSON API call to run untrusted code in a new sandbox. There's even snapshotting support so I can roll back to a known state after running that code.

I wrote more a bunch more about this here: https://simonwillison.net/2026/Jan/9/sprites-dev/

I really want to love this, but my experience in the first 20 seconds is unfortunately like some of my other experiences coding against Fly APIs, they're broken.

https://sprites.dev/api has this command:

$ curl -X POST "https://api.sprites.dev/v1/sprites" \ -H "Authorization: Bearer $SPRITES_TOKEN" \ -d '{"name": "my-sprite"}'

which responds with

{"error":"name is required"}

if you use the request body in the full "Create Sprite" documentation at https://sprites.dev/api/sprites#create then it does work.

can I live with some rough edges for some personal workflows that only impact me when things break? sure. however, I was thinking about playing with some CI/CD stuff using sprites that would impact our whole team if things broke and I'm really on the fence because of this experience in the first 20 seconds.

Fly team - please put some black box probes or just better testing on the example you give in the quick start. if you document it, test it.

I might have missed this in the docs, but is there a way to fork/clone a sprite, or restore a checkpoint into a new one?

Use cases: set up my preferred env in one sprite and use that as a template for others; or fire off a few independent sprites with claude code exploring alternative solutions, then choose a winner and reap the rest.

> Claude is a hyper-productive five-year-old savant. It’s uncannily smart, wants to stick its finger in every available electrical socket, and works best when you find a way to let it zap itself.

This alone was worth the upvote!

This is seriously cool - it's exactly the DX and API I've been waiting for from sandboxed execution providers.

I'd love to be able to configure the base image/VM in a way that doesn't bundle coding tools or anything else I don't need, and comes with some other binaries installed (I'm more interested in using this as an API for a sandbox use-case I have). Is there a way to do this at the moment / is this on the roadmap?

Another option would be configuring the sprite via checkpoint and then cloning the checkpoint from a base sprite, but I don't see this option anywhere either.

Philosophically, I like Fly and have been a customer since very early on.

That said, I dread having to do anything CLI related, which for hobby projects is like once every few weeks.

Glancing at the docs for Sprite, I worry that this will be another CLI where a good 95% of the time that I go to invoke a command, my workflow is interrupted by an auto-updater that takes longer than whatever interaction I'm trying to do and derails my train of thought.

I know it's one me for thinking this -- since the domain is fly.io -- but I was really hoping this is some local solution. Not self-hosted, but just local. A thin command line wrapper to something (docker? bubblewrap?) that gave me sort of a containerized "VM" experience for my local machine using CoW.

I want something like this, but running on my own box. I now have a Linux box with plenty of RAM and storage under my desk. (It happens to be an NVIDIA DGX Spark, but I'm not really interested in passing the GPU through to these sandboxed VMs; I know that's not practical anyway.) Maybe I'll see if I can hack together a local solution like this using Firecracker.

I've been having so much fun working on sprites (and working with sprites) the last the several months. There's some neat parts of the Elixir side of this we're going to open source soon.

Also check out the 5 min demo we put out where I walk thru some sprite basics: https://www.youtube.com/watch?v=7BfTLlwO4hw

fly.io is doing really good work. I've super enjoyed building our product on their platform. I love fly-replay combined with super fast start-up.

I've been thinking a lot about how to run agents (and skills) securely while giving them a lot of powerful capabilities.

I recently used their macaroons library to turn arbitrary API keys (e.g. for stripe's API) into macaroons. I route requests for an upstream host (like stripe) through Envoy as a mitm proxy which injects the real creds after verifying the macaroon.

It is such a powerful pattern. I'm always worried about leaking sensitive keys through prompt injection attacks (or just sending them to anthropic), but in this model you can attenuate the keys (both capabilities & validity window) client side. The Envoy proxy lives inside my flycast network so it can't be accessed externally.

It would be so cool if fly built something like this into sprites.dev (though I can see how it would be spooky to have fly install their own certs for stripe, etc...)