Spin (Fermyon) alternatives
The 5 alternatives below are grouped by kind of sandbox, and each says what it does differently from Spin (Fermyon). Start from whatever made you look: missing GPUs, session limits, self-hosting, pricing or isolation.
Why teams look beyond Spin (Fermyon)
Choose Spin for Wasm-isolated function endpoints you can run anywhere; not a general code-execution sandbox.
- Handlers are stateless and short-lived (30 s on Fermyon Cloud Starter); not a workspace for a coding agent
- Only languages with Wasm component toolchains; no native packages
- Hosted offerings are beta or preview with unpublished pricing, and ownership changed to Akamai in late 2025
- No GPU
Spin (Fermyon) alternatives, by kind
Hosted sandbox platforms
SDK-driven sandboxes you create, run code in and destroy through an API.
Cloudflare Sandbox SDK
A TypeScript SDK for Cloudflare Workers that runs untrusted code in Linux sandboxes backed by Cloudflare Containers and Durable Objects.
- MicroVM (Containers)
- Open source
- Snapshots
How it differs: Teams building on Cloudflare Workers that want per-user sandboxes with egress and credentials controlled in code. A strong, programmable option for Workers developers; less suited to Python-first agent stacks.
Compute platforms with sandboxes
General serverless or app platforms that also offer sandboxes, often with GPUs.
Fly Machines
Fly.io's low-level API for Firecracker VMs that start and stop in under a second and can be suspended to disk; the primitive underneath Fly.io's Sprites product.
- Firecracker microVM
- Pause/resume
How it differs: Teams that want raw, per-second-billed Firecracker VMs they orchestrate themselves rather than a sandbox SDK. A fast, well-priced Firecracker VM primitive for teams that want to assemble their own sandbox layer; for an agent-ready product on the same infrastructure look at Fly.io Sprites.
Isolation primitives and runtimes
The hypervisors, user-space kernels, OS sandboxes and WebAssembly runtimes that sandbox platforms build on.
Extism
A BSD-licensed WebAssembly plug-in system from Dylibso with host SDKs for 15+ languages and manifest-level memory, host and path limits, built on Wasmtime.
- Wasm plug-in sandbox
- Open source
- Self-hostable
How it differs: Letting users or agents supply code that runs as a sandboxed plug-in inside your application, in almost any host language. The cleanest way to run agent tools as sandboxed Wasm plug-ins inside your own app; use a VM sandbox for anything that needs an OS.
Wasmer
An MIT-licensed WebAssembly runtime and WASIX ecosystem that runs registry packages such as Python, Bash and PHP in local sandboxes, with Wasmer Edge as the hosted option.
- Wasm sandbox
- Open source
- Self-hostable
How it differs: Running interpreter packages (Python, PHP, Bash) in Wasm sandboxes from JavaScript or Python, locally, in the browser or on Wasmer Edge. A practical way to embed interpreter sandboxes in JS or Python apps; pick Wasmtime for a pure engine and a hosted VM sandbox for full Linux.
Wasmtime
The Bytecode Alliance's standalone WebAssembly and WASI runtime, embeddable from Rust, C, Python, Go, .NET and Ruby, and the engine under Spin, Extism, Akamai Functions and Fastly.
- Wasm sandbox
- Open source
- Self-hostable
How it differs: Embedding a capability-based sandbox for plug-ins, functions and tool code inside your own application. The default WebAssembly engine for building a sandbox into your own software; choose it for plug-ins and tool code rather than whole-OS workloads.
Spin (Fermyon) vs alternatives
| Sandbox | Isolation | Open source | Self-host / BYOC | Cold start (vendor) | Max session | Snapshots / pause | GPU | SDKs |
|---|---|---|---|---|---|---|---|---|
| Spin (Fermyon) | Wasm component | Yes | Yes / No | ms (claim) | 30 s (Fermyon Cloud) | No / No | No | CLI, Rust, JavaScript/TypeScript, Go, Python |
| Cloudflare Sandbox SDK | MicroVM (Containers) | Yes | No / No | 1–3 s | No fixed cap | Yes / Not documented | Not documented | TypeScript (Workers) |
| Extism | Wasm plug-in sandbox | Yes | Yes / No | Not documented | Host-set | No / No | No | Rust, JavaScript/TypeScript, Go, Python, Ruby, .NET, Java, PHP, Elixir, Haskell, OCaml, Perl, Zig, C, C++ |
| Fly Machines | Firecracker microVM | No | No / No | <1 s start (claimed) | Not documented | Yes / Yes | Not documented | Go, CLI, REST API |
| Wasmer | Wasm sandbox | Yes | Yes / No | Not documented | Not documented | Not documented / Not documented | No | CLI, JavaScript/TypeScript, Python, Rust, Swift |
| Wasmtime | Wasm sandbox | Yes | Yes / No | Not documented | Embedder-set | No / Not documented | No | CLI, Rust, C, C++, Python, .NET, Go, Ruby |
Frequently asked questions
What are the main alternatives to Spin (Fermyon)?
Is there an open-source alternative to Spin (Fermyon)?
Cite this page
Agent Sandboxes. (2026). Spin (Fermyon) alternatives. agentsandboxes.org. Last reviewed November 9, 2026. https://agentsandboxes.org/alternatives/fermyon-spin/
Found an error or a missing sandbox? Submit a correction — every entry links to the sources it relies on.