Fly.io

Fly.io has carved out a niche as the infrastructure layer for AI agents that need persistent, isolated compute. The Sprites product is a step beyond traditional serverless: each agent gets a hardware-isolated Linux VM that checkpoints automatically, so state survives sleep and restart. This is a genuine differentiator for agent builders who are tired of re-architecting around stateless functions or gluing together external databases just to maintain context. The strengths are clear. The checkpoint/restore model makes persistent state the default, which is a huge productivity win for coding agents like Claude or Codex—they pick up exactly where they left off. The Sprite Block Device (in private beta) promises infinite scalability with billing only for bytes you actually write, removing disk-sizing decisions. Sprites Connectors solve the credential management problem by centralizing API keys and rotating them automatically, which is a real security improvement over pasting tokens into every VM. The per-second billing model is refreshingly transparent. The free tier gives you access to core features with unlimited users, and pay-as-you-go charges only for what you use. For agent workloads that are often idle, the bill genuinely approaches zero. That said, usage-based pricing can be unpredictable for steady-state workloads—if you have always-on services, consider a Machine Reservation to get 40% off. The weaknesses are mostly about the learning curve. This is not a GUI-first platform. You need comfort with the CLI (flyctl) and basic infrastructure concepts. The docs are thorough, but there's an expectation that you can debug networking or volume issues yourself. Support is excellent—they have dedicated engineers starting at $29/month—but at the free tier, you're mostly on your own with community support. Where it fits best: AI agent startups, teams building MCP servers, and developers who need to run untrusted code safely. It's also a solid choice for globally distributed apps that need low latency—18+ regions and sub-second machine boot times are hard to beat. Where it doesn't fit: simple static sites (overkill), teams that want fully managed serverless like AWS Lambda, and non-technical users who need a GUI. If you're on Heroku and outgrowing it, the migration path is documented and straightforward. One thing to watch: Fly.io has made a strategic pivot toward Sprites, as the CEO's blog post 'Turn And Face The Strange' spells out. This means the platform is betting big on the AI agent market. That's exciting, but it also means you should evaluate whether the core Machine product continues to get the same attention. For now, both products are fully supported, and the shared infrastructure means improvements to one often benefit the other. Overall, Fly.io is a developer-first platform that rewards those willing to invest in learning it. If you're building agents that need persistence and isolation, it's arguably the best option available. If