Fly Machines vs Modal
Comparing architecture, runtime limits, open-source licenses, and monthly costs for autonomous agent pipelines.
Detailed Specifications & Compatibility Matrix
Extracted directly from GitHub REST API & official developer documentation
| Technical Feature / Metric | Fly Machines | Modal |
|---|---|---|
| Developer / Organization | Fly.io Inc. (Kurt Mackey & Team) | Modal Labs Inc. (Erik Bernhardsson) |
| Open-Source Engine | ✓ Open Source (Apache-2.0) | ✓ Open Source (Apache-2.0) |
| GitHub Stars (Repo/SDK) | ★ 1,719 GitHub Stars | ★ 528 GitHub Stars |
| Core Repository Language | Go | Python |
| Supported SDK Clients | ||
| Self-Hosted Deployment | Hosted Only | Hosted Only |
| Docker / Container Ready | ✓ Official Image | ✓ Official Image |
| Model Context Protocol (MCP) | Standard REST/gRPC | ✓ Native MCP |
| Billing Architecture | usage based | usage based |
| Developer Free Tier | ✓ Yes 3 shared-cpu-1x microVMs allowance | ✓ Yes $30 USD in free compute credits every month |
| Entry Paid Tier (Monthly) | $1.94 USD / mo | Free / Custom |
| Pricing & Cost Architecture | Pay-as-you-go billed per second: shared CPU microVMs start at ~$0.0000022/second (~$1.94/month if running 24/7). Stopped machines pay only for attached NVMe disk storage ($0.15/GB/mo). | Every user receives $30/month in free compute credits perpetually. Pay-as-you-go CPU starts at $0.000015/core-second; NVIDIA GPUs (T4 to H100) are metered per millisecond. |
| Key Engineering Insight | Operates custom bare-metal servers across 35+ global edge datacenters, booting Linux kernels directly on KVM without container orchestration overhead. | Founded by Erik Bernhardsson (former CTO of Better and creator of Spotify's Annoy algorithm); designed to make cloud infrastructure and GPU clusters feel as seamless as a local Python import. |
Strengths & Trade-Offs
Objective engineering evaluation of both platforms
Fly Machines Evaluation
Key Advantages
- ✓ Sub-300ms boot times for custom Docker images running in 35+ global edge data centers close to end users
- ✓ Full persistent NVMe volume support with customizable memory/vCPU ratios per individual machine instance
- ✓ Fast REST API allowing agents to dynamically spawn, pause, snapshot, and destroy microVMs programmatically
Limitations & Trade-Offs
- ✕ Requires managing base Linux Docker images, security firewall configurations, and internal WireGuard routing
- ✕ Lacks a specialized high-level code execution SDK out of the box (requires building custom API wrappers)
Modal Evaluation
Key Advantages
- ✓ Pure Python infrastructure as code: define container images and cloud jobs using simple '@app.function' decorators
- ✓ Sub-2 second container cold starts with on-demand access to NVIDIA A100, H100, and L4 GPUs without provisioning
- ✓ Automated horizontal scaling across thousands of parallel workers with built-in queueing and output streaming
Limitations & Trade-Offs
- ✕ Proprietary cloud runtime with no self-hosted on-premise execution engine available
- ✕ Workloads must be structured around Modal's Python decorator conventions and cloud serialization rules
Source Quotes
Direct excerpts from official documentation backing our extracted specifications
Fly Machines Documentation Proof
"Shared CPU instances start at $0.0000022/second (~$1.94/mo)."
"Free resource allowances include up to 3 shared-cpu-1x microVMs."
"Global microVM platform running on Fly.io bare metal hardware."
Modal Documentation Proof
"Pay-as-you-go CPU from $0.000015/core-second; GPU compute metered per millisecond."
"Every account gets $30/month in free credits renewing monthly."
"Hosted serverless cloud execution platform managed by Modal Labs."
Frequently Asked Questions: Fly Machines vs Modal
Architectural trade-offs and decision criteria
Is Fly Machines or Modal cheaper for developers?
Fly Machines has a starting price of $1.94/mo (usage based), while Modal starts at $0/mo (usage based). Fly Machines includes a free tier (3 shared-cpu-1x microVMs allowance). Modal offers a free tier ($30 USD in free compute credits every month).
Can I self-host Fly Machines and Modal in my own infrastructure?
Fly Machines is a cloud-managed service only. In comparison, Modal is proprietary cloud infrastructure.
Do Fly Machines and Modal support the Model Context Protocol (MCP)?
Fly Machines does not currently list native MCP server compatibility. Modal fully supports Model Context Protocol integrations.
Which programming languages have official SDKs for Fly Machines vs Modal?
Fly Machines provides official SDKs in: go, curl, python. Meanwhile, Modal supports: python.