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You can build an AI agent from scratch with the OpenAI Agents SDK, or you can use a managed platform that handles infrastructure, scaling, and monitoring. The build-vs-buy decision depends on your team size, budget, and how much control you need.
The landscape
| Category | Examples | You handle | They handle |
|---|---|---|---|
| Raw SDKs | OpenAI Agents SDK, LangChain | Everything | Model API |
| Agent platforms | Vercel AI, Cloudflare Agents | Business logic | Infra, scaling, deployment |
| No-code agents | Zapier Agents, Make AI | Configuration | Everything |
| Full managed | Claude Code Routines, Devin | Prompts | Everything |
Build: when and why
Build your own agent infrastructure when:
You need full control. Managed platforms make decisions for you — model routing, retry logic, caching, state management. If those decisions need to be yours (regulated industries, specific performance requirements), build.
You have unique requirements. Custom tool integrations, proprietary data pipelines, specific security constraints. Platforms offer flexibility, but not infinite flexibility.
Cost optimization at scale. At 10,000+ daily agent interactions, managed platforms get expensive. Self-built infrastructure with self-hosted models can be 5-10x cheaper.
The build stack:
- OpenAI Agents SDK or LangChain for agent logic
- Cloudflare Sandbox or Docker for code execution
- PostgreSQL for state management
- Helicone or Langfuse for observability
- Railway or VPS for deployment
Estimated cost: $50-200/month infrastructure + engineering time.
Buy: when and why
Use a managed platform when:
Speed matters more than control. A Vercel AI agent can be deployed in an afternoon. Building equivalent infrastructure from scratch takes weeks.
Your team is small. A 2-person startup shouldn’t spend 40% of engineering time on agent infrastructure. Use a platform and focus on your product.
You need enterprise features. SOC 2 compliance, SSO, audit logs, role-based access. Building these from scratch is months of work.
The buy stack:
- Zapier Agents for no-code automation
- Vercel AI for Next.js-based agent UIs
- Claude Code Routines for scheduled dev tasks
- Cloudflare Workers AI for edge-deployed agents
Estimated cost: $20-500/month platform fees, minimal engineering time.
The hybrid approach
Most successful teams do both:
┌─────────────────────────────────────┐
│ Custom agent logic (built) │
│ - Domain-specific tools │
│ - Proprietary data access │
│ - Custom evaluation pipeline │
├─────────────────────────────────────┤
│ Platform infrastructure (bought) │
│ - Hosting (Vercel/Railway) │
│ - Observability (Helicone) │
│ - App integrations (Zapier SDK) │
│ - Sandbox execution (Cloudflare) │
└─────────────────────────────────────┘Build the parts that are unique to your product. Buy the parts that are commodity infrastructure.
Cost comparison at different scales
| Scale | Build cost | Buy cost | Winner |
|---|---|---|---|
| Prototype (100 users) | $200/mo + 2 weeks eng | $50/mo + 2 days | Buy |
| Early product (1K users) | $300/mo + ongoing eng | $200/mo | Buy |
| Growing (10K users) | $500/mo + 1 eng | $1,000/mo | Build |
| Scale (100K users) | $2,000/mo + 2 eng | $5,000-10,000/mo | Build |
The crossover is around 10,000 users. Below that, platform fees are cheaper than engineering time. Above that, the per-user cost of platforms makes building worthwhile.
Decision checklist
Choose build if you check 3+ of these:
- Regulated industry (healthcare, finance, legal)
- 10,000+ daily agent interactions
- Custom model requirements (fine-tuned, self-hosted)
- Unique tool integrations not available on platforms
- Engineering team of 3+ people
- Need to own the full stack for competitive advantage
Choose buy if you check 3+ of these:
- Team of 1-3 people
- Need to ship in weeks, not months
- Standard use cases (chat, code review, automation)
- Under 10,000 daily interactions
- Enterprise compliance features needed immediately
- Budget for platform fees, not engineering time
Related: OpenAI Agents SDK Guide · OpenAI SDK vs LangChain vs CrewAI · Deploy AI Agents to Production · Zapier Agent SDK Guide · Cloudflare Sandbox for AI Agents · Self-Hosted vs Cloud AI Agents · AI Agent Cost Management