Build vs. Buy an LLM Gateway: A Decision Framework

The proxy is the easy part

Forwarding a JSON request takes little code. Production work includes streaming, cancellation, retries, idempotency, provider errors, model catalogs, price updates, secret rotation, tenant isolation, rate limits, audit logs, cache safety, and on-call response.

Estimate the system you must operate, not the first demo endpoint.

Identify nonnegotiable control

List requirements for data location, VPC deployment, provider contracts, custom models, identity, latency, policy explainability, and export. If a managed product cannot meet one hard constraint, that narrows the decision quickly.

Then separate strategic differentiation from preferences. A proprietary router trained on outcome data can be strategic; a custom dashboard may not be.

Calculate total operating cost

Compare subscription or usage fees with engineering build time, ongoing maintenance, infrastructure, observability, security review, incident response, and opportunity cost. Include migration and exit costs for both choices.

Usage-based gateway fees deserve special scrutiny because the control layer can become more expensive as the savings program succeeds. Fixed pricing has different risks, including capacity limits and tier jumps.

• Time to safe monitor mode
• Provider and feature coverage
• Reliability and latency budget
• Security and compliance ownership
• Policy and data portability
• Three-year engineering and vendor cost

Preserve reversibility

Keep an internal request interface, export the decision ledger, and avoid vendor-specific behavior in every application. A gateway should reduce provider lock-in, not replace it with another unmovable dependency.