The decision matrix

| Factor | Build (custom gateway) | Buy (Portkey, Helicone, etc.) | |--------|------------------------|-------------------------------| | Setup time | 4–8 weeks | 1–2 days | | Monthly cost | Infra only (~£2k) | £500–£5k+ | | Provider lock-in | None | Low–Medium | | PII/Compliance | Full control | Vendor-dependent | | Custom routing | Unlimited | Feature-gated | | Team expertise needed | Senior backend + ML ops | Low |

When to build

• Strict data residency (healthcare, finance, gov)
• Multi-tenant with per-tenant cost ceilings
• Custom routing logic (fallback chains, semantic routing)
• You already have the infra team

When to buy

• Speed to market > control
• Single-tenant, standard use cases
• No dedicated ML ops capacity
• Budget < £50k/year

The hidden costs

Buying: vendor price increases, feature gaps you can't fix, data egress fees, compliance audits.

Building: 2–3 senior engineers × 6 weeks = £150k+ before first request. Ongoing: model updates, security patches, observability.

Our default for clients

Start with a managed gateway (Portkey/Helicone). Migrate to custom when you hit a hard constraint: data residency, per-tenant kill-switches, or routing logic the vendors don't support. The migration path is clean if you abstract the gateway interface from day one.