Model Routing Cost Checklist: Hosted APIs, Open Models, Or Self-Hosted Inference?

# Model Routing Cost Checklist: Hosted APIs, Open Models, Or Self-Hosted Inference?

The model question founders ask is usually too broad: "Should we use hosted APIs or self-host?"

The better question is narrower: "Which workload deserves which model path?"

A support summarizer, a code-review assistant, a legal document extractor, and an internal analytics agent do not need the same latency, privacy posture, context window, or reasoning depth. If you route them all to the same premium model, you are buying simplicity at the exact point where usage starts compounding.

This is the checklist we use before a team commits to one AI vendor or one self-hosting plan.

Start With Workload Classes

Split requests into classes before comparing prices:

This one table prevents the common mistake: using a premium interactive model for every background job.

Cost Is More Than Token Price

Token price matters, but it is not the full bill. Add:

For one client, the cheapest model on paper became expensive because it failed JSON formatting often enough that the app retried the same request twice. A slightly better model cut retries and won on total cost.

Use A Routing Ledger

Every production AI workload should have a small ledger:

workload: support_ticket_summary
data_class: customer_pii
latency_target_ms: 2500
monthly_requests: 180000
avg_input_tokens: 1800
avg_output_tokens: 220
review_required: false
default_route: hosted_mid_tier
fallback_route: hosted_premium
blocked_route: public_free_tier
owner: support-platform

This forces a decision. It also gives finance and engineering the same vocabulary.

When Hosted APIs Win

Hosted APIs usually win when:

For seed and Series A teams, this is often the right starting point. The trap is never revisiting the route after usage grows.

When Open Models Win

Open models can win when:

The key phrase is "good enough." Do not self-host because it feels independent. Self-host because the workload is stable enough for the operating burden to pay back.

When Hybrid Routing Wins

Most serious teams end up hybrid. Cheap route first. Premium route on low confidence. Private route for sensitive classes. Batch route for nightly jobs.

A simple policy:

if data_class in ["finance", "customer_pii"]:
    route = "private_controlled"
elif confidence_required > 0.95:
    route = "premium_hosted"
elif batch_job:
    route = "low_cost_batch"
else:
    route = "mid_tier_hosted"

The routing policy should live in code, not in a spreadsheet. The spreadsheet is for review; the application needs deterministic behavior.

The Practical Takeaway

Do not make AI infrastructure a binary hosted-versus-self-hosted argument. Treat it like traffic routing.

Classify the workload. Price the full path. Define allowed and blocked routes. Review the ledger monthly. Then move only the stable, high-volume, privacy-sensitive workloads to a more controlled path.

TechSaaS helps startups build model-routing ledgers, cost reviews, and production AI infrastructure without turning it into a research project: techsaas.cloud/contact