AI API proxy for cost control
Put cost policy in front of every LLM provider call.
An AI API cost control proxy creates one synchronous boundary between product code and model providers. It can observe the final request, apply policy consistently, and prevent calls that a reporting-only integration can merely record.
Summary
An AI API proxy for cost control authenticates the project, resolves customer and feature metadata, evaluates routing and policy, serves eligible zero-cost cache hits, validates model pricing, atomically reserves rolling spend budgets, and forwards only allowed traffic to the selected provider.
Integration
Provider-compatible base URL
Control point
Before the upstream fetch
Credential model
Provider keys encrypted server-side
Why cost control needs a synchronous request boundary.
An SDK event sent after a provider response is excellent for reporting because it does not add a network hop. It cannot stop the request that generated the event. A proxy trades that simplicity for the ability to evaluate budgets, policy, routing, and cache before upstream spend occurs.
The architectural choice is therefore operational, not cosmetic. Use asynchronous reporting when visibility is enough. Use an in-path proxy when the system must make or enforce a decision before provider execution.
A cost-control proxy has a defined request lifecycle.
Halvr authenticates the project API key, parses attribution metadata, checks exact and semantic cache eligibility, validates verified model pricing, evaluates policy rules, and reserves rolling spend budgets before constructing the upstream request. The provider response supplies actual usage for atomic cost reconciliation.
Keeping these phases explicit makes the decision auditable. A request record can show what the application asked for, which policy matched, which provider and model were resolved, whether cache was used, and why traffic was allowed or blocked.
- Ingress: authenticate the Halvr key and validate the request body.
- Attribute: attach customer, feature, session, agent, and tool context.
- Decide: evaluate budget, policy, cache, and routing rules.
- Execute: call the selected public provider endpoint and record actual usage.
Keep the application integration narrow.
For OpenAI-compatible clients, change the base URL and use the Halvr project key. Attach product metadata to the request body. The same control path can resolve OpenAI, Anthropic, Gemini, or configured OpenAI-compatible endpoints without shipping provider credentials to application clients.
const client = new OpenAI({
apiKey: process.env.HALVR_API_KEY,
baseURL: "https://api.halvr.io/v1",
});
await client.chat.completions.create({
model: "gpt-4o-mini",
messages,
metadata: {
customerId: "customer_123",
feature: "support_copilot",
},
});Treat the proxy as a high-trust service.
A model proxy handles credentials and may process sensitive prompts. Provider keys should be encrypted at rest, secrets must remain server-only, outbound custom endpoints must reject private networks, redirects should not bypass validation, and request retention should default to the least data the product needs.
Halvr supports metadata-only, redacted, and full retention modes. The cost-control path does not require full prompt storage, so teams can preserve attribution and usage evidence while reducing retained content.
Define behavior for proxy and provider failures.
A proxy adds a dependency to the inference path. Measure its latency separately from provider latency, expose health and readiness probes, bound request and response sizes, and decide where retries belong. Automatic retries in both the application and proxy can multiply spend.
Fail-open behavior preserves availability but can violate a hard budget. Fail-closed behavior preserves the control boundary but interrupts traffic. Halvr treats exhausted budgets as explicit 402 responses and provider failures as upstream errors so callers can choose a product-appropriate fallback.
Evaluate a proxy with production-shaped traffic.
Test streaming, large contexts, tool calls, provider errors, cache hits, custom metadata, and an exhausted budget. Compare p50 and p95 proxy overhead, usage accuracy, retry behavior, and the clarity of audit records.
- Confirm the client SDK receives streaming chunks without buffering regressions.
- Verify provider and project secrets never appear in logs or browser bundles.
- Attempt private and redirecting custom endpoints to validate SSRF controls.
- Compare provider usage with recorded tokens and calculated cost.
Try Halvr
Route a real request through Halvr.
Keep your current SDK. Change the base URL, attach customer and feature metadata, and set a spend limit.