The tiered inference gateway — local-first AI routing

A tiered inference gateway routes every AI request through a hierarchy of compute tiers, selecting the least expensive capable tier for each request. Routine work runs on hardware the organization owns. Burst capacity on rented GPU handles work that exceeds local capability. An external commercial API provides a final fallback. Each tier degrades gracefully to the one below it; no tier is a single point of failure.

Why local-first matters

Routing all inference to an external service is simple to operate but has structural costs. Every request crosses an organizational boundary, exposing the content of prompts and responses to a third-party provider. Cost is proportional to usage with no amortization. The organization has no way to adapt the model to its own vocabulary, processes, or accumulated knowledge.

A local-first gateway eliminates these costs for the majority of work. The local model handles requests that fall within its capability. External resources handle what it cannot. Over time, the local model improves through usage-derived training, narrowing the set of requests that require external compute.

The three tiers

Tier A — local inference

Tier A is an inference server running on the organization's own hardware. It is always running, produces responses in seconds, and costs nothing per request beyond the amortized hardware. It is the default destination for all requests.

The local model is purpose-trained or fine-tuned for the organization's domain. It is smaller and faster than models at higher tiers. It answers the majority of routine requests competently: summarization, classification, entity extraction from known document types, code generation in known patterns.

Tier A does not handle grammar-constrained structured output well at small model sizes. Requests requiring precise JSON schema enforcement are routed to Tier B.

Tier B — burst GPU node

Tier B is one or more remote inference nodes running a larger, more capable model on dedicated GPU hardware. Nodes start on demand and stop when idle, so the cost is proportional to actual use rather than availability.

The gateway maintains a per-node circuit breaker and a VM lifecycle state machine. When a Tier B request arrives and the target node is stopped, the gateway starts it automatically. The caller receives a 202 Accepted response with a polling endpoint while the node boots. Once the node is ready, the request is served.

When the node is running, requests are dispatched immediately. When the circuit breaker opens — after consecutive health probe failures — requests fall back to Tier A or queue until the node recovers.

Tier B nodes are organized by label. A batch label handles background work: corpus extraction, training data processing, scheduled maintenance. An express label handles time-sensitive work that cannot wait for a cold start.

Tier C — external inference provider

Tier C is an optional connection to a commercial language model API. It serves as a final fallback when both Tier A and Tier B are unavailable, and as a direct route for tasks the organization has explicitly designated as external.

Tier C is never used as a source of training data. An organization that routes inference to an external provider and then fine-tunes on those responses is building a dependency on a third party's output quality and terms of service. The boundary is enforced in the gateway's routing logic.

Tier C requires an explicit API key to activate. Without the key, requests that reach Tier C fall back to Tier A.

Request routing

Every request carries a complexity hint and, optionally, a tier label. The gateway selects the tier using this decision sequence:

1. If a kill switch is closed for the requested tier, the request is rejected or falls to the next tier depending on configuration.
2. If an explicit tier label is present, the request is routed to that tier.
3. If no label is present, the routing policy applies:
   • balanced: low and medium complexity → Tier A; high complexity → Tier B.
   • drain-batch: all non-express work routes to the batch node.
   • drain-express: all work routes to the express node to clear a backlog.
   • local-only: all work routes to Tier A regardless of complexity.
4. If the selected tier is unavailable, the request falls to the next tier unless tier affinity is required (for example, structured extraction requires Tier B and does not fall back to Tier A).

The routing policy is configurable at runtime without restarting the gateway:

POST /v1/flow/policy  { "policy": "balanced" }

The kill switch

Every tier has an independent kill switch. Closing a kill switch stops all new dispatching to that tier immediately. In-flight requests complete; no new requests start. Queued work accumulates and drains when the kill switch is reopened.

The kill switch is the operator's billing control. Closing the express node switch stops the A100 from starting; the cost drops to zero. Closing the global switch stops all Tier B and Tier C spending while allowing Tier A to continue serving.

The express lane — which bypasses the file-backed queue for time-sensitive work — still checks the kill switch. Nothing bypasses the kill switch.

The priority queue

Background work — apprenticeship briefs, corpus extraction, training corpus generation — is processed through a file-backed priority queue with three levels:

• P0 routes exclusively to the local model for lightweight classification.
• P1 routes to the batch GPU node for extraction work requiring structured output.
• P2 routes to the batch GPU node for training corpus generation and similar long-running background tasks.

The queue drain worker processes one item from each level per cycle, in P0 → P1 → P2 order, then repeats. This prevents a large batch of P2 work from blocking P1 extraction tasks for an extended period.

Organizational memory context

Before dispatching any request to any tier, the gateway queries the organizational knowledge graph for entities relevant to the current request. Matching entities are injected into the system prompt as structured context. The model sees the organization's known relationships, decisions, and policies without those facts needing to be re-derived from inference.

This context injection is non-fatal: if the graph service is unavailable, the request proceeds without context. A circuit breaker on the graph query path prevents a slow graph service from blocking inference.

The MCP server

The gateway exposes an organizational memory interface via the Model Context Protocol at a second port. Any MCP-capable AI client can connect to this interface using its built-in subscription — no separate API key is required. The client's reasoning capability combines with the gateway's organizational knowledge graph to produce responses that are grounded in the organization's actual data.

This is the primary path for interactive use by operators who already have a subscription to an MCP-capable client. The gateway handles memory; the client handles reasoning.