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What the agentgateway data plane actually does today, stated precisely, because two of its behaviors are easy to overclaim: the external-provider egress path (implemented) and the warm fallback to an alternative gateway (documented, not built). This page separates them so the difference is explicit.
Operating the gateway: Inference gateway.

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Egress to external providers like Anthropic, OpenAI etc

All model traffic, local and external, exits through one governed data plane. External commercial APIs are not attached at LiteLLM; they route through agentgateway in its normalizing-egress role. This path is feature-gated (features.egress, default off): the egress group carries an anthropic-api-key ExternalSecret that needs a real provider key, so a default fork stays clean and needs no Anthropic account. Enable it with features.egress: true (then make resolve-groups) once the key is in the secret backend; the claude-haiku LiteLLM alias only routes when it is on. What is actually deployed when enabled: one AgentgatewayBackend for Anthropic (claude-haiku-4-5) plus an HTTPRoute that matches it by X-Gateway-Base-Model-Name (routing/gateway-api-inference/egress/). On that path agentgateway takes an OpenAI /v1/chat/completions request, translates it to the Anthropic /v1/messages shape, and normalizes the reply back to OpenAI form including a usage object, so LiteLLM keeps metering spend (usage x its pricing table). The upstream provider key lives in the data plane (synced by External Secrets); LiteLLM never holds it. Two roles, kept honest:
  • Inference-aware router for self-hosted vLLM (GIE InferencePool / EPP, KV-cache and queue aware). Local only.
  • Normalizing-egress proxy for external SaaS (the AIProvider path). External SaaS has no KV-cache or queue to observe, so it deliberately does not go through an InferencePool. GIE routing does not apply to a SaaS endpoint, and the platform does not claim otherwise.
Scope of what ships: one provider backend (Anthropic) as the worked example. Adding OpenAI, Gemini, or Bedrock is another AgentgatewayBackend of the same shape, not new machinery. It is an extensible pattern with one concrete instance, not a multi-provider catalog.

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MCP gateway

The governed MCP tool plane is an optional, off-by-default capability group. The split is deliberate: the gateway (auth, rate-limit, trace over tool access) is platform substrate; the MCP server behind it is a swappable example, not a core deliverable.

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Warm fallback (documented, not implemented)

This needs the plainest possible statement: there is no warm fallback in the deployment. It is a design note, not a runtime feature. The reasoning is sound and recorded: the standard agentgateway implements (Gateway API Inference Extension) is GA, so the data plane is swappable in principle. The note recommends keeping Envoy Gateway, kgateway, or GKE Gateway as a documented escape hatch so a fork is never locked into a single implementation (see the roadmap entry). What is not present today:
  • No alternative gateway is deployed. The repo ships agentgateway only; there are zero Envoy Gateway, kgateway, or GKE Gateway manifests.
  • There is no dual-path, no automated failover, and no health-triggered switchover. “Warm” overstates it: nothing is kept warm.
  • There is no migration runbook for switching data planes.
The honest description is: the routing layer targets a GA, portable standard, so swapping the proxy is feasible; the fallback itself is unbuilt. It is a deferred item with a trigger (before depending on agentgateway in a production posture), not a control in place.

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The principle

The egress path and the MCP gateway are real and exercised; their limits (one example provider, one example MCP server, tracing pending a backend, JWT shape pending live validation) are stated rather than glossed. The warm fallback is a portability claim about the standard, not a feature of the deployment, and is labeled as such. Treating “the standard is swappable” as if it were “a fallback is wired” would be the overclaim this page exists to prevent.