diff --git a/src/api/routes/admin/model-providers.ts b/src/api/routes/admin/model-providers.ts
index 66a2e0987..7ae287e95 100644
--- a/src/api/routes/admin/model-providers.ts
+++ b/src/api/routes/admin/model-providers.ts
@@ -1,24 +1,34 @@
-import { isModelProvider, type ModelProvider } from "../../../model/pi-models.ts";
+import { isModelProvider, providerBaseUrl, type ModelProvider } from "../../../model/pi-models.ts";
 import { selectableModelCatalog } from "../../../model/model-catalog.ts";
 import { sendJson } from "../../http.ts";
 import type { ApiCtx } from "../route.ts";
 import { audit, authorizeAdmin, orgScope } from "../shared.ts";
 
-const VALIDATION_REQUESTS: Record<ModelProvider, { url: string; headers: (apiKey: string) => Record<string, string> }> =
-  {
-    anthropic: {
-      url: "https://api.anthropic.com/v1/models",
-      headers: (apiKey) => ({ "x-api-key": apiKey, "anthropic-version": "2023-06-01" }),
-    },
-    openai: {
-      url: "https://api.openai.com/v1/models",
-      headers: (apiKey) => ({ authorization: `Bearer ${apiKey}` }),
-    },
-    openrouter: {
-      url: "https://openrouter.ai/api/v1/key",
-      headers: (apiKey) => ({ authorization: `Bearer ${apiKey}` }),
-    },
-  };
+const VALIDATION_REQUESTS: Record<
+  ModelProvider,
+  { baseUrl: string; path: string; headers: (apiKey: string) => Record<string, string> }
+> = {
+  anthropic: {
+    baseUrl: "https://api.anthropic.com",
+    path: "/v1/models",
+    headers: (apiKey) => ({ "x-api-key": apiKey, "anthropic-version": "2023-06-01" }),
+  },
+  openai: {
+    baseUrl: "https://api.openai.com/v1",
+    path: "/models",
+    headers: (apiKey) => ({ authorization: `Bearer ${apiKey}` }),
+  },
+  openrouter: {
+    baseUrl: "https://openrouter.ai/api/v1",
+    path: "/key",
+    headers: (apiKey) => ({ authorization: `Bearer ${apiKey}` }),
+  },
+};
+
+function validationUrl(provider: ModelProvider): string {
+  const request = VALIDATION_REQUESTS[provider];
+  return `${providerBaseUrl(provider) ?? request.baseUrl}${request.path}`;
+}
 
 async function actor(ctx: ApiCtx) {
   const scope = orgScope(ctx.deps);
@@ -26,10 +36,9 @@ async function actor(ctx: ApiCtx) {
 }
 
 async function validate(ctx: ApiCtx, provider: ModelProvider, apiKey: string): Promise<boolean> {
-  const request = VALIDATION_REQUESTS[provider];
   try {
-    const response = await (ctx.deps.modelCredentialFetch ?? fetch)(request.url, {
-      headers: request.headers(apiKey),
+    const response = await (ctx.deps.modelCredentialFetch ?? fetch)(validationUrl(provider), {
+      headers: VALIDATION_REQUESTS[provider].headers(apiKey),
       signal: AbortSignal.timeout(5_000),
     });
     return response.ok;
diff --git a/src/config.ts b/src/config.ts
index 534134b09..6d7eacba3 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -49,6 +49,7 @@ export interface Config {
   anthropicApiKey?: string;
   openaiApiKey?: string;
   openrouterApiKey?: string;
+  providerBaseUrls: Partial<Record<ModelProvider, string>>;
   modelProvider?: ModelProvider;
   piCaptureRequests: boolean;
   piSystemCacheSplit: boolean;
@@ -375,6 +376,21 @@ export function orgId(): string {
   return process.env.ORG_ID ?? DEFAULT_ORG_ID;
 }
 
+const PROVIDER_BASE_URL_ENV: Record<ModelProvider, string> = {
+  anthropic: "ANTHROPIC_BASE_URL",
+  openai: "OPENAI_BASE_URL",
+  openrouter: "OPENROUTER_BASE_URL",
+};
+
+export function providerBaseUrlsFromEnv(env: NodeJS.ProcessEnv): Partial<Record<ModelProvider, string>> {
+  const urls: Partial<Record<ModelProvider, string>> = {};
+  for (const provider of MODEL_PROVIDERS) {
+    const configured = env[PROVIDER_BASE_URL_ENV[provider]]?.trim().replace(/\/+$/, "");
+    if (configured) urls[provider] = configured;
+  }
+  return urls;
+}
+
 export function orgScope(): string {
   return `org:${orgId()}`;
 }
@@ -727,6 +743,7 @@ export function loadConfig(env: NodeJS.ProcessEnv = process.env): Config {
     ...(env.ANTHROPIC_API_KEY ? { anthropicApiKey: env.ANTHROPIC_API_KEY } : {}),
     ...(env.OPENAI_API_KEY ? { openaiApiKey: env.OPENAI_API_KEY } : {}),
     ...(env.OPENROUTER_API_KEY ? { openrouterApiKey: env.OPENROUTER_API_KEY } : {}),
+    providerBaseUrls: providerBaseUrlsFromEnv(env),
     ...(modelProvider ? { modelProvider } : {}),
     ...(env.ADMIN_GRANTS ? { adminGrants: env.ADMIN_GRANTS } : {}),
     piCaptureRequests: boolEnvStrict("PI_CAPTURE_REQUESTS", env.PI_CAPTURE_REQUESTS) ?? true,
diff --git a/src/model/pi-models.ts b/src/model/pi-models.ts
index a57462ef8..c14ac34e8 100644
--- a/src/model/pi-models.ts
+++ b/src/model/pi-models.ts
@@ -20,6 +20,16 @@ export function isHarnessId(value: unknown): value is HarnessId {
   return typeof value === "string" && (HARNESS_IDS as readonly string[]).includes(value);
 }
 
+let configuredBaseUrls: Partial<Record<ModelProvider, string>> = {};
+
+export function setProviderBaseUrls(urls: Partial<Record<ModelProvider, string>>): void {
+  configuredBaseUrls = { ...urls };
+}
+
+export function providerBaseUrl(provider: ModelProvider): string | undefined {
+  return configuredBaseUrls[provider];
+}
+
 type PiModel = Model<Api>;
 
 interface ModelEntry {
@@ -103,10 +113,15 @@ export const SELECTABLE_BASE_MODELS: ReadonlyArray<{ id: string; name: string }>
   (m) => m.base,
 ).map((m) => ({ id: m.id, name: m.name }));
 
+function atConfiguredBaseUrl(model: PiModel): PiModel {
+  const baseUrl = configuredBaseUrls[model.provider as ModelProvider];
+  return baseUrl && baseUrl !== model.baseUrl ? { ...model, baseUrl } : model;
+}
+
 function builtinModel(id: string): PiModel | undefined {
   for (const provider of MODEL_PROVIDERS) {
     const m = getModel(provider, id);
-    if (m) return m;
+    if (m) return atConfiguredBaseUrl(m);
   }
   return undefined;
 }
diff --git a/src/wiring.ts b/src/wiring.ts
index 684365420..1936458fb 100644
--- a/src/wiring.ts
+++ b/src/wiring.ts
@@ -238,6 +238,7 @@ import {
   defaultModelForHarness,
   modelProviderAvailabilityFor,
   type HarnessId,
+  setProviderBaseUrls,
 } from "./model/pi-models.ts";
 import { createAdminService, bootAdminGrantSeed, type AdminService } from "./admin/admin-service.ts";
 import { createAdminGrantStore, createMapAdminGrantPersistence, type AdminGrant } from "./admin/admin-grant-store.ts";
@@ -369,6 +370,7 @@ export function buildApp(
     modelCredentialFetch?: typeof fetch;
   } = {},
 ): BuiltApp {
+  setProviderBaseUrls(config.providerBaseUrls);
   if (config.databaseUrl && !config.connectorSecretKey) {
     throw new Error("CONNECTOR_SECRET_KEY is required with durable storage");
   }
diff --git a/test/config.test.ts b/test/config.test.ts
index ee5ba307f..5712fbf07 100644
--- a/test/config.test.ts
+++ b/test/config.test.ts
@@ -409,3 +409,15 @@ test("baseModelProviders constrains the base model only when a provider is decla
     "with no declaration the shipped default stands, so upgrading never moves a deployment's model or its billing",
   );
 });
+
+test("provider base urls are read from env and normalized", () => {
+  assert.deepEqual(loadConfig({}).providerBaseUrls, {});
+  assert.deepEqual(
+    loadConfig({
+      ANTHROPIC_BASE_URL: "https://gateway.example.com/",
+      OPENAI_BASE_URL: "  https://oai.example.com/v1//  ",
+    }).providerBaseUrls,
+    { anthropic: "https://gateway.example.com", openai: "https://oai.example.com/v1" },
+  );
+  assert.deepEqual(loadConfig({ OPENROUTER_BASE_URL: "   " }).providerBaseUrls, {});
+});
diff --git a/test/pi-models.test.ts b/test/pi-models.test.ts
index 5b03e44bc..6492604d1 100644
--- a/test/pi-models.test.ts
+++ b/test/pi-models.test.ts
@@ -13,6 +13,7 @@ import {
   MODEL_PROVIDERS,
   SELECTABLE_BASE_MODELS,
   contextTokenBudgetForModel,
+  setProviderBaseUrls,
 } from "../src/model/pi-models.ts";
 
 test("every selectable base model resolves against the pi-ai registry", () => {
@@ -175,3 +176,31 @@ test("context token budget is half of each model's real input room", () => {
     assert.ok(budget !== undefined && budget >= 60_000, `${m.id} budget ${budget} suspiciously small`);
   }
 });
+
+test("a configured provider base url replaces the vendor endpoint, including for cloned models", () => {
+  const gateway = "https://gateway.example.com";
+  try {
+    assert.equal(getRequiredModel("claude-opus-4-8").baseUrl, "https://api.anthropic.com");
+    assert.equal(getRequiredModel("claude-opus-5").baseUrl, "https://api.anthropic.com");
+
+    setProviderBaseUrls({ anthropic: gateway });
+
+    assert.equal(getRequiredModel("claude-opus-4-8").baseUrl, gateway, "direct builtin follows the gateway");
+    assert.equal(getRequiredModel("claude-opus-5").baseUrl, gateway, "cloned model inherits the gateway");
+    assert.equal(getRequiredModel("claude-opus-5").id, "claude-opus-5", "the clone keeps its own id");
+    assert.ok(getRequiredModel("gpt-5.6-sol").baseUrl?.startsWith("https://api.openai.com"), "openai untouched");
+  } finally {
+    setProviderBaseUrls({});
+  }
+  assert.equal(getRequiredModel("claude-opus-5").baseUrl, "https://api.anthropic.com", "clearing restores the vendor");
+});
+
+test("each provider is redirected independently", () => {
+  try {
+    setProviderBaseUrls({ openai: "https://oai.example.com/v1" });
+    assert.equal(getRequiredModel("gpt-5.6-sol").baseUrl, "https://oai.example.com/v1");
+    assert.equal(getRequiredModel("claude-opus-5").baseUrl, "https://api.anthropic.com");
+  } finally {
+    setProviderBaseUrls({});
+  }
+});