diff --git a/docs/features/nexus-model-routing.md b/docs/features/nexus-model-routing.md
index deb46619a..dfd804ce5 100644
--- a/docs/features/nexus-model-routing.md
+++ b/docs/features/nexus-model-routing.md
@@ -8,7 +8,7 @@ Nexus defaults to **Standard** mode. Users see one Nexus experience instead of a
 2. Apply the existing K-12 input guardrail before classifier traffic without rewriting allowed request text.
 3. Apply deterministic capability rules for image generation, PSD-data, web search/current information, and common instructional requests.
 4. Send ambiguous requests to Amazon Nova Micro on Bedrock for a provider-neutral `intent`, `tier`, `confidence`, and reason codes.
-5. Resolve an accessible, active Nexus model from the configured ordered candidates. If none is configured, use `providerMetadata.nexusRouterTier` or model-name conventions. If no tier match is available, use the closest tier in the requested family. Auto may finally use the existing client model as a safe fallback; an explicit Advanced family never silently crosses into another family.
+5. Resolve an accessible, active Nexus model from the configured ordered candidates. Models whose provider credentials are not configured (checked through the settings manager with environment fallback; Bedrock always counts as configured because it can use the ambient AWS credential chain) are excluded from routed selection, so routing never picks a model whose provider creation would fail at stream time. If none is configured, use `providerMetadata.nexusRouterTier` or model-name conventions. If no tier match is available, use the closest tier in the requested family. Auto may finally use the existing client model as a safe fallback — an explicitly selected client model keeps its honest provider-configuration error rather than being silently rerouted; an explicit Advanced family never silently crosses into another family.
 6. Automatically select an image-capable model for image intent, attach the existing database-backed PSD-data MCP server for PSD-data intent, or select a web-search-capable Gemini model and enable its native Google Search tool for web-search intent.
 7. Persist the route decision on assistant-message metadata and expose it in `X-Nexus-Routing` for evaluation.
 
diff --git a/lib/ai/__tests__/provider-credentials.test.ts b/lib/ai/__tests__/provider-credentials.test.ts
new file mode 100644
index 000000000..6d132fd38
--- /dev/null
+++ b/lib/ai/__tests__/provider-credentials.test.ts
@@ -0,0 +1,62 @@
+/** @jest-environment node */
+
+const mockGetOpenAI = jest.fn()
+const mockGetGoogleAI = jest.fn()
+const mockGetAzureOpenAI = jest.fn()
+const mockGetLatimer = jest.fn()
+
+jest.mock("@/lib/settings-manager", () => ({
+  Settings: {
+    getOpenAI: () => mockGetOpenAI(),
+    getGoogleAI: () => mockGetGoogleAI(),
+    getAzureOpenAI: () => mockGetAzureOpenAI(),
+    getLatimer: () => mockGetLatimer(),
+  },
+}))
+jest.mock("@/lib/logger", () => ({
+  createLogger: () => ({ info: jest.fn(), warn: jest.fn(), error: jest.fn(), debug: jest.fn() }),
+}))
+
+import { getConfiguredChatProviders } from "../provider-credentials"
+
+describe("getConfiguredChatProviders", () => {
+  beforeEach(() => {
+    jest.clearAllMocks()
+    mockGetOpenAI.mockResolvedValue(null)
+    mockGetGoogleAI.mockResolvedValue(null)
+    mockGetAzureOpenAI.mockResolvedValue({ key: null, endpoint: null, resourceName: null })
+    mockGetLatimer.mockResolvedValue(null)
+  })
+
+  it("always includes amazon-bedrock even with no keys configured", async () => {
+    const configured = await getConfiguredChatProviders()
+    expect(configured).toEqual(new Set(["amazon-bedrock"]))
+  })
+
+  it("includes every provider whose credential is present", async () => {
+    mockGetOpenAI.mockResolvedValue("sk-test")
+    mockGetGoogleAI.mockResolvedValue("google-key")
+    mockGetAzureOpenAI.mockResolvedValue({ key: "azure-key", endpoint: null, resourceName: "resource" })
+    mockGetLatimer.mockResolvedValue("latimer-key")
+    const configured = await getConfiguredChatProviders()
+    expect(configured).toEqual(new Set(["openai", "google", "amazon-bedrock", "azure", "latimer"]))
+  })
+
+  it("treats whitespace-only keys as not configured", async () => {
+    mockGetOpenAI.mockResolvedValue("   ")
+    const configured = await getConfiguredChatProviders()
+    expect(configured.has("openai")).toBe(false)
+  })
+
+  it("requires both the Azure key and resource name", async () => {
+    mockGetAzureOpenAI.mockResolvedValue({ key: "azure-key", endpoint: null, resourceName: null })
+    const configured = await getConfiguredChatProviders()
+    expect(configured.has("azure")).toBe(false)
+  })
+
+  it("fails open when the credential probe throws", async () => {
+    mockGetOpenAI.mockRejectedValue(new Error("settings unavailable"))
+    const configured = await getConfiguredChatProviders()
+    expect(configured).toEqual(new Set(["openai", "google", "amazon-bedrock", "azure", "latimer"]))
+  })
+})
diff --git a/lib/ai/provider-credentials.ts b/lib/ai/provider-credentials.ts
new file mode 100644
index 000000000..14172715f
--- /dev/null
+++ b/lib/ai/provider-credentials.ts
@@ -0,0 +1,39 @@
+import { Settings } from "@/lib/settings-manager"
+import { createLogger } from "@/lib/logger"
+
+const log = createLogger({ module: "provider-credentials" })
+
+const ALL_CHAT_PROVIDERS = ["openai", "google", "amazon-bedrock", "azure", "latimer"] as const
+
+/**
+ * Returns the lowercase provider identifiers whose credentials are configured
+ * (database settings with environment fallback, cached by the settings
+ * manager), so routing can skip models that would fail provider creation.
+ *
+ * amazon-bedrock is always included: it can authenticate through the default
+ * AWS credential chain (ECS/Lambda IAM roles), which cannot be probed here.
+ *
+ * Fails open — a probe failure must not take chat down, so every provider is
+ * treated as configured and a missing key surfaces at stream time as before.
+ */
+export async function getConfiguredChatProviders(): Promise<Set<string>> {
+  try {
+    const [openAiKey, googleKey, azure, latimerKey] = await Promise.all([
+      Settings.getOpenAI(),
+      Settings.getGoogleAI(),
+      Settings.getAzureOpenAI(),
+      Settings.getLatimer(),
+    ])
+    const configured = new Set<string>(["amazon-bedrock"])
+    if (openAiKey?.trim()) configured.add("openai")
+    if (googleKey?.trim()) configured.add("google")
+    if (azure.key?.trim() && azure.resourceName?.trim()) configured.add("azure")
+    if (latimerKey?.trim()) configured.add("latimer")
+    return configured
+  } catch (error) {
+    log.warn("Provider credential probe failed; treating every provider as configured", {
+      error: error instanceof Error ? error.message : String(error),
+    })
+    return new Set(ALL_CHAT_PROVIDERS)
+  }
+}
diff --git a/lib/nexus/model-router/__tests__/router.test.ts b/lib/nexus/model-router/__tests__/router.test.ts
index 6356e0ae9..699b27b23 100644
--- a/lib/nexus/model-router/__tests__/router.test.ts
+++ b/lib/nexus/model-router/__tests__/router.test.ts
@@ -5,8 +5,12 @@ const mockFilterAccessibleResourceIds = jest.fn()
 const mockGetConfig = jest.fn()
 const mockClassify = jest.fn()
 const mockExecuteQuery = jest.fn()
+const mockGetConfiguredChatProviders = jest.fn()
 
 jest.mock("@/lib/db/drizzle", () => ({ getNexusEnabledModels: () => mockGetNexusEnabledModels() }))
+jest.mock("@/lib/ai/provider-credentials", () => ({
+  getConfiguredChatProviders: () => mockGetConfiguredChatProviders(),
+}))
 jest.mock("@/lib/db/drizzle/resource-access", () => ({
   filterAccessibleResourceIds: (...args: unknown[]) => mockFilterAccessibleResourceIds(...args),
 }))
@@ -51,6 +55,9 @@ function defineNexusModelRouterSuite1Part1() {
     mockGetNexusEnabledModels.mockResolvedValue(models)
     mockFilterAccessibleResourceIds.mockResolvedValue(models.map(model => String(model.id)))
     mockGetConfig.mockResolvedValue({ config, mode: "active" })
+    mockGetConfiguredChatProviders.mockResolvedValue(
+      new Set(["openai", "google", "amazon-bedrock", "azure", "latimer"])
+    )
     mockClassify.mockResolvedValue({
       intent: "general", tier: "medium", confidence: 0.9,
       reasonCodes: ["normal_request"], source: "classifier",
@@ -343,3 +350,92 @@ const defineNexusModelRouterSuite1 = () => {
 };
 
 describe("Nexus model router", defineNexusModelRouterSuite1)
+
+describe("Nexus model router credential filtering", () => {
+  beforeEach(() => {
+    jest.clearAllMocks()
+    mockGetNexusEnabledModels.mockResolvedValue(models)
+    mockFilterAccessibleResourceIds.mockResolvedValue(models.map(model => String(model.id)))
+    mockGetConfig.mockResolvedValue({ config, mode: "active" })
+    mockClassify.mockResolvedValue({
+      intent: "general", tier: "medium", confidence: 0.9,
+      reasonCodes: ["normal_request"], source: "classifier",
+    })
+  })
+
+  it("routes AUTO past a candidate whose provider credential is not configured", async () => {
+    const autoConfig = nexusRouterConfigSchema.parse({
+      auto: { light: [], medium: ["gpt-terra", "us.anthropic.claude-sonnet"], high: [] },
+    })
+    mockGetConfig.mockResolvedValue({ config: autoConfig, mode: "active" })
+    mockGetConfiguredChatProviders.mockResolvedValue(new Set(["amazon-bedrock", "google"]))
+
+    const result = await routeNexusRequest({
+      text: "Help", fallbackModelId: "gpt-terra", experienceMode: "standard",
+      requestedFamily: "auto", enabledConnectorIds: [], userId: 7,
+    })
+
+    expect(result.modelId).toBe("us.anthropic.claude-sonnet")
+    expect(result.metadata.selectedFamily).toBe("anthropic")
+  })
+
+  it("keeps the explicitly selected model when routing is off, even without its provider key", async () => {
+    mockGetConfig.mockResolvedValue({ config, mode: "off" })
+    mockGetConfiguredChatProviders.mockResolvedValue(new Set(["amazon-bedrock", "google"]))
+
+    const result = await routeNexusRequest({
+      text: "Help", fallbackModelId: "gpt-terra", experienceMode: "standard",
+      requestedFamily: "auto", enabledConnectorIds: [], userId: 7,
+    })
+
+    expect(result.modelId).toBe("gpt-terra")
+  })
+
+  it("fails clearly when the requested Advanced family's provider is not configured", async () => {
+    mockGetConfiguredChatProviders.mockResolvedValue(new Set(["amazon-bedrock", "google"]))
+
+    await expect(routeNexusRequest({
+      text: "Help", fallbackModelId: "us.anthropic.claude-sonnet", experienceMode: "advanced",
+      requestedFamily: "openai", enabledConnectorIds: [], userId: 7,
+    })).rejects.toThrow("openai family")
+  })
+
+  it("re-routes required tools to a configured provider when routing is off and the explicit model's provider is not", async () => {
+    mockGetConfig.mockResolvedValue({ config, mode: "off" })
+    mockGetConfiguredChatProviders.mockResolvedValue(new Set(["amazon-bedrock", "google"]))
+
+    const result = await routeNexusRequest({
+      text: "Summarize my attachment", fallbackModelId: "gpt-terra", experienceMode: "standard",
+      requestedFamily: "auto", enabledConnectorIds: [],
+      enabledToolNames: ["searchNexusAttachments"], userId: 7,
+    })
+
+    expect(result.modelId).toBe("us.anthropic.claude-sonnet")
+    expect(result.metadata.reasonCodes).toContain("required_tools_enforced")
+  })
+
+  it("fails fast before provider creation when no configured provider has an accessible model", async () => {
+    // The explicitly selected model's provider being unconfigured must NOT be
+    // executed as a last resort here — that is the stream-time missing-key 500
+    // this filter exists to prevent. Exhaustion fails fast with a clear error.
+    mockGetConfiguredChatProviders.mockResolvedValue(new Set(["azure"]))
+
+    await expect(routeNexusRequest({
+      text: "Help", fallbackModelId: "gpt-terra", experienceMode: "standard",
+      requestedFamily: "auto", enabledConnectorIds: [], userId: 7,
+    })).rejects.toThrow("No accessible Nexus model is available")
+  })
+
+  it("does not offer image generation through an unconfigured provider", async () => {
+    mockClassify.mockResolvedValue({
+      intent: "image", tier: "medium", confidence: 0.99,
+      reasonCodes: ["explicit_image_request"], source: "deterministic",
+    })
+    mockGetConfiguredChatProviders.mockResolvedValue(new Set(["amazon-bedrock", "openai"]))
+
+    await expect(routeNexusRequest({
+      text: "Create an image", fallbackModelId: "gpt-terra", experienceMode: "standard",
+      requestedFamily: "auto", enabledConnectorIds: [], userId: 7,
+    })).rejects.toThrow("Image generation is not available")
+  })
+})
diff --git a/lib/nexus/model-router/router.ts b/lib/nexus/model-router/router.ts
index 1b1a267d3..e91da9c4a 100644
--- a/lib/nexus/model-router/router.ts
+++ b/lib/nexus/model-router/router.ts
@@ -5,6 +5,7 @@ import { nexusMcpServers } from "@/lib/db/schema"
 import { filterAccessibleResourceIds } from "@/lib/db/drizzle/resource-access"
 import { createLogger } from "@/lib/logger"
 import { hasCapability } from "@/lib/ai/capability-utils"
+import { getConfiguredChatProviders } from "@/lib/ai/provider-credentials"
 import {
   inferModelFamily,
   inferModelTier,
@@ -422,17 +423,37 @@ export async function routeNexusRequest(
     "model",
     models.map(model => model.id)
   ))
+  // The fallback (the model the client explicitly selected) is looked up in
+  // the unfiltered list on purpose: an explicit selection keeps its honest
+  // provider-configuration error instead of being silently rerouted.
   const fallback = models.find(model =>
     model.modelId === args.fallbackModelId
     || String(model.id) === args.fallbackModelId
   )
   if (!fallback) throw new Error("The fallback Nexus model is unavailable")
+  // Routed selection must never pick a model whose provider credential is not
+  // configured — provider creation would throw at stream time and fail the
+  // whole request, which the router's fallback cannot catch.
+  const configuredProviders = await getConfiguredChatProviders()
+  const routableModels = models.filter(model =>
+    configuredProviders.has(model.provider.toLowerCase())
+  )
+  if (routableModels.length < models.length) {
+    const excludedProviders = [...new Set(
+      models
+        .filter(model => !configuredProviders.has(model.provider.toLowerCase()))
+        .map(model => model.provider)
+    )]
+    log.info("Excluding models from routing; provider credentials not configured", {
+      excludedProviders,
+    })
+  }
   const requiredTools = [...new Set(args.enabledToolNames ?? [])]
   if (mode === "off") {
     return buildRouterOffResult({
       args,
       config,
-      models,
+      models: routableModels,
       fallback,
       accessibleIds,
       requiredTools,
@@ -442,7 +463,7 @@ export async function routeNexusRequest(
     args,
     config,
     mode,
-    models,
+    models: routableModels,
     fallback,
     accessibleIds,
     requiredTools,