diff --git a/.gittensory.yml.example b/.gittensory.yml.example
index 51c61614ea..2cb246b6dc 100644
--- a/.gittensory.yml.example
+++ b/.gittensory.yml.example
@@ -899,7 +899,8 @@ settings:
   #   e2eTestGen: false    # Auto-generated E2E test scaffolding. Default: false.
   #   planner: false       # The @gittensory plan / issue-planner completion. Default: false.
   #   summaries: false     # AI summaries/rewrite text. Default: false.
-  #   chatQa: false        # @gittensory chat <question> grounded LLM Q&A. Ollama-ONLY (never the frontier env.AI); needs env.AI_ADVISORY set. Co-requisite: commandRateLimitPolicy: hold (defaults off). Default: false.
+  #   chatQa: false        # @gittensory chat <question> grounded LLM Q&A. Ollama-first (never the frontier env.AI unless chatQaFrontierFallback below is also true); needs env.AI_ADVISORY set. Co-requisite: commandRateLimitPolicy: hold (defaults off). Default: false.
+  #   chatQaFrontierFallback: false  # Opt-in only: falls back to the frontier env.AI chain if env.AI_ADVISORY is unconfigured, instead of declining. Meaningless unless chatQa is also true. Default: false.
 
 # Maintainer AI review tuning (`.gittensory.yml` top-level `review:` block). These knobs shape the advisory AI
 # review prompt and file selection only — gate/slop/secret-scan are unaffected.
diff --git a/apps/gittensory-ui/public/openapi.json b/apps/gittensory-ui/public/openapi.json
index d7e1d7a103..d1b00c33d2 100644
--- a/apps/gittensory-ui/public/openapi.json
+++ b/apps/gittensory-ui/public/openapi.json
@@ -9170,7 +9170,11 @@
               },
               "chatQa": {
                 "type": "boolean",
-                "description": "Opt the `@gittensory chat <question>` grounded Q&A surface (#4595) into local Ollama inference. Ollama-only: unlike the four capabilities above it NEVER falls back to the frontier env.AI when off; it declines unless this is true AND env.AI_ADVISORY is configured. Co-requisite: set `commandRateLimitPolicy` to `hold` (it defaults to `off` fleet-wide) so the tighter `commandRateLimitAiMaxPerWindow` ceiling actually throttles this cost-bearing command."
+                "description": "Opt the `@gittensory chat <question>` grounded Q&A surface (#4595) into local Ollama inference. Ollama-first: unlike the four capabilities above, it declines instead of falling back to the frontier env.AI when env.AI_ADVISORY is unconfigured, unless `chatQaFrontierFallback` is also enabled. Co-requisite: set `commandRateLimitPolicy` to `hold` (it defaults to `off` fleet-wide) so the tighter `commandRateLimitAiMaxPerWindow` ceiling actually throttles this cost-bearing command."
+              },
+              "chatQaFrontierFallback": {
+                "type": "boolean",
+                "description": "Opt-in only (#4595 follow-up): when true, `@gittensory chat` falls back to the shared frontier env.AI chain if env.AI_ADVISORY is unconfigured, instead of declining. Meaningless unless `chatQa` is also true. Default false -- a self-hoster without a local GPU may enable this to use their own frontier subscription/tokens for chat instead."
               }
             },
             "required": [
@@ -9178,7 +9182,8 @@
               "e2eTestGen",
               "planner",
               "summaries",
-              "chatQa"
+              "chatQa",
+              "chatQaFrontierFallback"
             ]
           },
           "gittensorLabel": {
diff --git a/config/examples/gittensory.full.yml b/config/examples/gittensory.full.yml
index b749475499..53ac17db39 100644
--- a/config/examples/gittensory.full.yml
+++ b/config/examples/gittensory.full.yml
@@ -912,7 +912,8 @@ settings:
   #   e2eTestGen: false    # Auto-generated E2E test scaffolding. Default: false.
   #   planner: false       # The @gittensory plan / issue-planner completion. Default: false.
   #   summaries: false     # AI summaries/rewrite text. Default: false.
-  #   chatQa: false        # @gittensory chat <question> grounded LLM Q&A. Ollama-ONLY (never the frontier env.AI); needs env.AI_ADVISORY set. Co-requisite: commandRateLimitPolicy: hold (defaults off). Default: false.
+  #   chatQa: false        # @gittensory chat <question> grounded LLM Q&A. Ollama-first (never the frontier env.AI unless chatQaFrontierFallback below is also true); needs env.AI_ADVISORY set. Co-requisite: commandRateLimitPolicy: hold (defaults off). Default: false.
+  #   chatQaFrontierFallback: false  # Opt-in only: falls back to the frontier env.AI chain if env.AI_ADVISORY is unconfigured, instead of declining. Meaningless unless chatQa is also true. Default: false.
 
 # Maintainer AI review tuning (`.gittensory.yml` top-level `review:` block). These knobs shape the advisory AI
 # review prompt and file selection only — gate/slop/secret-scan are unaffected.
diff --git a/packages/gittensory-engine/src/focus-manifest.ts b/packages/gittensory-engine/src/focus-manifest.ts
index 0b0114d302..8e84564e2f 100644
--- a/packages/gittensory-engine/src/focus-manifest.ts
+++ b/packages/gittensory-engine/src/focus-manifest.ts
@@ -1960,6 +1960,7 @@ function parseSettingsOverride(value: JsonValue | undefined, warnings: string[],
     if (typeof rawRouting.planner === "boolean") sparseRouting.planner = validated.planner;
     if (typeof rawRouting.summaries === "boolean") sparseRouting.summaries = validated.summaries;
     if (typeof rawRouting.chatQa === "boolean") sparseRouting.chatQa = validated.chatQa;
+    if (typeof rawRouting.chatQaFrontierFallback === "boolean") sparseRouting.chatQaFrontierFallback = validated.chatQaFrontierFallback;
     out.advisoryAiRouting = sparseRouting;
   } else if (r.advisoryAiRouting !== undefined) {
     warnings.push(`Manifest "settings.advisoryAiRouting" must be an object; ignoring it and keeping any existing policy.`);
diff --git a/packages/gittensory-engine/src/review/advisory-ai-routing-config.ts b/packages/gittensory-engine/src/review/advisory-ai-routing-config.ts
index 5ea588697f..ed90b1e54e 100644
--- a/packages/gittensory-engine/src/review/advisory-ai-routing-config.ts
+++ b/packages/gittensory-engine/src/review/advisory-ai-routing-config.ts
@@ -6,6 +6,7 @@ export const DEFAULT_ADVISORY_AI_ROUTING: AdvisoryAiRoutingConfig = {
   planner: false,
   summaries: false,
   chatQa: false,
+  chatQaFrontierFallback: false,
 };
 
 function normalizeField(value: unknown, field: keyof AdvisoryAiRoutingConfig, warnings: string[]): boolean {
@@ -33,5 +34,6 @@ export function normalizeAdvisoryAiRoutingConfig(input: unknown, warnings: strin
     planner: normalizeField(record.planner, "planner", warnings),
     summaries: normalizeField(record.summaries, "summaries", warnings),
     chatQa: normalizeField(record.chatQa, "chatQa", warnings),
+    chatQaFrontierFallback: normalizeField(record.chatQaFrontierFallback, "chatQaFrontierFallback", warnings),
   };
 }
diff --git a/packages/gittensory-engine/src/types/manifest-deps-types.ts b/packages/gittensory-engine/src/types/manifest-deps-types.ts
index 7ea7e43318..5b7ade1acd 100644
--- a/packages/gittensory-engine/src/types/manifest-deps-types.ts
+++ b/packages/gittensory-engine/src/types/manifest-deps-types.ts
@@ -112,9 +112,13 @@ export type AdvisoryAiRoutingConfig = {
   e2eTestGen: boolean;
   planner: boolean;
   summaries: boolean;
-  /** Grounded `@gittensory chat <question>` LLM Q&A (#4595). Ollama-only: unlike the four fields above it NEVER
-   *  falls back to the frontier env.AI when off -- it simply declines. Default false. */
+  /** Grounded `@gittensory chat <question>` LLM Q&A (#4595). Ollama-first: declines when off or when
+   *  env.AI_ADVISORY is unconfigured and {@link chatQaFrontierFallback} is not also enabled. Default false. */
   chatQa: boolean;
+  /** Opt-in ONLY (#4595 follow-up): when true, chat falls back to the shared frontier env.AI chain if
+   *  env.AI_ADVISORY is unconfigured, instead of declining. Meaningless unless {@link chatQa} is also true.
+   *  Default false. */
+  chatQaFrontierFallback: boolean;
 };
 
 export type ContributorBlacklistEntry = {
diff --git a/src/openapi/schemas.ts b/src/openapi/schemas.ts
index b6454f1e42..3f31d79c62 100644
--- a/src/openapi/schemas.ts
+++ b/src/openapi/schemas.ts
@@ -762,7 +762,12 @@ export const RepositorySettingsSchema = z
         chatQa: z
           .boolean()
           .describe(
-            "Opt the `@gittensory chat <question>` grounded Q&A surface (#4595) into local Ollama inference. Ollama-only: unlike the four capabilities above it NEVER falls back to the frontier env.AI when off; it declines unless this is true AND env.AI_ADVISORY is configured. Co-requisite: set `commandRateLimitPolicy` to `hold` (it defaults to `off` fleet-wide) so the tighter `commandRateLimitAiMaxPerWindow` ceiling actually throttles this cost-bearing command.",
+            "Opt the `@gittensory chat <question>` grounded Q&A surface (#4595) into local Ollama inference. Ollama-first: unlike the four capabilities above, it declines instead of falling back to the frontier env.AI when env.AI_ADVISORY is unconfigured, unless `chatQaFrontierFallback` is also enabled. Co-requisite: set `commandRateLimitPolicy` to `hold` (it defaults to `off` fleet-wide) so the tighter `commandRateLimitAiMaxPerWindow` ceiling actually throttles this cost-bearing command.",
+          ),
+        chatQaFrontierFallback: z
+          .boolean()
+          .describe(
+            "Opt-in only (#4595 follow-up): when true, `@gittensory chat` falls back to the shared frontier env.AI chain if env.AI_ADVISORY is unconfigured, instead of declining. Meaningless unless `chatQa` is also true. Default false -- a self-hoster without a local GPU may enable this to use their own frontier subscription/tokens for chat instead.",
           ),
       })
       .optional(),
diff --git a/src/review/advisory-ai-routing-config.ts b/src/review/advisory-ai-routing-config.ts
index e6032cbedf..1be773e972 100644
--- a/src/review/advisory-ai-routing-config.ts
+++ b/src/review/advisory-ai-routing-config.ts
@@ -6,6 +6,7 @@ export const DEFAULT_ADVISORY_AI_ROUTING: AdvisoryAiRoutingConfig = {
   planner: false,
   summaries: false,
   chatQa: false,
+  chatQaFrontierFallback: false,
 };
 
 function normalizeField(value: unknown, field: keyof AdvisoryAiRoutingConfig, warnings: string[]): boolean {
@@ -33,5 +34,6 @@ export function normalizeAdvisoryAiRoutingConfig(input: unknown, warnings: strin
     planner: normalizeField(record.planner, "planner", warnings),
     summaries: normalizeField(record.summaries, "summaries", warnings),
     chatQa: normalizeField(record.chatQa, "chatQa", warnings),
+    chatQaFrontierFallback: normalizeField(record.chatQaFrontierFallback, "chatQaFrontierFallback", warnings),
   };
 }
diff --git a/src/services/ai-chat-qa.ts b/src/services/ai-chat-qa.ts
index 67ec63f54f..ad2def9d6b 100644
--- a/src/services/ai-chat-qa.ts
+++ b/src/services/ai-chat-qa.ts
@@ -13,11 +13,12 @@ import type { AgentRunBundle } from "./agent-orchestrator";
 // ALREADY-deterministic decision-pack facts in the bundle (PR verdict, which checks/findings are blocking,
 // what a finding means) into natural prose; it never synthesizes new claims.
 //
-// Ollama-ONLY, by hard requirement (#4595 requirement 5): unlike the four sibling advisoryAiRouting
-// capabilities (slop/e2eTestGen/planner/summaries), which silently fall back to the shared frontier env.AI when
-// their flag is off, this surface NEVER touches the frontier. It declines whenever advisoryAiRouting.chatQa is
-// not true or env.AI_ADVISORY is unconfigured -- it does not call withAdvisoryAiEnv(env, false) and let a
-// frontier token be spent.
+// Ollama-FIRST by default (#4595 requirement 5): unlike the four sibling advisoryAiRouting capabilities
+// (slop/e2eTestGen/planner/summaries), which silently fall back to the shared frontier env.AI whenever their
+// OWN flag is off, this surface declines instead of spending a frontier token when env.AI_ADVISORY is
+// unconfigured -- UNLESS the operator explicitly opts into advisoryAiRouting.chatQaFrontierFallback (a
+// self-hoster without a local GPU may prefer their own frontier subscription over declining outright). Default
+// false preserves the original Ollama-only behavior for every existing deployment.
 
 export type ChatQaResult =
   | { status: "disabled"; reason: string }
@@ -80,14 +81,21 @@ type ChatGroundingBundle = {
 };
 
 export async function generateChatQaAnswer(env: Env, req: ChatQaRequest): Promise<ChatQaResult> {
-  // (#4595 req 5) Ollama-only enablement. BOTH gates are hard declines, never a frontier fallback.
   if (req.advisoryAiRouting?.chatQa !== true) {
     return { status: "disabled", reason: "Chat Q&A is not enabled on this instance (settings.advisoryAiRouting.chatQa is off)." };
   }
-  if (!env.AI_ADVISORY) {
+  // Ollama-first: env.AI_ADVISORY is always preferred. env.AI (frontier) is only ever touched when the
+  // operator has explicitly opted in via advisoryAiRouting.chatQaFrontierFallback (#4595 follow-up) --
+  // otherwise this stays exactly as Ollama-only as it originally shipped.
+  const frontierFallbackAllowed = req.advisoryAiRouting?.chatQaFrontierFallback === true;
+  const ai = env.AI_ADVISORY ?? (frontierFallbackAllowed ? env.AI : undefined);
+  const usedFrontier = !env.AI_ADVISORY && ai !== undefined;
+  if (!ai) {
     return {
       status: "unavailable",
-      reason: "Local advisory inference (env.AI_ADVISORY) is not configured; chat Q&A never falls back to the frontier model.",
+      reason: frontierFallbackAllowed
+        ? "Neither local advisory inference (env.AI_ADVISORY) nor the frontier model (env.AI) is configured."
+        : "Local advisory inference (env.AI_ADVISORY) is not configured; chat Q&A does not fall back to the frontier model unless advisoryAiRouting.chatQaFrontierFallback is enabled.",
     };
   }
 
@@ -134,12 +142,13 @@ export async function generateChatQaAnswer(env: Env, req: ChatQaRequest): Promis
       status: "quota_exceeded",
       estimatedNeurons: 0,
       detail: `estimated ${estimatedNeurons} neurons exceeds remaining budget ${remainingBudget}`,
+      usedFrontier,
     });
     return { status: "quota_exceeded", model, estimatedNeurons, remainingBudget };
   }
 
   try {
-    const response = await env.AI_ADVISORY.run(model, {
+    const response = await ai.run(model, {
       messages: [
         { role: "system", content: CHAT_QA_SYSTEM_PROMPT },
         { role: "user", content: prompt },
@@ -150,14 +159,14 @@ export async function generateChatQaAnswer(env: Env, req: ChatQaRequest): Promis
     const rawText = extractAiText(response);
     if (!rawText) throw new Error("empty_chat_answer");
     if (containsPublicForbiddenText(rawText)) {
-      await recordChatAi(env, req, { model, status: "unsafe", estimatedNeurons, detail: "chat answer failed public sanitizer" });
+      await recordChatAi(env, req, { model, status: "unsafe", estimatedNeurons, detail: "chat answer failed public sanitizer", usedFrontier });
       return { status: "unsafe", model, estimatedNeurons, reason: "chat answer failed public sanitizer" };
     }
-    await recordChatAi(env, req, { model, status: "ok", estimatedNeurons, detail: "chat answer generated" });
+    await recordChatAi(env, req, { model, status: "ok", estimatedNeurons, detail: "chat answer generated", usedFrontier });
     return { status: "ok", model, estimatedNeurons, text: rawText.trim() };
   } catch (error) {
     const reason = error instanceof Error ? error.message : "chat_answer_failed";
-    await recordChatAi(env, req, { model, status: "error", estimatedNeurons: 0, detail: reason });
+    await recordChatAi(env, req, { model, status: "error", estimatedNeurons: 0, detail: reason, usedFrontier });
     return { status: "error", model, estimatedNeurons, reason };
   }
 }
@@ -240,7 +249,7 @@ function auditOutcomeForAiStatus(status: string): "success" | "denied" | "error"
 async function recordChatAi(
   env: Env,
   req: ChatQaRequest,
-  event: { model: string; status: string; estimatedNeurons: number; detail: string },
+  event: { model: string; status: string; estimatedNeurons: number; detail: string; usedFrontier: boolean },
 ): Promise<void> {
   await recordAiUsageEvent(env, {
     feature: "chat_qa",
@@ -250,7 +259,9 @@ async function recordChatAi(
     status: event.status,
     estimatedNeurons: event.estimatedNeurons,
     detail: event.detail,
-    metadata: { repoFullName: req.repoFullName, issueNumber: req.issueNumber },
+    // provider is observability-only: lets an operator who opted into chatQaFrontierFallback see, per event,
+    // whether a given answer actually spent a frontier token or stayed on the (free) local GPU.
+    metadata: { repoFullName: req.repoFullName, issueNumber: req.issueNumber, provider: event.usedFrontier ? "frontier" : "advisory" },
   });
   await recordAuditEvent(env, {
     eventType: "ai.chat_qa",
@@ -258,7 +269,13 @@ async function recordChatAi(
     route: req.route,
     outcome: auditOutcomeForAiStatus(event.status),
     detail: event.detail,
-    metadata: { repoFullName: req.repoFullName, issueNumber: req.issueNumber, model: event.model, estimatedNeurons: event.estimatedNeurons },
+    metadata: {
+      repoFullName: req.repoFullName,
+      issueNumber: req.issueNumber,
+      model: event.model,
+      estimatedNeurons: event.estimatedNeurons,
+      provider: event.usedFrontier ? "frontier" : "advisory",
+    },
   });
 }
 
diff --git a/src/signals/focus-manifest.ts b/src/signals/focus-manifest.ts
index e52c6cd4d2..cf509de45b 100644
--- a/src/signals/focus-manifest.ts
+++ b/src/signals/focus-manifest.ts
@@ -599,6 +599,7 @@ export function resolveEffectiveSettings(
       planner: advisoryAiRoutingOverride.planner ?? base.planner,
       summaries: advisoryAiRoutingOverride.summaries ?? base.summaries,
       chatQa: advisoryAiRoutingOverride.chatQa ?? base.chatQa,
+      chatQaFrontierFallback: advisoryAiRoutingOverride.chatQaFrontierFallback ?? base.chatQaFrontierFallback,
     };
   }
   applyGateConfigOverrides(effective, manifest.gate);
diff --git a/src/types.ts b/src/types.ts
index d9235bc316..541bed4b73 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -1281,18 +1281,25 @@ export type UnlinkedIssueGuardrailConfig = {
  *  settings.advisoryAiRouting` (global default in shared/root config, per-repo override); defaults all-false
  *  so an operator must deliberately opt each capability in.
  *
- *  `chatQa` (#4595) is the ONE capability that does NOT share the others' silent-frontier fallback: the four
- *  cost-optimizing capabilities above quietly fall back to the shared frontier env.AI when their flag is off,
- *  but the `@gittensory chat` grounded Q&A surface is "Ollama only" -- it declines/skips whenever
- *  `chatQa !== true` or `env.AI_ADVISORY` is unconfigured rather than ever spending a frontier token. */
+ *  `chatQa` (#4595) is the ONE capability that does NOT share the others' silent-frontier fallback BY DEFAULT:
+ *  the four cost-optimizing capabilities above quietly fall back to the shared frontier env.AI when their flag
+ *  is off, but the `@gittensory chat` grounded Q&A surface declines/skips whenever `chatQa !== true` or
+ *  `env.AI_ADVISORY` is unconfigured, rather than ever spending a frontier token -- UNLESS `chatQaFrontierFallback`
+ *  is also explicitly enabled (a self-hoster without a local GPU may prefer their own frontier subscription
+ *  over an outright decline). */
 export type AdvisoryAiRoutingConfig = {
   slop: boolean;
   e2eTestGen: boolean;
   planner: boolean;
   summaries: boolean;
-  /** Grounded `@gittensory chat <question>` LLM Q&A (#4595). Ollama-only: unlike the four fields above it NEVER
-   *  falls back to the frontier env.AI when off -- it simply declines. Default false. */
+  /** Grounded `@gittensory chat <question>` LLM Q&A (#4595). Ollama-first: declines when off or when
+   *  env.AI_ADVISORY is unconfigured and {@link chatQaFrontierFallback} is not also enabled. Default false. */
   chatQa: boolean;
+  /** Opt-in ONLY (#4595 follow-up): when true, chat falls back to the shared frontier env.AI chain if
+   *  env.AI_ADVISORY is unconfigured, instead of declining. Meaningless unless {@link chatQa} is also true.
+   *  Default false -- preserves the original Ollama-only behavior for every existing deployment; a self-hoster
+   *  without a local GPU may enable this to use their own frontier subscription/tokens for chat instead. */
+  chatQaFrontierFallback: boolean;
 };
 
 /** A blocked contributor (#1425, anti-abuse): a GitHub `login` plus optional maintainer metadata. The converged
diff --git a/test/unit/advisory-ai-routing-call-sites.test.ts b/test/unit/advisory-ai-routing-call-sites.test.ts
index d0aa430882..54eca10a2d 100644
--- a/test/unit/advisory-ai-routing-call-sites.test.ts
+++ b/test/unit/advisory-ai-routing-call-sites.test.ts
@@ -35,7 +35,7 @@ describe("runAiSlopForAdvisory routes through AI_ADVISORY (#4364)", () => {
     });
     await runAiSlopForAdvisory(env, {
       mode: "live",
-      settings: settingsFixture({ slop: true, e2eTestGen: false, planner: false, summaries: false, chatQa: false }),
+      settings: settingsFixture({ slop: true, e2eTestGen: false, planner: false, summaries: false, chatQa: false, chatQaFrontierFallback: false }),
       advisory,
       repoFullName: "owner/repo",
       pr: { number: 1, title: "t" },
@@ -80,7 +80,7 @@ describe("runAiSlopForAdvisory routes through AI_ADVISORY (#4364)", () => {
     const env = createTestEnv({ AI_SUMMARIES_ENABLED: "true", AI_PUBLIC_COMMENTS_ENABLED: "true", AI: { run: frontierRun } as unknown as Ai });
     await runAiSlopForAdvisory(env, {
       mode: "live",
-      settings: settingsFixture({ slop: true, e2eTestGen: false, planner: false, summaries: false, chatQa: false }),
+      settings: settingsFixture({ slop: true, e2eTestGen: false, planner: false, summaries: false, chatQa: false, chatQaFrontierFallback: false }),
       advisory,
       repoFullName: "owner/repo",
       pr: { number: 3, title: "t" },
diff --git a/test/unit/advisory-ai-routing-config-engine.test.ts b/test/unit/advisory-ai-routing-config-engine.test.ts
index 752b7058b3..54cba24847 100644
--- a/test/unit/advisory-ai-routing-config-engine.test.ts
+++ b/test/unit/advisory-ai-routing-config-engine.test.ts
@@ -11,28 +11,34 @@ describe("normalizeAdvisoryAiRoutingConfig", () => {
 
   it("normalizes a fully-valid config", () => {
     const warnings: string[] = [];
-    expect(normalizeAdvisoryAiRoutingConfig({ slop: true, e2eTestGen: true, planner: true, summaries: true, chatQa: true }, warnings)).toEqual({
+    expect(
+      normalizeAdvisoryAiRoutingConfig({ slop: true, e2eTestGen: true, planner: true, summaries: true, chatQa: true, chatQaFrontierFallback: true }, warnings),
+    ).toEqual({
       slop: true,
       e2eTestGen: true,
       planner: true,
       summaries: true,
       chatQa: true,
+      chatQaFrontierFallback: true,
     });
     expect(warnings).toEqual([]);
   });
 
-  it.each(["slop", "e2eTestGen", "planner", "summaries", "chatQa"] as const)("defaults %s to false when omitted", (field) => {
+  it.each(["slop", "e2eTestGen", "planner", "summaries", "chatQa", "chatQaFrontierFallback"] as const)("defaults %s to false when omitted", (field) => {
     const warnings: string[] = [];
     expect(normalizeAdvisoryAiRoutingConfig({}, warnings)[field]).toBe(false);
     expect(warnings).toEqual([]);
   });
 
-  it.each(["slop", "e2eTestGen", "planner", "summaries", "chatQa"] as const)("falls back to false and warns on a non-boolean %s", (field) => {
-    const warnings: string[] = [];
-    const cfg = normalizeAdvisoryAiRoutingConfig({ [field]: "yes" }, warnings);
-    expect(cfg[field]).toBe(false);
-    expect(warnings).toEqual([`settings.advisoryAiRouting.${field} must be a boolean; using the default "false".`]);
-  });
+  it.each(["slop", "e2eTestGen", "planner", "summaries", "chatQa", "chatQaFrontierFallback"] as const)(
+    "falls back to false and warns on a non-boolean %s",
+    (field) => {
+      const warnings: string[] = [];
+      const cfg = normalizeAdvisoryAiRoutingConfig({ [field]: "yes" }, warnings);
+      expect(cfg[field]).toBe(false);
+      expect(warnings).toEqual([`settings.advisoryAiRouting.${field} must be a boolean; using the default "false".`]);
+    },
+  );
 
   it.each([
     ["an array", []],
diff --git a/test/unit/advisory-ai-routing-config.test.ts b/test/unit/advisory-ai-routing-config.test.ts
index d9db0f038d..6b7bb10426 100644
--- a/test/unit/advisory-ai-routing-config.test.ts
+++ b/test/unit/advisory-ai-routing-config.test.ts
@@ -10,33 +10,39 @@ describe("normalizeAdvisoryAiRoutingConfig", () => {
 
   it("normalizes a fully-valid config", () => {
     const warnings: string[] = [];
-    expect(normalizeAdvisoryAiRoutingConfig({ slop: true, e2eTestGen: true, planner: true, summaries: true, chatQa: true }, warnings)).toEqual({
+    expect(
+      normalizeAdvisoryAiRoutingConfig({ slop: true, e2eTestGen: true, planner: true, summaries: true, chatQa: true, chatQaFrontierFallback: true }, warnings),
+    ).toEqual({
       slop: true,
       e2eTestGen: true,
       planner: true,
       summaries: true,
       chatQa: true,
+      chatQaFrontierFallback: true,
     });
     expect(warnings).toEqual([]);
   });
 
-  it.each(["slop", "e2eTestGen", "planner", "summaries", "chatQa"] as const)("defaults %s to false when omitted", (field) => {
+  it.each(["slop", "e2eTestGen", "planner", "summaries", "chatQa", "chatQaFrontierFallback"] as const)("defaults %s to false when omitted", (field) => {
     const warnings: string[] = [];
     expect(normalizeAdvisoryAiRoutingConfig({}, warnings)[field]).toBe(false);
     expect(warnings).toEqual([]);
   });
 
-  it.each(["slop", "e2eTestGen", "planner", "summaries", "chatQa"] as const)("falls back to false and warns on a non-boolean %s", (field) => {
-    const warnings: string[] = [];
-    const cfg = normalizeAdvisoryAiRoutingConfig({ [field]: "yes" }, warnings);
-    expect(cfg[field]).toBe(false);
-    expect(warnings).toEqual([`settings.advisoryAiRouting.${field} must be a boolean; using the default "false".`]);
-  });
+  it.each(["slop", "e2eTestGen", "planner", "summaries", "chatQa", "chatQaFrontierFallback"] as const)(
+    "falls back to false and warns on a non-boolean %s",
+    (field) => {
+      const warnings: string[] = [];
+      const cfg = normalizeAdvisoryAiRoutingConfig({ [field]: "yes" }, warnings);
+      expect(cfg[field]).toBe(false);
+      expect(warnings).toEqual([`settings.advisoryAiRouting.${field} must be a boolean; using the default "false".`]);
+    },
+  );
 
   it("normalizes one valid field alongside one invalid field independently", () => {
     const warnings: string[] = [];
     const cfg = normalizeAdvisoryAiRoutingConfig({ slop: true, planner: "nope" }, warnings);
-    expect(cfg).toEqual({ slop: true, e2eTestGen: false, planner: false, summaries: false, chatQa: false });
+    expect(cfg).toEqual({ slop: true, e2eTestGen: false, planner: false, summaries: false, chatQa: false, chatQaFrontierFallback: false });
     expect(warnings).toEqual([`settings.advisoryAiRouting.planner must be a boolean; using the default "false".`]);
   });
 
diff --git a/test/unit/ai-chat-qa.test.ts b/test/unit/ai-chat-qa.test.ts
index 1530f64ee4..0047ba2222 100644
--- a/test/unit/ai-chat-qa.test.ts
+++ b/test/unit/ai-chat-qa.test.ts
@@ -3,8 +3,9 @@ import { __chatQaInternals, CHAT_QA_FALLBACK_COMMAND, generateChatQaAnswer } fro
 import type { AgentRunBundle } from "../../src/services/agent-orchestrator";
 import { createTestEnv } from "../helpers/d1";
 
-const ADVISORY_ON = { slop: false, e2eTestGen: false, planner: false, summaries: false, chatQa: true };
-const ADVISORY_OFF = { slop: false, e2eTestGen: false, planner: false, summaries: false, chatQa: false };
+const ADVISORY_ON = { slop: false, e2eTestGen: false, planner: false, summaries: false, chatQa: true, chatQaFrontierFallback: false };
+const ADVISORY_OFF = { slop: false, e2eTestGen: false, planner: false, summaries: false, chatQa: false, chatQaFrontierFallback: false };
+const ADVISORY_ON_FRONTIER_FALLBACK = { slop: false, e2eTestGen: false, planner: false, summaries: false, chatQa: true, chatQaFrontierFallback: true };
 
 function bundleFixture(runOverrides?: Partial<AgentRunBundle["run"]>, actionOverrides?: Partial<AgentRunBundle["actions"][number]>): AgentRunBundle {
   return {
@@ -79,7 +80,7 @@ describe("generateChatQaAnswer", () => {
     expect(result.status).toBe("disabled");
   });
 
-  it("never falls back to the frontier chain: reports unavailable when chatQa is on but AI_ADVISORY is unconfigured", async () => {
+  it("by default (chatQaFrontierFallback off) never falls back to the frontier chain: reports unavailable when chatQa is on but AI_ADVISORY is unconfigured", async () => {
     const frontierRun = vi.fn();
     const env = createTestEnv({ AI: { run: frontierRun } as unknown as Ai });
     const result = await generateChatQaAnswer(env, {
@@ -90,9 +91,57 @@ describe("generateChatQaAnswer", () => {
       issueNumber: 1,
     });
     expect(result).toMatchObject({ status: "unavailable" });
+    expect(result.status === "unavailable" ? result.reason : "").toContain("does not fall back to the frontier model");
     expect(frontierRun).not.toHaveBeenCalled();
   });
 
+  it("#4595 follow-up: falls back to the frontier chain when chatQaFrontierFallback is enabled and AI_ADVISORY is unconfigured", async () => {
+    const frontierRun = vi.fn(async () => ({ response: "Frontier-served answer." }));
+    const env = createTestEnv({ AI: { run: frontierRun } as unknown as Ai, AI_DAILY_NEURON_BUDGET: "10000" });
+    const result = await generateChatQaAnswer(env, {
+      bundle: bundleFixture(),
+      question: "why is this blocked?",
+      advisoryAiRouting: ADVISORY_ON_FRONTIER_FALLBACK,
+      repoFullName: "owner/repo",
+      issueNumber: 1,
+    });
+    expect(result).toMatchObject({ status: "ok", text: "Frontier-served answer." });
+    expect(frontierRun).toHaveBeenCalled();
+  });
+
+  it("#4595 follow-up: still prefers AI_ADVISORY (Ollama) over the frontier chain even when chatQaFrontierFallback is enabled", async () => {
+    const advisoryRun = vi.fn(async () => ({ response: "Ollama-served answer." }));
+    const frontierRun = vi.fn();
+    const env = createTestEnv({
+      AI_ADVISORY: { run: advisoryRun } as unknown as Ai,
+      AI: { run: frontierRun } as unknown as Ai,
+      AI_DAILY_NEURON_BUDGET: "10000",
+    });
+    const result = await generateChatQaAnswer(env, {
+      bundle: bundleFixture(),
+      question: "why is this blocked?",
+      advisoryAiRouting: ADVISORY_ON_FRONTIER_FALLBACK,
+      repoFullName: "owner/repo",
+      issueNumber: 1,
+    });
+    expect(result).toMatchObject({ status: "ok", text: "Ollama-served answer." });
+    expect(advisoryRun).toHaveBeenCalled();
+    expect(frontierRun).not.toHaveBeenCalled();
+  });
+
+  it("#4595 follow-up: reports unavailable with a distinct message when chatQaFrontierFallback is enabled but NEITHER provider is configured", async () => {
+    const env = createTestEnv({});
+    const result = await generateChatQaAnswer(env, {
+      bundle: bundleFixture(),
+      question: "why is this blocked?",
+      advisoryAiRouting: ADVISORY_ON_FRONTIER_FALLBACK,
+      repoFullName: "owner/repo",
+      issueNumber: 1,
+    });
+    expect(result).toMatchObject({ status: "unavailable" });
+    expect(result.status === "unavailable" ? result.reason : "").toContain("Neither local advisory inference");
+  });
+
   it("declines when no question is supplied", async () => {
     const advisoryRun = vi.fn();
     const env = createTestEnv({ AI_ADVISORY: { run: advisoryRun } as unknown as Ai });
diff --git a/test/unit/focus-manifest.test.ts b/test/unit/focus-manifest.test.ts
index c3f5520d77..6f12e31ce1 100644
--- a/test/unit/focus-manifest.test.ts
+++ b/test/unit/focus-manifest.test.ts
@@ -3048,7 +3048,7 @@ describe("parseFocusManifest settings override + resolveEffectiveSettings", () =
   it("resolveEffectiveSettings falls back to the all-off built-in default when the DB layer has no advisoryAiRouting at all (#4364)", () => {
     const db = {} as unknown as RepositorySettings;
     const eff = resolveEffectiveSettings(db, parseFocusManifest({ settings: { advisoryAiRouting: { planner: true } } }));
-    expect(eff.advisoryAiRouting).toEqual({ slop: false, e2eTestGen: false, planner: true, summaries: false, chatQa: false });
+    expect(eff.advisoryAiRouting).toEqual({ slop: false, e2eTestGen: false, planner: true, summaries: false, chatQa: false, chatQaFrontierFallback: false });
   });
 
   it("wires settings.advisoryAiRouting.chatQa into the manifest parser as a sparse override (#4595)", () => {
@@ -3058,15 +3058,41 @@ describe("parseFocusManifest settings override + resolveEffectiveSettings", () =
   });
 
   it("resolveEffectiveSettings merges an explicit chatQa override over the DB layer's value (#4595)", () => {
-    const db = { advisoryAiRouting: { slop: false, e2eTestGen: false, planner: false, summaries: false, chatQa: false } } as unknown as RepositorySettings;
+    const db = {
+      advisoryAiRouting: { slop: false, e2eTestGen: false, planner: false, summaries: false, chatQa: false, chatQaFrontierFallback: false },
+    } as unknown as RepositorySettings;
     const eff = resolveEffectiveSettings(db, parseFocusManifest({ settings: { advisoryAiRouting: { chatQa: true } } }));
-    expect(eff.advisoryAiRouting).toEqual({ slop: false, e2eTestGen: false, planner: false, summaries: false, chatQa: true });
+    expect(eff.advisoryAiRouting).toEqual({ slop: false, e2eTestGen: false, planner: false, summaries: false, chatQa: true, chatQaFrontierFallback: false });
   });
 
   it("resolveEffectiveSettings keeps the DB layer's chatQa when the manifest override omits it (#4595)", () => {
-    const db = { advisoryAiRouting: { slop: false, e2eTestGen: false, planner: false, summaries: false, chatQa: true } } as unknown as RepositorySettings;
+    const db = {
+      advisoryAiRouting: { slop: false, e2eTestGen: false, planner: false, summaries: false, chatQa: true, chatQaFrontierFallback: false },
+    } as unknown as RepositorySettings;
+    const eff = resolveEffectiveSettings(db, parseFocusManifest({ settings: { advisoryAiRouting: { slop: true } } }));
+    expect(eff.advisoryAiRouting).toEqual({ slop: true, e2eTestGen: false, planner: false, summaries: false, chatQa: true, chatQaFrontierFallback: false });
+  });
+
+  it("wires settings.advisoryAiRouting.chatQaFrontierFallback into the manifest parser as a sparse override (#4595 follow-up)", () => {
+    const parsed = parseFocusManifest({ settings: { advisoryAiRouting: { chatQaFrontierFallback: true } } });
+    expect(parsed.settings.advisoryAiRouting).toEqual({ chatQaFrontierFallback: true });
+    expect(parsed.warnings).toEqual([]);
+  });
+
+  it("resolveEffectiveSettings merges an explicit chatQaFrontierFallback override over the DB layer's value (#4595 follow-up)", () => {
+    const db = {
+      advisoryAiRouting: { slop: false, e2eTestGen: false, planner: false, summaries: false, chatQa: true, chatQaFrontierFallback: false },
+    } as unknown as RepositorySettings;
+    const eff = resolveEffectiveSettings(db, parseFocusManifest({ settings: { advisoryAiRouting: { chatQaFrontierFallback: true } } }));
+    expect(eff.advisoryAiRouting).toEqual({ slop: false, e2eTestGen: false, planner: false, summaries: false, chatQa: true, chatQaFrontierFallback: true });
+  });
+
+  it("resolveEffectiveSettings keeps the DB layer's chatQaFrontierFallback when the manifest override omits it (#4595 follow-up)", () => {
+    const db = {
+      advisoryAiRouting: { slop: false, e2eTestGen: false, planner: false, summaries: false, chatQa: true, chatQaFrontierFallback: true },
+    } as unknown as RepositorySettings;
     const eff = resolveEffectiveSettings(db, parseFocusManifest({ settings: { advisoryAiRouting: { slop: true } } }));
-    expect(eff.advisoryAiRouting).toEqual({ slop: true, e2eTestGen: false, planner: false, summaries: false, chatQa: true });
+    expect(eff.advisoryAiRouting).toEqual({ slop: true, e2eTestGen: false, planner: false, summaries: false, chatQa: true, chatQaFrontierFallback: true });
   });
 
   it("drops a malformed advisoryAiRouting.slop field instead of replacing existing policy with defaults (#4364)", () => {