diff --git a/docs/api/openapi.yaml b/docs/api/openapi.yaml
index 25431a0bd..e92efe758 100644
--- a/docs/api/openapi.yaml
+++ b/docs/api/openapi.yaml
@@ -25855,6 +25855,28 @@ components:
               minimum: 10
               maximum: 600
             - type: "null"
+        localReasoningEffort:
+          description: Reasoning setting of the Local provider entry, stored on that entry of the provider chain. `none` = Off,
+            `null` = Default (nothing sent). Omitted leaves it untouched.
+          anyOf:
+            - type: string
+              enum:
+                - none
+                - low
+                - medium
+                - high
+            - type: "null"
+        compatReasoningEffort:
+          description: Reasoning setting of the OpenAI-compatible gateway entry, stored on that entry of the provider chain.
+            `none` = Off, `null` = Default (nothing sent). Omitted leaves it untouched.
+          anyOf:
+            - type: string
+              enum:
+                - none
+                - low
+                - medium
+                - high
+            - type: "null"
       description: "Partial update of the calling user's AI-provider configuration. An omitted key is left untouched; `null`
         (or an empty string, on the string fields) clears the column. At least one recognised key must be present, or
         the write is refused. Key material is write-only: it is encrypted on the way in and never returned. Unknown keys
@@ -27071,6 +27093,7 @@ components:
       properties:
         chain:
           minItems: 1
+          maxItems: 7
           type: array
           items:
             type: object
@@ -27096,15 +27119,30 @@ components:
                 maximum: 9007199254740991
               enabled:
                 type: boolean
+              reasoningEffort:
+                description: Only on a `local` or `openai-compatible` entry; refused on any other. Omitted keeps the value already
+                  stored for that provider, `null` restores Default, `none` / `low` / `medium` / `high` are sent as
+                  `reasoning_effort`.
+                anyOf:
+                  - type: string
+                    enum:
+                      - none
+                      - low
+                      - medium
+                      - high
+                  - type: "null"
             required:
               - providerType
               - enabled
+            additionalProperties: false
           description: The whole chain, in the order it should be walked. At least one entry and at most one per known provider
             type; a repeated type is refused.
       required:
         - chain
+      additionalProperties: false
       description: Replaces the account's provider chain wholesale. No credential is written or read here — only which
-        provider types exist, in what order, and which are enabled.
+        provider types exist, in what order, which are enabled, and the reasoning setting of the Local and
+        OpenAI-compatible entries.
     InsightsFeedbackRequest:
       type: object
       properties:
@@ -48543,6 +48581,27 @@ components:
             - type: "null"
           description: v1.22 (#89) — per-user response timeout for AI generation, in seconds (10–600). Null = the built-in
             comprehensive-briefing default (~120 s). Mainly for slow local/self-hosted backends.
+        localReasoningEffort:
+          anyOf:
+            - type: string
+              enum:
+                - none
+                - low
+                - medium
+                - high
+            - type: "null"
+          description: "#1126 — reasoning setting of the Local provider entry, sent as `reasoning_effort` (`none` = Off). Null =
+            Default: the key is not sent."
+        compatReasoningEffort:
+          anyOf:
+            - type: string
+              enum:
+                - none
+                - low
+                - medium
+                - high
+            - type: "null"
+          description: "#1126 — the same for the OpenAI-compatible gateway entry."
         serverProviderHealth:
           type: string
           enum:
@@ -48587,6 +48646,8 @@ components:
         - compatModel
         - hasCompatKey
         - responseTimeoutSeconds
+        - localReasoningEffort
+        - compatReasoningEffort
         - serverProviderHealth
         - serverProviderOffer
         - serverProviderConsent
diff --git a/src/__tests__/ai-reasoning-effort-guard.test.ts b/src/__tests__/ai-reasoning-effort-guard.test.ts
new file mode 100644
index 000000000..e555ab141
--- /dev/null
+++ b/src/__tests__/ai-reasoning-effort-guard.test.ts
@@ -0,0 +1,124 @@
+/**
+ * Structural guard (#1126): `reasoning_effort` reaches a model only through
+ * the setting the resolver bound to the provider instance.
+ *
+ * Default must send nothing, so the key may not appear on any wire except as
+ * the bound value, and only the two clients whose endpoint a person chose may
+ * carry it. Pinned here:
+ *
+ *   1. the key appears in exactly the Local client and the OpenAI client,
+ *      once each, and only as `reasoning_effort: this.reasoningEffort`;
+ *   2. nothing but the binder assigns `.reasoningEffort`;
+ *   3. every exported resolver in `provider.ts` calls `bindReasoningEffort`.
+ *
+ * That clients are constructed only in `provider.ts` (so a resolver always
+ * binds them) is frozen by `ai-call-timeout-guard.test.ts`.
+ *
+ * Its limit: it reads source text. A body built under a computed key, or a
+ * resolver that binds through an alias, would slip it.
+ * `reasoning-effort.test.ts` and `provider-reasoning-effort.test.ts` prove
+ * the behaviour on the wire.
+ *
+ * Mutation check: hard-code `reasoning_effort: "none"` into either client,
+ * set `client.reasoningEffort = ...` in a route, or drop `bindReasoningEffort`
+ * from `resolveProviderForTest`: each one goes red here.
+ */
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+
+import { describe, expect, it } from "vitest";
+
+import { walkSourceFiles } from "./helpers/source-files";
+
+const SRC = join(process.cwd(), "src");
+
+function stripComments(source: string): string {
+  return source
+    .replace(/\/\*[\s\S]*?\*\//g, "")
+    .replace(/(^|[^:])\/\/.*$/gm, "$1");
+}
+
+function code(rel: string): string {
+  return stripComments(readFileSync(join(SRC, rel), "utf8"));
+}
+
+const files = walkSourceFiles(SRC, { floor: 3000 })
+  .filter((p) => !p.startsWith("generated/"))
+  .filter((p) => !p.includes("__tests__"))
+  .filter((p) => !p.endsWith(".test.ts") && !p.endsWith(".test.tsx"));
+
+describe("reasoning_effort on the wire", () => {
+  // As an object key: the published descriptions name the field in prose.
+  const KEY = /\breasoning_effort["']?\s*:/g;
+  const sites = files.filter((rel) => new RegExp(KEY).test(code(rel)));
+
+  it("appears in the Local and the OpenAI client only", () => {
+    expect(sites.sort()).toEqual([
+      "lib/ai/local-client.ts",
+      "lib/ai/openai-client.ts",
+    ]);
+  });
+
+  it.each(["lib/ai/local-client.ts", "lib/ai/openai-client.ts"])(
+    "%s sends it once, as the bound value",
+    (rel) => {
+      const source = code(rel);
+      expect(source.match(new RegExp(KEY))?.length).toBe(1);
+      expect(source).toMatch(
+        /\breasoning_effort\s*:\s*this\s*\.\s*reasoningEffort\b/,
+      );
+    },
+  );
+});
+
+/** Where `.reasoningEffort` may be assigned, and why. */
+const ASSIGNMENT_SITES: Record<string, string> = {
+  "lib/ai/reasoning-effort.ts":
+    "The binder, the one place a provider instance gets its value.",
+  "lib/ai/provider-chain.ts":
+    "Writes the stored chain entry, not a provider instance.",
+};
+
+describe("only the binder assigns it to a provider", () => {
+  it("names every assignment site, with a reason", () => {
+    const sites = files.filter((rel) =>
+      /\.\s*reasoningEffort\s*=(?!=)/.test(code(rel)),
+    );
+    expect(sites.sort()).toEqual(Object.keys(ASSIGNMENT_SITES).sort());
+  });
+});
+
+describe("every exported resolver binds it", () => {
+  const source = code("lib/ai/provider.ts");
+  const resolvers = source
+    .split(/\nexport\s+/)
+    .map((chunk) => {
+      const m = /^async\s+function\s+(\w+)\s*\(/.exec(chunk);
+      if (!m) return null;
+      const header = chunk.slice(0, chunk.indexOf("{\n"));
+      if (
+        !/Promise<\s*(?:AIProvider|ProviderChainResolved\[\])\s*>/.test(header)
+      ) {
+        return null;
+      }
+      const end = chunk.indexOf("\n}\n");
+      return { name: m[1], body: chunk.slice(header.length, end) };
+    })
+    .filter((r): r is { name: string; body: string } => r !== null);
+
+  it("finds the resolvers (an empty set is a failure, not a pass)", () => {
+    expect(resolvers.map((r) => r.name).sort()).toEqual([
+      "resolveProvider",
+      "resolveProviderChain",
+      "resolveProviderForTest",
+    ]);
+  });
+
+  it.each(resolvers.map((r) => r.name))(
+    "%s calls bindReasoningEffort",
+    (name) => {
+      const resolver = resolvers.find((r) => r.name === name);
+      expect(resolver?.body ?? "").toMatch(/\bbindReasoningEffort\s*\(/);
+    },
+  );
+});
diff --git a/src/app/api/insights/provider-chain/__tests__/put.test.ts b/src/app/api/insights/provider-chain/__tests__/put.test.ts
index 510fa5fe7..3413fc0a2 100644
--- a/src/app/api/insights/provider-chain/__tests__/put.test.ts
+++ b/src/app/api/insights/provider-chain/__tests__/put.test.ts
@@ -53,6 +53,8 @@ vi.mock("@/lib/db", () => ({
   prisma: {
     user: {
       update: vi.fn(),
+      // #1126 — the stored chain, read for the reasoning settings it carries.
+      findUnique: vi.fn(async () => null),
     },
   },
 }));
@@ -172,4 +174,93 @@ describe("PUT /api/insights/provider-chain", () => {
       { providerType: "codex", priority: 2, enabled: true },
     ]);
   });
+
+  // #1126 — the reasoning setting rides on the local / openai-compatible
+  // entries. The chain editor only reorders and toggles, so saving the order
+  // must not wipe a value it never sent.
+  describe("reasoning setting", () => {
+    function storedChain(chain: unknown) {
+      vi.mocked(prisma.user.findUnique).mockResolvedValueOnce({
+        aiProviderChain: chain,
+      } as never);
+    }
+    async function put(chain: unknown[]) {
+      vi.mocked(prisma.user.update).mockResolvedValueOnce({} as never);
+      return (PUT as (req: Request) => Promise<Response>)(
+        jsonRequest({ chain }),
+      );
+    }
+    function persisted() {
+      return vi.mocked(prisma.user.update).mock.calls[0][0].data
+        .aiProviderChain;
+    }
+
+    it("persists a value sent on a local entry", async () => {
+      storedChain(null);
+      const res = await put([
+        { providerType: "local", enabled: true, reasoningEffort: "none" },
+        { providerType: "openai", enabled: true },
+      ]);
+      expect(res.status).toBe(200);
+      expect(persisted()).toEqual([
+        {
+          providerType: "local",
+          priority: 1,
+          enabled: true,
+          reasoningEffort: "none",
+        },
+        { providerType: "openai", priority: 2, enabled: true },
+      ]);
+    });
+
+    it("keeps the stored value when the body leaves it out", async () => {
+      storedChain([
+        { providerType: "openai", priority: 1, enabled: true },
+        {
+          providerType: "openai-compatible",
+          priority: 2,
+          enabled: false,
+          reasoningEffort: "high",
+        },
+      ]);
+      await put([
+        { providerType: "openai-compatible", enabled: true },
+        { providerType: "openai", enabled: true },
+      ]);
+      expect(persisted()).toEqual([
+        {
+          providerType: "openai-compatible",
+          priority: 1,
+          enabled: true,
+          reasoningEffort: "high",
+        },
+        { providerType: "openai", priority: 2, enabled: true },
+      ]);
+    });
+
+    it("clears it on null", async () => {
+      storedChain([
+        {
+          providerType: "local",
+          priority: 1,
+          enabled: true,
+          reasoningEffort: "low",
+        },
+      ]);
+      await put([
+        { providerType: "local", enabled: true, reasoningEffort: null },
+      ]);
+      expect(persisted()).toEqual([
+        { providerType: "local", priority: 1, enabled: true },
+      ]);
+    });
+
+    it("refuses it on an entry that cannot carry it", async () => {
+      const res = await put([
+        { providerType: "anthropic", enabled: true, reasoningEffort: "none" },
+      ]);
+      expect(res.status).toBe(422);
+      expect(prisma.user.update).not.toHaveBeenCalled();
+    });
+  });
 });
diff --git a/src/app/api/insights/provider-chain/route.ts b/src/app/api/insights/provider-chain/route.ts
index 8ea535990..477cb8159 100644
--- a/src/app/api/insights/provider-chain/route.ts
+++ b/src/app/api/insights/provider-chain/route.ts
@@ -1,6 +1,4 @@
 import type { NextRequest } from "next/server";
-import { z } from "zod/v4";
-
 import { apiHandler, HttpError, requireAuth } from "@/lib/api-handler";
 import {
   apiSuccess,
@@ -15,10 +13,9 @@ import {
   getLastWorkingProvider,
 } from "@/lib/ai/provider-runner";
 import { prisma } from "@/lib/db";
-import {
-  parseProviderChain,
-  PROVIDER_CHAIN_TYPES,
-} from "@/lib/ai/provider-chain";
+import { parseProviderChain } from "@/lib/ai/provider-chain";
+import { isReasoningProviderType } from "@/lib/ai/reasoning-effort";
+import { providerChainPutSchema } from "@/lib/validations/ai-provider";
 
 /**
  * v1.4.16 phase B5b — read-only chain summary for the Settings → AI
@@ -85,29 +82,6 @@ export const GET = apiHandler(async () => {
   });
 });
 
-const chainEntrySchema = z
-  .object({
-    providerType: z.enum(
-      PROVIDER_CHAIN_TYPES as unknown as [string, ...string[]],
-    ),
-    // Priority is recomputed server-side from insertion order so a stale
-    // client cannot persist a chain whose displayed order disagrees with
-    // its priority field. The number is accepted (and may be present) but
-    // ignored on the wire.
-    priority: z.number().int().optional(),
-    enabled: z.boolean(),
-  })
-  .strict();
-
-const chainBodySchema = z
-  .object({
-    chain: z
-      .array(chainEntrySchema)
-      .min(1, "Chain must contain at least one provider")
-      .max(PROVIDER_CHAIN_TYPES.length, "Too many providers"),
-  })
-  .strict();
-
 export const PUT = apiHandler(async (request: NextRequest) => {
   const { user } = await requireAuth();
   annotate({ action: { name: "insights.provider_chain.update" } });
@@ -117,7 +91,7 @@ export const PUT = apiHandler(async (request: NextRequest) => {
   });
   if (error) return error;
 
-  const parsed = chainBodySchema.safeParse(body);
+  const parsed = providerChainPutSchema.safeParse(body);
   if (!parsed.success) {
     return apiValidationError(
       "Invalid provider chain payload",
@@ -142,11 +116,35 @@ export const PUT = apiHandler(async (request: NextRequest) => {
   // Normalise priority to insertion order (1-based). UI hands us the
   // visual order it wants persisted; we make priority match so a later
   // GET reflects the same order without depending on the client's math.
-  const normalised = parsed.data.chain.map((entry, idx) => ({
-    providerType: entry.providerType,
-    priority: idx + 1,
-    enabled: entry.enabled,
-  }));
+  //
+  // #1126 — a reasoning setting the body leaves out is carried over from the
+  // stored entry of the same type, so the chain editor (which only reorders
+  // and toggles) and an older client cannot wipe it by saving the order.
+  // `null` clears it; the schema has already refused it on any type other
+  // than `local` / `openai-compatible`.
+  const stored = await prisma.user.findUnique({
+    where: { id: user.id },
+    select: { aiProviderChain: true },
+  });
+  const storedEffort = new Map(
+    parseProviderChain(stored?.aiProviderChain ?? null).map((e) => [
+      e.providerType,
+      e.reasoningEffort ?? null,
+    ]),
+  );
+  const normalised = parsed.data.chain.map((entry, idx) => {
+    const reasoningEffort = isReasoningProviderType(entry.providerType)
+      ? entry.reasoningEffort === undefined
+        ? (storedEffort.get(entry.providerType) ?? null)
+        : entry.reasoningEffort
+      : null;
+    return {
+      providerType: entry.providerType,
+      priority: idx + 1,
+      enabled: entry.enabled,
+      ...(reasoningEffort ? { reasoningEffort } : {}),
+    };
+  });
 
   await prisma.user.update({
     where: { id: user.id },
diff --git a/src/app/api/user/ai-provider/__tests__/route.test.ts b/src/app/api/user/ai-provider/__tests__/route.test.ts
index 9c5e5809b..0eb415494 100644
--- a/src/app/api/user/ai-provider/__tests__/route.test.ts
+++ b/src/app/api/user/ai-provider/__tests__/route.test.ts
@@ -623,3 +623,96 @@ describe("GET /api/user/ai-provider — the shared-provider offer", () => {
     }
   });
 });
+
+// #1126 — the Local and gateway entries' reasoning setting, written from the
+// provider forms onto the chain entry and read back from it.
+describe("PATCH /api/user/ai-provider — reasoning setting (#1126)", () => {
+  const patch = PATCH as (req: Request) => Promise<Response>;
+  function storedChain(chain: unknown) {
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({
+      aiProviderChain: chain,
+    } as never);
+  }
+  function written() {
+    return vi.mocked(prisma.user.update).mock.calls[0]?.[0].data as
+      Record<string, unknown> | undefined;
+  }
+
+  it("stores Off on the local entry of a chain that was never customised", async () => {
+    storedChain(null);
+    const res = await patch(
+      patchRequest({ provider: "LOCAL", localReasoningEffort: "none" }),
+    );
+    expect(res.status).toBe(200);
+    const chain = written()?.aiProviderChain as Array<{
+      providerType: string;
+      reasoningEffort?: string;
+    }>;
+    expect(chain.find((e) => e.providerType === "local")).toMatchObject({
+      enabled: true,
+      reasoningEffort: "none",
+    });
+    expect(chain.filter((e) => e.reasoningEffort)).toHaveLength(1);
+  });
+
+  it("holds the gateway's value on a disabled entry when the chain lacks it", async () => {
+    storedChain([{ providerType: "local", priority: 1, enabled: true }]);
+    await patch(patchRequest({ compatReasoningEffort: "high" }));
+    expect(written()?.aiProviderChain).toEqual([
+      { providerType: "local", priority: 1, enabled: true },
+      {
+        providerType: "openai-compatible",
+        priority: 2,
+        enabled: false,
+        reasoningEffort: "high",
+      },
+    ]);
+  });
+
+  it("does not touch the chain when Default is restated on a default chain", async () => {
+    storedChain(null);
+    await patch(
+      patchRequest({ provider: "LOCAL", localReasoningEffort: null }),
+    );
+    expect(written()).toEqual({ aiProvider: "LOCAL" });
+  });
+
+  it("answers 200 for a body that only restates Default", async () => {
+    storedChain(null);
+    const res = await patch(patchRequest({ localReasoningEffort: null }));
+    expect(res.status).toBe(200);
+    expect(prisma.user.update).not.toHaveBeenCalled();
+  });
+
+  it("refuses a value outside the five", async () => {
+    const res = await patch(patchRequest({ localReasoningEffort: "max" }));
+    expect(res.status).toBe(422);
+    expect(prisma.user.update).not.toHaveBeenCalled();
+  });
+});
+
+describe("GET /api/user/ai-provider — reasoning setting (#1126)", () => {
+  it("reads both values from the chain, null for Default", async () => {
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({
+      aiProvider: "LOCAL",
+      aiProviderChain: [
+        {
+          providerType: "local",
+          priority: 1,
+          enabled: true,
+          reasoningEffort: "none",
+        },
+      ],
+    } as never);
+    vi.mocked(resolveProviderAvailability).mockResolvedValue({
+      aiAvailable: true,
+      managedBy: "local",
+    });
+    const res = await (GET as () => Promise<Response>)();
+    const body = (await res.json()) as {
+      data: { localReasoningEffort: unknown; compatReasoningEffort: unknown };
+    };
+    expect(body.data.localReasoningEffort).toBe("none");
+    expect(body.data.compatReasoningEffort).toBeNull();
+  });
+});
diff --git a/src/app/api/user/ai-provider/route.ts b/src/app/api/user/ai-provider/route.ts
index 7f19b619b..1b976d5ec 100644
--- a/src/app/api/user/ai-provider/route.ts
+++ b/src/app/api/user/ai-provider/route.ts
@@ -20,6 +20,12 @@ import {
 } from "@/lib/sharing/provider-work-authority";
 import { annotate } from "@/lib/logging/context";
 import { aiProviderPatchSchema } from "@/lib/validations/ai-provider";
+import {
+  chainWithReasoningEffort,
+  parseProviderChain,
+  serializeProviderChain,
+} from "@/lib/ai/provider-chain";
+import { reasoningEffortFor } from "@/lib/ai/reasoning-effort";
 
 export const dynamic = "force-dynamic";
 
@@ -42,6 +48,8 @@ export const GET = apiHandler(async () => {
       aiCompatModel: true,
       // v1.22 (#89)
       aiResponseTimeoutSeconds: true,
+      // #1126 — the reasoning settings live on the chain entries.
+      aiProviderChain: true,
       // v1.38.19 — a managed profile is never the party that gives
       // consent for itself; the offer below has to know.
       managedProfileAt: true,
@@ -141,6 +149,13 @@ export const GET = apiHandler(async () => {
     hasCompatKey: Boolean(u?.aiCompatKeyEncrypted),
     // v1.22 (#89) — per-user response timeout, in seconds (null = default).
     responseTimeoutSeconds: u?.aiResponseTimeoutSeconds ?? null,
+    // #1126 — the Local and gateway entries' reasoning settings (null =
+    // Default), read from the chain where they are stored.
+    localReasoningEffort: reasoningEffortFor(u?.aiProviderChain, "local"),
+    compatReasoningEffort: reasoningEffortFor(
+      u?.aiProviderChain,
+      "openai-compatible",
+    ),
     // v1.38.19 — see the block above. A tri-state and two booleans;
     // no count, no timestamp and no other account is inferable from them.
     serverProviderHealth,
@@ -297,7 +312,45 @@ export const PATCH = apiHandler(async (request: NextRequest) => {
     updates.aiResponseTimeoutSeconds = body.responseTimeoutSeconds;
   }
 
-  if (Object.keys(updates).length === 0) {
+  // ── #1126 — reasoning settings of the Local and gateway entries ──
+  // Stored on the entry in `aiProviderChain` rather than in a column of their
+  // own, so the setting is per entry and a chain can mix a thinking model with
+  // one that does not know the field. See `chainWithReasoningEffort` for how a
+  // default chain, or a provider absent from the chain, holds the value.
+  const reasoningTouched =
+    body.localReasoningEffort !== undefined ||
+    body.compatReasoningEffort !== undefined;
+  if (reasoningTouched) {
+    const current = await prisma.user.findUnique({
+      where: { id: user.id },
+      select: { aiProviderChain: true },
+    });
+    let chain: unknown = current?.aiProviderChain ?? null;
+    if (body.localReasoningEffort !== undefined) {
+      chain = chainWithReasoningEffort(
+        chain,
+        "local",
+        body.localReasoningEffort,
+      );
+    }
+    if (body.compatReasoningEffort !== undefined) {
+      chain = chainWithReasoningEffort(
+        chain,
+        "openai-compatible",
+        body.compatReasoningEffort,
+      );
+    }
+    // Written only when it changed: restating Default on a chain that was
+    // never customised must not freeze today's default chain into the row.
+    const before = serializeProviderChain(
+      parseProviderChain(current?.aiProviderChain ?? null),
+    );
+    if (serializeProviderChain(parseProviderChain(chain)) !== before) {
+      updates.aiProviderChain = chain;
+    }
+  }
+
+  if (Object.keys(updates).length === 0 && !reasoningTouched) {
     return apiError("No valid fields", 422, {
       errorCode: "ai_provider.no_fields",
     });
@@ -317,7 +370,9 @@ export const PATCH = apiHandler(async (request: NextRequest) => {
     updates.aiBaseUrl = null;
   }
 
-  await prisma.user.update({ where: { id: user.id }, data: updates });
+  if (Object.keys(updates).length > 0) {
+    await prisma.user.update({ where: { id: user.id }, data: updates });
+  }
 
   return apiSuccess({ updated: true });
 });
diff --git a/src/lib/ai/__tests__/provider-reasoning-effort.test.ts b/src/lib/ai/__tests__/provider-reasoning-effort.test.ts
new file mode 100644
index 000000000..0da8b93c1
--- /dev/null
+++ b/src/lib/ai/__tests__/provider-reasoning-effort.test.ts
@@ -0,0 +1,192 @@
+/**
+ * #1126 — every exported resolver hands out providers carrying their own
+ * chain entry's reasoning setting, and the request each one then sends
+ * carries exactly that value. A chain mixing a thinking model with one that
+ * does not know the field is the case the setting exists for.
+ */
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+vi.mock("@/lib/db", () => ({
+  prisma: {
+    user: { findUnique: vi.fn(), update: vi.fn() },
+    appSettings: { findUnique: vi.fn() },
+  },
+}));
+vi.mock("@/lib/crypto", () => ({
+  decrypt: vi.fn((v: string) => `decrypted:${v}`),
+  encrypt: vi.fn((v: string) => `encrypted:${v}`),
+}));
+vi.mock("@/lib/logging/context", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("@/lib/logging/context")>()),
+  annotate: vi.fn(),
+}));
+vi.mock("@/lib/safe-fetch", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("@/lib/safe-fetch")>()),
+  safeFetch: (url: string, init: RequestInit) => fetch(url, init),
+}));
+
+import { prisma } from "@/lib/db";
+import {
+  resolveProvider,
+  resolveProviderChain,
+  resolveProviderForTest,
+} from "../provider";
+import { resetLocalJsonDialectCache } from "../local-client";
+import { singleUserTurn, type AIProvider } from "../types";
+
+const ROW = {
+  aiProvider: "LOCAL",
+  aiModel: "gemma4:12b",
+  aiBaseUrl: "https://ollama.example.org/v1",
+  aiAnthropicKeyEncrypted: null,
+  aiLocalKeyEncrypted: null,
+  aiOpenaiKeyEncrypted: "openai-key",
+  aiCompatBaseUrl: "https://gateway.example.org/v1",
+  aiCompatKeyEncrypted: null,
+  aiCompatModel: "llama3",
+  role: "USER",
+  useCentralCodex: false,
+  managedProfileAt: null,
+  aiResponseTimeoutSeconds: null,
+};
+
+function withChain(aiProviderChain: unknown) {
+  vi.mocked(prisma.user.findUnique).mockResolvedValue({
+    ...ROW,
+    aiProviderChain,
+  } as never);
+  vi.mocked(prisma.appSettings.findUnique).mockResolvedValue(null as never);
+}
+
+const MIXED = [
+  {
+    providerType: "local",
+    priority: 1,
+    enabled: true,
+    reasoningEffort: "none",
+  },
+  { providerType: "openai-compatible", priority: 2, enabled: true },
+  { providerType: "openai", priority: 3, enabled: true },
+];
+
+/** The `reasoning_effort` the provider actually puts on the wire. */
+async function sentEffort(provider: AIProvider): Promise<unknown> {
+  const mock = vi.fn().mockResolvedValue({
+    ok: true,
+    json: () =>
+      Promise.resolve({
+        choices: [{ message: { content: "ok" }, finish_reason: "stop" }],
+        usage: { total_tokens: 1 },
+      }),
+  });
+  vi.stubGlobal("fetch", mock);
+  await provider.generateCompletion(singleUserTurn({ system: "s", user: "u" }));
+  vi.unstubAllGlobals();
+  const body = JSON.parse(mock.mock.calls[0][1].body as string);
+  return "reasoning_effort" in body ? body.reasoning_effort : "(absent)";
+}
+
+beforeEach(() => {
+  vi.resetAllMocks();
+  resetLocalJsonDialectCache();
+});
+
+describe("resolveProviderChain binds each entry's own setting", () => {
+  it("a mixed chain sends none, nothing, nothing", async () => {
+    withChain(MIXED);
+    const chain = await resolveProviderChain("user-1");
+    expect(chain.map((e) => e.providerType)).toEqual([
+      "local",
+      "openai-compatible",
+      "openai",
+    ]);
+    expect(chain.map((e) => e.instance.reasoningEffort)).toEqual([
+      "none",
+      null,
+      null,
+    ]);
+    const sent = [];
+    for (const entry of chain) sent.push(await sentEffort(entry.instance));
+    expect(sent).toEqual(["none", "(absent)", "(absent)"]);
+  });
+
+  it("the gateway's own value reaches the gateway", async () => {
+    withChain([
+      { providerType: "local", priority: 1, enabled: true },
+      {
+        providerType: "openai-compatible",
+        priority: 2,
+        enabled: true,
+        reasoningEffort: "high",
+      },
+    ]);
+    const chain = await resolveProviderChain("user-1");
+    expect(await sentEffort(chain[0].instance)).toBe("(absent)");
+    expect(await sentEffort(chain[1].instance)).toBe("high");
+  });
+});
+
+describe("resolveProvider", () => {
+  it("binds the selected Local provider's setting", async () => {
+    withChain(MIXED);
+    const provider = await resolveProvider("user-1");
+    expect(provider.type).toBe("local");
+    expect(await sentEffort(provider)).toBe("none");
+  });
+
+  it("reaches a selected gateway whose value sits on a disabled entry", async () => {
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({
+      ...ROW,
+      aiProvider: "OPENAI_COMPATIBLE",
+      aiProviderChain: [
+        { providerType: "codex", priority: 1, enabled: true },
+        {
+          providerType: "openai-compatible",
+          priority: 2,
+          enabled: false,
+          reasoningEffort: "low",
+        },
+      ],
+    } as never);
+    const provider = await resolveProvider("user-1");
+    expect(provider.type).toBe("openai-compatible");
+    expect(await sentEffort(provider)).toBe("low");
+  });
+});
+
+describe("resolveProviderForTest — the test button runs with the setting", () => {
+  it("testing the saved config (empty body) uses the saved provider's entry", async () => {
+    withChain(MIXED);
+    const provider = await resolveProviderForTest("user-1", {});
+    expect(provider.type).toBe("local");
+    expect(await sentEffort(provider)).toBe("none");
+  });
+
+  it("with no provider selected, the test runs the chain head with its value", async () => {
+    vi.mocked(prisma.user.findUnique).mockResolvedValue({
+      ...ROW,
+      aiProvider: null,
+      aiProviderChain: MIXED,
+    } as never);
+    vi.mocked(prisma.appSettings.findUnique).mockResolvedValue(null as never);
+    const provider = await resolveProviderForTest("user-1", {});
+    expect(provider.type).toBe("local");
+    expect(await sentEffort(provider)).toBe("none");
+  });
+
+  it("testing a named Local provider uses its entry's value", async () => {
+    withChain(MIXED);
+    const provider = await resolveProviderForTest("user-1", {
+      provider: "LOCAL",
+    });
+    expect(await sentEffort(provider)).toBe("none");
+  });
+
+  it("testing the personal OpenAI key never sends it", async () => {
+    withChain(MIXED);
+    const provider = await resolveProviderForTest("user-1", {
+      provider: "OPENAI",
+    });
+    expect(await sentEffort(provider)).toBe("(absent)");
+  });
+});
diff --git a/src/lib/ai/__tests__/reasoning-effort.test.ts b/src/lib/ai/__tests__/reasoning-effort.test.ts
new file mode 100644
index 000000000..420c88bbb
--- /dev/null
+++ b/src/lib/ai/__tests__/reasoning-effort.test.ts
@@ -0,0 +1,366 @@
+/**
+ * #1126 — the per-entry reasoning setting on the wire and in the schemas.
+ *
+ * Default must leave the request body byte-identical to what a setup that
+ * never touched the setting has always sent, so the Default cases compare the
+ * whole body string against a literal captured before the setting existed.
+ * Every other choice adds exactly one key, `reasoning_effort`, and only on the
+ * Local client and the OpenAI-compatible gateway.
+ */
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+vi.mock("../local-host-allowlist", () => ({
+  aiEgressPolicyFor: () => ({}),
+  isLocalAiHostAllowed: () => false,
+}));
+vi.mock("@/lib/logging/context", () => ({ annotate: vi.fn() }));
+// The pinned tags dial through undici's own fetch; route every call to the
+// stubbed global so the body can be read whatever the egress policy.
+vi.mock("@/lib/safe-fetch", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("@/lib/safe-fetch")>()),
+  safeFetch: (url: string, init: RequestInit) => fetch(url, init),
+}));
+
+import { bindReasoningEffort, reasoningEffortFor } from "../reasoning-effort";
+import {
+  LocalOpenAICompatibleClient,
+  resetLocalJsonDialectCache,
+} from "../local-client";
+import { OpenAIClient } from "../openai-client";
+import { AnthropicClient } from "../anthropic-client";
+import {
+  chainWithReasoningEffort,
+  parseProviderChain,
+  PROVIDER_CHAIN_DEFAULT,
+  serializeProviderChain,
+} from "../provider-chain";
+import { singleUserTurn, type AIProvider } from "../types";
+import {
+  aiProviderPatchSchema,
+  providerChainEntrySchema,
+  providerChainPutSchema,
+} from "@/lib/validations/ai-provider";
+
+const PARAMS = {
+  ...singleUserTurn({ system: "s", user: "u" }),
+  maxTokens: 250,
+};
+
+function okFetch(content = "ok") {
+  const mock = vi.fn().mockResolvedValue({
+    ok: true,
+    json: () =>
+      Promise.resolve({
+        choices: [{ message: { content }, finish_reason: "stop" }],
+        usage: { total_tokens: 5 },
+      }),
+  });
+  vi.stubGlobal("fetch", mock);
+  return mock;
+}
+
+function sentBody(mock: ReturnType<typeof okFetch>): string {
+  return mock.mock.calls[0][1].body as string;
+}
+
+function localClient() {
+  return new LocalOpenAICompatibleClient({
+    apiKey: null,
+    model: "gemma4:12b",
+    baseUrl: "http://ollama.example.org:11434/v1",
+  });
+}
+
+function gatewayClient() {
+  return new OpenAIClient({
+    apiKey: "",
+    model: "qwen3",
+    baseUrl: "https://gateway.example.org/v1",
+    providerType: "openai-compatible",
+  });
+}
+
+// Captured from the clients before the setting existed. Default must keep
+// sending exactly this.
+const LOCAL_BODY_BEFORE =
+  '{"model":"gemma4:12b","messages":[{"role":"system","content":"s"},{"role":"user","content":"Return strict JSON only, no markdown, no commentary.\\n\\nu"}],"temperature":0.3,"max_tokens":250}';
+const GATEWAY_BODY_BEFORE =
+  '{"model":"qwen3","messages":[{"role":"system","content":"s"},{"role":"user","content":"u"}],"max_tokens":250,"temperature":0.3}';
+
+beforeEach(() => {
+  vi.restoreAllMocks();
+  vi.unstubAllGlobals();
+  resetLocalJsonDialectCache();
+});
+
+describe("Local client", () => {
+  it("Default sends the body it always sent, byte for byte", async () => {
+    const mock = okFetch();
+    await localClient().generateCompletion(PARAMS);
+    expect(sentBody(mock)).toBe(LOCAL_BODY_BEFORE);
+    expect(JSON.parse(sentBody(mock))).not.toHaveProperty("reasoning_effort");
+  });
+
+  it("Off sends reasoning_effort none and nothing else new", async () => {
+    const mock = okFetch();
+    const client = localClient();
+    client.reasoningEffort = "none";
+    await client.generateCompletion(PARAMS);
+    const body = JSON.parse(sentBody(mock));
+    expect(body.reasoning_effort).toBe("none");
+    const { reasoning_effort: _dropped, ...rest } = body;
+    expect(JSON.stringify(rest)).toBe(LOCAL_BODY_BEFORE);
+  });
+
+  it.each(["low", "medium", "high"] as const)("%s is sent as is", async (v) => {
+    const mock = okFetch();
+    const client = localClient();
+    client.reasoningEffort = v;
+    await client.generateCompletion(PARAMS);
+    expect(JSON.parse(sentBody(mock)).reasoning_effort).toBe(v);
+  });
+
+  it("the streaming request carries it too", async () => {
+    const mock = okFetch();
+    const client = localClient();
+    client.reasoningEffort = "none";
+    // A buffered answer to a stream request falls back cleanly; only the
+    // first request body matters here.
+    await client.generateCompletionStream(PARAMS, () => {}).catch(() => {});
+    const body = JSON.parse(sentBody(mock));
+    expect(body.stream).toBe(true);
+    expect(body.reasoning_effort).toBe("none");
+  });
+});
+
+describe("OpenAI-compatible gateway", () => {
+  it("Default sends the body it always sent, byte for byte", async () => {
+    const mock = okFetch();
+    await gatewayClient().generateCompletion(PARAMS);
+    expect(sentBody(mock)).toBe(GATEWAY_BODY_BEFORE);
+  });
+
+  it("Off sends reasoning_effort none", async () => {
+    const mock = okFetch();
+    const client = gatewayClient();
+    client.reasoningEffort = "none";
+    await client.generateCompletion(PARAMS);
+    expect(JSON.parse(sentBody(mock)).reasoning_effort).toBe("none");
+  });
+
+  it("the OpenAI and Codex tags never send it, whatever is stamped", async () => {
+    for (const providerType of ["admin-key", "codex"] as const) {
+      vi.unstubAllGlobals();
+      const mock = okFetch();
+      const client = new OpenAIClient({
+        apiKey: "k",
+        model: "gpt-4o",
+        baseUrl: "https://gateway.example.org/v1",
+        providerType,
+      });
+      client.reasoningEffort = "high";
+      await client.generateCompletion(PARAMS);
+      expect(JSON.parse(sentBody(mock))).not.toHaveProperty("reasoning_effort");
+    }
+  });
+});
+
+describe("bindReasoningEffort", () => {
+  const chain = [
+    {
+      providerType: "local",
+      priority: 1,
+      enabled: true,
+      reasoningEffort: "none",
+    },
+    {
+      providerType: "openai-compatible",
+      priority: 2,
+      enabled: true,
+      reasoningEffort: "high",
+    },
+    { providerType: "openai", priority: 3, enabled: true },
+  ];
+
+  it("stamps each entry's own value, keyed on the instance type", () => {
+    expect(bindReasoningEffort(localClient(), chain).reasoningEffort).toBe(
+      "none",
+    );
+    expect(bindReasoningEffort(gatewayClient(), chain).reasoningEffort).toBe(
+      "high",
+    );
+  });
+
+  it("stamps null on every other provider", () => {
+    const openai = new OpenAIClient({
+      apiKey: "k",
+      model: "gpt-4o",
+      baseUrl: "https://api.openai.com/v1",
+    });
+    const anthropic: AIProvider = new AnthropicClient({
+      apiKey: "k",
+      model: "m",
+    });
+    expect(bindReasoningEffort(openai, chain).reasoningEffort).toBeNull();
+    expect(bindReasoningEffort(anthropic, chain).reasoningEffort).toBeNull();
+  });
+
+  it("stamps null for a chain that was never customised", () => {
+    expect(bindReasoningEffort(localClient(), null).reasoningEffort).toBeNull();
+  });
+});
+
+describe("the stored chain", () => {
+  it("keeps a valid value on local / openai-compatible and drops it elsewhere", () => {
+    const parsed = parseProviderChain([
+      {
+        providerType: "local",
+        priority: 1,
+        enabled: true,
+        reasoningEffort: "low",
+      },
+      {
+        providerType: "openai",
+        priority: 2,
+        enabled: true,
+        reasoningEffort: "low",
+      },
+      {
+        providerType: "openai-compatible",
+        priority: 3,
+        enabled: true,
+        reasoningEffort: "max",
+      },
+    ]);
+    expect(parsed.map((e) => e.reasoningEffort)).toEqual([
+      "low",
+      undefined,
+      undefined,
+    ]);
+    expect(serializeProviderChain(parsed)).toBe(
+      '[{"providerType":"local","priority":1,"enabled":true,"reasoningEffort":"low"},{"providerType":"openai","priority":2,"enabled":true},{"providerType":"openai-compatible","priority":3,"enabled":true}]',
+    );
+  });
+
+  it("serialises a chain without the setting exactly as before", () => {
+    expect(serializeProviderChain(PROVIDER_CHAIN_DEFAULT)).not.toContain(
+      "reasoningEffort",
+    );
+  });
+
+  it("materialises the default chain to hold a value", () => {
+    const next = chainWithReasoningEffort(null, "local", "none");
+    expect(next.map((e) => e.providerType)).toEqual(
+      PROVIDER_CHAIN_DEFAULT.map((e) => e.providerType),
+    );
+    expect(reasoningEffortFor(next, "local")).toBe("none");
+  });
+
+  it("holds a value for a provider absent from the chain on a disabled entry", () => {
+    const stored = [{ providerType: "codex", priority: 7, enabled: true }];
+    const next = chainWithReasoningEffort(stored, "openai-compatible", "high");
+    expect(next).toEqual([
+      { providerType: "codex", priority: 7, enabled: true },
+      {
+        providerType: "openai-compatible",
+        priority: 8,
+        enabled: false,
+        reasoningEffort: "high",
+      },
+    ]);
+  });
+
+  it("clears without adding an entry", () => {
+    const stored = [
+      {
+        providerType: "local",
+        priority: 1,
+        enabled: true,
+        reasoningEffort: "low",
+      },
+    ];
+    expect(chainWithReasoningEffort(stored, "local", null)).toEqual([
+      { providerType: "local", priority: 1, enabled: true },
+    ]);
+    expect(chainWithReasoningEffort(stored, "openai-compatible", null)).toEqual(
+      [
+        {
+          providerType: "local",
+          priority: 1,
+          enabled: true,
+          reasoningEffort: "low",
+        },
+      ],
+    );
+  });
+});
+
+describe("schemas", () => {
+  const VALUES = [null, "none", "low", "medium", "high"] as const;
+
+  it.each(["local", "openai-compatible"])(
+    "a %s chain entry accepts Default, Off, Low, Medium and High",
+    (providerType) => {
+      for (const reasoningEffort of VALUES) {
+        expect(
+          providerChainEntrySchema.safeParse({
+            providerType,
+            enabled: true,
+            reasoningEffort,
+          }).success,
+        ).toBe(true);
+      }
+    },
+  );
+
+  it("refuses a value outside the five", () => {
+    expect(
+      providerChainEntrySchema.safeParse({
+        providerType: "local",
+        enabled: true,
+        reasoningEffort: "max",
+      }).success,
+    ).toBe(false);
+  });
+
+  it.each(["openai", "anthropic", "codex", "admin-openai", "admin-codex"])(
+    "refuses the setting on a %s entry, null included",
+    (providerType) => {
+      for (const reasoningEffort of VALUES) {
+        const result = providerChainEntrySchema.safeParse({
+          providerType,
+          enabled: true,
+          reasoningEffort,
+        });
+        expect(result.success).toBe(false);
+        expect(result.error?.issues[0].path).toEqual(["reasoningEffort"]);
+      }
+      expect(
+        providerChainEntrySchema.safeParse({ providerType, enabled: true })
+          .success,
+      ).toBe(true);
+    },
+  );
+
+  it("the chain body still accepts a chain without the setting", () => {
+    expect(
+      providerChainPutSchema.safeParse({
+        chain: [{ providerType: "local", priority: 1, enabled: true }],
+      }).success,
+    ).toBe(true);
+  });
+
+  it("the provider PATCH accepts the five values for both entries", () => {
+    for (const v of VALUES) {
+      expect(
+        aiProviderPatchSchema.safeParse({
+          localReasoningEffort: v,
+          compatReasoningEffort: v,
+        }).success,
+      ).toBe(true);
+    }
+    expect(
+      aiProviderPatchSchema.safeParse({ localReasoningEffort: "max" }).success,
+    ).toBe(false);
+  });
+});
diff --git a/src/lib/ai/local-client.ts b/src/lib/ai/local-client.ts
index 27c96df89..e753050ef 100644
--- a/src/lib/ai/local-client.ts
+++ b/src/lib/ai/local-client.ts
@@ -23,6 +23,7 @@ import {
   resetJsonModeDialectCache,
   type JsonModeDialect,
 } from "./json-dialect";
+import type { ReasoningEffort } from "./reasoning-effort";
 
 interface LocalClientConfig {
   apiKey?: string | null;
@@ -108,6 +109,8 @@ export class LocalOpenAICompatibleClient implements AIProvider {
   readonly type = "local" as const;
   /** See `AIProvider.responseTimeoutSeconds`; stamped by the resolver. */
   responseTimeoutSeconds: number | null = null;
+  /** See `AIProvider.reasoningEffort`; stamped by the resolver. */
+  reasoningEffort: ReasoningEffort | null = null;
   /** Local servers commonly reject an unknown `tools` field — never send it. */
   readonly supportsTools = false;
   private config: LocalClientConfig;
@@ -164,6 +167,12 @@ export class LocalOpenAICompatibleClient implements AIProvider {
       // most OpenAI-compatible local servers honour it; servers that
       // ignore it simply disregard the field. Omitted when unset.
       ...(params.seed !== undefined ? { seed: params.seed } : {}),
+      // #1126 — the entry's reasoning setting. Default sends nothing, so the
+      // body of a setup that never touched it stays byte-identical; "Off" is
+      // `none`, which stops a thinking model spending the answer budget.
+      ...(this.reasoningEffort
+        ? { reasoning_effort: this.reasoningEffort }
+        : {}),
       // v1.28.28 (#470) — the JSON surfaces opt in via `responseFormat:
       // "json"`. Default dialect sends the STANDARD OpenAI field (the
       // top-level Ollama-native `format: "json"` this client used to send
diff --git a/src/lib/ai/openai-client.ts b/src/lib/ai/openai-client.ts
index 63464563c..f54ea1bf1 100644
--- a/src/lib/ai/openai-client.ts
+++ b/src/lib/ai/openai-client.ts
@@ -10,6 +10,7 @@ import {
   rememberJsonModeDialect,
 } from "./json-dialect";
 import { aiEgressPolicyFor } from "./local-host-allowlist";
+import type { ReasoningEffort } from "./reasoning-effort";
 import {
   buildOpenAIMessages,
   buildOpenAITools,
@@ -62,6 +63,11 @@ export class OpenAIClient implements AIProvider {
   readonly type: OpenAIProviderType;
   /** See `AIProvider.responseTimeoutSeconds`; stamped by the resolver. */
   responseTimeoutSeconds: number | null = null;
+  /**
+   * See `AIProvider.reasoningEffort`; stamped by the resolver. Only the
+   * gateway tag ever sends it (`isGateway` below), whatever is stamped here.
+   */
+  reasoningEffort: ReasoningEffort | null = null;
   private config: OpenAIClientConfig;
 
   constructor(config: OpenAIClientConfig) {
@@ -150,6 +156,11 @@ export class OpenAIClient implements AIProvider {
             : {}),
           ...(tools ? { tools } : {}),
           ...(params.toolChoice ? { tool_choice: params.toolChoice } : {}),
+          // #1126 — the gateway entry's reasoning setting; Default sends
+          // nothing. `api.openai.com` and Codex never get it.
+          ...(this.isGateway && this.reasoningEffort
+            ? { reasoning_effort: this.reasoningEffort }
+            : {}),
         }),
       },
       // 60 s ceiling so a tar-pit upstream cannot pin a worker
diff --git a/src/lib/ai/provider-chain.ts b/src/lib/ai/provider-chain.ts
index 6a92ad27a..ccfa8409d 100644
--- a/src/lib/ai/provider-chain.ts
+++ b/src/lib/ai/provider-chain.ts
@@ -18,6 +18,13 @@
  * `PROVIDER_CHAIN_DEFAULT`.
  */
 
+import {
+  isReasoningEffort,
+  isReasoningProviderType,
+  type ReasoningEffort,
+  type ReasoningProviderType,
+} from "./reasoning-effort";
+
 /**
  * Provider tags used in the chain. `admin-openai` is the legacy
  * `AppSettings.adminAiKeyEncrypted` fallback (so misconfigured users
@@ -63,6 +70,8 @@ export interface ProviderChainEntry {
   providerType: ProviderChainType;
   priority: number;
   enabled: boolean;
+  /** Only ever set on a `REASONING_PROVIDER_TYPES` entry. Absent = Default. */
+  reasoningEffort?: ReasoningEffort;
 }
 
 /**
@@ -113,6 +122,7 @@ export function parseProviderChain(
       providerType?: unknown;
       priority?: unknown;
       enabled?: unknown;
+      reasoningEffort?: unknown;
     };
     const providerType = candidate.providerType;
     if (typeof providerType !== "string") continue;
@@ -128,10 +138,18 @@ export function parseProviderChain(
         : valid.length + 1;
     const enabled =
       typeof candidate.enabled === "boolean" ? candidate.enabled : true;
+    // A reasoning effort survives only on an entry that may carry one and
+    // only with a known value; anything else reads as Default.
+    const reasoningEffort =
+      isReasoningProviderType(providerType) &&
+      isReasoningEffort(candidate.reasoningEffort)
+        ? candidate.reasoningEffort
+        : undefined;
     valid.push({
       providerType: providerType as ProviderChainType,
       priority,
       enabled,
+      ...(reasoningEffort ? { reasoningEffort } : {}),
     });
   }
 
@@ -153,6 +171,39 @@ export function serializeProviderChain(
       providerType: e.providerType,
       priority: e.priority,
       enabled: e.enabled,
+      ...(e.reasoningEffort ? { reasoningEffort: e.reasoningEffort } : {}),
     })),
   );
 }
+
+/**
+ * The chain to persist after setting (or, with `null`, clearing) one entry's
+ * reasoning effort from that provider's own settings form.
+ *
+ * The setting lives on the chain entry, so a chain that was never customised
+ * is materialised from the default first. A provider that is not in the chain
+ * at all gets a DISABLED entry to hold the value: the setting must reach the
+ * provider when it is resolved as the selected one, and a disabled entry is
+ * inert everywhere else (every reader filters on `enabled`). Clearing on an
+ * absent entry writes nothing new.
+ */
+export function chainWithReasoningEffort(
+  rawChain: unknown,
+  providerType: ReasoningProviderType,
+  effort: ReasoningEffort | null,
+): ProviderChainEntry[] {
+  const chain = parseProviderChain(rawChain).map((e) => ({ ...e }));
+  const entry = chain.find((e) => e.providerType === providerType);
+  if (entry) {
+    if (effort) entry.reasoningEffort = effort;
+    else delete entry.reasoningEffort;
+  } else if (effort) {
+    chain.push({
+      providerType,
+      priority: Math.max(0, ...chain.map((e) => e.priority)) + 1,
+      enabled: false,
+      reasoningEffort: effort,
+    });
+  }
+  return chain;
+}
diff --git a/src/lib/ai/provider.ts b/src/lib/ai/provider.ts
index 89bc856a0..a88e6e5ad 100644
--- a/src/lib/ai/provider.ts
+++ b/src/lib/ai/provider.ts
@@ -1,5 +1,6 @@
 import type { AIProvider, CompletionResult } from "./types";
 import { bindResponseTimeout } from "./effective-timeout";
+import { bindReasoningEffort } from "./reasoning-effort";
 import { prisma } from "@/lib/db";
 import { decrypt } from "@/lib/crypto";
 import { CodexClient, resolveCodexVisionSlug } from "./codex-client";
@@ -501,13 +502,19 @@ export async function resolveProvider(userId: string): Promise<AIProvider> {
       role: true,
       managedProfileAt: true,
       aiResponseTimeoutSeconds: true,
+      aiProviderChain: true,
     },
   });
   // The record's response-timeout setting rides on whatever this returns, on
   // every branch, the operator-key fallback for a managed profile included:
-  // the person waiting on the record is who the call serves.
+  // the person waiting on the record is who the call serves. The reasoning
+  // effort (#1126) rides the same way; it only lands on a Local or gateway
+  // instance, so the operator fallback never picks one up.
   const bind = (provider: AIProvider): AIProvider =>
-    bindResponseTimeout(provider, userRow?.aiResponseTimeoutSeconds);
+    bindReasoningEffort(
+      bindResponseTimeout(provider, userRow?.aiResponseTimeoutSeconds),
+      userRow?.aiProviderChain,
+    );
   const policy = providerCredentialPolicy(
     authority,
     userRow?.managedProfileAt ?? null,
@@ -533,18 +540,23 @@ export async function resolveProvider(userId: string): Promise<AIProvider> {
 }
 
 /**
- * The record owner's `aiResponseTimeoutSeconds`, for `resolveProviderForTest`,
- * whose many branches (saved config, unsaved override, the chain) are bound in
- * one place on the way out. The other two resolvers read it with their row.
+ * The record owner's `aiResponseTimeoutSeconds` and `aiProviderChain`, for
+ * `resolveProviderForTest`, whose many branches (saved config, unsaved
+ * override, the chain) are bound in one place on the way out. The other two
+ * resolvers read them with their row.
  */
-async function readResponseTimeoutSeconds(
-  userId: string,
-): Promise<number | null> {
+async function readBoundSettings(userId: string): Promise<{
+  aiResponseTimeoutSeconds: number | null;
+  aiProviderChain: unknown;
+}> {
   const row = await prisma.user.findUnique({
     where: { id: userId },
-    select: { aiResponseTimeoutSeconds: true },
+    select: { aiResponseTimeoutSeconds: true, aiProviderChain: true },
   });
-  return row?.aiResponseTimeoutSeconds ?? null;
+  return {
+    aiResponseTimeoutSeconds: row?.aiResponseTimeoutSeconds ?? null,
+    aiProviderChain: row?.aiProviderChain ?? null,
+  };
 }
 
 /**
@@ -595,9 +607,12 @@ export async function resolveProviderChain(
       aiResponseTimeoutSeconds: true,
     },
   });
-  // See `resolveProvider`: every instance carries the record's setting.
+  // See `resolveProvider`: every instance carries the record's settings.
   const bind = (provider: AIProvider): AIProvider =>
-    bindResponseTimeout(provider, userRow?.aiResponseTimeoutSeconds);
+    bindReasoningEffort(
+      bindResponseTimeout(provider, userRow?.aiResponseTimeoutSeconds),
+      userRow?.aiProviderChain,
+    );
   const policy = providerCredentialPolicy(
     authority,
     userRow?.managedProfileAt ?? null,
@@ -1184,10 +1199,13 @@ export async function resolveProviderForTest(
 ): Promise<AIProvider> {
   // The test runs under the same timeout generation would, so a slow local
   // model that needs a raised setting is not reported as dead by the test.
+  // The same holds for the entry's reasoning effort (#1126): a thinking model
+  // that only answers with reasoning switched off must test green with it off.
   const provider = await resolveProviderForTestUnbound(userId, override);
-  return bindResponseTimeout(
-    provider,
-    await readResponseTimeoutSeconds(userId),
+  const settings = await readBoundSettings(userId);
+  return bindReasoningEffort(
+    bindResponseTimeout(provider, settings.aiResponseTimeoutSeconds),
+    settings.aiProviderChain,
   );
 }
 
diff --git a/src/lib/ai/reasoning-effort.ts b/src/lib/ai/reasoning-effort.ts
new file mode 100644
index 000000000..ccf1f6906
--- /dev/null
+++ b/src/lib/ai/reasoning-effort.ts
@@ -0,0 +1,83 @@
+/**
+ * #1126 — the per-entry reasoning setting of the Local and OpenAI-compatible
+ * providers, and the binder that stamps it onto a resolved provider.
+ *
+ * A leaf on purpose: `types.ts` and the binder are reachable from workers that
+ * must not reach the provider machinery (`data-arrival-provider-isolation`),
+ * so nothing here imports `provider-chain.ts`. The stored entry is read from
+ * the raw chain directly, first match wins, the same rule
+ * `parseProviderChain` dedupes by.
+ */
+import type { AIProvider } from "./types";
+
+/**
+ * The `reasoning_effort` values a chain entry may carry. "Off" in the settings
+ * is `none` on the wire. The absence of the key is "Default": nothing is sent
+ * and the model decides, which is what every chain stored before the setting
+ * existed keeps doing.
+ */
+export const REASONING_EFFORTS = ["none", "low", "medium", "high"] as const;
+
+export type ReasoningEffort = (typeof REASONING_EFFORTS)[number];
+
+/**
+ * The entries that may carry a reasoning effort: the two whose wire is a
+ * person-chosen `/chat/completions` endpoint serving a model of their choice.
+ * OpenAI, Anthropic and Codex pin their own model families and parameters,
+ * so the setting is refused for them rather than silently dropped.
+ */
+export const REASONING_PROVIDER_TYPES = ["local", "openai-compatible"] as const;
+
+export type ReasoningProviderType = (typeof REASONING_PROVIDER_TYPES)[number];
+
+export function isReasoningProviderType(
+  providerType: string,
+): providerType is ReasoningProviderType {
+  return (REASONING_PROVIDER_TYPES as readonly string[]).includes(providerType);
+}
+
+export function isReasoningEffort(value: unknown): value is ReasoningEffort {
+  return (
+    typeof value === "string" &&
+    (REASONING_EFFORTS as readonly string[]).includes(value)
+  );
+}
+
+/**
+ * The reasoning effort stored on a provider type's entry in a persisted chain,
+ * enabled or not. `null` is Default: no chain, no entry, no valid value, or a
+ * type that cannot carry one.
+ */
+export function reasoningEffortFor(
+  rawChain: unknown,
+  providerType: string,
+): ReasoningEffort | null {
+  if (!isReasoningProviderType(providerType) || !Array.isArray(rawChain)) {
+    return null;
+  }
+  const entry = rawChain.find(
+    (item): item is { reasoningEffort?: unknown } =>
+      item != null &&
+      typeof item === "object" &&
+      (item as { providerType?: unknown }).providerType === providerType,
+  );
+  return isReasoningEffort(entry?.reasoningEffort)
+    ? entry.reasoningEffort
+    : null;
+}
+
+/**
+ * Stamp the record owner's reasoning effort onto a resolved provider. Keyed on
+ * the instance's runtime type, so only a Local client or an OpenAI-compatible
+ * gateway can ever carry one: the operator's provider, the personal OpenAI
+ * key, Anthropic and Codex resolve to `null` whatever the stored chain says.
+ * Called by every exported resolver in `provider.ts` next to
+ * `bindResponseTimeout`, with the raw `User.aiProviderChain` value.
+ */
+export function bindReasoningEffort<P extends AIProvider>(
+  provider: P,
+  aiProviderChain: unknown,
+): P {
+  provider.reasoningEffort = reasoningEffortFor(aiProviderChain, provider.type);
+  return provider;
+}
diff --git a/src/lib/ai/types.ts b/src/lib/ai/types.ts
index 541dcbb24..7ad8be174 100644
--- a/src/lib/ai/types.ts
+++ b/src/lib/ai/types.ts
@@ -1,3 +1,4 @@
+import type { ReasoningEffort } from "./reasoning-effort";
 import { z } from "zod/v4";
 
 // ─── Insight Result Schema ─────────────────────────────────
@@ -123,6 +124,13 @@ export interface AIProvider {
    * `null` / absent → the surface's `timeoutMs`, else the 60 s default.
    */
   responseTimeoutSeconds?: number | null;
+  /**
+   * #1126 — the `reasoning_effort` the record owner chose for this provider's
+   * chain entry, stamped by the resolver (`bindReasoningEffort`). Only the
+   * Local client and the OpenAI-compatible gateway read it, and only they are
+   * ever stamped with a value. `null` / absent → Default: the key is not sent.
+   */
+  reasoningEffort?: ReasoningEffort | null;
   generateCompletion(params: CompletionParams): Promise<CompletionResult>;
   /**
    * v1.22 (#89) — optional true-streaming variant. A provider that can emit
diff --git a/src/lib/export/__tests__/account-settings-backup.test.ts b/src/lib/export/__tests__/account-settings-backup.test.ts
index b0768b7e9..3414b51d1 100644
--- a/src/lib/export/__tests__/account-settings-backup.test.ts
+++ b/src/lib/export/__tests__/account-settings-backup.test.ts
@@ -19,6 +19,7 @@ import {
   buildAccountSettingsBackupSection,
 } from "@/lib/export/account-settings-backup";
 import { UNREADABLE_EXPORT_MARKER } from "@/lib/export/unreadable-marker";
+import { reasoningEffortFor } from "@/lib/ai/reasoning-effort";
 
 /** A 1x1 PNG, the smallest image the avatar upload accepts. */
 const PNG_1X1 =
@@ -190,6 +191,38 @@ describe("admitAccountSettings", () => {
     ]);
   });
 
+  // #1126 — the reasoning setting lives on the provider chain entries, so
+  // the chain column carries it through a backup unchanged.
+  it("carries the provider chain's reasoning settings through a round trip", async () => {
+    const chain = [
+      {
+        providerType: "local",
+        priority: 1,
+        enabled: true,
+        reasoningEffort: "none",
+      },
+      {
+        providerType: "openai-compatible",
+        priority: 2,
+        enabled: false,
+        reasoningEffort: "high",
+      },
+      { providerType: "openai", priority: 3, enabled: true },
+    ];
+    const { accountSettings } = await buildAccountSettingsBackupSection(
+      prismaReturning(rowWith({ aiProviderChain: chain })),
+      "u1",
+      { purpose: "disaster-recovery" },
+    );
+    const restored = admitAccountSettings(
+      JSON.parse(JSON.stringify(accountSettings)),
+      ctx,
+    ).data.aiProviderChain;
+    expect(restored).toEqual(chain);
+    expect(reasoningEffortFor(restored, "local")).toBe("none");
+    expect(reasoningEffortFor(restored, "openai-compatible")).toBe("high");
+  });
+
   it("writes a database null for a JSON setting the file clears", () => {
     expect(
       admitAccountSettings({ dashboardWidgetsJson: null }, ctx).data
diff --git a/src/lib/openapi/routes/insights/schemas.ts b/src/lib/openapi/routes/insights/schemas.ts
index cc49e7eca..16b65fd5b 100644
--- a/src/lib/openapi/routes/insights/schemas.ts
+++ b/src/lib/openapi/routes/insights/schemas.ts
@@ -18,7 +18,7 @@ import {
   SPARKLINE_MAX_POINTS,
 } from "@/lib/insights/derived/types";
 import { ANALYTICS_RANGES } from "@/lib/analytics/range-delta";
-import { PROVIDER_CHAIN_TYPES } from "@/lib/ai/provider-chain";
+import { providerChainPutSchema } from "@/lib/validations/ai-provider";
 import { PERIOD_DAYS } from "@/lib/insights/narrative/period-narrative";
 import { aiCapabilityState } from "../profile";
 
@@ -2531,36 +2531,11 @@ export const providerChainResponse = z
       "The account's AI-provider chain as the settings surface reads it. Provider TYPES and boolean state only — no key, token or account id is ever on this wire.",
   });
 
-export const providerChainPutRequest = z
-  .object({
-    chain: z
-      .array(
-        z.object({
-          providerType: z
-            .enum(PROVIDER_CHAIN_TYPES as unknown as [string, ...string[]])
-            .describe(
-              "Closed allow-list. The mock provider is excluded from it structurally, which is what keeps production from reaching one.",
-            ),
-          priority: z
-            .number()
-            .int()
-            .optional()
-            .describe(
-              "ACCEPTED AND IGNORED. Priority is recomputed from the array's insertion order, so a stale client cannot persist a chain whose displayed order disagrees with its stored one. Send the order you want as the order of the array.",
-            ),
-          enabled: z.boolean(),
-        }),
-      )
-      .min(1)
-      .describe(
-        "The whole chain, in the order it should be walked. At least one entry and at most one per known provider type; a repeated type is refused.",
-      ),
-  })
-  .meta({
-    id: "ProviderChainPutRequest",
-    description:
-      "Replaces the account's provider chain wholesale. No credential is written or read here — only which provider types exist, in what order, and which are enabled.",
-  });
+export const providerChainPutRequest = providerChainPutSchema.meta({
+  id: "ProviderChainPutRequest",
+  description:
+    "Replaces the account's provider chain wholesale. No credential is written or read here — only which provider types exist, in what order, which are enabled, and the reasoning setting of the Local and OpenAI-compatible entries.",
+});
 
 // ── Read-only advisor + generation (`/api/insights/generate`) ─────────
 
diff --git a/src/lib/openapi/routes/profile.ts b/src/lib/openapi/routes/profile.ts
index 257f01428..261cd63a5 100644
--- a/src/lib/openapi/routes/profile.ts
+++ b/src/lib/openapi/routes/profile.ts
@@ -36,6 +36,7 @@ import {
 } from "@/lib/validations/user-prefs";
 import {
   aiProviderPatchSchema,
+  reasoningEffortSchema,
   aiTestOverrideSchema,
 } from "@/lib/validations/ai-provider";
 import {
@@ -674,6 +675,12 @@ const aiProviderResponse = z
       .describe(
         "v1.22 (#89) — per-user response timeout for AI generation, in seconds (10–600). Null = the built-in comprehensive-briefing default (~120 s). Mainly for slow local/self-hosted backends.",
       ),
+    localReasoningEffort: reasoningEffortSchema.describe(
+      "#1126 — reasoning setting of the Local provider entry, sent as `reasoning_effort` (`none` = Off). Null = Default: the key is not sent.",
+    ),
+    compatReasoningEffort: reasoningEffortSchema.describe(
+      "#1126 — the same for the OpenAI-compatible gateway entry.",
+    ),
     // v1.38.19 — the setup flow's last screen used to promise
     // that insights "work for you right away" as soon as `managedBy` read
     // `server`. That is a presence read; it never knew whether the key
diff --git a/src/lib/validations/ai-provider.ts b/src/lib/validations/ai-provider.ts
index 7b51bcffe..dc8f92802 100644
--- a/src/lib/validations/ai-provider.ts
+++ b/src/lib/validations/ai-provider.ts
@@ -16,6 +16,12 @@
  */
 import { z } from "zod/v4";
 
+import { PROVIDER_CHAIN_TYPES } from "@/lib/ai/provider-chain";
+import {
+  isReasoningProviderType,
+  REASONING_EFFORTS,
+} from "@/lib/ai/reasoning-effort";
+
 /** The five provider kinds a user may select. */
 export const AI_PROVIDER_KINDS = [
   "OPENAI",
@@ -38,6 +44,17 @@ export const aiProviderKindSchema = z.enum(AI_PROVIDER_KINDS);
  */
 const clearableString = z.string().nullable();
 
+/**
+ * #1126 — a provider entry's reasoning setting. `null` is "Default": nothing
+ * is sent and the model decides. `none` is "Off".
+ */
+export const reasoningEffortSchema = z
+  .enum(REASONING_EFFORTS)
+  .nullable()
+  .describe(
+    "Reasoning setting for a Local or OpenAI-compatible provider, sent as `reasoning_effort` in the `/chat/completions` body. `none` switches reasoning off, which stops a thinking model (Gemma, Qwen and the like) spending the answer budget on reasoning. `null` is Default: the key is not sent at all and the model decides.",
+  );
+
 /**
  * `PATCH /api/user/ai-provider` — a partial update of the provider config.
  *
@@ -93,6 +110,22 @@ export const aiProviderPatchSchema = z.object({
     .max(600, "Response timeout must be between 10 and 600 seconds")
     .nullable()
     .optional(),
+  /**
+   * #1126 — the reasoning setting of the Local entry. Stored on the entry in
+   * the provider chain; a chain never customised is materialised from the
+   * default to hold it. `null` restores Default.
+   */
+  localReasoningEffort: reasoningEffortSchema
+    .optional()
+    .describe(
+      "Reasoning setting of the Local provider entry, stored on that entry of the provider chain. `none` = Off, `null` = Default (nothing sent). Omitted leaves it untouched.",
+    ),
+  /** #1126 — the same for the OpenAI-compatible gateway entry. */
+  compatReasoningEffort: reasoningEffortSchema
+    .optional()
+    .describe(
+      "Reasoning setting of the OpenAI-compatible gateway entry, stored on that entry of the provider chain. `none` = Off, `null` = Default (nothing sent). Omitted leaves it untouched.",
+    ),
 });
 
 export type AiProviderPatchInput = z.infer<typeof aiProviderPatchSchema>;
@@ -115,3 +148,61 @@ export const aiTestOverrideSchema = z
   .strict();
 
 export type AiTestOverrideInput = z.infer<typeof aiTestOverrideSchema>;
+
+/**
+ * One entry of `PUT /api/insights/provider-chain`. Shared by the route and the
+ * OpenAPI registry, so the published contract and the parser are one object.
+ */
+export const providerChainEntrySchema = z
+  .object({
+    providerType: z
+      .enum(PROVIDER_CHAIN_TYPES)
+      .describe(
+        "Closed allow-list. The mock provider is excluded from it structurally, which is what keeps production from reaching one.",
+      ),
+    // Priority is recomputed server-side from insertion order so a stale
+    // client cannot persist a chain whose displayed order disagrees with
+    // its priority field. The number is accepted (and may be present) but
+    // ignored on the wire.
+    priority: z
+      .number()
+      .int()
+      .optional()
+      .describe(
+        "ACCEPTED AND IGNORED. Priority is recomputed from the array's insertion order, so a stale client cannot persist a chain whose displayed order disagrees with its stored one. Send the order you want as the order of the array.",
+      ),
+    enabled: z.boolean(),
+    reasoningEffort: reasoningEffortSchema
+      .optional()
+      .describe(
+        "Only on a `local` or `openai-compatible` entry; refused on any other. Omitted keeps the value already stored for that provider, `null` restores Default, `none` / `low` / `medium` / `high` are sent as `reasoning_effort`.",
+      ),
+  })
+  .strict()
+  .superRefine((entry, ctx) => {
+    if (
+      entry.reasoningEffort !== undefined &&
+      !isReasoningProviderType(entry.providerType)
+    ) {
+      ctx.addIssue({
+        code: "custom",
+        path: ["reasoningEffort"],
+        message:
+          "A reasoning setting applies to the local and openai-compatible providers only",
+      });
+    }
+  });
+
+export const providerChainPutSchema = z
+  .object({
+    chain: z
+      .array(providerChainEntrySchema)
+      .min(1, "Chain must contain at least one provider")
+      .max(PROVIDER_CHAIN_TYPES.length, "Too many providers")
+      .describe(
+        "The whole chain, in the order it should be walked. At least one entry and at most one per known provider type; a repeated type is refused.",
+      ),
+  })
+  .strict();
+
+export type ProviderChainPutInput = z.infer<typeof providerChainPutSchema>;