diff --git a/apps/journal/app/lib/api-guard.server.test.ts b/apps/journal/app/lib/api-guard.server.test.ts
new file mode 100644
index 0000000..695086b
--- /dev/null
+++ b/apps/journal/app/lib/api-guard.server.test.ts
@@ -0,0 +1,70 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { TERMS_VERSION } from "./legal";
+
+const mockGetAuthenticatedUser = vi.fn();
+
+vi.mock("./oauth.server.ts", () => ({
+  getAuthenticatedUser: mockGetAuthenticatedUser,
+}));
+
+beforeEach(() => {
+  vi.clearAllMocks();
+});
+
+describe("requireApiUser", () => {
+  it("returns 401 when unauthenticated", async () => {
+    mockGetAuthenticatedUser.mockResolvedValue(null);
+    const { requireApiUser } = await import("./api-guard.server.ts");
+
+    try {
+      await requireApiUser(new Request("http://localhost/api/v1/routes"));
+      expect.fail("should throw");
+    } catch (err) {
+      expect(err).toBeInstanceOf(Response);
+      expect((err as Response).status).toBe(401);
+      const body = await (err as Response).json();
+      expect(body.code).toBe("UNAUTHORIZED");
+    }
+  });
+
+  it("returns the user when termsVersion matches", async () => {
+    const user = { id: "u1", termsVersion: TERMS_VERSION };
+    mockGetAuthenticatedUser.mockResolvedValue(user);
+    const { requireApiUser } = await import("./api-guard.server.ts");
+
+    const result = await requireApiUser(new Request("http://localhost/api/v1/routes"));
+    expect(result).toBe(user);
+  });
+
+  it("returns 403 TERMS_OUTDATED when termsVersion is stale", async () => {
+    mockGetAuthenticatedUser.mockResolvedValue({ id: "u1", termsVersion: "2020-01-01" });
+    const { requireApiUser } = await import("./api-guard.server.ts");
+
+    try {
+      await requireApiUser(new Request("http://localhost/api/v1/routes"));
+      expect.fail("should throw");
+    } catch (err) {
+      expect(err).toBeInstanceOf(Response);
+      expect((err as Response).status).toBe(403);
+      const body = await (err as Response).json();
+      expect(body.code).toBe("TERMS_OUTDATED");
+      expect(body.currentTermsVersion).toBe(TERMS_VERSION);
+    }
+  });
+
+  it("returns 403 TERMS_OUTDATED when termsVersion is null", async () => {
+    mockGetAuthenticatedUser.mockResolvedValue({ id: "u1", termsVersion: null });
+    const { requireApiUser } = await import("./api-guard.server.ts");
+
+    try {
+      await requireApiUser(new Request("http://localhost/api/v1/routes"));
+      expect.fail("should throw");
+    } catch (err) {
+      expect(err).toBeInstanceOf(Response);
+      expect((err as Response).status).toBe(403);
+      const body = await (err as Response).json();
+      expect(body.code).toBe("TERMS_OUTDATED");
+      expect(body.currentTermsVersion).toBe(TERMS_VERSION);
+    }
+  });
+});
diff --git a/apps/journal/app/lib/api-guard.server.ts b/apps/journal/app/lib/api-guard.server.ts
index bf480b2..18c6be9 100644
--- a/apps/journal/app/lib/api-guard.server.ts
+++ b/apps/journal/app/lib/api-guard.server.ts
@@ -1,8 +1,13 @@
 import { getAuthenticatedUser } from "./oauth.server.ts";
+import { TERMS_VERSION } from "./legal.ts";
 import { ERROR_CODES } from "@trails-cool/api";
 
 /**
- * Require authentication for an API route. Returns the user or throws a 401 Response.
+ * Require authentication for an API route. Returns the user or throws a
+ * Response: 401 if unauthenticated, 403 with `TERMS_OUTDATED` if the user's
+ * stored `terms_version` is missing or stale relative to the current
+ * `TERMS_VERSION`. Mirrors the cookie-session terms gate enforced by the
+ * root loader, so bearer-token API traffic can't bypass it.
  */
 export async function requireApiUser(request: Request) {
   const user = await getAuthenticatedUser(request);
@@ -12,6 +17,16 @@ export async function requireApiUser(request: Request) {
       { status: 401 },
     );
   }
+  if (user.termsVersion !== TERMS_VERSION) {
+    throw Response.json(
+      {
+        error: "Terms of Service have been updated and must be re-accepted",
+        code: ERROR_CODES.TERMS_OUTDATED,
+        currentTermsVersion: TERMS_VERSION,
+      },
+      { status: 403 },
+    );
+  }
   return user;
 }
 
diff --git a/apps/journal/app/routes/api.v1.routes.test.ts b/apps/journal/app/routes/api.v1.routes.test.ts
index a8c4664..b3c6afb 100644
--- a/apps/journal/app/routes/api.v1.routes.test.ts
+++ b/apps/journal/app/routes/api.v1.routes.test.ts
@@ -1,6 +1,8 @@
 import { describe, it, expect, vi, beforeEach } from "vitest";
 
-const mockUser = { id: "user-1", email: "test@test.com", username: "test", domain: "localhost", displayName: null, bio: null, createdAt: new Date() };
+import { TERMS_VERSION } from "~/lib/legal";
+
+const mockUser = { id: "user-1", email: "test@test.com", username: "test", domain: "localhost", displayName: null, bio: null, createdAt: new Date(), termsVersion: TERMS_VERSION };
 const mockGetAuthenticatedUser = vi.fn();
 const mockListRoutes = vi.fn();
 const mockCreateRoute = vi.fn();
diff --git a/openspec/changes/mobile-terms-gate/proposal.md b/openspec/changes/mobile-terms-gate/proposal.md
new file mode 100644
index 0000000..b6e49e7
--- /dev/null
+++ b/openspec/changes/mobile-terms-gate/proposal.md
@@ -0,0 +1,29 @@
+## Why
+
+Mobile API requests authenticated via OAuth2 bearer tokens currently bypass the Terms gate. Web users with a stale `users.terms_version` are redirected to `/auth/accept-terms` by the journal root loader (`apps/journal/app/root.tsx:58`), but mobile clients hitting `/api/v1/*` with the same stale version get a normal 200 response. The Terms gate (defined in `journal-auth/spec.md`) is meant to apply to **all** authenticated requests, not only cookie-session traffic.
+
+## What Changes
+
+- Extend the bearer-token API chokepoint (`requireApiUser` in `apps/journal/app/lib/api-guard.server.ts`) to compare the authenticated user's `termsVersion` against the current `TERMS_VERSION`. On mismatch, return a structured **HTTP 403** with `{ error, code: "TERMS_OUTDATED", currentTermsVersion }` so the mobile app can surface its own UI (or open the web Terms page in a webview).
+- Add `TERMS_OUTDATED` to `packages/api/src/errors.ts` `ERROR_CODES` so clients have a stable code to switch on.
+- Spec delta on `journal-auth`: add a requirement that the Terms gate also applies to bearer-token API auth, with the structured-error contract as a scenario.
+
+Web cookie-session behaviour is unchanged (still a redirect via the root loader). Only the API chokepoint changes.
+
+## Capabilities
+
+### New Capabilities
+
+(none)
+
+### Modified Capabilities
+
+- `journal-auth`: adds a requirement that the Terms-version gate applies to bearer-token API requests, returning HTTP 403 with a structured `terms_outdated` payload instead of a redirect.
+
+## Impact
+
+- **Code**: one function (`requireApiUser`) gains a terms check; one constant added to `@trails-cool/api`.
+- **Clients**: the mobile app needs to handle `403 { code: "TERMS_OUTDATED" }` (out of scope for this change — tracked separately on the mobile side).
+- **Tests**: unit test for `requireApiUser` covering stale / current / null `termsVersion`.
+- **Specs**: 1 spec delta on `journal-auth` (added requirement).
+- **Out of scope**: mobile client UI for the new error; any change to web cookie-session behaviour.
diff --git a/openspec/changes/mobile-terms-gate/specs/journal-auth/spec.md b/openspec/changes/mobile-terms-gate/specs/journal-auth/spec.md
new file mode 100644
index 0000000..7458598
--- /dev/null
+++ b/openspec/changes/mobile-terms-gate/specs/journal-auth/spec.md
@@ -0,0 +1,17 @@
+## ADDED Requirements
+
+### Requirement: Terms gate applies to bearer-token API requests
+Authenticated API requests carrying an OAuth2 bearer token SHALL be subject to the same Terms-version gate as cookie-session requests. When the authenticated user's stored `terms_version` is NULL or differs from the current `TERMS_VERSION`, the API chokepoint (`requireApiUser`) SHALL reject the request with HTTP 403 and a structured JSON body `{ error, code: "TERMS_OUTDATED", currentTermsVersion: <current> }` instead of returning the resource. Cookie-session web traffic continues to be handled by the root-loader redirect to `/auth/accept-terms`; only the API path uses the structured 403.
+
+#### Scenario: Stale bearer token receives structured 403
+- **WHEN** a request to `/api/v1/*` arrives with a valid bearer token whose user has `terms_version` NULL or different from the current `TERMS_VERSION`
+- **THEN** the server responds with HTTP 403 and JSON `{ error: <message>, code: "TERMS_OUTDATED", currentTermsVersion: <current> }`
+- **AND** the requested resource is not returned
+
+#### Scenario: Up-to-date bearer token is allowed through
+- **WHEN** a request to `/api/v1/*` arrives with a valid bearer token whose user's `terms_version` matches the current `TERMS_VERSION`
+- **THEN** the request proceeds normally
+
+#### Scenario: Anonymous API request still 401
+- **WHEN** a request to `/api/v1/*` arrives without a bearer token (or with an invalid one)
+- **THEN** the server responds with HTTP 401 `UNAUTHORIZED` as before — the Terms check only applies after authentication succeeds
diff --git a/openspec/changes/mobile-terms-gate/tasks.md b/openspec/changes/mobile-terms-gate/tasks.md
new file mode 100644
index 0000000..f8328ab
--- /dev/null
+++ b/openspec/changes/mobile-terms-gate/tasks.md
@@ -0,0 +1,13 @@
+## 1. Implementation
+
+- [x] 1.1 Add `TERMS_OUTDATED: "TERMS_OUTDATED"` to `ERROR_CODES` in `packages/api/src/errors.ts`.
+- [x] 1.2 Extend `requireApiUser` in `apps/journal/app/lib/api-guard.server.ts` to compare the authenticated user's `termsVersion` to `TERMS_VERSION` (from `~/lib/legal`). On mismatch (or NULL), throw a `Response` with status 403 and JSON body `{ error, code: ERROR_CODES.TERMS_OUTDATED, currentTermsVersion: TERMS_VERSION }`.
+
+## 2. Tests
+
+- [x] 2.1 Add `apps/journal/app/lib/api-guard.server.test.ts` covering: stale `termsVersion` → 403 with `TERMS_OUTDATED` + `currentTermsVersion`; matching `termsVersion` → returns user; null `termsVersion` → 403; no auth → 401 (unchanged).
+
+## 3. Verification
+
+- [x] 3.1 Run `pnpm typecheck && pnpm lint && pnpm test` — all green.
+- [ ] 3.2 Open draft PR against `main`.
diff --git a/packages/api/src/errors.ts b/packages/api/src/errors.ts
index 381dd95..5152b95 100644
--- a/packages/api/src/errors.ts
+++ b/packages/api/src/errors.ts
@@ -35,4 +35,5 @@ export const ERROR_CODES = {
   CONFLICT: "CONFLICT",
   RATE_LIMITED: "RATE_LIMITED",
   INTERNAL_ERROR: "INTERNAL_ERROR",
+  TERMS_OUTDATED: "TERMS_OUTDATED",
 } as const;