diff --git a/.changeset/25128-tenant-column-never-null-comments.md b/.changeset/25128-tenant-column-never-null-comments.md
new file mode 100644
index 00000000000..0aad4fd92c9
--- /dev/null
+++ b/.changeset/25128-tenant-column-never-null-comments.md
@@ -0,0 +1,10 @@
+---
+'@objectstack/spec': patch
+---
+
+docs(spec): the `systemFields` docblock no longer says `organization_id` stays NULL on single-tenant stacks
+
+Clause-②: no (comment and docblock text only: no accept set, response, status, error, outcome or export moves)
+Metadata-protocol: none
+
+The `organization_id` bullet of `ObjectSchema`'s `systemFields` docblock now says what the runtime does: org-scoping stamps the tenant column on insert (under `single` with the Default Organization), and it is never NULL (ADR-0131 D1). Only the column's index is still gated on multi-tenant mode. No schema, `.describe()` text or behavior changes.
diff --git a/packages/objectql/src/registry-tenant-index-declaration.test.ts b/packages/objectql/src/registry-tenant-index-declaration.test.ts
index 8ac0acf0584..08eab1551ad 100644
--- a/packages/objectql/src/registry-tenant-index-declaration.test.ts
+++ b/packages/objectql/src/registry-tenant-index-declaration.test.ts
@@ -149,7 +149,8 @@ describe('#6810 — a registry-backed object reads back valid at both /meta exit
     expect(tenantIndexes(def)).toEqual([]);
     // And the COLUMN is still provisioned either way — that decoupling is
     // older than this fix and must survive it (sudo writers stamp the column
-    // on single-tenant stacks; it just stays NULL).
+    // on single-tenant stacks; org-scoping stamps it on insert under `single`
+    // with the Default Organization, and it is never NULL, ADR-0131 D1).
     expect(def.fields.organization_id).toBeDefined();
   });
 
diff --git a/packages/objectql/src/registry.ts b/packages/objectql/src/registry.ts
index ac37fff7fff..c45b8ab4945 100644
--- a/packages/objectql/src/registry.ts
+++ b/packages/objectql/src/registry.ts
@@ -774,8 +774,9 @@ export function applySystemFields(
   // global multi-tenant flag. Decoupling "does the column exist" from "is
   // tenancy enabled" is what stops sudo writers (audit / messaging / inbox /
   // outbox …) from failing with "no column named organization_id" on
-  // single-tenant stacks: they can always stamp the column, it just stays NULL
-  // when no tenant context exists. The multi-tenant flag now governs only
+  // single-tenant stacks: they can always stamp the column, and org-scoping
+  // stamps it on insert (under `single` with the Default Organization), so it
+  // is never NULL (ADR-0131 D1). The multi-tenant flag now governs only
   // whether the column is INDEXED — on a single-tenant DB nothing ever filters
   // by organization, so the index would be dead weight. That is also why the
   // plan takes no `multiTenant` input: the flag cannot change what EXISTS, only
diff --git a/packages/spec/src/data/object.zod.ts b/packages/spec/src/data/object.zod.ts
index 01a03df6aea..a80dcd22824 100644
--- a/packages/spec/src/data/object.zod.ts
+++ b/packages/spec/src/data/object.zod.ts
@@ -2496,9 +2496,10 @@ const ObjectSchemaBase = strictObject(
    *
    *   - `organization_id` — `lookup → sys_organization`. The COLUMN is
    *     provisioned unconditionally (subject to the opt-outs below); only its
-   *     DB index is gated on multi-tenant mode. It stays NULL on single-tenant
-   *     stacks and is auto-stamped on insert by `@objectstack/organizations`
-   *     (the `org-scoping` service) in multi-tenant mode.
+   *     DB index is gated on multi-tenant mode. Org-scoping stamps it on
+   *     insert (`@objectstack/organizations`, the `org-scoping` service, in
+   *     multi-tenant mode; under `single` with the Default Organization), and
+   *     it is never NULL (ADR-0131 D1).
    *   - Audit columns — `created_at`, `created_by`, `updated_at`, `updated_by`
    *     (`readonly` + `system`). Gated by `audit` below.
    *   - `owner_id` — `lookup → sys_user`, auto-provisioned on user-authored