diff --git a/.changeset/single-source-multi-org-flag.md b/.changeset/single-source-multi-org-flag.md
new file mode 100644
index 0000000000..211750ebab
--- /dev/null
+++ b/.changeset/single-source-multi-org-flag.md
@@ -0,0 +1,34 @@
+---
+"@objectstack/types": patch
+---
+
+refactor: single-source the multi-org (`OS_MULTI_ORG_ENABLED`) flag resolution
+
+"Is this deployment multi-org?" was resolved in 10 places across 8 packages
+with three subtly different inline expressions:
+
+- the canonical `String(readEnvWithDeprecation('OS_MULTI_ORG_ENABLED',
+  'OS_MULTI_TENANT') ?? 'false').toLowerCase() !== 'false'` (objectql registry,
+  plugin-dev, runtime app-plugin, cli serve/verify, cloud-connection),
+- a redundant `env.OS_MULTI_ORG_ENABLED !== undefined ? … : …` variant in
+  plugin-auth (auth-manager `/auth/config` features + `beforeCreateOrganization`
+  guard),
+- and a bare `process.env.OS_MULTI_ORG_ENABLED ?? process.env.OS_MULTI_TENANT`
+  read in the SQL driver's `isMultiTenantMode()` — which skipped the
+  `OS_MULTI_TENANT` deprecation warning every other site emits.
+
+Because the SQL driver computed the mode independently of the auth/security
+layer, the driver's tenant-audit gate and the rest of the system could in
+principle disagree about whether tenant isolation is active.
+
+Introduces `resolveMultiOrgEnabled()` in `@objectstack/types` (next to
+`readEnvWithDeprecation`, the natural leaf dependency) as the single source of
+truth, and routes all 10 sites through it. `@objectstack/driver-sql` gains a
+direct `@objectstack/types` dependency (previously it read `process.env`
+directly).
+
+Behaviour is unchanged everywhere except the SQL driver, which now also emits
+the one-shot `OS_MULTI_TENANT`-is-deprecated warning — consistent with every
+other site. This mirrors the `resolveAuthzContext` single-source pattern in
+`@objectstack/core`. Follow-up (not in this change): a lint gate forbidding new
+inline reads of these env vars outside the helper.
diff --git a/packages/cli/src/commands/serve.ts b/packages/cli/src/commands/serve.ts
index a988b48b63..bd976682ed 100644
--- a/packages/cli/src/commands/serve.ts
+++ b/packages/cli/src/commands/serve.ts
@@ -8,7 +8,7 @@ import chalk from 'chalk';
 import { bundleRequire } from 'bundle-require';
 import { loadConfig, BUNDLE_REQUIRE_EXTERNALS } from '../utils/config.js';
 import { isHostConfig, shouldBootWithLibrary } from '../utils/plugin-detection.js';
-import { readEnvWithDeprecation } from '@objectstack/types';
+import { readEnvWithDeprecation, resolveMultiOrgEnabled } from '@objectstack/types';
 import { resolveObjectStackHome } from '@objectstack/runtime';
 import { LOG_LEVELS, resolveLogLevel, readLogLevelEnv } from '../utils/log-level.js';
 import {
@@ -1263,7 +1263,7 @@ export default class Serve extends Command {
             // the `org-scoping` service at start() time and conditionally
             // strips the wildcard `tenant_isolation` RLS when this plugin
             // is absent — so registration order matters.
-            const multiTenant = String(readEnvWithDeprecation('OS_MULTI_ORG_ENABLED', 'OS_MULTI_TENANT') ?? 'false').toLowerCase() !== 'false';
+            const multiTenant = resolveMultiOrgEnabled();
             if (multiTenant) {
               try {
                 const orgScopingPkg = '@objectstack/plugin-org-scoping';
@@ -2066,7 +2066,7 @@ export default class Serve extends Command {
         consolePath: loadedPlugins.includes('ConsoleUI') ? CONSOLE_PATH : undefined,
         driverLabel: resolvedDriverLabel,
         databaseUrl: redactDbUrl(resolvedDatabaseUrl),
-        multiTenant: String(readEnvWithDeprecation('OS_MULTI_ORG_ENABLED', 'OS_MULTI_TENANT') ?? 'false').toLowerCase() !== 'false',
+        multiTenant: resolveMultiOrgEnabled(),
         seededAdmin,
       });
 
diff --git a/packages/cli/src/commands/verify.ts b/packages/cli/src/commands/verify.ts
index c81c5929ca..141a269d12 100644
--- a/packages/cli/src/commands/verify.ts
+++ b/packages/cli/src/commands/verify.ts
@@ -2,7 +2,7 @@
 
 import { Command, Flags } from '@oclif/core';
 import chalk from 'chalk';
-import { readEnvWithDeprecation } from '@objectstack/types';
+import { resolveMultiOrgEnabled } from '@objectstack/types';
 import {
   bootStack,
   runCrudVerification,
@@ -53,10 +53,7 @@ export default class Verify extends Command {
 
     const { config, absolutePath } = await loadConfig(flags.app);
 
-    const multiTenant =
-      flags['multi-tenant'] ||
-      String(readEnvWithDeprecation('OS_MULTI_ORG_ENABLED', 'OS_MULTI_TENANT') ?? 'false').toLowerCase() !==
-        'false';
+    const multiTenant = flags['multi-tenant'] || resolveMultiOrgEnabled();
 
     // Data fidelity runs on its own pristine stack.
     let crud: VerifyReport;
diff --git a/packages/cloud-connection/src/marketplace-install-local-plugin.ts b/packages/cloud-connection/src/marketplace-install-local-plugin.ts
index 4c460ac58e..bf53f95085 100644
--- a/packages/cloud-connection/src/marketplace-install-local-plugin.ts
+++ b/packages/cloud-connection/src/marketplace-install-local-plugin.ts
@@ -42,7 +42,7 @@
  */
 
 import type { Plugin, PluginContext } from '@objectstack/core';
-import { readEnvWithDeprecation } from '@objectstack/types';
+import { resolveMultiOrgEnabled } from '@objectstack/types';
 import { resolveCloudUrl } from './cloud-url.js';
 import { resolveMarketplacePublicBaseUrl } from './marketplace-public-url.js';
 import { LocalManifestSource, type InstalledManifestEntry } from './local-manifest-source.js';
@@ -789,7 +789,7 @@ export class MarketplaceInstallLocalPlugin implements Plugin {
         // writes tenant-scoped rows the same way AppPlugin's
         // single-tenant branch + SecurityPlugin's per-org replay do.
         if (opts.seedNow && datasets.length > 0) {
-            const multiTenant = String(readEnvWithDeprecation('OS_MULTI_ORG_ENABLED', 'OS_MULTI_TENANT') ?? 'false').toLowerCase() !== 'false';
+            const multiTenant = resolveMultiOrgEnabled();
             try {
                 const ql: any = ctx.getService('objectql');
                 let metadata: any;
diff --git a/packages/objectql/src/registry.ts b/packages/objectql/src/registry.ts
index 0c3fc5af84..ecf0124d78 100644
--- a/packages/objectql/src/registry.ts
+++ b/packages/objectql/src/registry.ts
@@ -1,7 +1,7 @@
 // Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
 
 import { ServiceObject, ObjectSchema, ObjectOwnership } from '@objectstack/spec/data';
-import { readEnvWithDeprecation } from '@objectstack/types';
+import { resolveMultiOrgEnabled } from '@objectstack/types';
 import { ObjectStackManifest, ManifestSchema, InstalledPackage, InstalledPackageSchema } from '@objectstack/spec/kernel';
 import { AppSchema } from '@objectstack/spec/ui';
 import { applyProtection } from '@objectstack/spec/shared';
@@ -420,8 +420,7 @@ export class SchemaRegistry {
       this.multiTenant = options.multiTenant;
     } else {
       // Mirror the SecurityPlugin / CLI banner default (env-driven, off by default).
-      this.multiTenant =
-        String(readEnvWithDeprecation('OS_MULTI_ORG_ENABLED', 'OS_MULTI_TENANT') ?? 'false').toLowerCase() !== 'false';
+      this.multiTenant = resolveMultiOrgEnabled();
     }
 
     // ADR-0048 — default to a loud error on cross-package collision; allow an
diff --git a/packages/plugins/driver-sql/package.json b/packages/plugins/driver-sql/package.json
index 0231250f95..de1a175550 100644
--- a/packages/plugins/driver-sql/package.json
+++ b/packages/plugins/driver-sql/package.json
@@ -20,6 +20,7 @@
   "dependencies": {
     "@objectstack/core": "workspace:*",
     "@objectstack/spec": "workspace:*",
+    "@objectstack/types": "workspace:*",
     "knex": "^3.2.10",
     "nanoid": "^5.1.15"
   },
diff --git a/packages/plugins/driver-sql/src/sql-driver.ts b/packages/plugins/driver-sql/src/sql-driver.ts
index 87746185f5..a1e97989a4 100644
--- a/packages/plugins/driver-sql/src/sql-driver.ts
+++ b/packages/plugins/driver-sql/src/sql-driver.ts
@@ -12,6 +12,7 @@ import { parseAutonumberFormat, renderAutonumber, missingFieldValues, type Auton
 import type { IDataDriver } from '@objectstack/spec/contracts';
 import { StorageNameMapping } from '@objectstack/spec/system';
 import { ExternalSchemaModeViolationError } from '@objectstack/spec/shared';
+import { resolveMultiOrgEnabled } from '@objectstack/types';
 import {
   diffManagedTable,
   driftKey,
@@ -2229,9 +2230,10 @@ export class SqlDriver implements IDataDriver {
   private _multiTenantMode?: boolean;
   protected isMultiTenantMode(): boolean {
     if (this._multiTenantMode === undefined) {
-      const raw =
-        process.env.OS_MULTI_ORG_ENABLED ?? process.env.OS_MULTI_TENANT ?? 'false';
-      this._multiTenantMode = String(raw).toLowerCase() !== 'false';
+      // Single source of truth (shared with auth/registry/CLI) — previously
+      // this read `process.env` inline and so never emitted the
+      // `OS_MULTI_TENANT` deprecation warning the other sites do.
+      this._multiTenantMode = resolveMultiOrgEnabled();
     }
     return this._multiTenantMode;
   }
diff --git a/packages/plugins/plugin-auth/src/auth-manager.ts b/packages/plugins/plugin-auth/src/auth-manager.ts
index e3f2658b11..63f2754ca8 100644
--- a/packages/plugins/plugin-auth/src/auth-manager.ts
+++ b/packages/plugins/plugin-auth/src/auth-manager.ts
@@ -12,7 +12,7 @@ import type {
 } from '@objectstack/spec/system';
 import type { IDataEngine } from '@objectstack/core';
 import type { IEmailService } from '@objectstack/spec/contracts';
-import { readEnvWithDeprecation } from '@objectstack/types';
+import { readEnvWithDeprecation, resolveMultiOrgEnabled } from '@objectstack/types';
 import { mapMembershipRole, BUILTIN_ROLE_PLATFORM_ADMIN } from '@objectstack/spec';
 import { createObjectQLAdapterFactory, withSystemReadContext } from './objectql-adapter.js';
 import {
@@ -827,13 +827,7 @@ export class AuthManager {
           // 2. else `OS_MULTI_TENANT` (multi-tenant deployments are always
           //    multi-org), default `'false'` → single-org / per-env runtime.
           beforeCreateOrganization: async () => {
-            const env = (globalThis as any)?.process?.env ?? {};
-            const explicit = env.OS_MULTI_ORG_ENABLED;
-            const legacy = explicit === undefined
-              ? readEnvWithDeprecation('OS_MULTI_ORG_ENABLED', 'OS_MULTI_TENANT')
-              : explicit;
-            const flag = String(legacy ?? 'false').toLowerCase();
-            if (flag === 'false') {
+            if (!resolveMultiOrgEnabled()) {
               const { APIError } = await import('better-auth/api');
               throw new APIError('FORBIDDEN', {
                 message:
@@ -1505,11 +1499,7 @@ export class AuthManager {
     // Resolution order: explicit `OS_MULTI_ORG_ENABLED` wins, else fall
     // back to legacy `OS_MULTI_TENANT` (multi-tenant deployments are always
     // multi-org); default `'false'` → single-org / per-env runtime.
-    const multiOrgEnv = (globalThis as any)?.process?.env ?? {};
-    const multiOrgRaw = multiOrgEnv.OS_MULTI_ORG_ENABLED !== undefined
-      ? multiOrgEnv.OS_MULTI_ORG_ENABLED
-      : (readEnvWithDeprecation('OS_MULTI_ORG_ENABLED', 'OS_MULTI_TENANT') ?? 'false');
-    const multiOrgEnabled = String(multiOrgRaw).toLowerCase() !== 'false';
+    const multiOrgEnabled = resolveMultiOrgEnabled();
 
     // Legal links shown beneath the login / register cards. Defaults to
     // the public ObjectStack pages so vanilla deployments don't link to
diff --git a/packages/plugins/plugin-dev/src/dev-plugin.ts b/packages/plugins/plugin-dev/src/dev-plugin.ts
index f33e25528e..ea93e70bad 100644
--- a/packages/plugins/plugin-dev/src/dev-plugin.ts
+++ b/packages/plugins/plugin-dev/src/dev-plugin.ts
@@ -1,7 +1,7 @@
 // Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
 
 import { Plugin, PluginContext, createMemoryCache, createMemoryQueue, createMemoryJob, createMemoryI18n } from '@objectstack/core';
-import { readEnvWithDeprecation } from '@objectstack/types';
+import { resolveMultiOrgEnabled } from '@objectstack/types';
 
 /**
  * All 17 core kernel service names as defined in CoreServiceName.
@@ -584,14 +584,14 @@ export class DevPlugin implements Plugin {
     // because SecurityPlugin.start() probes the `org-scoping` service and
     // caches the result for the lifetime of the plugin.
     if (enabled('security')) {
-      const multiTenant = String(readEnvWithDeprecation('OS_MULTI_ORG_ENABLED', 'OS_MULTI_TENANT') ?? 'false').toLowerCase() !== 'false';
+      const multiTenant = resolveMultiOrgEnabled();
       if (multiTenant) {
         try {
           const { OrgScopingPlugin } = await import('@objectstack/plugin-org-scoping') as any;
           this.childPlugins.push(new OrgScopingPlugin());
           ctx.logger.info('  ✔ Org-scoping plugin enabled (multi-tenant: organization_id auto-stamp, per-org seed)');
         } catch {
-          ctx.logger.warn('  ✘ OS_MULTI_TENANT=true but @objectstack/plugin-org-scoping not installed');
+          ctx.logger.warn('  ✘ OS_MULTI_ORG_ENABLED=true but @objectstack/plugin-org-scoping not installed');
         }
       }
       try {
diff --git a/packages/runtime/src/app-plugin.ts b/packages/runtime/src/app-plugin.ts
index e65acebce8..71894f42fc 100644
--- a/packages/runtime/src/app-plugin.ts
+++ b/packages/runtime/src/app-plugin.ts
@@ -1,7 +1,7 @@
 // Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
 
 import { Plugin, PluginContext } from '@objectstack/core';
-import { readEnvWithDeprecation } from '@objectstack/types';
+import { resolveMultiOrgEnabled } from '@objectstack/types';
 import { SeedLoaderService } from './seed-loader.js';
 import { loadDisabledPackageIds } from './package-state-store.js';
 import type { IMetadataService, II18nService } from '@objectstack/spec/contracts';
@@ -662,7 +662,7 @@ export class AppPlugin implements Plugin {
              // step. So we skip it. Single-tenant deployments keep the
              // legacy behaviour: seed immediately at boot so there's
              // always demo data without needing an org insert.
-             const multiTenant = String(readEnvWithDeprecation('OS_MULTI_ORG_ENABLED', 'OS_MULTI_TENANT') ?? 'false').toLowerCase() !== 'false';
+             const multiTenant = resolveMultiOrgEnabled();
              if (multiTenant) {
                  ctx.logger.info('[Seeder] multi-tenant mode — skipping inline seed; per-org replay will run on sys_organization insert');
              } else {
diff --git a/packages/types/src/env.ts b/packages/types/src/env.ts
index 28820fdfc5..aa4784747a 100644
--- a/packages/types/src/env.ts
+++ b/packages/types/src/env.ts
@@ -79,6 +79,30 @@ export function readEnvWithDeprecation(
   return undefined;
 }
 
+/**
+ * Resolve whether the deployment runs in multi-org (a.k.a. multi-tenant) mode.
+ *
+ * Single source of truth for the `OS_MULTI_ORG_ENABLED` flag. Resolution: the
+ * canonical `OS_MULTI_ORG_ENABLED` wins; else the deprecated `OS_MULTI_TENANT`
+ * (which fires the one-shot rename warning via {@link readEnvWithDeprecation});
+ * else `false`. Any value other than a case-insensitive `'false'` enables it.
+ *
+ * Every site that needs to know "is this multi-org?" — the SQL driver's
+ * tenant-audit gate, the auth manager's `/auth/config` feature flag and
+ * org-create guard, the CLI / dev / runtime org-scoping plugin wiring — MUST
+ * call this instead of re-reading the env, so the driver, the security layer,
+ * and the UI can never disagree about the mode. Previously each site inlined
+ * its own `String(... ?? 'false').toLowerCase() !== 'false'` (and the SQL
+ * driver read `process.env` directly, skipping the deprecation warning).
+ *
+ * Reads `process.env` live on each call; memoise at the call site if the
+ * result must be stable for the process lifetime.
+ */
+export function resolveMultiOrgEnabled(): boolean {
+  const raw = readEnvWithDeprecation('OS_MULTI_ORG_ENABLED', 'OS_MULTI_TENANT');
+  return String(raw ?? 'false').toLowerCase() !== 'false';
+}
+
 /**
  * Internal: clear the dedupe set. Test-only; exposed so suite-wide
  * deprecation warnings don't bleed between tests.
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index ba930fa33b..03da441dc2 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -1158,6 +1158,9 @@ importers:
       '@objectstack/spec':
         specifier: workspace:*
         version: link:../../spec
+      '@objectstack/types':
+        specifier: workspace:*
+        version: link:../../types
       knex:
         specifier: ^3.2.10
         version: 3.2.10(better-sqlite3@12.11.1)(mysql2@3.22.4(@types/node@26.0.0))(pg@8.21.0)(sqlite3@5.1.7)(tedious@18.6.2(@azure/core-client@1.10.2))