@@ -0,0 +1,14 @@
+---
+'@objectstack/plugin-auth': patch
+---
+
+Clause-②: no
+Metadata-protocol: none
+
+A new organization now gets its default currency from its creator's language or region. When an organization is created through `POST /api/v1/auth/organization/create`, the server reads the creator's stored language (`sys_user.locale`), or else the creating request's `Accept-Language`. It writes that region's ISO 4217 currency as the organization's `localization.currency`: `zh-CN` gives `CNY`, `ja` gives `JPY`, `en-GB` gives `GBP`. The value is an ordinary tenant setting, so Setup → Localization shows it and can change it. Amounts in `currencyMode: 'dynamic'` fields then show that currency instead of a plain number.
+
+When there is nothing to derive from (no stored language, no `Accept-Language`, or a tag with no country such as `es-419`), nothing is written and the setting stays unset, as before. There is no fallback to the `default_country` or `locale` platform defaults. A value already set on any rung (the organization's own, a global row, or an `OS_LOCALIZATION_CURRENCY` override) is never overwritten. A host's own `onOrganizationCreated` callback still runs, before this step.
+
+The `os dev` seed does the same for its admin's workspace from the host's POSIX locale (`LC_ALL`, then `LC_MONETARY`, then `LANG`), beside its time-zone seeding. `C`, `POSIX`, and a host with no locale set write nothing.
+
+The region-to-currency table is a checked-in snapshot of CLDR 48 `currencyData`.
@@ -1320,8 +1320,12 @@ export function authEmailLocaleFromRequest(source: unknown): string | undefined
  * context, or anything carrying either. Never throws: a vendor changing the
  * shape it hands a callback must degrade to the deployment default, never fail
  * the send.
+ *
+ * Exported for `organization-default-currency.ts`, which reads the creating
+ * request's language off the endpoint context the same way (#25495): one
+ * reader, not two.
  */
-function acceptLanguageHeader(source: unknown): string | undefined {
+export function acceptLanguageHeader(source: unknown): string | undefined {
   if (!source || typeof source !== 'object') return undefined;
   const nested = (source as { request?: unknown }).request;
   const bags = [
 
@@ -75,6 +75,11 @@ import { runRegisterSsoProviderFromForm, runRegisterSamlProviderFromForm, runReq
 import { runResendVerificationEmail } from './send-verification-email.js';
 import { runSysSessionRevoke, sysSessionRevokeDepsFor } from './sys-session-revoke.js';
 import { readJsonRequestBody } from './request-json-body.js';
+import {
+  seedDevWorkspaceCurrency,
+  withOrganizationDefaultCurrency,
+  type CurrencySettingsDoor,
+} from './organization-default-currency.js';
 import type { CounterStore } from './rate-limit-storage.js';
 import { authIdentityManifest } from './manifest.js';
 import { scheduleLegacySsoSecretMigration } from './sso-client-secret.js';
@@ -680,6 +685,26 @@ export class AuthPlugin implements Plugin {
       }
     };
 
+    // [#25495] A new organization takes its creator's default currency
+    // (`localization.currency`), derived from their stored language or the
+    // creating request's `Accept-Language`; nothing derivable ⇒ nothing
+    // written, a value already set ⇒ left alone. Wrapped AFTER
+    // `auth:configure` so a host's own `onOrganizationCreated`, from the
+    // plugin options or from a configure handler, still runs, and runs first.
+    // The settings service is resolved when an organization is created, not
+    // here: it starts after this plugin.
+    authConfig.onOrganizationCreated = withOrganizationDefaultCurrency(authConfig.onOrganizationCreated, {
+      dataEngine,
+      getSettings: () => {
+        try {
+          return ctx.getService<CurrencySettingsDoor>('settings');
+        } catch {
+          return undefined;
+        }
+      },
+      logger: ctx.logger,
+    });
+
     // Initialize auth manager with data engine
     this.authManager = new AuthManager(authConfig);
     // ADR-0092 D6 — remember the storage better-auth will actually use so the
@@ -2487,6 +2512,17 @@ export class AuthPlugin implements Plugin {
       // creator's — see the method. Only on the seeding boot: a later boot
       // takes the database as it finds it.
       if (seededId) await this.seedDevWorkspaceTimezone(ctx, ql, seededId);
+      // [#25495] And with the host's currency, by the rule a new
+      // organization's creator gets (`organization-default-currency.ts`).
+      if (seededId) {
+        let settings: CurrencySettingsDoor | undefined;
+        try {
+          settings = ctx.getService<CurrencySettingsDoor>('settings');
+        } catch {
+          settings = undefined;
+        }
+        await seedDevWorkspaceCurrency({ settings, ql, userId: seededId, logger: ctx.logger });
+      }
       ctx.logger.info(`🔑 Dev admin seeded: ${email} / ${password}`);
       // Surface the credentials in the `serve` startup banner. The
       // ctx.logger line above is swallowed by serve's boot-quiet window
 
@@ -69,6 +69,12 @@ const ENV_KEYS = [
   'OS_MULTI_ORG_ENABLED',
   'OS_PLATFORM_OWNER_EMAIL',
   'OS_LOCALIZATION_TIMEZONE',
+  // [#25495] The same seed writes `localization.currency` from the host's
+  // POSIX locale; cleared so the "no localization write" cases below cannot
+  // pick up a currency write from the machine running them.
+  'LC_ALL',
+  'LC_MONETARY',
+  'LANG',
 ] as const;
 
 /** Publishes an in-memory SQLite driver the way a datasource plugin does. */