diff --git a/addons/api/addon/serializers/auth-method.js b/addons/api/addon/serializers/auth-method.js
index 4b9940999..2ad329ab8 100644
--- a/addons/api/addon/serializers/auth-method.js
+++ b/addons/api/addon/serializers/auth-method.js
@@ -48,6 +48,18 @@ export default class AuthMethodSerializer extends ApplicationSerializer {
     } else {
       delete serialized.attributes.state;
     }
+
+    // Don't send account_claim_maps on update if there's a saved 'sub' mapping
+    // The API doesn't allow updating when 'sub' claim mappings exist
+    if (!snapshot.record.isNew && snapshot.record.account_claim_maps) {
+      const hasSubClaimMap = snapshot.record.account_claim_maps.some(
+        (item) => item?.value === 'sub',
+      );
+
+      if (hasSubClaimMap) {
+        delete serialized.attributes.account_claim_maps;
+      }
+    }
     return serialized;
   }
 
diff --git a/addons/api/tests/unit/serializers/auth-method-test.js b/addons/api/tests/unit/serializers/auth-method-test.js
index 75297023e..6c8d5ff71 100644
--- a/addons/api/tests/unit/serializers/auth-method-test.js
+++ b/addons/api/tests/unit/serializers/auth-method-test.js
@@ -506,4 +506,90 @@ module('Unit | Serializer | auth method', function (hooks) {
     assert.strictEqual(record.client_certificate_key, '');
     assert.strictEqual(record.bind_password, '');
   });
+
+  test('it includes account_claim_maps when serializing new OIDC records', function (assert) {
+    const store = this.owner.lookup('service:store');
+    const serializer = store.serializerFor('auth-method');
+    const record = store.createRecord('auth-method', {
+      type: TYPE_AUTH_METHOD_OIDC,
+      name: 'Test OIDC',
+      account_claim_maps: [
+        { key: 'email', value: 'email' },
+        { key: 'name', value: 'sub' },
+      ],
+    });
+    const snapshot = record._createSnapshot();
+    const serializedRecord = serializer.serialize(snapshot);
+
+    assert.ok(
+      serializedRecord.attributes.account_claim_maps,
+      'account_claim_maps is included for new records',
+    );
+
+    assert.deepEqual(serializedRecord.attributes.account_claim_maps, [
+      'email=email',
+      'name=sub',
+    ]);
+  });
+
+  test('it excludes account_claim_maps when serializing existing OIDC records with "sub" mapping', function (assert) {
+    const store = this.owner.lookup('service:store');
+    const serializer = store.serializerFor('auth-method');
+
+    const record = store.push({
+      data: {
+        id: 'oidc123',
+        type: 'auth-method',
+        attributes: {
+          type: TYPE_AUTH_METHOD_OIDC,
+          name: 'Test OIDC',
+          account_claim_maps: [
+            { key: 'email', value: 'email' },
+            { key: 'name', value: 'sub' },
+          ],
+        },
+      },
+    });
+
+    const snapshot = record._createSnapshot();
+    const serializedRecord = serializer.serialize(snapshot);
+
+    assert.notOk(
+      serializedRecord.attributes.account_claim_maps,
+      'account_claim_maps is excluded when updating with "sub" mapping',
+    );
+  });
+
+  test('it includes account_claim_maps when serializing existing OIDC records without "sub" mapping', function (assert) {
+    const store = this.owner.lookup('service:store');
+    const serializer = store.serializerFor('auth-method');
+
+    const record = store.push({
+      data: {
+        id: 'oidc456',
+        type: 'auth-method',
+        attributes: {
+          type: TYPE_AUTH_METHOD_OIDC,
+          name: 'Test OIDC',
+          account_claim_maps: [
+            { key: 'email', value: 'email' },
+            { key: 'name', value: 'name' },
+          ],
+        },
+      },
+    });
+
+    const snapshot = record._createSnapshot();
+    const serializedRecord = serializer.serialize(snapshot);
+
+    assert.ok(
+      serializedRecord.attributes.account_claim_maps,
+      'account_claim_maps is included when updating without "sub" mapping',
+    );
+
+    assert.deepEqual(serializedRecord.attributes.account_claim_maps, [
+      'email=email',
+      'name=name',
+    ]);
+  });
 });
diff --git a/ui/admin/app/components/form/auth-method/oidc/index.hbs b/ui/admin/app/components/form/auth-method/oidc/index.hbs
index b62b37d8a..154740e02 100644
--- a/ui/admin/app/components/form/auth-method/oidc/index.hbs
+++ b/ui/admin/app/components/form/auth-method/oidc/index.hbs
@@ -242,7 +242,7 @@
     @data={{@model.account_claim_maps}}
     @legend={{t 'form.account_claim_maps.label'}}
     @helperText={{t 'form.account_claim_maps.help'}}
-    @disabled={{form.disabled}}
+    @disabled={{or form.disabled this.hasSavedSubClaimMap}}
     @isOptional={{true}}
   >
     <:row as |R|>
@@ -264,7 +264,7 @@
           <option disabled hidden selected value=''>
             {{t 'titles.choose-an-option'}}
           </option>
-          {{#each this.toClaims as |claim|}}
+          {{#each (this.toClaimOptions R.rowData) as |claim|}}
             <option value={{claim}} selected={{eq R.rowData.value claim}}>
               {{claim}}
             </option>
diff --git a/ui/admin/app/components/form/auth-method/oidc/index.js b/ui/admin/app/components/form/auth-method/oidc/index.js
index 0419e43f2..f078cbbbe 100644
--- a/ui/admin/app/components/form/auth-method/oidc/index.js
+++ b/ui/admin/app/components/form/auth-method/oidc/index.js
@@ -39,6 +39,35 @@ export default class FormAuthMethodOidcComponent extends Component {
   @tracked selectedPrompts = this.parsePromptsArray();
   @tracked skipPromptsList = this.isToggleChecked();
 
+  /**
+   * @returns {boolean}
+   */
+  get hasSavedSubClaimMap() {
+    return (
+      !this.args.model?.isNew &&
+      this.args.model.account_claim_maps?.some((item) => item?.value === 'sub')
+    );
+  }
+
+  /**
+   * Filter 'sub' from dropdown options when updating
+   * On creation, show all options including sub.
+   * On update, hide sub unless it's the current value of the row (to display it when disabled).
+   * @param {Object} rowData - The current row data
+   * @returns {string[]}
+   */
+  toClaimOptions = (rowData) => {
+    // On creation, show all options
+    if (this.args.model?.isNew) {
+      return this.toClaims;
+    }
+
+    // On update, filter "sub" unless it's the current value
+    return this.toClaims.filter(
+      (claim) => claim !== 'sub' || rowData?.value === 'sub',
+    );
+  };
+
   /**
    * @returns {string}
    */
diff --git a/ui/admin/tests/acceptance/auth-methods/create-test.js b/ui/admin/tests/acceptance/auth-methods/create-test.js
index 88084c3a1..a9d4f58f3 100644
--- a/ui/admin/tests/acceptance/auth-methods/create-test.js
+++ b/ui/admin/tests/acceptance/auth-methods/create-test.js
@@ -120,6 +120,9 @@ module('Acceptance | auth-methods | create', function (hooks) {
     );
     await click(selectors.FIELD_CLAIMS_SCOPES_ADD_BTN);
 
+    // Verify Account Claim Maps field is editable during creation
+    assert.dom(selectors.FIELD_ACCOUNT_CLAIM_MAPS).isNotDisabled();
+
     await fillIn(
       selectors.FIELD_ACCOUNT_CLAIM_MAPS_FROM_CLAIM,
       selectors.FIELD_ACCOUNT_CLAIM_MAPS_FROM_CLAIM_VALUE,
diff --git a/ui/admin/tests/acceptance/auth-methods/selectors.js b/ui/admin/tests/acceptance/auth-methods/selectors.js
index 17821088b..26c09a1e6 100644
--- a/ui/admin/tests/acceptance/auth-methods/selectors.js
+++ b/ui/admin/tests/acceptance/auth-methods/selectors.js
@@ -30,12 +30,13 @@ export const FIELD_CLAIMS_SCOPES_ADD_BTN =
   '[name=claims_scopes] [data-test-add-button]';
 export const FIELD_CLAIMS_SCOPES_DELETE_BTN =
   '[name=claims_scopes] [data-test-delete-button]';
+export const FIELD_ACCOUNT_CLAIM_MAPS = '[name=account_claim_maps]';
 export const FIELD_ACCOUNT_CLAIM_MAPS_FROM_CLAIM =
   '[name=account_claim_maps] [data-test-key-input]';
 export const FIELD_ACCOUNT_CLAIM_MAPS_FROM_CLAIM_VALUE = 'from_claim';
 export const FIELD_ACCOUNT_CLAIM_MAPS_TO_CLAIM =
   '[name=account_claim_maps] [data-test-value-select]';
-export const FIELD_ACCOUNT_CLAIM_MAPS_TO_CLAIM_VALUE = 'email';
+export const FIELD_ACCOUNT_CLAIM_MAPS_TO_CLAIM_VALUE = 'sub';
 export const FIELD_ACCOUNT_CLAIM_MAPS_DELETE_BTN =
   '[name=account_claim_maps] [data-test-delete-button]';
 export const FIELD_IDP_CERTS = '[name=idp_ca_certs] [data-test-value-input]';
diff --git a/ui/admin/tests/acceptance/auth-methods/update-test.js b/ui/admin/tests/acceptance/auth-methods/update-test.js
index eabdf1bac..5fab662b5 100644
--- a/ui/admin/tests/acceptance/auth-methods/update-test.js
+++ b/ui/admin/tests/acceptance/auth-methods/update-test.js
@@ -169,14 +169,16 @@ module('Acceptance | auth-methods | update', function (hooks) {
       await click(element);
     }
 
-    await fillIn(
-      selectors.FIELD_ACCOUNT_CLAIM_MAPS_FROM_CLAIM,
-      selectors.FIELD_ACCOUNT_CLAIM_MAPS_FROM_CLAIM_VALUE,
-    );
-    await select(
-      selectors.FIELD_ACCOUNT_CLAIM_MAPS_TO_CLAIM,
-      selectors.FIELD_ACCOUNT_CLAIM_MAPS_TO_CLAIM_VALUE,
-    );
+    await fillIn(selectors.FIELD_ACCOUNT_CLAIM_MAPS_FROM_CLAIM, 'test_claim');
+
+    // Verify "sub" option is not available during update
+    await click(selectors.FIELD_ACCOUNT_CLAIM_MAPS_TO_CLAIM);
+    assert
+      .dom(`${selectors.FIELD_ACCOUNT_CLAIM_MAPS_TO_CLAIM} option[value="sub"]`)
+      .doesNotExist('"sub" option is not available during update');
+
+    // Select 'email' instead since 'sub' is not available
+    await select(selectors.FIELD_ACCOUNT_CLAIM_MAPS_TO_CLAIM, 'email');
 
     // Remove all certificates
     const certificatesList = findAll(selectors.FIELD_IDP_CERTS_DELETE_BTN);
@@ -223,7 +225,7 @@ module('Acceptance | auth-methods | update', function (hooks) {
       selectors.FIELD_CLAIMS_SCOPES_VALUE,
     ]);
     assert.deepEqual(authMethod.attributes.account_claim_maps, [
-      'from_claim=email',
+      'test_claim=email',
     ]);
     assert.deepEqual(authMethod.attributes.idp_ca_certs, [
       selectors.FIELD_IDP_CERTS_VALUE,
@@ -239,6 +241,62 @@ module('Acceptance | auth-methods | update', function (hooks) {
     assert.deepEqual(authMethod.attributes.prompts, ['none']);
   });
 
+  test('account claim maps field is disabled when sub mapping exists', async function (assert) {
+    setRunOptions({
+      rules: {
+        'color-contrast': {
+          // [ember-a11y-ignore]: axe rule "color-contrast" automatically ignored on 2026-06-02
+          enabled: false,
+        },
+      },
+    });
+
+    // Create OIDC auth method with a 'sub' mapping
+    instances.authMethod = this.server.create('auth-method', {
+      scope: instances.scopes.org,
+      type: TYPE_AUTH_METHOD_OIDC,
+    });
+    instances.authMethod.attributes.account_claim_maps = ['username=sub'];
+
+    await visit(urls.authMethods);
+
+    await click(
+      commonSelectors.HREF(`${urls.authMethods}/${instances.authMethod.id}`),
+    );
+    await click(commonSelectors.EDIT_BTN);
+
+    assert.dom(selectors.FIELD_ACCOUNT_CLAIM_MAPS).isDisabled();
+  });
+
+  test('account claim maps field is editable when no sub mapping exists', async function (assert) {
+    setRunOptions({
+      rules: {
+        'color-contrast': {
+          // [ember-a11y-ignore]: axe rule "color-contrast" automatically ignored on 2026-06-02
+          enabled: false,
+        },
+      },
+    });
+
+    // Create OIDC auth method with email/name mappings (no 'sub')
+    instances.authMethod = this.server.create('auth-method', {
+      scope: instances.scopes.org,
+      type: TYPE_AUTH_METHOD_OIDC,
+    });
+    instances.authMethod.attributes.account_claim_maps = [
+      'username=email',
+      'fullname=name',
+    ];
+
+    await visit(urls.authMethods);
+    await click(
+      commonSelectors.HREF(`${urls.authMethods}/${instances.authMethod.id}`),
+    );
+    await click(commonSelectors.EDIT_BTN);
+
+    assert.dom(selectors.FIELD_ACCOUNT_CLAIM_MAPS).isNotDisabled();
+  });
+
   test('can update an ldap auth method and save changes', async function (assert) {
     setRunOptions({
       rules: {