diff --git a/.github/workflows/deploy.yaml b/.github/workflows/deploy.yaml
index 7588331..e8dd908 100644
--- a/.github/workflows/deploy.yaml
+++ b/.github/workflows/deploy.yaml
@@ -22,7 +22,7 @@ jobs:
     uses: Sea-Haven-Industries/.github/.github/workflows/cd-cdk.yaml@e5691d8a7f96ac4d5a841a82975ff0a4354d53ac # v1.0.7
     with:
       node-version: "24"
-      stacks: "account-baseline dynamodb-cmk regional-baseline-us-west-2 regional-baseline-us-east-2 backup-offsite backup org-governance"
+      stacks: "account-baseline dynamodb-cmk regional-baseline-us-west-2 regional-baseline-us-east-2 backup-offsite backup org-governance platform-access"
     secrets:
       deploy-role-arn: ${{ secrets.AWS_DEPLOY_ROLE_ARN }}
 
diff --git a/bin/app.ts b/bin/app.ts
index bc42311..974391a 100644
--- a/bin/app.ts
+++ b/bin/app.ts
@@ -13,6 +13,7 @@ import { AppWebAclStack } from "../lib/app-web-acl-stack";
 import { SeahavenSiteHcptfStack } from "../lib/seahaven-site-hcptf-stack";
 import { MemberBaselineStack } from "../lib/member-baseline-stack";
 import { OrgGovernanceStack } from "../lib/org-governance-stack";
+import { PlatformAccessStack } from "../lib/platform-access-stack";
 
 const ACCOUNT = "328440206208";
 const EXTERNAL_DEV_ACCOUNT = "396287094661";
@@ -79,6 +80,12 @@ new OrgGovernanceStack(app, "org-governance", {
   env: { account: ACCOUNT, region: "us-east-1" },
 });
 
+new PlatformAccessStack(app, "platform-access", {
+  stackName: "seahaven-platform-access",
+  // Same management-account region as org-governance above.
+  env: { account: ACCOUNT, region: "us-east-1" }, // pragma: allowlist secret
+});
+
 new MemberBaselineStack(app, "external-dev-baseline", {
   stackName: "seahaven-external-dev-baseline",
   env: { account: EXTERNAL_DEV_ACCOUNT, region: "us-east-1" },
diff --git a/lib/cis-monitoring.ts b/lib/cis-monitoring.ts
index 3b6debd..9a415f7 100644
--- a/lib/cis-monitoring.ts
+++ b/lib/cis-monitoring.ts
@@ -264,6 +264,53 @@ export class CisMonitoring extends Construct {
       alarm.addAlarmAction(new cwactions.SnsAction(topic));
     }
 
+    // SEC-37. Not a CIS control. Same topic as the CIS alarms.
+    // SCP exemptions for OrganizationAccountAccessRole stay in place.
+    //
+    // A 1/1 alarm on every assume would page for each Platform operator
+    // session and each run of the bootstrap and substrate scripts. CIS 4.1
+    // treats that single-event paging on a routine path as alert fatigue.
+    // Successful assumes are excluded only for those callers:
+    //   * the Platform permission set (AWSReservedSSO_Platform_*)
+    //   * session plat-145-hcptf-bootstrap (create-hcptf-bootstrap-roles.sh)
+    //   * session plat-147-tf-substrate (delete-terraform-substrate-prod-dev.sh)
+    // Any errorCode still counts, including a failed call from those callers.
+    //
+    // Residual: roleSessionName is chosen by the caller, so a successful
+    // assume that copies one of those two session names is not counted.
+    // The scripts stay on OrganizationAccountAccessRole until the permission
+    // set is deployed and a real sign-in has assumed the member role.
+    const orgAdminAssume = new logs.MetricFilter(
+      this,
+      "OrganizationAccountAccessRoleAssumeFilter",
+      {
+        logGroup,
+        filterPattern: logs.FilterPattern.literal(
+          '{ ($.eventName = "AssumeRole") && ($.requestParameters.roleArn = "*OrganizationAccountAccessRole") && (($.errorCode = "*") || (($.userIdentity.arn != "*AWSReservedSSO_Platform_*") && ($.requestParameters.roleSessionName != "plat-145-hcptf-bootstrap") && ($.requestParameters.roleSessionName != "plat-147-tf-substrate"))) }',
+        ),
+        metricNamespace: "SeahavenSecurity",
+        metricName: "OrganizationAccountAccessRoleAssume",
+        metricValue: "1",
+        defaultValue: 0,
+      },
+    );
+    const orgAdminAlarm = orgAdminAssume
+      .metric({
+        statistic: "Sum",
+        period: cdk.Duration.minutes(5),
+      })
+      .createAlarm(this, "OrganizationAccountAccessRoleAssumeAlarm", {
+        alarmName: "organization-account-access-role-assume",
+        alarmDescription:
+          "AssumeRole of OrganizationAccountAccessRole outside the Platform permission set and the two repo script sessions. Failed attempts count for every principal.",
+        threshold: 1,
+        comparisonOperator:
+          cloudwatch.ComparisonOperator.GREATER_THAN_OR_EQUAL_TO_THRESHOLD,
+        evaluationPeriods: 1,
+        treatMissingData: cloudwatch.TreatMissingData.NOT_BREACHING,
+      });
+    orgAdminAlarm.addAlarmAction(new cwactions.SnsAction(topic));
+
     new cdk.CfnOutput(this, "CisAlarmTopicArn", { value: topic.topicArn });
   }
 }
diff --git a/lib/platform-access-stack.ts b/lib/platform-access-stack.ts
new file mode 100644
index 0000000..9a9e5e6
--- /dev/null
+++ b/lib/platform-access-stack.ts
@@ -0,0 +1,64 @@
+import * as cdk from "aws-cdk-lib";
+import * as identitystore from "aws-cdk-lib/aws-identitystore";
+import * as sso from "aws-cdk-lib/aws-sso";
+import { Construct } from "constructs";
+
+const IDENTITY_CENTER_INSTANCE_ARN =
+  "arn:aws:sso:::instance/ssoins-722321f42ca610e4";
+const IDENTITY_STORE_ID = "d-9067ec8e26";
+const MANAGEMENT_ACCOUNT_ID = "328440206208";
+
+/**
+ * Identity Center group and permission set for platform operators (SEC-37).
+ *
+ * Assigned only to the management account. ReadOnlyAccess plus
+ * sts:AssumeRole on OrganizationAccountAccessRole, so the existing
+ * bootstrap and teardown scripts keep working after a person uses this
+ * set. Those scripts still assume OrganizationAccountAccessRole directly.
+ * Retarget them only after this set is deployed and a real sign-in has
+ * assumed the member role.
+ *
+ * This is not an SCP exemption. /platform/ path denies exempt the
+ * reserved SSO role name AWSReservedSSO_Platform_* once the set exists.
+ */
+export class PlatformAccessStack extends cdk.Stack {
+  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
+    super(scope, id, props);
+
+    const group = new identitystore.CfnGroup(this, "PlatformGroup", {
+      identityStoreId: IDENTITY_STORE_ID,
+      displayName: "platform",
+      description:
+        "Platform operators. Management account only. Assumes OrganizationAccountAccessRole for bootstrap.",
+    });
+
+    const permissionSet = new sso.CfnPermissionSet(this, "PlatformPermissionSet", {
+      instanceArn: IDENTITY_CENTER_INSTANCE_ARN,
+      name: "Platform",
+      description:
+        "Read-only in the management account, plus assume OrganizationAccountAccessRole.",
+      sessionDuration: "PT8H",
+      managedPolicies: ["arn:aws:iam::aws:policy/ReadOnlyAccess"],
+      inlinePolicy: {
+        Version: "2012-10-17",
+        Statement: [
+          {
+            Sid: "AssumeOrganizationAccountAccessRole",
+            Effect: "Allow",
+            Action: "sts:AssumeRole",
+            Resource: "arn:aws:iam::*:role/OrganizationAccountAccessRole",
+          },
+        ],
+      },
+    });
+
+    new sso.CfnAssignment(this, "PlatformManagementAssignment", {
+      instanceArn: IDENTITY_CENTER_INSTANCE_ARN,
+      permissionSetArn: permissionSet.attrPermissionSetArn,
+      principalId: group.attrGroupId,
+      principalType: "GROUP",
+      targetId: MANAGEMENT_ACCOUNT_ID,
+      targetType: "AWS_ACCOUNT",
+    });
+  }
+}