diff --git a/.github/workflows/deploy.yaml b/.github/workflows/deploy.yaml
index cdb57a9..e70cfd5 100644
--- a/.github/workflows/deploy.yaml
+++ b/.github/workflows/deploy.yaml
@@ -41,3 +41,12 @@ jobs:
       stack-name: "seahaven-security-baseline"
     secrets:
       deploy-role-arn: ${{ secrets.AWS_DEPLOY_ROLE_ARN_SECURITY }}
+
+  deploy-dev:
+    uses: Sea-Haven-Industries/.github/.github/workflows/cd-cdk.yaml@3cde673b9d05c0e68aac4d997d582f2543853d20 # main
+    with:
+      node-version: "24"
+      stacks: "dev-baseline"
+      stack-name: "seahaven-dev-baseline"
+    secrets:
+      deploy-role-arn: ${{ secrets.AWS_DEPLOY_ROLE_ARN_DEV }}
diff --git a/README.md b/README.md
index 78ce524..0d54e7e 100644
--- a/README.md
+++ b/README.md
@@ -30,6 +30,7 @@ Stacks (deployed by the CD workflow — one job per target account):
 | `seahaven-backup-offsite` | 328440206208 | us-west-2 | Governance-locked offsite copy vault (C-7) |
 | `seahaven-external-dev-baseline` | 396287094661 | us-east-1 | Member-account baseline: Config, GuardDuty, Security Hub (FSBP + CIS v3.0), Access Analyzer, flow logs, budget |
 | `seahaven-security-baseline` | 001520130573 | us-east-1 | Member-account baseline for the delegated security-admin account (same construct set) |
+| `seahaven-dev-baseline` | 710827005802 | us-east-1 | Member-account baseline for internal dev/staging (org-managed detection — no local GuardDuty/SecurityHub) |
 
 ## CDK app
 
@@ -59,6 +60,7 @@ the TypeScript source — no separate compile step needed for `cdk synth` /
 | `backup` | `seahaven-backup` | 328440206208 | us-east-1 | `lib/backup-stack.ts` |
 | `external-dev-baseline` | `seahaven-external-dev-baseline` | 396287094661 | us-east-1 | `lib/member-baseline-stack.ts` |
 | `security-baseline` | `seahaven-security-baseline` | 001520130573 | us-east-1 | `lib/member-baseline-stack.ts` |
+| `dev-baseline` | `seahaven-dev-baseline` | 710827005802 | us-east-1 | `lib/member-baseline-stack.ts` (orgManagedDetection) |
 
 The member-account stack (`external-dev-baseline`) deploys with credentials for
 **396287094661** — the CD workflow runs it as a separate job assuming that
diff --git a/bin/app.ts b/bin/app.ts
index 813ee3f..3e3f7dd 100644
--- a/bin/app.ts
+++ b/bin/app.ts
@@ -12,6 +12,7 @@ import { OrgGovernanceStack } from "../lib/org-governance-stack";
 const ACCOUNT = "328440206208";
 const EXTERNAL_DEV_ACCOUNT = "396287094661";
 const SECURITY_ACCOUNT = "001520130573";
+const DEV_ACCOUNT = "710827005802";
 
 // All 5 VPCs in 328440206208 / us-east-1 (4 custom + default), audit Agent 7.
 // Index-derived logical IDs — append only, never reorder.
@@ -100,6 +101,26 @@ new MemberBaselineStack(app, "security-baseline", {
   managedByTag: "seahaven-org-baseline",
 });
 
+// ── Member-account baseline: seahaven-dev (Phase 4) ─────────────────────────
+// Internal dev/staging workloads (NOT the external-dev engagement account).
+// Created 2026-07-14 AFTER org delegation went live, so GuardDuty/SecurityHub/
+// analyzer are org-managed (auto-enrollment verified) — orgManagedDetection
+// keeps this stack from creating colliding local duplicates. Same lifecycle
+// rule as the other new accounts: root-harden at org ROOT, then move-account
+// into the nonprod OU (ou-nbuj-zpt5ka98).
+new MemberBaselineStack(app, "dev-baseline", {
+  stackName: "seahaven-dev-baseline",
+  env: { account: DEV_ACCOUNT, region: "us-east-1" },
+  namePrefix: "seahaven-dev",
+  monthlyBudgetUsd: 150,
+  budgetAlertEmail: "aws@seahaven.com",
+  ownerEmail: "adam@seahaven.com",
+  // Default VPC kept (dev runs real workloads) — logged from day one.
+  flowLogVpcIds: ["vpc-08f07dc5edeea621f"],
+  managedByTag: "seahaven-org-baseline",
+  orgManagedDetection: true,
+});
+
 // ── Shared DynamoDB CMK (INFRA-95 / M-3) ─────────────────────────────────────
 // Dedicated, standalone stack so the customer-managed key for sensitive
 // finance/PII DynamoDB tables is an independent shared dependency for the owning
diff --git a/lib/detective-controls.ts b/lib/detective-controls.ts
index a3fa3bd..f8d0c6f 100644
--- a/lib/detective-controls.ts
+++ b/lib/detective-controls.ts
@@ -31,6 +31,16 @@ export interface DetectiveControlsProps {
    * custom resources; keep it stable per account.
    */
   readonly namePrefix: string;
+  /**
+   * Create the account-local GuardDuty detector / Security Hub hub + standards /
+   * account Access Analyzer. Default TRUE (pre-delegation accounts own these).
+   * Set FALSE for accounts created AFTER org delegation went live (2026-07-14):
+   * GuardDuty/Security Hub auto-enroll new members and CREATE these resources
+   * themselves — a CFN-owned duplicate fails (one detector/hub per account),
+   * and the org analyzer supersedes the account analyzer. The Config recorder
+   * is always created: recorders stay per-account, delegation never makes one.
+   */
+  readonly localDetectiveServices?: boolean;
 }
 
 export class DetectiveControls extends Construct {
@@ -297,12 +307,14 @@ export class DetectiveControls extends Construct {
     });
 
     // ──────────────────────────────────────────────────────────────────────
-    // H-3  GuardDuty
+    // H-3  GuardDuty, H-4 Security Hub, M-5 Access Analyzer — skipped when the
+    // org delegated admin owns them (localDetectiveServices: false).
     // ──────────────────────────────────────────────────────────────────────
-    new guardduty.CfnDetector(this, "GuardDutyDetector", {
-      enable: true,
-      findingPublishingFrequency: "FIFTEEN_MINUTES",
-    });
+    if (props.localDetectiveServices ?? true) {
+      new guardduty.CfnDetector(this, "GuardDutyDetector", {
+        enable: true,
+        findingPublishingFrequency: "FIFTEEN_MINUTES",
+      });
 
     // ──────────────────────────────────────────────────────────────────────
     // H-4  Security Hub (FSBP + CIS v3.0)
@@ -354,6 +366,7 @@ export class DetectiveControls extends Construct {
       analyzerName: `${prefix}-account-analyzer`,
       type: "ACCOUNT",
     });
+    }
 
     new cdk.CfnOutput(this, "ConfigBucketName", {
       value: configBucket.bucketName,
diff --git a/lib/member-baseline-stack.ts b/lib/member-baseline-stack.ts
index f6677a8..efc61e9 100644
--- a/lib/member-baseline-stack.ts
+++ b/lib/member-baseline-stack.ts
@@ -21,6 +21,12 @@ export interface MemberBaselineStackProps extends cdk.StackProps {
   readonly flowLogVpcIds: string[];
   /** Value for the ManagedBy tag on every resource in the stack. */
   readonly managedByTag: string;
+  /**
+   * TRUE for accounts created after org delegation (2026-07-14): GuardDuty /
+   * Security Hub / analyzer are org-managed (auto-enrolled), so the stack must
+   * not create local duplicates. Default FALSE (pre-delegation accounts).
+   */
+  readonly orgManagedDetection?: boolean;
 }
 
 /**
@@ -47,6 +53,7 @@ export class MemberBaselineStack extends cdk.Stack {
 
     new DetectiveControls(this, "DetectiveControls", {
       namePrefix: props.namePrefix,
+      localDetectiveServices: !(props.orgManagedDetection ?? false),
     });
 
     new FlowLogs(this, "FlowLogs", {