diff --git a/cdk/src/constructs/bedrock-models.ts b/cdk/src/constructs/bedrock-models.ts
index 9f3d3493..c1c05203 100644
--- a/cdk/src/constructs/bedrock-models.ts
+++ b/cdk/src/constructs/bedrock-models.ts
@@ -41,6 +41,15 @@ export const DEFAULT_BEDROCK_MODEL_IDS: readonly string[] = [
   // this entry and that default in the same change — a fallback the role cannot
   // invoke fails every task on the stack, not just an edge case.
   'anthropic.claude-opus-4-8',
+  // Claude Opus 5 — granted ahead of anything selecting it (#744). The grant
+  // must be DEPLOYED before the platform default flips, or every task fails at
+  // turn 0 with AccessDenied. Bare ID by contract: Bedrock refuses the bare ID
+  // for on-demand invocation ("ValidationException: … isn't supported. Retry
+  // your request with the ID or ARN of an inference profile"), and both grant
+  // sites derive the `us.`-prefixed inference-profile ARN — the invocable one —
+  // from this entry. Opus 4.8 above stays granted: blueprints may pin it
+  // per-repo, so removing it would fail those repos at turn 0.
+  'anthropic.claude-opus-5',
   'anthropic.claude-haiku-4-5-20251001-v1:0',
 ];
 
diff --git a/cdk/src/handlers/shared/workflows.ts b/cdk/src/handlers/shared/workflows.ts
index 84524d05..dfc720b9 100644
--- a/cdk/src/handlers/shared/workflows.ts
+++ b/cdk/src/handlers/shared/workflows.ts
@@ -94,6 +94,14 @@ export const WORKFLOW_MODEL_ALLOWLIST: readonly string[] = [
   // `bedrockModels` context) in the same change.
   'anthropic.claude-opus-4-8',
   'us.anthropic.claude-opus-4-8',
+  // Claude Opus 5 (#744) — kept in step with the IAM grant added to
+  // DEFAULT_BEDROCK_MODEL_IDS in the same change, per the note above. Only the
+  // bare and `us.`-prefixed forms: `global.anthropic.claude-opus-5` is a live
+  // profile but is deliberately withheld until the grant sites derive the
+  // `global.` ARN (#747) — admitting it here first would pass admission and then
+  // fail at turn 0 with AccessDenied, exactly the drift this comment warns about.
+  'anthropic.claude-opus-5',
+  'us.anthropic.claude-opus-5',
   'anthropic.claude-haiku-4-5-20251001-v1:0',
   'us.anthropic.claude-haiku-4-5-20251001-v1:0',
 ];
diff --git a/cdk/test/constructs/ecs-agent-cluster.test.ts b/cdk/test/constructs/ecs-agent-cluster.test.ts
index df1393a8..e6c1ecfd 100644
--- a/cdk/test/constructs/ecs-agent-cluster.test.ts
+++ b/cdk/test/constructs/ecs-agent-cluster.test.ts
@@ -416,6 +416,14 @@ describe('EcsAgentCluster construct', () => {
     expect(serialized).toContain('inference-profile/us.anthropic.claude-sonnet-4-6');
     expect(serialized).toContain('anthropic.claude-opus-4-20250514-v1:0');
     expect(serialized).toContain('anthropic.claude-haiku-4-5-20251001-v1:0');
+    // Claude Opus 5 (#744) — AgentCore/ECS parity. Both ARNs: the bare id isn't
+    // on-demand invocable, so the `us.` profile is the one actually called.
+    expect(serialized).toContain('foundation-model/anthropic.claude-opus-5');
+    expect(serialized).toContain('inference-profile/us.anthropic.claude-opus-5');
+    // REGRESSION (#744): Opus 4.8 stays granted alongside Opus 5 — blueprints may
+    // pin it per-repo, so dropping it would fail those repos at turn 0.
+    expect(serialized).toContain('foundation-model/anthropic.claude-opus-4-8');
+    expect(serialized).toContain('inference-profile/us.anthropic.claude-opus-4-8');
   });
 
   test('task role can DescribeAvailabilityZones so a CDK target repo can `cdk synth` on a fresh clone (ECS-parity)', () => {
diff --git a/cdk/test/stacks/agent.test.ts b/cdk/test/stacks/agent.test.ts
index 902b9dc0..e7c91748 100644
--- a/cdk/test/stacks/agent.test.ts
+++ b/cdk/test/stacks/agent.test.ts
@@ -259,13 +259,24 @@ describe('AgentStack', () => {
 
   test('runtime is granted the default Bedrock model set', () => {
     // Default (no bedrockModels context): the runtime execution role must hold
-    // bedrock:InvokeModel on the three default foundation models + their US
-    // inference profiles, scoped (never Resource: '*').
+    // bedrock:InvokeModel on every default foundation model + its US
+    // inference profile, scoped (never Resource: '*').
     const serialized = JSON.stringify(template.findResources('AWS::IAM::Policy'));
     expect(serialized).toContain('foundation-model/anthropic.claude-sonnet-4-6');
     expect(serialized).toContain('inference-profile/us.anthropic.claude-sonnet-4-6');
     expect(serialized).toContain('anthropic.claude-opus-4-20250514-v1:0');
     expect(serialized).toContain('anthropic.claude-haiku-4-5-20251001-v1:0');
+    // Claude Opus 5 (#744). Granted ahead of any default flip: the bare id is
+    // not on-demand invocable (Bedrock returns ValidationException), so the
+    // `us.`-prefixed inference profile is the one actually called — both ARNs
+    // must be present or the agent gets AccessDenied at turn 0.
+    expect(serialized).toContain('foundation-model/anthropic.claude-opus-5');
+    expect(serialized).toContain('inference-profile/us.anthropic.claude-opus-5');
+    // REGRESSION (#744): Opus 4.8 stays granted alongside Opus 5. Blueprints may
+    // pin 4.8 per-repo; dropping it would fail those repos at turn 0. Retiring
+    // 4.8 is a separate, announced change — not a side effect of adding 5.
+    expect(serialized).toContain('foundation-model/anthropic.claude-opus-4-8');
+    expect(serialized).toContain('inference-profile/us.anthropic.claude-opus-4-8');
   });
 
   test('bedrockModels context override propagates to the runtime execution role', () => {