diff --git a/cdk/src/constructs/bedrock-models.ts b/cdk/src/constructs/bedrock-models.ts
new file mode 100644
index 00000000..df3e127c
--- /dev/null
+++ b/cdk/src/constructs/bedrock-models.ts
@@ -0,0 +1,86 @@
+/**
+ *  MIT No Attribution
+ *
+ *  Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ *  Permission is hereby granted, free of charge, to any person obtaining a copy of
+ *  the Software without restriction, including without limitation the rights to
+ *  use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ *  the Software, and to permit persons to whom the Software is furnished to do so.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ *  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ *  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ *  SOFTWARE.
+ */
+
+import { Node } from 'constructs';
+
+/**
+ * Single source of truth for the Bedrock **foundation-model IDs** the agent
+ * runtime may invoke. Both grant sites — the AgentCore runtime in
+ * `stacks/agent.ts` and the ECS task role in `constructs/ecs-agent-cluster.ts`
+ * — derive their `grantInvoke` / IAM ARNs from this one list, so the two
+ * backends can never drift (they were previously two hand-synced arrays; #433).
+ *
+ * Scoping is intentionally per-model (explicit foundation-model +
+ * cross-Region inference-profile ARNs), NOT a `Resource: '*'` wildcard — that
+ * hardening is preserved. Account-level Bedrock model access remains the outer
+ * gate; this list only controls the IAM grant.
+ */
+export const DEFAULT_BEDROCK_MODEL_IDS: readonly string[] = [
+  'anthropic.claude-sonnet-4-6',
+  'anthropic.claude-opus-4-20250514-v1:0',
+  'anthropic.claude-haiku-4-5-20251001-v1:0',
+];
+
+/** CDK context key whose value (a string array) overrides the model set. */
+export const BEDROCK_MODELS_CONTEXT_KEY = 'bedrockModels';
+
+/**
+ * Resolves the invocable foundation-model IDs: CDK context `bedrockModels`
+ * (an array of **bare foundation-model IDs**) when provided, else
+ * {@link DEFAULT_BEDROCK_MODEL_IDS}. Set via `cdk.json` `context` or
+ * `-c bedrockModels='["anthropic.claude-opus-4-8", …]'`, then redeploy, to add
+ * a model the runtime may invoke — no construct edits needed.
+ *
+ * **Use the bare foundation-model ID (`anthropic.claude-…`), NOT the
+ * `us.`-prefixed inference-profile ID.** Both grant sites derive the US
+ * inference-profile ARN by prefixing `us.`, so passing `us.anthropic.…` here
+ * would produce an invalid `us.us.anthropic.…` ARN. The resolver rejects a
+ * `us.`/`eu.`/`apac.`-prefixed entry to catch that early.
+ *
+ * Throws on a malformed override (non-array, non-string / empty entries, or a
+ * region-prefixed ID) so a typo fails synth loudly instead of silently
+ * granting nothing or an invalid ARN.
+ */
+export function resolveBedrockModelIds(node: Node): readonly string[] {
+  const override = node.tryGetContext(BEDROCK_MODELS_CONTEXT_KEY);
+  if (override === undefined || override === null) {
+    return DEFAULT_BEDROCK_MODEL_IDS;
+  }
+  if (!Array.isArray(override) || override.length === 0) {
+    throw new Error(
+      `Context '${BEDROCK_MODELS_CONTEXT_KEY}' must be a non-empty array of foundation-model IDs `
+      + `(e.g. ["anthropic.claude-sonnet-4-6"]); got ${JSON.stringify(override)}.`,
+    );
+  }
+  for (const id of override) {
+    if (typeof id !== 'string' || id.trim().length === 0) {
+      throw new Error(
+        `Context '${BEDROCK_MODELS_CONTEXT_KEY}' entries must be non-empty strings; got ${JSON.stringify(id)}.`,
+      );
+    }
+    if (/^(us|eu|apac)\./.test(id)) {
+      throw new Error(
+        `Context '${BEDROCK_MODELS_CONTEXT_KEY}' expects bare foundation-model IDs, not region-prefixed `
+        + `inference-profile IDs — got '${id}'. Use '${id.replace(/^(us|eu|apac)\./, '')}'; `
+        + 'the US inference-profile ARN is derived automatically.',
+      );
+    }
+  }
+  return override as string[];
+}
diff --git a/cdk/src/constructs/ecs-agent-cluster.ts b/cdk/src/constructs/ecs-agent-cluster.ts
index 1ccbf7c4..4d6d16d1 100644
--- a/cdk/src/constructs/ecs-agent-cluster.ts
+++ b/cdk/src/constructs/ecs-agent-cluster.ts
@@ -28,6 +28,7 @@ import * as secretsmanager from 'aws-cdk-lib/aws-secretsmanager';
 import { NagSuppressions } from 'cdk-nag';
 import { Construct } from 'constructs';
 import { AgentSessionRole } from './agent-session-role';
+import { resolveBedrockModelIds } from './bedrock-models';
 
 export interface EcsAgentClusterProps {
   readonly vpc: ec2.IVpc;
@@ -50,18 +51,6 @@ export interface EcsAgentClusterProps {
   readonly agentSessionRole?: AgentSessionRole;
 }
 
-/**
- * Bedrock model IDs the agent may invoke (kept in sync with the AgentCore
- * runtime grants in agent.ts). Used to scope the ECS task role's Bedrock
- * permissions to explicit foundation-model + inference-profile ARNs instead of
- * a `Resource: '*'` wildcard.
- */
-const BEDROCK_MODEL_IDS = [
-  'anthropic.claude-sonnet-4-6',
-  'anthropic.claude-opus-4-20250514-v1:0',
-  'anthropic.claude-haiku-4-5-20251001-v1:0',
-];
-
 /** HTTPS port — the only egress allowed from the agent task ENIs. */
 const HTTPS_PORT = 443;
 
@@ -162,10 +151,12 @@ export class EcsAgentCluster extends Construct {
 
     // Bedrock model invocation — scoped to explicit foundation-model and
     // cross-region inference-profile ARNs (parity with the AgentCore runtime
-    // grants in agent.ts), replacing the prior Resource: '*' wildcard.
+    // grants in agent.ts), NOT a Resource: '*' wildcard. The model set is the
+    // shared, context-overridable list (constructs/bedrock-models.ts) so the
+    // ECS and AgentCore backends can't drift.
     const stack = Stack.of(this);
     const bedrockResources: string[] = [];
-    for (const modelId of BEDROCK_MODEL_IDS) {
+    for (const modelId of resolveBedrockModelIds(this.node)) {
       bedrockResources.push(
         stack.formatArn({
           service: 'bedrock',
diff --git a/cdk/src/handlers/shared/workflows.ts b/cdk/src/handlers/shared/workflows.ts
index ca665531..470b81c0 100644
--- a/cdk/src/handlers/shared/workflows.ts
+++ b/cdk/src/handlers/shared/workflows.ts
@@ -68,12 +68,18 @@ export interface WorkflowDescriptor {
 
 /**
  * Platform allow-list of Bedrock model ids a workflow may pin via
- * `agent_config.model.id` (WORKFLOWS.md rule 13 / §"Model selection"). Mirrors
- * the foundation models the agent runtime is granted to invoke (`BEDROCK_MODEL_IDS`
- * in `cdk/src/constructs/ecs-agent-cluster.ts`), accepting both the bare id and
- * the `us.`-prefixed cross-region inference-profile form the runtime resolves.
- * A future Phase 4 will source this from the repo Blueprint; until then it is a
- * single platform-wide list checked at admission.
+ * `agent_config.model.id` (WORKFLOWS.md rule 13 / §"Model selection"). Should
+ * mirror the foundation models the agent runtime is granted to invoke — the
+ * shared list in `cdk/src/constructs/bedrock-models.ts`
+ * (`DEFAULT_BEDROCK_MODEL_IDS` / the `bedrockModels` context, #433) — accepting
+ * both the bare id and the `us.`-prefixed cross-region inference-profile form.
+ *
+ * NOTE (#433 follow-up): this is a SEPARATE, hand-maintained list from the IAM
+ * grant source. The `repo onboard --model` path is NOT gated by it (repo
+ * `model_id` isn't validated here), but a custom workflow pinning a model added
+ * via the `bedrockModels` context would still be rejected at create-task until
+ * it's added here too. A future Phase 4 will source this from the repo
+ * Blueprint; consolidating it with `bedrock-models.ts` is tracked separately.
  */
 export const WORKFLOW_MODEL_ALLOWLIST: readonly string[] = [
   'anthropic.claude-sonnet-4-6',
diff --git a/cdk/src/stacks/agent.ts b/cdk/src/stacks/agent.ts
index 192496d3..604f794d 100644
--- a/cdk/src/stacks/agent.ts
+++ b/cdk/src/stacks/agent.ts
@@ -35,6 +35,7 @@ import { AgentSessionRole } from '../constructs/agent-session-role';
 import { AgentVpc } from '../constructs/agent-vpc';
 import { ApprovalMetricsPublisherConsumer } from '../constructs/approval-metrics-publisher-consumer';
 import { AttachmentsBucket } from '../constructs/attachments-bucket';
+import { resolveBedrockModelIds } from '../constructs/bedrock-models';
 import { Blueprint } from '../constructs/blueprint';
 import { CedarWasmLayer } from '../constructs/cedar-wasm-layer';
 import { ConcurrencyReconciler } from '../constructs/concurrency-reconciler';
@@ -420,44 +421,24 @@ export class AgentStack extends Stack {
     applicationLogGroup.grantWrite(runtime);
     agentMemory.grantReadWrite(runtime);
 
-    const model = new bedrock.BedrockFoundationModel('anthropic.claude-sonnet-4-6', {
-      supportsAgents: true,
-      supportsCrossRegion: true,
-    });
-
-    // Create a cross-region inference profile for Claude Sonnet 4.6
-    const inferenceProfile = bedrock.CrossRegionInferenceProfile.fromConfig({
-      geoRegion: bedrock.CrossRegionInferenceProfileRegion.US,
-      model: model,
-    });
-
-    const model3 = new bedrock.BedrockFoundationModel('anthropic.claude-opus-4-20250514-v1:0', {
-      supportsAgents: true,
-      supportsCrossRegion: true,
-    });
-
-    const inferenceProfile3 = bedrock.CrossRegionInferenceProfile.fromConfig({
-      geoRegion: bedrock.CrossRegionInferenceProfileRegion.US,
-      model: model3,
-    });
-
-    const model2 = new bedrock.BedrockFoundationModel('anthropic.claude-haiku-4-5-20251001-v1:0', {
-      supportsAgents: true,
-      supportsCrossRegion: true,
-    });
-
-    // Create a cross-region inference profile for Claude Haiku 4.5
-    const inferenceProfile2 = bedrock.CrossRegionInferenceProfile.fromConfig({
-      geoRegion: bedrock.CrossRegionInferenceProfileRegion.US,
-      model: model2,
-    });
-
-    model.grantInvoke(runtime);
-    inferenceProfile.grantInvoke(runtime);
-    model3.grantInvoke(runtime);
-    inferenceProfile3.grantInvoke(runtime);
-    model2.grantInvoke(runtime);
-    inferenceProfile2.grantInvoke(runtime);
+    // Grant the runtime invoke on each configured foundation model + its
+    // US cross-Region inference profile. The model set is a single source of
+    // truth (constructs/bedrock-models.ts), shared with the ECS task role, and
+    // overridable via the `bedrockModels` CDK context — add a model by config,
+    // no construct edits. Scoping stays per-model (no Resource:'*'); account-
+    // level Bedrock access remains the outer gate.
+    for (const modelId of resolveBedrockModelIds(this.node)) {
+      const foundationModel = new bedrock.BedrockFoundationModel(modelId, {
+        supportsAgents: true,
+        supportsCrossRegion: true,
+      });
+      const crossRegionProfile = bedrock.CrossRegionInferenceProfile.fromConfig({
+        geoRegion: bedrock.CrossRegionInferenceProfileRegion.US,
+        model: foundationModel,
+      });
+      foundationModel.grantInvoke(runtime);
+      crossRegionProfile.grantInvoke(runtime);
+    }
 
     // --- Per-task SessionRole (#209) ---
     // Holds the tenant-data grants (the four task_id-partitioned tables, plus
diff --git a/cdk/test/constructs/bedrock-models.test.ts b/cdk/test/constructs/bedrock-models.test.ts
new file mode 100644
index 00000000..e39ff504
--- /dev/null
+++ b/cdk/test/constructs/bedrock-models.test.ts
@@ -0,0 +1,72 @@
+/**
+ *  MIT No Attribution
+ *
+ *  Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ *
+ *  Permission is hereby granted, free of charge, to any person obtaining a copy of
+ *  the Software without restriction, including without limitation the rights to
+ *  use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+ *  the Software, and to permit persons to whom the Software is furnished to do so.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ *  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ *  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ *  SOFTWARE.
+ */
+
+import { App, Stack } from 'aws-cdk-lib';
+import {
+  BEDROCK_MODELS_CONTEXT_KEY,
+  DEFAULT_BEDROCK_MODEL_IDS,
+  resolveBedrockModelIds,
+} from '../../src/constructs/bedrock-models';
+
+function nodeWithContext(context?: Record<string, unknown>) {
+  const app = new App({ context });
+  return new Stack(app, 'TestStack').node;
+}
+
+describe('resolveBedrockModelIds', () => {
+  it('returns the default set when no context override is present', () => {
+    const ids = resolveBedrockModelIds(nodeWithContext());
+    expect(ids).toEqual(DEFAULT_BEDROCK_MODEL_IDS);
+  });
+
+  it('returns the context override when provided', () => {
+    const override = ['anthropic.claude-opus-4-8', 'anthropic.claude-sonnet-4-6'];
+    const ids = resolveBedrockModelIds(nodeWithContext({ [BEDROCK_MODELS_CONTEXT_KEY]: override }));
+    expect(ids).toEqual(override);
+  });
+
+  it('throws on a non-array override (typo guard)', () => {
+    expect(() =>
+      resolveBedrockModelIds(nodeWithContext({ [BEDROCK_MODELS_CONTEXT_KEY]: 'anthropic.claude-opus-4-8' })),
+    ).toThrow(/must be a non-empty array/);
+  });
+
+  it('throws on an empty-array override', () => {
+    expect(() =>
+      resolveBedrockModelIds(nodeWithContext({ [BEDROCK_MODELS_CONTEXT_KEY]: [] })),
+    ).toThrow(/must be a non-empty array/);
+  });
+
+  it('throws on a non-string / empty entry', () => {
+    expect(() =>
+      resolveBedrockModelIds(nodeWithContext({ [BEDROCK_MODELS_CONTEXT_KEY]: ['anthropic.claude-sonnet-4-6', ''] })),
+    ).toThrow(/non-empty strings/);
+  });
+
+  it('throws on a region-prefixed (us./eu./apac.) inference-profile ID', () => {
+    // Guards the us.us.… double-prefix footgun: both grant sites derive the
+    // inference-profile ARN by prefixing `us.`, so the context wants the bare id.
+    expect(() =>
+      resolveBedrockModelIds(nodeWithContext({ [BEDROCK_MODELS_CONTEXT_KEY]: ['us.anthropic.claude-opus-4-8'] })),
+    ).toThrow(/bare foundation-model IDs/);
+    expect(() =>
+      resolveBedrockModelIds(nodeWithContext({ [BEDROCK_MODELS_CONTEXT_KEY]: ['eu.anthropic.claude-sonnet-4-6'] })),
+    ).toThrow(/bare foundation-model IDs/);
+  });
+});
diff --git a/cdk/test/constructs/ecs-agent-cluster.test.ts b/cdk/test/constructs/ecs-agent-cluster.test.ts
index a6164a56..e190aa8f 100644
--- a/cdk/test/constructs/ecs-agent-cluster.test.ts
+++ b/cdk/test/constructs/ecs-agent-cluster.test.ts
@@ -29,8 +29,10 @@ import * as secretsmanager from 'aws-cdk-lib/aws-secretsmanager';
 import { AgentSessionRole } from '../../src/constructs/agent-session-role';
 import { EcsAgentCluster } from '../../src/constructs/ecs-agent-cluster';
 
-function createStack(overrides?: { memoryId?: string }): { stack: Stack; template: Template } {
-  const app = new App();
+function createStack(overrides?: { memoryId?: string; bedrockModels?: string[] }): { stack: Stack; template: Template } {
+  const app = new App({
+    context: overrides?.bedrockModels ? { bedrockModels: overrides.bedrockModels } : undefined,
+  });
   const stack = new Stack(app, 'TestStack');
 
   const vpc = new ec2.Vpc(stack, 'Vpc', { maxAzs: 2 });
@@ -174,6 +176,29 @@ describe('EcsAgentCluster construct', () => {
     expect(serialized).toContain('anthropic.claude-haiku-4-5-20251001-v1:0');
   });
 
+  test('bedrockModels context override changes the granted model ARNs (#433)', () => {
+    const template = createStack({ bedrockModels: ['anthropic.claude-opus-4-8'] }).template;
+    const policies = template.findResources('AWS::IAM::Policy');
+    let bedrockStatement: { Resource: unknown } | undefined;
+    for (const policy of Object.values(policies)) {
+      for (const s of policy.Properties.PolicyDocument.Statement) {
+        const actions = Array.isArray(s.Action) ? s.Action : [s.Action];
+        if (actions.includes('bedrock:InvokeModel')) {
+          bedrockStatement = s;
+        }
+      }
+    }
+    expect(bedrockStatement).toBeDefined();
+    const serialized = JSON.stringify(bedrockStatement!.Resource);
+    // The override model is granted...
+    expect(serialized).toContain('foundation-model/anthropic.claude-opus-4-8');
+    expect(serialized).toContain('inference-profile/us.anthropic.claude-opus-4-8');
+    // ...and the defaults are NOT (the override replaces, not appends).
+    expect(serialized).not.toContain('claude-sonnet-4-6');
+    // Still scoped, never a wildcard.
+    expect(bedrockStatement!.Resource).not.toEqual('*');
+  });
+
   test('container has required environment variables', () => {
     baseTemplate.hasResourceProperties('AWS::ECS::TaskDefinition', {
       ContainerDefinitions: Match.arrayWith([
diff --git a/cdk/test/stacks/agent.test.ts b/cdk/test/stacks/agent.test.ts
index 22a295fd..486b4ad9 100644
--- a/cdk/test/stacks/agent.test.ts
+++ b/cdk/test/stacks/agent.test.ts
@@ -230,6 +230,50 @@ describe('AgentStack', () => {
     expect(serialized).toMatch(/"Fn::GetAtt":\["Runtime[0-9A-F]+","AgentRuntimeArn"\]/);
   });
 
+  test('runtime is granted the default Bedrock model set (#433)', () => {
+    // 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: '*').
+    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');
+  });
+
+  test('bedrockModels context override propagates to the runtime execution role (#433)', () => {
+    // The other half of #433's acceptance criteria (the ECS side is covered in
+    // ecs-agent-cluster.test.ts): a context override must replace the runtime's
+    // granted models too — overridden model present, defaults absent, still scoped.
+    const app = new App({ context: { bedrockModels: ['anthropic.claude-opus-4-8'] } });
+    const stack = new AgentStack(app, 'OverrideAgentStack', {
+      env: { account: '123456789012', region: 'us-east-1' },
+    });
+    const overridden = Template.fromStack(stack);
+
+    // Collect every bedrock:InvokeModel statement's Resource across IAM policies.
+    const policies = overridden.findResources('AWS::IAM::Policy');
+    const bedrockResources: unknown[] = [];
+    for (const p of Object.values(policies)) {
+      for (const s of (p.Properties?.PolicyDocument?.Statement ?? []) as Array<{ Action?: string | string[]; Resource?: unknown }>) {
+        const actions = Array.isArray(s.Action) ? s.Action : [s.Action];
+        if (actions.some((a) => typeof a === 'string' && a.startsWith('bedrock:InvokeModel'))) {
+          bedrockResources.push(s.Resource);
+        }
+      }
+    }
+    const serialized = JSON.stringify(bedrockResources);
+    expect(bedrockResources.length).toBeGreaterThan(0);
+    // Overridden model is granted...
+    expect(serialized).toContain('foundation-model/anthropic.claude-opus-4-8');
+    expect(serialized).toContain('inference-profile/us.anthropic.claude-opus-4-8');
+    // ...defaults are NOT (override replaces, not appends)...
+    expect(serialized).not.toContain('claude-sonnet-4-6');
+    expect(serialized).not.toContain('claude-haiku-4-5');
+    // ...and the grant is never a bare wildcard.
+    expect(serialized).not.toContain('"*"');
+  });
+
   test('outputs ApiUrl', () => {
     template.hasOutput('ApiUrl', {
       Description: 'URL of the Task API',