diff --git a/packages/sdk/browser/contract-tests/entity/src/ClientEntity.ts b/packages/sdk/browser/contract-tests/entity/src/ClientEntity.ts
index 739bfd7c61..124d31ae41 100644
--- a/packages/sdk/browser/contract-tests/entity/src/ClientEntity.ts
+++ b/packages/sdk/browser/contract-tests/entity/src/ClientEntity.ts
@@ -354,7 +354,11 @@ export async function newSdkClientEntity(options: CreateInstanceParams) {
     initialContext,
     sdkConfig,
   );
-  const { status } = await client.start({ timeout: timeout / 1000 });
+  const bootstrap = options.configuration.clientSide?.bootstrap;
+  const { status } = await client.start({
+    timeout: timeout / 1000,
+    ...(bootstrap != null && { bootstrap }),
+  });
   const failed = status !== 'complete';
   if (failed && !options.configuration.initCanFail) {
     client.close();
diff --git a/packages/sdk/browser/contract-tests/entity/src/TestHarnessWebSocket.ts b/packages/sdk/browser/contract-tests/entity/src/TestHarnessWebSocket.ts
index de8f5f5c6d..9bde09419b 100644
--- a/packages/sdk/browser/contract-tests/entity/src/TestHarnessWebSocket.ts
+++ b/packages/sdk/browser/contract-tests/entity/src/TestHarnessWebSocket.ts
@@ -46,6 +46,7 @@ export default class TestHarnessWebSocket {
             'client-per-context-summaries',
             'track-hooks',
             'fdv1-fallback',
+            'bootstrap',
           ];
 
           break;
diff --git a/packages/sdk/node-client/contract-tests/src/index.ts b/packages/sdk/node-client/contract-tests/src/index.ts
index 64e19c7fc9..9dd67b80ad 100644
--- a/packages/sdk/node-client/contract-tests/src/index.ts
+++ b/packages/sdk/node-client/contract-tests/src/index.ts
@@ -43,6 +43,7 @@ app.get('/', (req: Request, res: Response) => {
       'wrapper',
       'fdv1-fallback',
       'client-event-source-http-errors',
+      'bootstrap',
     ],
   });
 });
diff --git a/packages/sdk/node-client/contract-tests/src/sdkClientEntity.ts b/packages/sdk/node-client/contract-tests/src/sdkClientEntity.ts
index a1cb6c06e1..d281d3ae96 100644
--- a/packages/sdk/node-client/contract-tests/src/sdkClientEntity.ts
+++ b/packages/sdk/node-client/contract-tests/src/sdkClientEntity.ts
@@ -277,7 +277,11 @@ export async function newSdkClientEntity(options: CreateInstanceParams): Promise
     initialContext,
     sdkConfig,
   );
-  const startResult = await client.start({ timeout: timeout / 1000 });
+  const bootstrap = options.configuration.clientSide?.bootstrap;
+  const startResult = await client.start({
+    timeout: timeout / 1000,
+    ...(bootstrap != null && { bootstrap }),
+  });
   const failed = startResult.status !== 'complete';
   if (failed && !options.configuration.initCanFail) {
     await client.close();
diff --git a/packages/sdk/react-native/contract-tests/entity/src/ClientEntity.ts b/packages/sdk/react-native/contract-tests/entity/src/ClientEntity.ts
index 21b8b5f257..979763e049 100644
--- a/packages/sdk/react-native/contract-tests/entity/src/ClientEntity.ts
+++ b/packages/sdk/react-native/contract-tests/entity/src/ClientEntity.ts
@@ -364,8 +364,13 @@ export async function newSdkClientEntity(options: CreateInstanceParams) {
 
   let failed = false;
   try {
+    const bootstrap = options.configuration.clientSide?.bootstrap;
     await Promise.race([
-      client.identify(initialContext, { timeout: timeout / 1000, waitForNetworkResults: true }),
+      client.identify(initialContext, {
+        timeout: timeout / 1000,
+        waitForNetworkResults: true,
+        ...(bootstrap != null && { bootstrap }),
+      }),
       new Promise((_resolve, reject) => {
         setTimeout(reject, timeout);
       }),
diff --git a/packages/sdk/react-native/contract-tests/entity/src/TestHarnessWebSocket.ts b/packages/sdk/react-native/contract-tests/entity/src/TestHarnessWebSocket.ts
index 979eb816ed..dad55c9f48 100644
--- a/packages/sdk/react-native/contract-tests/entity/src/TestHarnessWebSocket.ts
+++ b/packages/sdk/react-native/contract-tests/entity/src/TestHarnessWebSocket.ts
@@ -60,6 +60,7 @@ export default class TestHarnessWebSocket {
             'track-hooks',
             'fdv1-fallback',
             'client-event-source-http-errors',
+            'bootstrap',
           ];
 
           break;
diff --git a/packages/sdk/react/contract-tests/app/ClientRoot.tsx b/packages/sdk/react/contract-tests/app/ClientRoot.tsx
index fb282868c0..5a47e65631 100644
--- a/packages/sdk/react/contract-tests/app/ClientRoot.tsx
+++ b/packages/sdk/react/contract-tests/app/ClientRoot.tsx
@@ -60,7 +60,11 @@ export default function ClientRoot({ children }: { children: React.ReactNode })
           sdkConfig,
         );
 
-        const { status } = await client.start({ timeout: timeout / 1000 });
+        const bootstrap = params.configuration.clientSide?.bootstrap;
+        const { status } = await client.start({
+          timeout: timeout / 1000,
+          ...(bootstrap != null && { bootstrap }),
+        });
 
         if (status === 'failed' && !params.configuration.initCanFail) {
           client.close();
diff --git a/packages/sdk/react/contract-tests/app/TestHarnessWebSocket.ts b/packages/sdk/react/contract-tests/app/TestHarnessWebSocket.ts
index 8d09d8c2de..e8c72d5c18 100644
--- a/packages/sdk/react/contract-tests/app/TestHarnessWebSocket.ts
+++ b/packages/sdk/react/contract-tests/app/TestHarnessWebSocket.ts
@@ -50,6 +50,7 @@ export default class TestHarnessWebSocket {
             'client-per-context-summaries',
             'track-hooks',
             'fdv1-fallback',
+            'bootstrap',
           ];
           break;
 
diff --git a/packages/sdk/vue/contract-tests/src/ClientEntity.ts b/packages/sdk/vue/contract-tests/src/ClientEntity.ts
index 3b5da3d559..618b789f5c 100644
--- a/packages/sdk/vue/contract-tests/src/ClientEntity.ts
+++ b/packages/sdk/vue/contract-tests/src/ClientEntity.ts
@@ -403,8 +403,10 @@ export async function newSdkClientEntity(options: CreateInstanceParams) {
     // Forward a harness-supplied secure mode hash as the `h` query parameter, only when
     // the harness actually configured one.
     const secureModeHash = options.configuration.clientSide?.hash;
+    const bootstrap = options.configuration.clientSide?.bootstrap;
     const result = await client.start({
       timeout: timeout / 1000,
+      ...(bootstrap != null && { bootstrap }),
       ...(secureModeHash !== undefined && { identifyOptions: { hash: secureModeHash } }),
     });
     if (result.status !== 'complete') {
diff --git a/packages/sdk/vue/contract-tests/src/TestHarnessWebSocket.ts b/packages/sdk/vue/contract-tests/src/TestHarnessWebSocket.ts
index 3d9ff65138..95de66e09e 100644
--- a/packages/sdk/vue/contract-tests/src/TestHarnessWebSocket.ts
+++ b/packages/sdk/vue/contract-tests/src/TestHarnessWebSocket.ts
@@ -50,6 +50,7 @@ export default class TestHarnessWebSocket {
             'secure-mode-hash',
             'flag-change-listeners',
             'fdv1-fallback',
+            'bootstrap',
           ];
 
           break;
diff --git a/packages/tooling/contract-test-utils/src/types/ConfigParams.ts b/packages/tooling/contract-test-utils/src/types/ConfigParams.ts
index 848fdde91f..25156ce07c 100644
--- a/packages/tooling/contract-test-utils/src/types/ConfigParams.ts
+++ b/packages/tooling/contract-test-utils/src/types/ConfigParams.ts
@@ -102,6 +102,7 @@ export interface SDKConfigClientSideParams {
   useReport?: boolean;
   includeEnvironmentAttributes?: boolean;
   hash?: string;
+  bootstrap?: unknown;
 }
 
 export interface SDKConfigEvaluationHookData {