diff --git a/src/ErrorBoundary.ts b/src/ErrorBoundary.ts
index bf3dc70..1c529fc 100644
--- a/src/ErrorBoundary.ts
+++ b/src/ErrorBoundary.ts
@@ -6,7 +6,7 @@ import {
   StatsigUninitializedError,
 } from './Errors';
 import OutputLogger from './OutputLogger';
-import { StatsigOptions } from './StatsigOptions';
+import { NetworkOverrideFunc, StatsigOptions } from './StatsigOptions';
 import { getSDKType, getSDKVersion, getStatsigMetadata } from './utils/core';
 import safeFetch from './utils/safeFetch';
 import { StatsigContext } from './utils/StatsigContext';
@@ -18,6 +18,7 @@ export default class ErrorBoundary {
   private optionsLoggingCopy: StatsigOptions;
   private statsigMetadata = getStatsigMetadata();
   private seen = new Set<string>();
+  private networkOverrideFunc: NetworkOverrideFunc | null;
 
   constructor(
     sdkKey: string,
@@ -27,6 +28,7 @@ export default class ErrorBoundary {
     this.sdkKey = sdkKey;
     this.optionsLoggingCopy = optionsLoggingCopy;
     this.statsigMetadata['sessionID'] = sessionID;
+    this.networkOverrideFunc = optionsLoggingCopy.networkOverrideFunc ?? null;
   }
 
   swallow<T>(task: (ctx: StatsigContext) => T, ctx: StatsigContext) {
@@ -113,7 +115,9 @@ export default class ErrorBoundary {
         statsigOptions: this.optionsLoggingCopy,
         ...ctx.getContextForLogging(),
       });
-      safeFetch(ExceptionEndpoint, {
+
+      const fetcher = this.networkOverrideFunc ?? safeFetch;
+      fetcher(ExceptionEndpoint, {
         method: 'POST',
         headers: {
           'STATSIG-API-KEY': this.sdkKey,
diff --git a/src/SpecStore.ts b/src/SpecStore.ts
index 8957792..f51a6ef 100644
--- a/src/SpecStore.ts
+++ b/src/SpecStore.ts
@@ -14,7 +14,11 @@ import { InitializationSource } from './InitializationDetails';
 import { DataAdapterKey, IDataAdapter } from './interfaces/IDataAdapter';
 import OutputLogger from './OutputLogger';
 import SDKFlags from './SDKFlags';
-import { ExplicitStatsigOptions, InitStrategy } from './StatsigOptions';
+import {
+  ExplicitStatsigOptions,
+  InitStrategy,
+  NetworkOverrideFunc,
+} from './StatsigOptions';
 import { poll } from './utils/core';
 import IDListUtil, { IDList } from './utils/IDListUtil';
 import safeFetch from './utils/safeFetch';
@@ -64,6 +68,7 @@ export default class SpecStore {
   private hashedClientSDKKeyToAppMap: Record<string, string> = {};
   private hashedSDKKeysToEntities: Record<string, APIEntityNames> = {};
   private primaryTargetAppID: string | null;
+  private networkOverrideFunc: NetworkOverrideFunc | null;
 
   public constructor(fetcher: StatsigFetcher, options: ExplicitStatsigOptions) {
     this.fetcher = fetcher;
@@ -77,6 +82,7 @@ export default class SpecStore {
       layers: {},
       experimentToLayer: {},
     };
+    this.networkOverrideFunc = options.networkOverrideFunc ?? null;
     this.rulesetsSyncInterval = options.rulesetsSyncIntervalMs;
     this.idListsSyncInterval = options.idListsSyncIntervalMs;
     this.disableRulesetsSync = options.disableRulesetsSync;
@@ -756,7 +762,9 @@ export default class SpecStore {
         url: url,
         markerID,
       });
-      res = await safeFetch(url, {
+
+      const fetcher = this.networkOverrideFunc ?? safeFetch;
+      res = await fetcher(url, {
         method: 'GET',
         headers: {
           Range: `bytes=${readSize}-`,
@@ -771,9 +779,11 @@ export default class SpecStore {
         markerID,
       });
     }
+
     if (threwNetworkError || !res) {
       return;
     }
+
     try {
       diagnostics?.process.start({ markerID });
       const contentLength = res.headers.get('content-length');
diff --git a/src/StatsigOptions.ts b/src/StatsigOptions.ts
index 6fffbc2..6412eeb 100644
--- a/src/StatsigOptions.ts
+++ b/src/StatsigOptions.ts
@@ -33,11 +33,17 @@ export interface LoggerInterface {
   logLevel: 'none' | 'debug' | 'info' | 'warn' | 'error';
 }
 
+export type NetworkOverrideFunc = (
+  url: string,
+  params: RequestInit,
+) => Promise<Response>;
+
 export type ExplicitStatsigOptions = {
   api: string;
   apiForDownloadConfigSpecs: string;
   apiForGetIdLists: string;
   fallbackToStatsigAPI: boolean;
+  networkOverrideFunc: NetworkOverrideFunc | null;
   bootstrapValues: string | null;
   environment: StatsigEnvironment | null;
   rulesUpdatedCallback: RulesUpdatedCallback | null;
@@ -80,6 +86,7 @@ export function OptionsWithDefaults(
       normalizeUrl(getString(opts, 'apiForGetIdLists', opts.api ?? null)) ??
       STATSIG_API,
     fallbackToStatsigAPI: getBoolean(opts, 'fallbackToStatsigAPI', false),
+    networkOverrideFunc: opts.networkOverrideFunc ?? null,
     bootstrapValues: getString(opts, 'bootstrapValues', null),
     environment: opts.environment
       ? (getObject(opts, 'environment', {}) as StatsigEnvironment)
diff --git a/src/__tests__/NetworkOverrideFunc.test.ts b/src/__tests__/NetworkOverrideFunc.test.ts
new file mode 100644
index 0000000..245800a
--- /dev/null
+++ b/src/__tests__/NetworkOverrideFunc.test.ts
@@ -0,0 +1,49 @@
+import * as statsigsdk from '../index';
+import StatsigInstanceUtils from '../StatsigInstanceUtils';
+
+const statsig = statsigsdk.default;
+
+jest.mock('node-fetch', () => jest.fn());
+
+function verifyDcsFetchCall(call: any[]) {
+  expect(call[0]).toEqual(
+    'https://api.statsigcdn.com/v1/download_config_specs/secret-key.json?sinceTime=0',
+  );
+  expect(call[1].method).toBe('GET');
+}
+
+function verifyGetIdListsFetchCall(call: any[]) {
+  expect(call[0]).toEqual('https://statsigapi.net/v1/get_id_lists');
+  expect(call[1].method).toBe('POST');
+}
+
+describe('NetworkOverrideFunc', () => {
+  const fetchSpy = require('node-fetch');
+  const networkOverrideSpy = jest.fn();
+
+  beforeEach(() => {
+    StatsigInstanceUtils.setInstance(null);
+
+    fetchSpy.mockClear();
+    networkOverrideSpy.mockClear();
+  });
+
+  it('calls the networkOverrideFunc', async () => {
+    await statsig.initialize('secret-key', {
+      networkOverrideFunc: networkOverrideSpy,
+    });
+
+    expect(fetchSpy).not.toHaveBeenCalled();
+
+    verifyDcsFetchCall(networkOverrideSpy.mock.calls[0]);
+    verifyGetIdListsFetchCall(networkOverrideSpy.mock.calls[1]);
+  });
+
+  it('calls fetch when no override is given', async () => {
+    await statsig.initialize('secret-key');
+    expect(networkOverrideSpy).not.toHaveBeenCalled();
+
+    verifyDcsFetchCall(fetchSpy.mock.calls[0]);
+    verifyGetIdListsFetchCall(fetchSpy.mock.calls[1]);
+  });
+});
diff --git a/src/utils/StatsigFetcher.ts b/src/utils/StatsigFetcher.ts
index 56f7e3a..08e8ec6 100644
--- a/src/utils/StatsigFetcher.ts
+++ b/src/utils/StatsigFetcher.ts
@@ -5,7 +5,11 @@ import {
   StatsigSDKKeyMismatchError,
   StatsigTooManyRequestsError,
 } from '../Errors';
-import { ExplicitStatsigOptions, RetryBackoffFunc } from '../StatsigOptions';
+import {
+  ExplicitStatsigOptions,
+  NetworkOverrideFunc,
+  RetryBackoffFunc,
+} from '../StatsigOptions';
 import { getSDKType, getSDKVersion } from './core';
 import Dispatcher from './Dispatcher';
 import getCompressionFunc from './getCompressionFunc';
@@ -38,6 +42,7 @@ export default class StatsigFetcher {
   private localMode: boolean;
   private sdkKey: string;
   private errorBoundry: ErrorBoundary;
+  private networkOverrideFunc: NetworkOverrideFunc | null;
 
   public constructor(
     secretKey: string,
@@ -55,6 +60,7 @@ export default class StatsigFetcher {
     this.localMode = options.localMode;
     this.sdkKey = secretKey;
     this.errorBoundry = errorBoundry;
+    this.networkOverrideFunc = options.networkOverrideFunc;
   }
 
   public validateSDKKeyUsed(hashedSDKKeyUsed: string): boolean {
@@ -158,11 +164,11 @@ export default class StatsigFetcher {
       ...options?.additionalHeaders,
       'Content-type': 'application/json; charset=UTF-8',
       'STATSIG-API-KEY': this.sdkKey,
-      'STATSIG-CLIENT-TIME': Date.now(),
+      'STATSIG-CLIENT-TIME': `${Date.now()}`,
       'STATSIG-SERVER-SESSION-ID': this.sessionID,
       'STATSIG-SDK-TYPE': getSDKType(),
       'STATSIG-SDK-VERSION': getSDKVersion(),
-    } as Record<string, string | number>;
+    } as Record<string, string>;
 
     let contents: BodyInit | undefined = undefined;
     const gzipSync = getCompressionFunc();
@@ -173,12 +179,6 @@ export default class StatsigFetcher {
     } else if (body) {
       contents = JSON.stringify(body);
     }
-    const params = {
-      method: method,
-      body: contents,
-      headers,
-      signal: signal,
-    };
 
     if (!isRetrying) {
       markDiagnostic?.start({});
@@ -186,7 +186,13 @@ export default class StatsigFetcher {
 
     let res: Response | undefined;
     let error: unknown;
-    return safeFetch(url, params)
+    const fetcher = this.networkOverrideFunc ?? safeFetch;
+    return fetcher(url, {
+      method: method,
+      body: contents,
+      headers,
+      signal: signal,
+    })
       .then((localRes) => {
         res = localRes;
         if ((!res.ok || retryStatusCodes.includes(res.status)) && retries > 0) {