diff --git a/docs/reference/QueryClient.md b/docs/reference/QueryClient.md
index 13bde1ffad0..8ede22a6a33 100644
--- a/docs/reference/QueryClient.md
+++ b/docs/reference/QueryClient.md
@@ -64,6 +64,16 @@ Its available methods are:
   - Optional
   - Define defaults for all queries and mutations using this queryClient.
   - You can also define defaults to be used for [hydration](../framework/react/reference/hydration.md)
+- `isServer?: boolean`
+  - Optional
+  - Overrides environment detection for this client.
+  - Defaults to the exported `isServer` value from `@tanstack/query-core`.
+  - Use this when your runtime does not match the default detection.
+
+**Properties**
+
+- `queryClient.isServer: boolean`
+  - The resolved server detection used by this `QueryClient` instance.
 
 ## `queryClient.fetchQuery`
 
diff --git a/packages/preact-query/src/__tests__/ssr-hydration.test.tsx b/packages/preact-query/src/__tests__/ssr-hydration.test.tsx
index 10154d01890..6e3bcd8cf8a 100644
--- a/packages/preact-query/src/__tests__/ssr-hydration.test.tsx
+++ b/packages/preact-query/src/__tests__/ssr-hydration.test.tsx
@@ -12,7 +12,6 @@ import {
   hydrate,
   useQuery,
 } from '..'
-import { setIsServer } from './utils'
 
 const PreactHydrate = (element: VNode, container: Element) => {
   act(() => {
@@ -62,11 +61,10 @@ describe('Server side rendering with de/rehydration', () => {
     }
 
     // -- Server part --
-    setIsServer(true)
-
     const prefetchCache = new QueryCache()
     const prefetchClient = new QueryClient({
       queryCache: prefetchCache,
+      isServer: true,
     })
     await prefetchClient.prefetchQuery({
       queryKey: ['success'],
@@ -76,6 +74,7 @@ describe('Server side rendering with de/rehydration', () => {
     const renderCache = new QueryCache()
     const renderClient = new QueryClient({
       queryCache: renderCache,
+      isServer: true,
     })
     hydrate(renderClient, dehydratedStateServer)
     const markup = renderToString(
@@ -85,7 +84,6 @@ describe('Server side rendering with de/rehydration', () => {
     )
     const stringifiedState = JSON.stringify(dehydratedStateServer)
     renderClient.clear()
-    setIsServer(false)
 
     const expectedMarkup =
       'SuccessComponent - status:success fetching:true data:success'
@@ -140,10 +138,10 @@ describe('Server side rendering with de/rehydration', () => {
     }
 
     // -- Server part --
-    setIsServer(true)
     const prefetchCache = new QueryCache()
     const prefetchClient = new QueryClient({
       queryCache: prefetchCache,
+      isServer: true,
     })
     await prefetchClient.prefetchQuery({
       queryKey: ['error'],
@@ -153,6 +151,7 @@ describe('Server side rendering with de/rehydration', () => {
     const renderCache = new QueryCache()
     const renderClient = new QueryClient({
       queryCache: renderCache,
+      isServer: true,
     })
     hydrate(renderClient, dehydratedStateServer)
     const markup = renderToString(
@@ -162,7 +161,6 @@ describe('Server side rendering with de/rehydration', () => {
     )
     const stringifiedState = JSON.stringify(dehydratedStateServer)
     renderClient.clear()
-    setIsServer(false)
 
     const expectedMarkup =
       'ErrorComponent - status:pending fetching:true data:undefined'
@@ -216,11 +214,9 @@ describe('Server side rendering with de/rehydration', () => {
     }
 
     // -- Server part --
-    setIsServer(true)
-
-    const prefetchClient = new QueryClient()
+    const prefetchClient = new QueryClient({ isServer: true })
     const dehydratedStateServer = dehydrate(prefetchClient)
-    const renderClient = new QueryClient()
+    const renderClient = new QueryClient({ isServer: true })
     hydrate(renderClient, dehydratedStateServer)
     const markup = renderToString(
       <QueryClientProvider client={renderClient}>
@@ -229,7 +225,6 @@ describe('Server side rendering with de/rehydration', () => {
     )
     const stringifiedState = JSON.stringify(dehydratedStateServer)
     renderClient.clear()
-    setIsServer(false)
 
     const expectedMarkup =
       'SuccessComponent - status:pending fetching:true data:undefined'
diff --git a/packages/preact-query/src/__tests__/ssr.test.tsx b/packages/preact-query/src/__tests__/ssr.test.tsx
index d543a57501f..907b69328b7 100644
--- a/packages/preact-query/src/__tests__/ssr.test.tsx
+++ b/packages/preact-query/src/__tests__/ssr.test.tsx
@@ -11,18 +11,15 @@ import {
   useMutationState,
   useQuery,
 } from '..'
-import { setIsServer } from './utils'
 
 describe('Server Side Rendering', () => {
-  setIsServer(true)
-
   let queryCache: QueryCache
   let queryClient: QueryClient
 
   beforeEach(() => {
     vi.useFakeTimers()
     queryCache = new QueryCache()
-    queryClient = new QueryClient({ queryCache })
+    queryClient = new QueryClient({ queryCache, isServer: true })
   })
 
   afterEach(() => {
diff --git a/packages/preact-query/src/__tests__/utils.tsx b/packages/preact-query/src/__tests__/utils.tsx
index d4f1dba05e9..a175de773a7 100644
--- a/packages/preact-query/src/__tests__/utils.tsx
+++ b/packages/preact-query/src/__tests__/utils.tsx
@@ -1,4 +1,3 @@
-import * as utils from '@tanstack/query-core'
 import { act, render } from '@testing-library/preact'
 import type { ComponentChildren, VNode } from 'preact'
 import { useEffect, useState } from 'preact/hooks'
@@ -57,18 +56,3 @@ export function setActTimeout(fn: () => void, ms?: number) {
     })
   }, ms)
 }
-
-// This monkey-patches the isServer-value from utils,
-// so that we can pretend to be in a server environment
-export function setIsServer(isServer: boolean) {
-  const original = utils.isServer
-  Object.defineProperty(utils, 'isServer', {
-    get: () => isServer,
-  })
-
-  return () => {
-    Object.defineProperty(utils, 'isServer', {
-      get: () => original,
-    })
-  }
-}
diff --git a/packages/preact-query/src/useBaseQuery.ts b/packages/preact-query/src/useBaseQuery.ts
index 84d75679162..5bc05069535 100644
--- a/packages/preact-query/src/useBaseQuery.ts
+++ b/packages/preact-query/src/useBaseQuery.ts
@@ -1,4 +1,4 @@
-import { isServer, noop, notifyManager } from '@tanstack/query-core'
+import { noop, notifyManager } from '@tanstack/query-core'
 import type {
   QueryClient,
   QueryKey,
@@ -147,7 +147,7 @@ export function useBaseQuery<
 
   if (
     defaultedOptions.experimental_prefetchInRender &&
-    !isServer &&
+    !client.isServer &&
     willFetch(result, isRestoring)
   ) {
     const promise = isNewCacheEntry
diff --git a/packages/query-core/src/__tests__/focusManager.test.tsx b/packages/query-core/src/__tests__/focusManager.test.tsx
index 3783361fb04..508e2b4c0fc 100644
--- a/packages/query-core/src/__tests__/focusManager.test.tsx
+++ b/packages/query-core/src/__tests__/focusManager.test.tsx
@@ -1,6 +1,5 @@
 import { afterEach, beforeEach, describe, expect, it, test, vi } from 'vitest'
 import { FocusManager } from '../focusManager'
-import { setIsServer } from './utils'
 
 describe('focusManager', () => {
   let focusManager: FocusManager
@@ -55,17 +54,22 @@ describe('focusManager', () => {
   })
 
   test('cleanup (removeEventListener) should not be called if window is not defined', () => {
-    const restoreIsServer = setIsServer(true)
-
+    const windowSpy = vi.spyOn(globalThis, 'window', 'get')
+    windowSpy.mockImplementation(
+      () => undefined as unknown as Window & typeof globalThis,
+    )
     const removeEventListenerSpy = vi.spyOn(globalThis, 'removeEventListener')
 
-    const unsubscribe = focusManager.subscribe(() => undefined)
+    const subscribe = () => focusManager.subscribe(() => undefined)
+
+    expect(subscribe).not.toThrow()
+    const unsubscribe = subscribe()
 
     unsubscribe()
 
     expect(removeEventListenerSpy).not.toHaveBeenCalled()
 
-    restoreIsServer()
+    windowSpy.mockRestore()
   })
 
   test('cleanup (removeEventListener) should not be called if window.addEventListener is not defined', () => {
diff --git a/packages/query-core/src/__tests__/onlineManager.test.tsx b/packages/query-core/src/__tests__/onlineManager.test.tsx
index 20a9439de9f..1a5245bfc80 100644
--- a/packages/query-core/src/__tests__/onlineManager.test.tsx
+++ b/packages/query-core/src/__tests__/onlineManager.test.tsx
@@ -1,6 +1,5 @@
 import { afterEach, beforeEach, describe, expect, test, vi } from 'vitest'
 import { OnlineManager } from '../onlineManager'
-import { setIsServer } from './utils'
 
 describe('onlineManager', () => {
   let onlineManager: OnlineManager
@@ -64,17 +63,22 @@ describe('onlineManager', () => {
   })
 
   test('cleanup (removeEventListener) should not be called if window is not defined', () => {
-    const restoreIsServer = setIsServer(true)
-
+    const windowSpy = vi.spyOn(globalThis, 'window', 'get')
+    windowSpy.mockImplementation(
+      () => undefined as unknown as Window & typeof globalThis,
+    )
     const removeEventListenerSpy = vi.spyOn(globalThis, 'removeEventListener')
 
-    const unsubscribe = onlineManager.subscribe(() => undefined)
+    const subscribe = () => onlineManager.subscribe(() => undefined)
+
+    expect(subscribe).not.toThrow()
+    const unsubscribe = subscribe()
 
     unsubscribe()
 
     expect(removeEventListenerSpy).not.toHaveBeenCalled()
 
-    restoreIsServer()
+    windowSpy.mockRestore()
   })
 
   test('cleanup (removeEventListener) should not be called if window.addEventListener is not defined', () => {
diff --git a/packages/query-core/src/__tests__/query.test.tsx b/packages/query-core/src/__tests__/query.test.tsx
index 93e5ea515f8..72b60438a73 100644
--- a/packages/query-core/src/__tests__/query.test.tsx
+++ b/packages/query-core/src/__tests__/query.test.tsx
@@ -13,7 +13,7 @@ import {
   hydrate,
 } from '..'
 import { hashQueryKeyByOptions } from '../utils'
-import { mockOnlineManagerIsOnline, setIsServer } from './utils'
+import { mockOnlineManagerIsOnline } from './utils'
 import type {
   QueryCache,
   QueryFunctionContext,
@@ -867,12 +867,12 @@ describe('query', () => {
   })
 
   it('should not retry on the server', async () => {
-    const resetIsServer = setIsServer(true)
+    const serverClient = new QueryClient({ isServer: true })
 
     const key = queryKey()
     let count = 0
 
-    const observer = new QueryObserver(queryClient, {
+    const observer = new QueryObserver(serverClient, {
       queryKey: key,
       queryFn: () => {
         count++
@@ -883,8 +883,6 @@ describe('query', () => {
     await observer.refetch()
 
     expect(count).toBe(1)
-
-    resetIsServer()
   })
 
   test('constructor should call initialDataUpdatedAt if defined as a function', async () => {
diff --git a/packages/query-core/src/__tests__/queryClient.test.tsx b/packages/query-core/src/__tests__/queryClient.test.tsx
index 2676717fb62..1902a5a86bc 100644
--- a/packages/query-core/src/__tests__/queryClient.test.tsx
+++ b/packages/query-core/src/__tests__/queryClient.test.tsx
@@ -58,6 +58,19 @@ describe('queryClient', () => {
       expect(newQuery?.options.gcTime).toBe(Infinity)
     })
 
+    test('should allow overriding server detection for gcTime defaults', async () => {
+      const key = queryKey()
+      const testClient = new QueryClient({ isServer: true })
+
+      await testClient.prefetchQuery({
+        queryKey: key,
+        queryFn: () => Promise.resolve('data'),
+      })
+
+      const newQuery = testClient.getQueryCache().find({ queryKey: key })
+      expect(newQuery?.gcTime).toBe(Infinity)
+    })
+
     test('should get defaultOptions', () => {
       const queryFn = () => 'data'
       const defaultOptions = { queries: { queryFn } }
diff --git a/packages/query-core/src/__tests__/utils.ts b/packages/query-core/src/__tests__/utils.ts
index f9ef89d7650..07ff00e652f 100644
--- a/packages/query-core/src/__tests__/utils.ts
+++ b/packages/query-core/src/__tests__/utils.ts
@@ -1,6 +1,5 @@
 import { vi } from 'vitest'
 import { onlineManager } from '..'
-import * as utils from '../utils'
 import type { MockInstance } from 'vitest'
 import type { MutationOptions, QueryClient } from '..'
 
@@ -20,18 +19,3 @@ export function executeMutation<TVariables>(
     .build(queryClient, options)
     .execute(variables)
 }
-
-// This monkey-patches the isServer-value from utils,
-// so that we can pretend to be in a server environment
-export function setIsServer(isServer: boolean) {
-  const original = utils.isServer
-  Object.defineProperty(utils, 'isServer', {
-    get: () => isServer,
-  })
-
-  return () => {
-    Object.defineProperty(utils, 'isServer', {
-      get: () => original,
-    })
-  }
-}
diff --git a/packages/query-core/src/focusManager.ts b/packages/query-core/src/focusManager.ts
index cb0d8598713..21be2612d3a 100644
--- a/packages/query-core/src/focusManager.ts
+++ b/packages/query-core/src/focusManager.ts
@@ -1,5 +1,4 @@
 import { Subscribable } from './subscribable'
-import { isServer } from './utils'
 
 type Listener = (focused: boolean) => void
 
@@ -18,7 +17,7 @@ export class FocusManager extends Subscribable<Listener> {
     this.#setup = (onFocus) => {
       // addEventListener does not exist in React Native, but window does
       // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
-      if (!isServer && window.addEventListener) {
+      if (typeof window !== 'undefined' && window.addEventListener) {
         const listener = () => onFocus()
         // Listen to visibilitychange
         window.addEventListener('visibilitychange', listener, false)
diff --git a/packages/query-core/src/index.ts b/packages/query-core/src/index.ts
index a7763cf6483..dfc6a8440cd 100644
--- a/packages/query-core/src/index.ts
+++ b/packages/query-core/src/index.ts
@@ -27,7 +27,6 @@ export {
 } from './timeoutManager'
 export {
   hashKey,
-  isServer,
   keepPreviousData,
   matchMutation,
   matchQuery,
@@ -39,6 +38,12 @@ export {
 } from './utils'
 export type { MutationFilters, QueryFilters, SkipToken, Updater } from './utils'
 
+/** @deprecated
+ * use `queryClient.isServer` instead.
+ * Override per client with `new QueryClient({ isServer })`.
+ */
+export const isServer = typeof window === 'undefined' || 'Deno' in globalThis
+
 export { streamedQuery as experimental_streamedQuery } from './streamedQuery'
 
 // Types
diff --git a/packages/query-core/src/mutation.ts b/packages/query-core/src/mutation.ts
index 2483b563366..1e3ecde5c45 100644
--- a/packages/query-core/src/mutation.ts
+++ b/packages/query-core/src/mutation.ts
@@ -118,7 +118,7 @@ export class Mutation<
   ): void {
     this.options = options
 
-    this.updateGcTime(this.options.gcTime)
+    this.updateGcTime(this.options.gcTime, this.#client.isServer)
   }
 
   get meta(): MutationMeta | undefined {
@@ -199,6 +199,7 @@ export class Mutation<
       retry: this.options.retry ?? 0,
       retryDelay: this.options.retryDelay,
       networkMode: this.options.networkMode,
+      isServer: this.#client.isServer,
       canRun: () => this.#mutationCache.canRun(this),
     })
 
diff --git a/packages/query-core/src/onlineManager.ts b/packages/query-core/src/onlineManager.ts
index daf77d5a4c2..6c59a14b908 100644
--- a/packages/query-core/src/onlineManager.ts
+++ b/packages/query-core/src/onlineManager.ts
@@ -1,5 +1,4 @@
 import { Subscribable } from './subscribable'
-import { isServer } from './utils'
 
 type Listener = (online: boolean) => void
 type SetupFn = (setOnline: Listener) => (() => void) | undefined
@@ -15,7 +14,7 @@ export class OnlineManager extends Subscribable<Listener> {
     this.#setup = (onOnline) => {
       // addEventListener does not exist in React Native, but window does
       // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
-      if (!isServer && window.addEventListener) {
+      if (typeof window !== 'undefined' && window.addEventListener) {
         const onlineListener = () => onOnline(true)
         const offlineListener = () => onOnline(false)
         // Listen to online
diff --git a/packages/query-core/src/query.ts b/packages/query-core/src/query.ts
index b29b64c0e3e..c593ba152d0 100644
--- a/packages/query-core/src/query.ts
+++ b/packages/query-core/src/query.ts
@@ -180,11 +180,11 @@ export class Query<
     super()
 
     this.#abortSignalConsumed = false
+    this.#client = config.client
+    this.#cache = this.#client.getQueryCache()
     this.#defaultOptions = config.defaultOptions
     this.setOptions(config.options)
     this.observers = []
-    this.#client = config.client
-    this.#cache = this.#client.getQueryCache()
     this.queryKey = config.queryKey
     this.queryHash = config.queryHash
     this.#initialState = getDefaultState(this.options)
@@ -204,7 +204,7 @@ export class Query<
   ): void {
     this.options = { ...this.#defaultOptions, ...options }
 
-    this.updateGcTime(this.options.gcTime)
+    this.updateGcTime(this.options.gcTime, this.#client.isServer)
 
     // eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
     if (this.state && this.state.data === undefined) {
@@ -539,6 +539,7 @@ export class Query<
       retry: context.options.retry,
       retryDelay: context.options.retryDelay,
       networkMode: context.options.networkMode,
+      isServer: this.#client.isServer,
       canRun: () => true,
     })
 
diff --git a/packages/query-core/src/queryClient.ts b/packages/query-core/src/queryClient.ts
index 80cc36668aa..47d6063e36a 100644
--- a/packages/query-core/src/queryClient.ts
+++ b/packages/query-core/src/queryClient.ts
@@ -67,6 +67,11 @@ export class QueryClient {
   #mountCount: number
   #unsubscribeFocus?: () => void
   #unsubscribeOnline?: () => void
+  /**
+   * Resolved server detection for this client instance.
+   * Derived from `QueryClientConfig.isServer` or the default `isServer` export.
+   */
+  readonly isServer: boolean
 
   constructor(config: QueryClientConfig = {}) {
     this.#queryCache = config.queryCache || new QueryCache()
@@ -75,6 +80,8 @@ export class QueryClient {
     this.#queryDefaults = new Map()
     this.#mutationDefaults = new Map()
     this.#mountCount = 0
+    this.isServer =
+      config.isServer ?? (typeof window === 'undefined' || 'Deno' in globalThis)
   }
 
   mount(): void {
diff --git a/packages/query-core/src/queryObserver.ts b/packages/query-core/src/queryObserver.ts
index 463407a0737..f77970f730d 100644
--- a/packages/query-core/src/queryObserver.ts
+++ b/packages/query-core/src/queryObserver.ts
@@ -4,7 +4,6 @@ import { fetchState } from './query'
 import { Subscribable } from './subscribable'
 import { pendingThenable } from './thenable'
 import {
-  isServer,
   isValidTimeout,
   noop,
   replaceData,
@@ -358,7 +357,11 @@ export class QueryObserver<
       this.#currentQuery,
     )
 
-    if (isServer || this.#currentResult.isStale || !isValidTimeout(staleTime)) {
+    if (
+      this.#client.isServer ||
+      this.#currentResult.isStale ||
+      !isValidTimeout(staleTime)
+    ) {
       return
     }
 
@@ -389,7 +392,7 @@ export class QueryObserver<
     this.#currentRefetchInterval = nextInterval
 
     if (
-      isServer ||
+      this.#client.isServer ||
       resolveEnabled(this.options.enabled, this.#currentQuery) === false ||
       !isValidTimeout(this.#currentRefetchInterval) ||
       this.#currentRefetchInterval === 0
diff --git a/packages/query-core/src/removable.ts b/packages/query-core/src/removable.ts
index 8642ab36ec2..d6a7761d7e7 100644
--- a/packages/query-core/src/removable.ts
+++ b/packages/query-core/src/removable.ts
@@ -1,7 +1,9 @@
 import { timeoutManager } from './timeoutManager'
-import { isServer, isValidTimeout } from './utils'
+import { isValidTimeout } from './utils'
 import type { ManagedTimerId } from './timeoutManager'
 
+const DEFAULT_GC_TIME = 5 * 60 * 1000
+
 export abstract class Removable {
   gcTime!: number
   #gcTimeout?: ManagedTimerId
@@ -20,11 +22,14 @@ export abstract class Removable {
     }
   }
 
-  protected updateGcTime(newGcTime: number | undefined): void {
+  protected updateGcTime(
+    newGcTime: number | undefined,
+    isServer: boolean,
+  ): void {
     // Default to 5 minutes (Infinity for server-side) if no gcTime is set
     this.gcTime = Math.max(
       this.gcTime || 0,
-      newGcTime ?? (isServer ? Infinity : 5 * 60 * 1000),
+      newGcTime ?? (isServer ? Infinity : DEFAULT_GC_TIME),
     )
   }
 
diff --git a/packages/query-core/src/retryer.ts b/packages/query-core/src/retryer.ts
index f4ada851c9f..b954f2c2e43 100644
--- a/packages/query-core/src/retryer.ts
+++ b/packages/query-core/src/retryer.ts
@@ -1,7 +1,7 @@
 import { focusManager } from './focusManager'
 import { onlineManager } from './onlineManager'
 import { pendingThenable } from './thenable'
-import { isServer, sleep } from './utils'
+import { sleep } from './utils'
 import type { Thenable } from './thenable'
 import type { CancelOptions, DefaultError, NetworkMode } from './types'
 
@@ -17,6 +17,7 @@ interface RetryerConfig<TData = unknown, TError = DefaultError> {
   retry?: RetryValue<TError>
   retryDelay?: RetryDelayValue<TError>
   networkMode: NetworkMode | undefined
+  isServer: boolean
   canRun: () => boolean
 }
 
@@ -166,7 +167,7 @@ export function createRetryer<TData = unknown, TError = DefaultError>(
         }
 
         // Do we need to retry the request?
-        const retry = config.retry ?? (isServer ? 0 : 3)
+        const retry = config.retry ?? (config.isServer ? 0 : 3)
         const retryDelay = config.retryDelay ?? defaultRetryDelay
         const delay =
           typeof retryDelay === 'function'
diff --git a/packages/query-core/src/types.ts b/packages/query-core/src/types.ts
index 4f3f4caed20..fa8ba51a070 100644
--- a/packages/query-core/src/types.ts
+++ b/packages/query-core/src/types.ts
@@ -1356,6 +1356,12 @@ export interface QueryClientConfig {
   queryCache?: QueryCache
   mutationCache?: MutationCache
   defaultOptions?: DefaultOptions
+  /**
+   * Overrides environment detection for this client.
+   * When `true`, defaults that depend on server detection behave as server-side.
+   * Defaults to the exported `isServer` value.
+   */
+  isServer?: boolean
 }
 
 export interface DefaultOptions<TError = DefaultError> {
diff --git a/packages/query-core/src/utils.ts b/packages/query-core/src/utils.ts
index 27d44bc98b3..0e740b60fe2 100644
--- a/packages/query-core/src/utils.ts
+++ b/packages/query-core/src/utils.ts
@@ -86,8 +86,6 @@ export type QueryTypeFilter = 'all' | 'active' | 'inactive'
 
 // UTILS
 
-export const isServer = typeof window === 'undefined' || 'Deno' in globalThis
-
 export function noop(): void
 export function noop(): undefined
 export function noop() {}
diff --git a/packages/react-query/src/__tests__/ssr-hydration.test.tsx b/packages/react-query/src/__tests__/ssr-hydration.test.tsx
index 07f469b5684..3f65d89a955 100644
--- a/packages/react-query/src/__tests__/ssr-hydration.test.tsx
+++ b/packages/react-query/src/__tests__/ssr-hydration.test.tsx
@@ -10,7 +10,6 @@ import {
   hydrate,
   useQuery,
 } from '..'
-import { setIsServer } from './utils'
 
 const ReactHydrate = (element: React.ReactElement, container: Element) => {
   let root: any
@@ -63,11 +62,10 @@ describe('Server side rendering with de/rehydration', () => {
     }
 
     // -- Server part --
-    setIsServer(true)
-
     const prefetchCache = new QueryCache()
     const prefetchClient = new QueryClient({
       queryCache: prefetchCache,
+      isServer: true,
     })
     await prefetchClient.prefetchQuery({
       queryKey: ['success'],
@@ -77,6 +75,7 @@ describe('Server side rendering with de/rehydration', () => {
     const renderCache = new QueryCache()
     const renderClient = new QueryClient({
       queryCache: renderCache,
+      isServer: true,
     })
     hydrate(renderClient, dehydratedStateServer)
     const markup = ReactDOMServer.renderToString(
@@ -86,7 +85,6 @@ describe('Server side rendering with de/rehydration', () => {
     )
     const stringifiedState = JSON.stringify(dehydratedStateServer)
     renderClient.clear()
-    setIsServer(false)
 
     const expectedMarkup =
       'SuccessComponent - status:success fetching:true data:success'
@@ -141,10 +139,10 @@ describe('Server side rendering with de/rehydration', () => {
     }
 
     // -- Server part --
-    setIsServer(true)
     const prefetchCache = new QueryCache()
     const prefetchClient = new QueryClient({
       queryCache: prefetchCache,
+      isServer: true,
     })
     await prefetchClient.prefetchQuery({
       queryKey: ['error'],
@@ -154,6 +152,7 @@ describe('Server side rendering with de/rehydration', () => {
     const renderCache = new QueryCache()
     const renderClient = new QueryClient({
       queryCache: renderCache,
+      isServer: true,
     })
     hydrate(renderClient, dehydratedStateServer)
     const markup = ReactDOMServer.renderToString(
@@ -163,7 +162,6 @@ describe('Server side rendering with de/rehydration', () => {
     )
     const stringifiedState = JSON.stringify(dehydratedStateServer)
     renderClient.clear()
-    setIsServer(false)
 
     const expectedMarkup =
       'ErrorComponent - status:pending fetching:true data:undefined'
@@ -217,11 +215,9 @@ describe('Server side rendering with de/rehydration', () => {
     }
 
     // -- Server part --
-    setIsServer(true)
-
-    const prefetchClient = new QueryClient()
+    const prefetchClient = new QueryClient({ isServer: true })
     const dehydratedStateServer = dehydrate(prefetchClient)
-    const renderClient = new QueryClient()
+    const renderClient = new QueryClient({ isServer: true })
     hydrate(renderClient, dehydratedStateServer)
     const markup = ReactDOMServer.renderToString(
       <QueryClientProvider client={renderClient}>
@@ -230,7 +226,6 @@ describe('Server side rendering with de/rehydration', () => {
     )
     const stringifiedState = JSON.stringify(dehydratedStateServer)
     renderClient.clear()
-    setIsServer(false)
 
     const expectedMarkup =
       'SuccessComponent - status:pending fetching:true data:undefined'
diff --git a/packages/react-query/src/__tests__/ssr.test.tsx b/packages/react-query/src/__tests__/ssr.test.tsx
index 8ca076c5478..9155c3a620d 100644
--- a/packages/react-query/src/__tests__/ssr.test.tsx
+++ b/packages/react-query/src/__tests__/ssr.test.tsx
@@ -13,18 +13,15 @@ import {
   useQueries,
   useQuery,
 } from '..'
-import { setIsServer } from './utils'
 
 describe('Server Side Rendering', () => {
-  setIsServer(true)
-
   let queryCache: QueryCache
   let queryClient: QueryClient
 
   beforeEach(() => {
     vi.useFakeTimers()
     queryCache = new QueryCache()
-    queryClient = new QueryClient({ queryCache })
+    queryClient = new QueryClient({ queryCache, isServer: true })
   })
 
   afterEach(() => {
diff --git a/packages/react-query/src/__tests__/utils.tsx b/packages/react-query/src/__tests__/utils.tsx
index 3734c1caf67..b8fcbf7adf5 100644
--- a/packages/react-query/src/__tests__/utils.tsx
+++ b/packages/react-query/src/__tests__/utils.tsx
@@ -1,7 +1,6 @@
 import { vi } from 'vitest'
 import * as React from 'react'
 import { act, render } from '@testing-library/react'
-import * as utils from '@tanstack/query-core'
 import { QueryClientProvider, onlineManager } from '..'
 import type { QueryClient } from '..'
 import type { MockInstance } from 'vitest'
@@ -55,18 +54,3 @@ export function setActTimeout(fn: () => void, ms?: number) {
     })
   }, ms)
 }
-
-// This monkey-patches the isServer-value from utils,
-// so that we can pretend to be in a server environment
-export function setIsServer(isServer: boolean) {
-  const original = utils.isServer
-  Object.defineProperty(utils, 'isServer', {
-    get: () => isServer,
-  })
-
-  return () => {
-    Object.defineProperty(utils, 'isServer', {
-      get: () => original,
-    })
-  }
-}
diff --git a/packages/react-query/src/useBaseQuery.ts b/packages/react-query/src/useBaseQuery.ts
index 2a151fe1137..bed1ee7892e 100644
--- a/packages/react-query/src/useBaseQuery.ts
+++ b/packages/react-query/src/useBaseQuery.ts
@@ -1,7 +1,7 @@
 'use client'
 import * as React from 'react'
 
-import { isServer, noop, notifyManager } from '@tanstack/query-core'
+import { noop, notifyManager } from '@tanstack/query-core'
 import { useQueryClient } from './QueryClientProvider'
 import { useQueryErrorResetBoundary } from './QueryErrorResetBoundary'
 import {
@@ -148,7 +148,7 @@ export function useBaseQuery<
 
   if (
     defaultedOptions.experimental_prefetchInRender &&
-    !isServer &&
+    !client.isServer &&
     willFetch(result, isRestoring)
   ) {
     const promise = isNewCacheEntry
diff --git a/packages/vue-query/src/__tests__/queryClient.test.ts b/packages/vue-query/src/__tests__/queryClient.test.ts
index c97be2db192..395e27bc599 100644
--- a/packages/vue-query/src/__tests__/queryClient.test.ts
+++ b/packages/vue-query/src/__tests__/queryClient.test.ts
@@ -4,6 +4,14 @@ import { QueryClient as QueryClientOrigin } from '@tanstack/query-core'
 import { QueryClient } from '../queryClient'
 import { infiniteQueryOptions } from '../infiniteQueryOptions'
 
+type QueryClientPrototypeMethod = {
+  [TKey in keyof typeof QueryClientOrigin.prototype]: (typeof QueryClientOrigin.prototype)[TKey] extends (
+    ...args: Array<any>
+  ) => any
+    ? TKey
+    : never
+}[keyof typeof QueryClientOrigin.prototype]
+
 vi.mock('@tanstack/query-core', async () => {
   const actual = await vi.importActual<{
     QueryClient: typeof QueryClientOrigin
@@ -12,7 +20,7 @@ vi.mock('@tanstack/query-core', async () => {
   // Get the prototype methods dynamically
   const prototypeMethods = Object.getOwnPropertyNames(
     actual.QueryClient.prototype,
-  ).filter((prop): prop is keyof typeof actual.QueryClient.prototype => {
+  ).filter((prop): prop is QueryClientPrototypeMethod => {
     const descriptor = Object.getOwnPropertyDescriptor(
       actual.QueryClient.prototype,
       prop,
diff --git a/packages/vue-query/src/queryClient.ts b/packages/vue-query/src/queryClient.ts
index 7f9a0894bfe..8ff9f4433e7 100644
--- a/packages/vue-query/src/queryClient.ts
+++ b/packages/vue-query/src/queryClient.ts
@@ -35,13 +35,18 @@ import type {
 } from '@tanstack/query-core'
 
 export class QueryClient extends QC {
+  readonly isServer: boolean
+
   constructor(config: QueryClientConfig = {}) {
     const vueQueryConfig = {
       defaultOptions: config.defaultOptions,
       queryCache: config.queryCache || new QueryCache(),
       mutationCache: config.mutationCache || new MutationCache(),
+      isServer: config.isServer,
     }
     super(vueQueryConfig)
+    this.isServer =
+      config.isServer ?? (typeof window === 'undefined' || 'Deno' in globalThis)
   }
 
   isRestoring?: Ref<boolean> = ref(false)
diff --git a/packages/vue-query/src/types.ts b/packages/vue-query/src/types.ts
index eb793c811eb..fd3dc193868 100644
--- a/packages/vue-query/src/types.ts
+++ b/packages/vue-query/src/types.ts
@@ -75,4 +75,5 @@ export interface QueryClientConfig {
   queryCache?: QueryCache
   mutationCache?: MutationCache
   defaultOptions?: DefaultOptions
+  isServer?: boolean
 }
diff --git a/packages/vue-query/src/vueQueryPlugin.ts b/packages/vue-query/src/vueQueryPlugin.ts
index 590d994d304..e077af293e9 100644
--- a/packages/vue-query/src/vueQueryPlugin.ts
+++ b/packages/vue-query/src/vueQueryPlugin.ts
@@ -1,5 +1,4 @@
 import { isVue2 } from 'vue-demi'
-import { isServer } from '@tanstack/query-core'
 
 import { QueryClient } from './queryClient'
 import { getClientKey } from './utils'
@@ -38,7 +37,7 @@ export const VueQueryPlugin = {
       client = new QueryClient(clientConfig)
     }
 
-    if (!isServer) {
+    if (!client.isServer) {
       client.mount()
     }