diff --git a/docs/framework/react/plugins/persistQueryClient.md b/docs/framework/react/plugins/persistQueryClient.md
index 77e9aa5b13..4cf6be9288 100644
--- a/docs/framework/react/plugins/persistQueryClient.md
+++ b/docs/framework/react/plugins/persistQueryClient.md
@@ -214,12 +214,12 @@ ReactDOM.createRoot(rootElement).render(
 
 - `persistOptions: PersistQueryClientOptions`
   - all [options](#options) you can pass to [persistQueryClient](#persistqueryclient) minus the QueryClient itself
-- `onSuccess?: () => Promise<unknown> | unknown`
+- `onSuccess?: () => Promise<void> | void`
   - optional
   - will be called when the initial restore is finished
   - can be used to [resumePausedMutations](../../../../reference/QueryClient.md#queryclientresumepausedmutations)
   - if a Promise is returned, it will be awaited; restoring is seen as ongoing until then
-- `onError?: () => Promise<unknown> | unknown`
+- `onError?: () => Promise<void> | void`
   - optional
   - will be called when an error is thrown during restoration
   - if a Promise is returned, it will be awaited
diff --git a/docs/framework/react/reference/useMutation.md b/docs/framework/react/reference/useMutation.md
index 9147c072ef..80545c517e 100644
--- a/docs/framework/react/reference/useMutation.md
+++ b/docs/framework/react/reference/useMutation.md
@@ -68,15 +68,15 @@ mutate(variables, {
   - This function will fire before the mutation function is fired and is passed the same variables the mutation function would receive
   - Useful to perform optimistic updates to a resource in hopes that the mutation succeeds
   - The value returned from this function will be passed to both the `onError` and `onSettled` functions in the event of a mutation failure and can be useful for rolling back optimistic updates.
-- `onSuccess: (data: TData, variables: TVariables, context: TContext) => Promise<unknown> | unknown`
+- `onSuccess: (data: TData, variables: TVariables, context: TContext) => Promise<void> | void`
   - Optional
   - This function will fire when the mutation is successful and will be passed the mutation's result.
   - If a promise is returned, it will be awaited and resolved before proceeding
-- `onError: (err: TError, variables: TVariables, context?: TContext) => Promise<unknown> | unknown`
+- `onError: (err: TError, variables: TVariables, context?: TContext) => Promise<void> | void`
   - Optional
   - This function will fire if the mutation encounters an error and will be passed the error.
   - If a promise is returned, it will be awaited and resolved before proceeding
-- `onSettled: (data: TData, error: TError, variables: TVariables, context?: TContext) => Promise<unknown> | unknown`
+- `onSettled: (data: TData, error: TError, variables: TVariables, context?: TContext) => Promise<void> | void`
   - Optional
   - This function will fire when the mutation is either successfully fetched or encounters an error and be passed either the data or error
   - If a promise is returned, it will be awaited and resolved before proceeding
diff --git a/docs/reference/MutationCache.md b/docs/reference/MutationCache.md
index 9e8ef2e61a..63c9a4133f 100644
--- a/docs/reference/MutationCache.md
+++ b/docs/reference/MutationCache.md
@@ -28,19 +28,19 @@ Its available methods are:
 
 **Options**
 
-- `onError?: (error: unknown, variables: unknown, context: unknown, mutation: Mutation) => Promise<unknown> | unknown`
+- `onError?: (error: unknown, variables: unknown, context: unknown, mutation: Mutation) => Promise<void> | void`
   - Optional
   - This function will be called if some mutation encounters an error.
   - If you return a Promise from it, it will be awaited
-- `onSuccess?: (data: unknown, variables: unknown, context: unknown, mutation: Mutation) => Promise<unknown> | unknown`
+- `onSuccess?: (data: unknown, variables: unknown, context: unknown, mutation: Mutation) => Promise<void> | void`
   - Optional
   - This function will be called if some mutation is successful.
   - If you return a Promise from it, it will be awaited
-- `onSettled?: (data: unknown | undefined, error: unknown | null, variables: unknown, context: unknown, mutation: Mutation) => Promise<unknown> | unknown`
+- `onSettled?: (data: unknown | undefined, error: unknown | null, variables: unknown, context: unknown, mutation: Mutation) => Promise<void> | void`
   - Optional
   - This function will be called if some mutation is settled (either successful or errored).
   - If you return a Promise from it, it will be awaited
-- `onMutate?: (variables: unknown, mutation: Mutation) => Promise<unknown> | unknown`
+- `onMutate?: (variables: unknown, mutation: Mutation) => Promise<void> | void`
   - Optional
   - This function will be called before some mutation executes.
   - If you return a Promise from it, it will be awaited
diff --git a/packages/angular-query-persist-client/src/with-persist-query-client.ts b/packages/angular-query-persist-client/src/with-persist-query-client.ts
index ceeeed01cd..d6ad609c8f 100644
--- a/packages/angular-query-persist-client/src/with-persist-query-client.ts
+++ b/packages/angular-query-persist-client/src/with-persist-query-client.ts
@@ -20,8 +20,8 @@ import type { PersistQueryClientFeature } from '@tanstack/angular-query-experime
 
 type PersistQueryClientOptions = {
   persistOptions: Omit<PersistQueryClientOptionsCore, 'queryClient'>
-  onSuccess?: () => Promise<unknown> | unknown
-  onError?: () => Promise<unknown> | unknown
+  onSuccess?: () => Promise<void> | void
+  onError?: () => Promise<void> | void
 }
 
 /**
diff --git a/packages/query-core/src/mutationCache.ts b/packages/query-core/src/mutationCache.ts
index 6ab95fbfed..3739388a64 100644
--- a/packages/query-core/src/mutationCache.ts
+++ b/packages/query-core/src/mutationCache.ts
@@ -16,24 +16,24 @@ interface MutationCacheConfig {
     variables: unknown,
     context: unknown,
     mutation: Mutation<unknown, unknown, unknown>,
-  ) => Promise<unknown> | unknown
+  ) => Promise<void> | void
   onSuccess?: (
     data: unknown,
     variables: unknown,
     context: unknown,
     mutation: Mutation<unknown, unknown, unknown>,
-  ) => Promise<unknown> | unknown
+  ) => Promise<void> | void
   onMutate?: (
     variables: unknown,
     mutation: Mutation<unknown, unknown, unknown>,
-  ) => Promise<unknown> | unknown
+  ) => Promise<void> | void
   onSettled?: (
     data: unknown | undefined,
     error: DefaultError | null,
     variables: unknown,
     context: unknown,
     mutation: Mutation<unknown, unknown, unknown>,
-  ) => Promise<unknown> | unknown
+  ) => Promise<void> | void
 }
 
 interface NotifyEventMutationAdded extends NotifyEvent {
diff --git a/packages/query-core/src/query.ts b/packages/query-core/src/query.ts
index e6ad4ca4ee..481480f656 100644
--- a/packages/query-core/src/query.ts
+++ b/packages/query-core/src/query.ts
@@ -65,7 +65,7 @@ export interface FetchContext<
   TData,
   TQueryKey extends QueryKey = QueryKey,
 > {
-  fetchFn: () => unknown | Promise<unknown>
+  fetchFn: () => Promise<unknown> | unknown
   fetchOptions?: FetchOptions
   signal: AbortSignal
   options: QueryOptions<TQueryFnData, TError, TData, any>
diff --git a/packages/query-core/src/types.ts b/packages/query-core/src/types.ts
index 735b8ea263..84f632c171 100644
--- a/packages/query-core/src/types.ts
+++ b/packages/query-core/src/types.ts
@@ -1105,18 +1105,18 @@ export interface MutationOptions<
     data: TData,
     variables: TVariables,
     context: TContext,
-  ) => Promise<unknown> | unknown
+  ) => Promise<void> | void
   onError?: (
     error: TError,
     variables: TVariables,
     context: TContext | undefined,
-  ) => Promise<unknown> | unknown
+  ) => Promise<void> | void
   onSettled?: (
     data: TData | undefined,
     error: TError | null,
     variables: TVariables,
     context: TContext | undefined,
-  ) => Promise<unknown> | unknown
+  ) => Promise<void> | void
   retry?: RetryValue<TError>
   retryDelay?: RetryDelayValue<TError>
   networkMode?: NetworkMode
diff --git a/packages/react-query-persist-client/src/PersistQueryClientProvider.tsx b/packages/react-query-persist-client/src/PersistQueryClientProvider.tsx
index b12dba8810..808a2e7a57 100644
--- a/packages/react-query-persist-client/src/PersistQueryClientProvider.tsx
+++ b/packages/react-query-persist-client/src/PersistQueryClientProvider.tsx
@@ -11,8 +11,8 @@ import type { OmitKeyof, QueryClientProviderProps } from '@tanstack/react-query'
 
 export type PersistQueryClientProviderProps = QueryClientProviderProps & {
   persistOptions: OmitKeyof<PersistQueryClientOptions, 'queryClient'>
-  onSuccess?: () => Promise<unknown> | unknown
-  onError?: () => Promise<unknown> | unknown
+  onSuccess?: () => Promise<void> | void
+  onError?: () => Promise<void> | void
 }
 
 export const PersistQueryClientProvider = ({