diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5d1263e2faf..fa6b5b705a4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -119,6 +119,9 @@
 - Make sure `ApolloContext` plays nicely with IE11 when storing the shared context.  <br/>
   [@ms](https://github.com/ms) in [#5840](https://github.com/apollographql/apollo-client/pull/5840)
 
+- Expose cache `modify` and `identify` to the mutate `update` function.  <br/>
+  [@hwillson](https://github.com/hwillson) in [#5956](https://github.com/apollographql/apollo-client/pull/5956)
+
 ### Bug Fixes
 
 - `useMutation` adjustments to help avoid an infinite loop / too many renders issue, caused by unintentionally modifying the `useState` based mutation result directly.  <br/>
diff --git a/src/cache/core/cache.ts b/src/cache/core/cache.ts
index dceca187a21..9a510135ce7 100644
--- a/src/cache/core/cache.ts
+++ b/src/cache/core/cache.ts
@@ -2,9 +2,11 @@ import { DocumentNode } from 'graphql';
 import { wrap } from 'optimism';
 
 import { getFragmentQueryDocument } from '../../utilities/graphql/fragments';
+import { StoreObject } from '../../utilities/graphql/storeUtils';
 import { DataProxy } from './types/DataProxy';
 import { Cache } from './types/Cache';
 import { queryFromPojo, fragmentFromPojo } from './utils';
+import { Modifier, Modifiers } from './types/common';
 
 const justTypenameQuery: DocumentNode = {
   kind: "Document",
@@ -61,23 +63,41 @@ export abstract class ApolloCache<TSerialized> implements DataProxy {
    */
   public abstract extract(optimistic?: boolean): TSerialized;
 
-  // optimistic API
+  // Optimistic API
+
   public abstract removeOptimistic(id: string): void;
 
-  // transactional API
+  // Transactional API
+
   public abstract performTransaction(
     transaction: Transaction<TSerialized>,
   ): void;
+
   public abstract recordOptimisticTransaction(
     transaction: Transaction<TSerialized>,
     id: string,
   ): void;
 
-  // optional API
+  // Optional API
+
   public transformDocument(document: DocumentNode): DocumentNode {
     return document;
   }
-  // experimental
+
+  public identify(object: StoreObject): string | null {
+    return null;
+  }
+
+  public modify(
+    dataId: string,
+    modifiers: Modifier<any> | Modifiers,
+    optimistic = false,
+  ): boolean {
+    return false;
+  }
+
+  // Experimental API
+
   public transformForLink(document: DocumentNode): DocumentNode {
     return document;
   }
diff --git a/src/cache/core/types/common.ts b/src/cache/core/types/common.ts
new file mode 100644
index 00000000000..9ba9f4a1c06
--- /dev/null
+++ b/src/cache/core/types/common.ts
@@ -0,0 +1,38 @@
+import { SelectionSetNode } from 'graphql';
+
+import {
+  isReference,
+  StoreValue,
+  StoreObject,
+  Reference
+} from '../../../utilities/graphql/storeUtils';
+import { FragmentMap } from '../../../utilities/graphql/fragments';
+
+// The Readonly<T> type only really works for object types, since it marks
+// all of the object's properties as readonly, but there are many cases when
+// a generic type parameter like TExisting might be a string or some other
+// primitive type, in which case we need to avoid wrapping it with Readonly.
+// SafeReadonly<string> collapses to just string, which makes string
+// assignable to SafeReadonly<any>, whereas string is not assignable to
+// Readonly<any>, somewhat surprisingly.
+export type SafeReadonly<T> = T extends object ? Readonly<T> : T;
+
+export type Modifier<T> = (value: T, details: {
+  DELETE: any;
+  fieldName: string;
+  storeFieldName: string;
+  isReference: typeof isReference;
+  toReference(
+    object: StoreObject,
+    selectionSet?: SelectionSetNode,
+    fragmentMap?: FragmentMap,
+  ): Reference;
+  readField<V = StoreValue>(
+    fieldName: string,
+    objOrRef?: StoreObject | Reference,
+  ): SafeReadonly<V>;
+}) => T;
+
+export type Modifiers = {
+  [fieldName: string]: Modifier<any>;
+}
diff --git a/src/cache/inmemory/entityStore.ts b/src/cache/inmemory/entityStore.ts
index 3afefc3bf39..de184cec086 100644
--- a/src/cache/inmemory/entityStore.ts
+++ b/src/cache/inmemory/entityStore.ts
@@ -1,32 +1,23 @@
 import { dep, OptimisticDependencyFunction, KeyTrie } from 'optimism';
 import { equal } from '@wry/equality';
 
-import { isReference, StoreValue, Reference, makeReference } from '../../utilities/graphql/storeUtils';
+import {
+  isReference,
+  StoreValue,
+  StoreObject,
+  Reference,
+  makeReference
+} from '../../utilities/graphql/storeUtils';
 import { DeepMerger } from '../../utilities/common/mergeDeep';
 import { maybeDeepFreeze } from '../../utilities/common/maybeDeepFreeze';
 import { canUseWeakMap } from '../../utilities/common/canUse';
-import { NormalizedCache, NormalizedCacheObject, StoreObject, SafeReadonly } from './types';
+import { NormalizedCache, NormalizedCacheObject } from './types';
 import { fieldNameFromStoreName } from './helpers';
 import { Policies } from './policies';
+import  { Modifier, Modifiers, SafeReadonly } from '../core/types/common';
 
 const hasOwn = Object.prototype.hasOwnProperty;
 
-export type Modifier<T> = (value: T, details: {
-  DELETE: typeof DELETE;
-  fieldName: string;
-  storeFieldName: string;
-  isReference: typeof isReference;
-  toReference: Policies["toReference"];
-  readField<V = StoreValue>(
-    fieldName: string,
-    objOrRef?: StoreObject | Reference,
-  ): SafeReadonly<V>;
-}) => T;
-
-export type Modifiers = {
-  [fieldName: string]: Modifier<any>;
-}
-
 const DELETE: any = Object.create(null);
 const delModifier: Modifier<any> = () => DELETE;
 
diff --git a/src/cache/inmemory/helpers.ts b/src/cache/inmemory/helpers.ts
index 232e4c050a2..9f7ca769031 100644
--- a/src/cache/inmemory/helpers.ts
+++ b/src/cache/inmemory/helpers.ts
@@ -1,6 +1,13 @@
 import { FieldNode } from 'graphql';
-import { NormalizedCache, StoreObject } from './types';
-import { Reference, isReference, StoreValue, isField } from '../../utilities/graphql/storeUtils';
+
+import { NormalizedCache } from './types';
+import {
+  Reference,
+  isReference,
+  StoreValue,
+  StoreObject,
+  isField
+} from '../../utilities/graphql/storeUtils';
 import { DeepMerger, ReconcilerFunction } from '../../utilities/common/mergeDeep';
 
 export function getTypenameFromStoreObject(
diff --git a/src/cache/inmemory/inMemoryCache.ts b/src/cache/inmemory/inMemoryCache.ts
index e3dbb16eb70..d2a2f66e8b7 100644
--- a/src/cache/inmemory/inMemoryCache.ts
+++ b/src/cache/inmemory/inMemoryCache.ts
@@ -6,15 +6,16 @@ import { dep, wrap } from 'optimism';
 
 import { ApolloCache, Transaction } from '../core/cache';
 import { Cache } from '../core/types/Cache';
+import { Modifier, Modifiers } from '../core/types/common';
 import { addTypenameToDocument } from '../../utilities/graphql/transform';
+import { StoreObject }  from '../../utilities/graphql/storeUtils';
 import {
   ApolloReducerConfig,
   NormalizedCacheObject,
-  StoreObject,
 } from './types';
 import { StoreReader } from './readFromStore';
 import { StoreWriter } from './writeToStore';
-import { EntityStore, supportsResultCaching, Modifiers, Modifier } from './entityStore';
+import { EntityStore, supportsResultCaching } from './entityStore';
 import {
   defaultDataIdFromObject,
   PossibleTypesMap,
diff --git a/src/cache/inmemory/policies.ts b/src/cache/inmemory/policies.ts
index 514a97335f4..a46ac91308f 100644
--- a/src/cache/inmemory/policies.ts
+++ b/src/cache/inmemory/policies.ts
@@ -12,32 +12,26 @@ import {
   FragmentMap,
   getFragmentFromSelection,
 } from '../../utilities/graphql/fragments';
-
 import {
   isField,
   getTypenameFromResult,
   storeKeyNameFromField,
   StoreValue,
+  StoreObject,
   argumentsObjectFromField,
   Reference,
   makeReference,
   isReference,
 } from '../../utilities/graphql/storeUtils';
-
 import { canUseWeakMap } from '../../utilities/common/canUse';
-
-import {
-  IdGetter,
-  StoreObject,
-  SafeReadonly,
-} from "./types";
-
+import { IdGetter } from "./types";
 import {
   fieldNameFromStoreName,
   FieldValueToBeMerged,
   isFieldValueToBeMerged,
 } from './helpers';
 import { FieldValueGetter } from './entityStore';
+import { SafeReadonly } from '../core/types/common';
 
 const hasOwn = Object.prototype.hasOwnProperty;
 
diff --git a/src/cache/inmemory/readFromStore.ts b/src/cache/inmemory/readFromStore.ts
index 1688f4343e3..99941d81b18 100644
--- a/src/cache/inmemory/readFromStore.ts
+++ b/src/cache/inmemory/readFromStore.ts
@@ -15,6 +15,7 @@ import {
   Reference,
   isReference,
   makeReference,
+  StoreObject,
 } from '../../utilities/graphql/storeUtils';
 import { createFragmentMap, FragmentMap } from '../../utilities/graphql/fragments';
 import { shouldInclude } from '../../utilities/graphql/directives';
@@ -31,7 +32,6 @@ import { Cache } from '../core/types/Cache';
 import {
   DiffQueryAgainstStoreOptions,
   ReadQueryOptions,
-  StoreObject,
   NormalizedCache,
 } from './types';
 import { supportsResultCaching } from './entityStore';
diff --git a/src/cache/inmemory/types.ts b/src/cache/inmemory/types.ts
index e66255c0c1a..06477429b8d 100644
--- a/src/cache/inmemory/types.ts
+++ b/src/cache/inmemory/types.ts
@@ -1,8 +1,9 @@
 import { DocumentNode } from 'graphql';
 
 import { Transaction } from '../core/cache';
-import { StoreValue } from '../../utilities/graphql/storeUtils';
-import { Modifiers, Modifier, FieldValueGetter } from './entityStore';
+import { Modifier, Modifiers } from '../core/types/common';
+import { StoreValue, StoreObject } from '../../utilities/graphql/storeUtils';
+import { FieldValueGetter } from './entityStore';
 export { StoreValue }
 
 export interface IdGetterObj extends Object {
@@ -59,20 +60,6 @@ export interface NormalizedCacheObject {
   [dataId: string]: StoreObject | undefined;
 }
 
-export interface StoreObject {
-  __typename?: string;
-  [storeFieldName: string]: StoreValue;
-}
-
-// The Readonly<T> type only really works for object types, since it marks
-// all of the object's properties as readonly, but there are many cases when
-// a generic type parameter like TExisting might be a string or some other
-// primitive type, in which case we need to avoid wrapping it with Readonly.
-// SafeReadonly<string> collapses to just string, which makes string
-// assignable to SafeReadonly<any>, whereas string is not assignable to
-// Readonly<any>, somewhat surprisingly.
-export type SafeReadonly<T> = T extends object ? Readonly<T> : T;
-
 export type OptimisticStoreItem = {
   id: string;
   data: NormalizedCacheObject;
diff --git a/src/cache/inmemory/writeToStore.ts b/src/cache/inmemory/writeToStore.ts
index 6087b58068e..2587566f5b2 100644
--- a/src/cache/inmemory/writeToStore.ts
+++ b/src/cache/inmemory/writeToStore.ts
@@ -19,6 +19,7 @@ import {
   isField,
   resultKeyNameFromField,
   StoreValue,
+  StoreObject,
 } from '../../utilities/graphql/storeUtils';
 
 import { shouldInclude } from '../../utilities/graphql/directives';
@@ -26,7 +27,7 @@ import { cloneDeep } from '../../utilities/common/cloneDeep';
 
 import { Policies } from './policies';
 import { defaultNormalizedCacheFactory } from './entityStore';
-import { NormalizedCache, StoreObject } from './types';
+import { NormalizedCache } from './types';
 import { makeProcessedFieldsMerger, FieldValueToBeMerged } from './helpers';
 
 export type WriteContext = {
diff --git a/src/core/QueryManager.ts b/src/core/QueryManager.ts
index 50eb63fc881..4360af1e33c 100644
--- a/src/core/QueryManager.ts
+++ b/src/core/QueryManager.ts
@@ -5,7 +5,6 @@ import { ApolloLink } from '../link/core/ApolloLink';
 import { execute } from '../link/core/execute';
 import { FetchResult } from '../link/core/types';
 import { Cache } from '../cache/core/types/Cache';
-import { DataProxy } from '../cache/core/types/DataProxy';
 
 import {
   getDefaultValues,
@@ -1452,7 +1451,9 @@ function markMutationResult<TStore>(
     document: DocumentNode;
     variables: any;
     queryUpdatersById: Record<string, QueryWithUpdater>;
-    update: ((proxy: DataProxy, mutationResult: Object) => void) | undefined;
+    update:
+      ((cache: ApolloCache<TStore>, mutationResult: Object) => void) |
+      undefined;
   },
   cache: ApolloCache<TStore>,
 ) {
diff --git a/src/core/watchQueryOptions.ts b/src/core/watchQueryOptions.ts
index f789dd93db8..934ab26f62a 100644
--- a/src/core/watchQueryOptions.ts
+++ b/src/core/watchQueryOptions.ts
@@ -1,7 +1,7 @@
 import { DocumentNode, ExecutionResult } from 'graphql';
 
+import { ApolloCache } from '../cache/core/cache';
 import { FetchResult } from '../link/core/types';
-import { DataProxy } from '../cache/core/types/DataProxy';
 import { MutationQueryReducersMap } from './types';
 import { PureQueryOptions, OperationVariables } from './types';
 
@@ -218,9 +218,9 @@ export interface MutationBaseOptions<
   awaitRefetchQueries?: boolean;
 
   /**
-   * A function which provides a {@link DataProxy} and the result of the
-   * mutation to allow the user to update the store based on the results of the
-   * mutation.
+   * A function which provides an {@link ApolloCache} instance, and the result
+   * of the mutation, to allow the user to update the store based on the
+   * results of the mutation.
    *
    * This function will be called twice over the lifecycle of a mutation. Once
    * at the very beginning if an `optimisticResponse` was provided. The writes
@@ -229,11 +229,6 @@ export interface MutationBaseOptions<
    * resolved. At that point `update` will be called with the *actual* mutation
    * result and those writes will not be rolled back.
    *
-   * The reason a {@link DataProxy} is provided instead of the user calling the
-   * methods directly on {@link ApolloClient} is that all of the writes are
-   * batched together at the end of the update, and it allows for writes
-   * generated by optimistic data to be rolled back.
-   *
    * Note that since this function is intended to be used to update the
    * store, it cannot be used with a `no-cache` fetch policy. If you're
    * interested in performing some action after a mutation has completed,
@@ -284,6 +279,6 @@ export interface MutationOptions<
 
 // Add a level of indirection for `typedoc`.
 export type MutationUpdaterFn<T = { [key: string]: any }> = (
-  proxy: DataProxy,
+  cache: ApolloCache<T>,
   mutationResult: FetchResult<T>,
 ) => void;
diff --git a/src/utilities/graphql/storeUtils.ts b/src/utilities/graphql/storeUtils.ts
index 5bf701f1a2c..9cb365d3a29 100644
--- a/src/utilities/graphql/storeUtils.ts
+++ b/src/utilities/graphql/storeUtils.ts
@@ -44,6 +44,11 @@ export type StoreValue =
   | void
   | Object;
 
+export interface StoreObject {
+  __typename?: string;
+  [storeFieldName: string]: StoreValue;
+}
+
 function isStringValue(value: ValueNode): value is StringValueNode {
   return value.kind === 'StringValue';
 }