diff --git a/CHANGELOG.md b/CHANGELOG.md
index 995f972b0..0b99bf85b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,7 +16,11 @@
   - The `numericRange` option removed from `Documentation` class constructor argument;
   - The `brandHandling` should consist of postprocessing functions altering the depiction made by Zod 4;
   - The `Depicter` type signature changed;
-- The `optionalPropStyle` option removed from `Integration` class constructor.
+- The `optionalPropStyle` option removed from `Integration` class constructor:
+  - Use `.optional()` to add question mark to the object property;
+  - Use `.or(z.undefined())` to add `undefined` to the type of the object property;
+  - Reasoning: https://x.com/colinhacks/status/1919292504861491252;
+  - `z.any()` and `z.unknown()` are not optional, details: https://v4.zod.dev/v4/changelog#changes-zunknown-optionality.
 - Changes to the plugin:
   - Brand is the only kind of metadata that withstands refinements and checks.
 
diff --git a/example/example.client.ts b/example/example.client.ts
index 61a7d056b..d3e9c7c65 100644
--- a/example/example.client.ts
+++ b/example/example.client.ts
@@ -1,6 +1,6 @@
 type Type1 = {
   title: string;
-  features?: Type1[] | undefined;
+  features?: Type1[];
 };
 
 type SomeOf<T> = T[keyof T];
@@ -265,15 +265,15 @@ interface PostV1AvatarRawNegativeResponseVariants {
 /** get /v1/events/stream */
 type GetV1EventsStreamInput = {
   /** @deprecated for testing error response */
-  trigger?: string | undefined;
+  trigger?: string;
 };
 
 /** get /v1/events/stream */
 type GetV1EventsStreamPositiveVariant1 = {
   data: number;
   event: "time";
-  id?: string | undefined;
-  retry?: number | undefined;
+  id?: string;
+  retry?: number;
 };
 
 /** get /v1/events/stream */
diff --git a/express-zod-api/src/common-helpers.ts b/express-zod-api/src/common-helpers.ts
index 5da0a03ad..991351170 100644
--- a/express-zod-api/src/common-helpers.ts
+++ b/express-zod-api/src/common-helpers.ts
@@ -1,4 +1,9 @@
-import type { $ZodObject, $ZodTransform, $ZodType } from "@zod/core";
+import type {
+  $ZodObject,
+  $ZodTransform,
+  $ZodType,
+  $ZodTypeInternals,
+} from "@zod/core";
 import { Request } from "express";
 import * as R from "ramda";
 import { globalRegistry, z } from "zod";
@@ -170,19 +175,17 @@ export const getTransformedType = R.tryCatch(
   R.always(undefined),
 );
 
-/**
- * @link https://github.com/colinhacks/zod/issues/4159
- * @todo replace undefined check with using using ._zod.optionality
- * @see https://github.com/RobinTail/express-zod-api/pull/2600/files#r2073174475
- * @link https://v4.zod.dev/v4/changelog#changes-zunknown-optionality
- * */
-export const doesAccept = R.tryCatch(
-  (schema: $ZodType, value: undefined | null) => {
-    z.parse(schema, value);
-    return true;
-  },
-  R.always(false),
-);
+const requestOptionality: Array<$ZodTypeInternals["optionality"]> = [
+  "optional",
+  "defaulted",
+];
+export const isOptional = (
+  { _zod: { optionality } }: $ZodType,
+  { isResponse }: { isResponse: boolean },
+) =>
+  isResponse
+    ? optionality === "optional"
+    : optionality && requestOptionality.includes(optionality);
 
 /** @desc can still be an array, use Array.isArray() or rather R.type() to exclude that case */
 export const isObject = (subject: unknown) =>
diff --git a/express-zod-api/src/documentation-helpers.ts b/express-zod-api/src/documentation-helpers.ts
index 152e7258d..dfd03fb23 100644
--- a/express-zod-api/src/documentation-helpers.ts
+++ b/express-zod-api/src/documentation-helpers.ts
@@ -26,12 +26,12 @@ import * as R from "ramda";
 import { globalRegistry, z } from "zod";
 import { ResponseVariant } from "./api-response";
 import {
-  doesAccept,
   FlatObject,
   getExamples,
   getRoutePathParams,
   getTransformedType,
   isObject,
+  isOptional,
   isSchema,
   makeCleanId,
   routePathParamsRegex,
@@ -174,7 +174,8 @@ export const depictObject: Depicter = (
   const result: string[] = [];
   for (const key of required) {
     const valueSchema = zodSchema._zod.def.shape[key];
-    if (valueSchema && !doesAccept(valueSchema, undefined)) result.push(key);
+    if (valueSchema && !isOptional(valueSchema, { isResponse }))
+      result.push(key);
   }
   return { ...jsonSchema, required: result };
 };
@@ -415,8 +416,6 @@ const depicters: Partial<Record<FirstPartyKind | ProprietaryBrand, Depicter>> =
 
 const onEach: Depicter = ({ zodSchema, jsonSchema }, { isResponse }) => {
   const result = { ...jsonSchema };
-  if (!isResponse && doesAccept(zodSchema, null))
-    Object.assign(result, { type: makeNullableType(jsonSchema.type) });
   const examples = getExamples({
     schema: zodSchema,
     variant: isResponse ? "parsed" : "original",
diff --git a/express-zod-api/src/zts.ts b/express-zod-api/src/zts.ts
index c1a4f8c15..cc890007d 100644
--- a/express-zod-api/src/zts.ts
+++ b/express-zod-api/src/zts.ts
@@ -21,7 +21,7 @@ import type {
 import * as R from "ramda";
 import ts from "typescript";
 import { globalRegistry, z } from "zod";
-import { doesAccept, getTransformedType, isSchema } from "./common-helpers";
+import { getTransformedType, isOptional, isSchema } from "./common-helpers";
 import { ezDateInBrand } from "./date-in-schema";
 import { ezDateOutBrand } from "./date-out-schema";
 import { hasCycle } from "./deep-checks";
@@ -77,15 +77,12 @@ const onObject: Producer = (
   const fn = () => {
     const members = Object.entries(obj._zod.def.shape).map<ts.TypeElement>(
       ([key, value]) => {
-        const isOptional = isResponse
-          ? isSchema<$ZodOptional>(value, "optional")
-          : doesAccept(value, undefined);
         const { description: comment, deprecated: isDeprecated } =
           globalRegistry.get(value) || {};
         return makeInterfaceProp(key, next(value), {
           comment,
           isDeprecated,
-          isOptional,
+          isOptional: isOptional(value, { isResponse }),
         });
       },
     );
@@ -118,10 +115,7 @@ const makeSample = (produced: ts.TypeNode) =>
   samples?.[produced.kind as keyof typeof samples];
 
 const onOptional: Producer = ({ _zod: { def } }: $ZodOptional, { next }) =>
-  f.createUnionTypeNode([
-    next(def.innerType),
-    ensureTypeNode(ts.SyntaxKind.UndefinedKeyword),
-  ]);
+  next(def.innerType);
 
 const onNullable: Producer = ({ _zod: { def } }: $ZodNullable, { next }) =>
   f.createUnionTypeNode([next(def.innerType), makeLiteralType(null)]);
diff --git a/express-zod-api/tests/__snapshots__/documentation-helpers.spec.ts.snap b/express-zod-api/tests/__snapshots__/documentation-helpers.spec.ts.snap
index d4657b06d..367203042 100644
--- a/express-zod-api/tests/__snapshots__/documentation-helpers.spec.ts.snap
+++ b/express-zod-api/tests/__snapshots__/documentation-helpers.spec.ts.snap
@@ -216,12 +216,27 @@ exports[`Documentation helpers > depictNullable() > should add null type to the
 }
 `;
 
-exports[`Documentation helpers > depictNullable() > should not add null type when it's already there 1`] = `
+exports[`Documentation helpers > depictNullable() > should not add null type when it's already there 0 1`] = `
 {
   "type": "null",
 }
 `;
 
+exports[`Documentation helpers > depictNullable() > should not add null type when it's already there 1 1`] = `
+{
+  "type": "null",
+}
+`;
+
+exports[`Documentation helpers > depictNullable() > should not add null type when it's already there 2 1`] = `
+{
+  "type": [
+    "string",
+    "null",
+  ],
+}
+`;
+
 exports[`Documentation helpers > depictObject() > should remove optional props from required for request 0 1`] = `
 {
   "properties": {
@@ -250,7 +265,9 @@ exports[`Documentation helpers > depictObject() > should remove optional props f
       "type": "string",
     },
   },
-  "required": [],
+  "required": [
+    "b",
+  ],
   "type": "object",
 }
 `;
diff --git a/express-zod-api/tests/__snapshots__/documentation.spec.ts.snap b/express-zod-api/tests/__snapshots__/documentation.spec.ts.snap
index cb45adc06..f789b9d7f 100644
--- a/express-zod-api/tests/__snapshots__/documentation.spec.ts.snap
+++ b/express-zod-api/tests/__snapshots__/documentation.spec.ts.snap
@@ -2147,7 +2147,7 @@ paths:
       parameters:
         - name: any
           in: query
-          required: false
+          required: true
           description: GET /v1/getSomething Parameter
           schema: {}
       responses:
@@ -2224,7 +2224,7 @@ paths:
       parameters:
         - name: string
           in: query
-          required: false
+          required: true
           description: GET /v1/getSomething Parameter
           schema:
             format: string (preprocessed)
diff --git a/express-zod-api/tests/__snapshots__/integration.spec.ts.snap b/express-zod-api/tests/__snapshots__/integration.spec.ts.snap
index 38e79e133..4e4a2c452 100644
--- a/express-zod-api/tests/__snapshots__/integration.spec.ts.snap
+++ b/express-zod-api/tests/__snapshots__/integration.spec.ts.snap
@@ -282,14 +282,14 @@ exports[`Integration > Should treat optionals the same way as z.infer() by defau
 
 /** post /v1/test-with-dashes */
 type PostV1TestWithDashesInput = {
-  opt?: string | undefined;
+  opt?: string;
 };
 
 /** post /v1/test-with-dashes */
 type PostV1TestWithDashesPositiveVariant1 = {
   status: "success";
   data: {
-    similar?: number | undefined;
+    similar?: number;
   };
 };
 
diff --git a/express-zod-api/tests/__snapshots__/zts.spec.ts.snap b/express-zod-api/tests/__snapshots__/zts.spec.ts.snap
index 4213a12e0..c0035bf4b 100644
--- a/express-zod-api/tests/__snapshots__/zts.spec.ts.snap
+++ b/express-zod-api/tests/__snapshots__/zts.spec.ts.snap
@@ -16,20 +16,20 @@ exports[`zod-to-ts > Example > should produce the expected results 1`] = `
     enum: "hi" | "bye";
     intersectionWithTransform: (number & bigint) & (number & string);
     date: any;
-    undefined?: undefined;
+    undefined: undefined;
     null: null;
-    void?: any;
-    any?: any;
-    unknown?: any;
+    void: any;
+    any: any;
+    unknown: any;
     never: any;
-    optionalString?: string | undefined;
+    optionalString?: string;
     nullablePartialObject: {
-        string?: string | undefined;
-        number?: number | undefined;
-        fixedArrayOfString?: string[] | undefined;
+        string?: string;
+        number?: number;
+        fixedArrayOfString?: string[];
         object?: {
             string: string;
-        } | undefined;
+        };
     } | null;
     tuple: [
         string,
@@ -57,8 +57,8 @@ exports[`zod-to-ts > Example > should produce the expected results 1`] = `
     set: any;
     intersection: (string & number) | bigint;
     promise: any;
-    optDefaultString?: string | undefined;
-    refinedStringWithSomeBullshit: (string | number) & ((bigint | null) | undefined);
+    optDefaultString?: string;
+    refinedStringWithSomeBullshit: (string | number) & (bigint | null);
     nativeEnum: "A" | "apple" | "banana" | "cantaloupe" | 5;
     lazy: SomeType;
     discUnion: {
@@ -73,7 +73,7 @@ exports[`zod-to-ts > Example > should produce the expected results 1`] = `
         y: number;
     };
     branded: string;
-    catch?: number;
+    catch: number;
     pipeline: string;
     readonly: string;
 }"
@@ -127,7 +127,7 @@ exports[`zod-to-ts > Issue #2352: intersection of objects having same prop %# >
 "{
     query: string;
 } & {
-    query?: string | undefined;
+    query?: string;
 }"
 `;
 
@@ -135,7 +135,7 @@ exports[`zod-to-ts > Issue #2352: intersection of objects having same prop %# >
 "{
     query: string;
 } & {
-    query?: string | undefined;
+    query?: string;
 }"
 `;
 
@@ -145,11 +145,11 @@ exports[`zod-to-ts > PrimitiveSchema > outputs correct typescript 1`] = `
     number: number;
     boolean: boolean;
     date: any;
-    undefined?: undefined;
+    undefined: undefined;
     null: null;
-    void?: any;
-    any?: any;
-    unknown?: any;
+    void: any;
+    any: any;
+    unknown: any;
     never: any;
 }"
 `;
@@ -230,10 +230,10 @@ exports[`zod-to-ts > z.object() > escapes correctly 1`] = `
     "'": string;
     "\`": string;
     "\\n": number;
-    $e?: any;
-    "4t"?: any;
-    _r?: any;
-    "-r"?: undefined;
+    $e: any;
+    "4t": any;
+    _r: any;
+    "-r": undefined;
 }"
 `;
 
@@ -268,21 +268,21 @@ exports[`zod-to-ts > z.object() > supports zod.describe() 1`] = `
 }"
 `;
 
-exports[`zod-to-ts > z.optional() > outputs correct typescript 1`] = `"string | undefined"`;
+exports[`zod-to-ts > z.optional() > Zod 4: does not add undefined to it, unwrap as is 1`] = `"string"`;
 
-exports[`zod-to-ts > z.optional() > should output \`?:\` and undefined union for optional properties 1`] = `
+exports[`zod-to-ts > z.optional() > Zod 4: should add question mark only to optional props 1`] = `
 "{
-    optional?: string | undefined;
+    optional?: string;
     required: string;
-    transform?: number | undefined;
-    or?: (number | undefined) | string;
+    transform: number;
+    or: number | string;
     tuple?: [
-        string | undefined,
+        string,
         number,
         {
-            optional?: string | undefined;
+            optional?: string;
             required: string;
         }
-    ] | undefined;
+    ];
 }"
 `;
diff --git a/express-zod-api/tests/documentation-helpers.spec.ts b/express-zod-api/tests/documentation-helpers.spec.ts
index b09e553bc..90a3c6d9f 100644
--- a/express-zod-api/tests/documentation-helpers.spec.ts
+++ b/express-zod-api/tests/documentation-helpers.spec.ts
@@ -309,10 +309,18 @@ describe("Documentation helpers", () => {
       },
     );
 
-    test("should not add null type when it's already there", () => {
-      const jsonSchema: JSONSchema.BaseSchema = {
+    test.each([
+      { type: "null" },
+      {
         anyOf: [{ type: "null" }, { type: "null" }],
-      };
+      },
+      {
+        anyOf: [
+          { type: ["string", "null"] as unknown as string }, // nullable of nullable case
+          { type: "null" },
+        ],
+      },
+    ])("should not add null type when it's already there %#", (jsonSchema) => {
       expect(
         depictNullable({ zodSchema: z.never(), jsonSchema }, requestCtx),
       ).toMatchSnapshot();
@@ -356,7 +364,7 @@ describe("Documentation helpers", () => {
         jsonSchema: {
           type: "object",
           properties: { a: { type: "number" }, b: { type: "string" } },
-          required: ["b"],
+          required: ["b"], // Zod 4: coerce remains
         },
       },
     ])(
diff --git a/express-zod-api/tests/zts.spec.ts b/express-zod-api/tests/zts.spec.ts
index 7bc689cd8..e1649ac48 100644
--- a/express-zod-api/tests/zts.spec.ts
+++ b/express-zod-api/tests/zts.spec.ts
@@ -202,12 +202,16 @@ describe("zod-to-ts", () => {
         .optional(),
     });
 
-    test("outputs correct typescript", () => {
+    test("Zod 4: does not add undefined to it, unwrap as is", () => {
       const node = zodToTs(optionalStringSchema, { ctx });
       expect(printNodeTest(node)).toMatchSnapshot();
     });
 
-    test("should output `?:` and undefined union for optional properties", () => {
+    /**
+     * @todo revisit when optional+transform fixed
+     * @link https://github.com/colinhacks/zod/issues/4322
+     * */
+    test("Zod 4: should add question mark only to optional props", () => {
       const node = zodToTs(objectWithOptionals, { ctx });
       expect(printNodeTest(node)).toMatchSnapshot();
     });