diff --git a/apps/content/content/docs/openapi/generator.mdx b/apps/content/content/docs/openapi/generator.mdx
index 7608fd3d..5f5c8b07 100644
--- a/apps/content/content/docs/openapi/generator.mdx
+++ b/apps/content/content/docs/openapi/generator.mdx
@@ -87,12 +87,18 @@ export const router = pub.router({
 To generate an OpenAPI specification, you need either the type of the [router](/docs/server/router)  you intend to use or the [contract](/docs/contract/builder).
 
 ```ts twoslash
-import { generateOpenAPI } from '@orpc/openapi'
+import { OpenAPIGenerator } from '@orpc/openapi'
+import { ZodToJsonSchemaConverter } from '@orpc/zod'
 import { router } from 'examples/server'
 import { contract } from 'examples/contract'
 
-const spec = generateOpenAPI({
-    router: contract, // both router and contract are supported
+const openAPIGenerator = new OpenAPIGenerator({
+  schemaConverters: [
+    new ZodToJsonSchemaConverter(),
+  ],
+})
+
+const spec = await openAPIGenerator.generate(contract /* or router */, {
     info: {
         title: 'My App',
         version: '0.0.0',
diff --git a/apps/content/examples/open-api.ts b/apps/content/examples/open-api.ts
index 30e551c4..033c7103 100644
--- a/apps/content/examples/open-api.ts
+++ b/apps/content/examples/open-api.ts
@@ -1,17 +1,22 @@
-import { generateOpenAPI } from '@orpc/openapi'
+import { OpenAPIGenerator } from '@orpc/openapi'
+import { ZodToJsonSchemaConverter } from '@orpc/zod'
 import { contract } from 'examples/contract'
 import { router } from 'examples/server'
 
-export const specFromServerRouter = generateOpenAPI({
-  router,
+const openAPIGenerator = new OpenAPIGenerator({
+  schemaConverters: [
+    new ZodToJsonSchemaConverter(),
+  ],
+})
+
+export const specFromServerRouter = await openAPIGenerator.generate(router, {
   info: {
     title: 'My App',
     version: '0.0.0',
   },
 })
 
-export const specFromContractRouter = generateOpenAPI({
-  router: contract,
+export const specFromContractRouter = await openAPIGenerator.generate(contract, {
   info: {
     title: 'My App',
     version: '0.0.0',
diff --git a/packages/next/src/action-form.ts b/packages/next/src/action-form.ts
index 1e526786..7aeea4e2 100644
--- a/packages/next/src/action-form.ts
+++ b/packages/next/src/action-form.ts
@@ -1,5 +1,6 @@
 import type { Schema, SchemaInput } from '@orpc/contract'
 import type { Context, CreateProcedureClientOptions } from '@orpc/server'
+import { JSONSerializer } from '@orpc/openapi'
 import { CompositeSchemaCoercer, OpenAPIPayloadCodec, type PublicOpenAPIPayloadCodec, type SchemaCoercer } from '@orpc/openapi/fetch'
 import { createProcedureClient, ORPCError, unlazy } from '@orpc/server'
 import { forbidden, notFound, unauthorized } from 'next/navigation'
@@ -21,7 +22,7 @@ export function createFormAction<
 
   const formAction = async (input: FormData): Promise<void> => {
     try {
-      const codec = opt.payloadCodec ?? new OpenAPIPayloadCodec()
+      const codec = opt.payloadCodec ?? new OpenAPIPayloadCodec(new JSONSerializer())
       const coercer = new CompositeSchemaCoercer(opt.schemaCoercers ?? [])
 
       const { default: procedure } = await unlazy(opt.procedure)
diff --git a/playgrounds/contract-openapi/src/main.ts b/playgrounds/contract-openapi/src/main.ts
index f0f3c84d..237d284d 100644
--- a/playgrounds/contract-openapi/src/main.ts
+++ b/playgrounds/contract-openapi/src/main.ts
@@ -1,8 +1,8 @@
 import { createServer } from 'node:http'
-import { generateOpenAPI } from '@orpc/openapi'
+import { OpenAPIGenerator } from '@orpc/openapi'
 import { OpenAPIServerHandler } from '@orpc/openapi/fetch'
 import { CompositeHandler, ORPCHandler } from '@orpc/server/fetch'
-import { ZodCoercer } from '@orpc/zod'
+import { ZodCoercer, ZodToJsonSchemaConverter } from '@orpc/zod'
 import { createServerAdapter } from '@whatwg-node/server'
 import { contract } from './contract'
 import { router } from './router'
@@ -23,6 +23,12 @@ const orpcHandler = new ORPCHandler(router, {
 })
 const compositeHandler = new CompositeHandler([openAPIHandler, orpcHandler])
 
+const openAPIGenerator = new OpenAPIGenerator({
+  schemaConverters: [
+    new ZodToJsonSchemaConverter(),
+  ],
+})
+
 const server = createServer(
   createServerAdapter(async (request: Request) => {
     const url = new URL(request.url)
@@ -39,8 +45,7 @@ const server = createServer(
     }
 
     if (url.pathname === '/spec.json') {
-      const spec = await generateOpenAPI({
-        router: contract,
+      const spec = await openAPIGenerator.generate(contract, {
         info: {
           title: 'ORPC Playground',
           version: '1.0.0',
diff --git a/playgrounds/expressjs/src/main.ts b/playgrounds/expressjs/src/main.ts
index 53dd322e..fb4f631a 100644
--- a/playgrounds/expressjs/src/main.ts
+++ b/playgrounds/expressjs/src/main.ts
@@ -1,7 +1,7 @@
-import { generateOpenAPI } from '@orpc/openapi'
+import { OpenAPIGenerator } from '@orpc/openapi'
 import { OpenAPIServerHandler } from '@orpc/openapi/fetch'
 import { CompositeHandler, ORPCHandler } from '@orpc/server/fetch'
-import { ZodCoercer } from '@orpc/zod'
+import { ZodCoercer, ZodToJsonSchemaConverter } from '@orpc/zod'
 import { createServerAdapter } from '@whatwg-node/server'
 import express from 'express'
 import { router } from './router'
@@ -37,10 +37,14 @@ app.all(
     })
   }),
 )
+const openAPIGenerator = new OpenAPIGenerator({
+  schemaConverters: [
+    new ZodToJsonSchemaConverter(),
+  ],
+})
 
 app.get('/spec.json', async (req, res) => {
-  const spec = await generateOpenAPI({
-    router,
+  const spec = await openAPIGenerator.generate(router, {
     info: {
       title: 'ORPC Playground',
       version: '1.0.0',
diff --git a/playgrounds/nextjs/src/app/spec/route.ts b/playgrounds/nextjs/src/app/spec/route.ts
index 5d403eac..168c07e3 100644
--- a/playgrounds/nextjs/src/app/spec/route.ts
+++ b/playgrounds/nextjs/src/app/spec/route.ts
@@ -1,9 +1,16 @@
-import { generateOpenAPI } from '@orpc/openapi'
+import { OpenAPIGenerator } from '@orpc/openapi'
+
+import { ZodToJsonSchemaConverter } from '@orpc/zod'
 import { router } from '../api/[...rest]/router'
 
+const openAPIGenerator = new OpenAPIGenerator({
+  schemaConverters: [
+    new ZodToJsonSchemaConverter(),
+  ],
+})
+
 export async function GET(request: Request) {
-  const spec = await generateOpenAPI({
-    router,
+  const spec = await openAPIGenerator.generate(router, {
     info: {
       title: 'ORPC Playground',
       version: '1.0.0',
diff --git a/playgrounds/openapi/src/main.ts b/playgrounds/openapi/src/main.ts
index 29c2a4da..92ba0692 100644
--- a/playgrounds/openapi/src/main.ts
+++ b/playgrounds/openapi/src/main.ts
@@ -1,8 +1,8 @@
 import { createServer } from 'node:http'
-import { generateOpenAPI } from '@orpc/openapi'
+import { OpenAPIGenerator } from '@orpc/openapi'
 import { OpenAPIServerHandler } from '@orpc/openapi/fetch'
 import { CompositeHandler, ORPCHandler } from '@orpc/server/fetch'
-import { ZodCoercer } from '@orpc/zod'
+import { ZodCoercer, ZodToJsonSchemaConverter } from '@orpc/zod'
 import { createServerAdapter } from '@whatwg-node/server'
 import { router } from './router'
 import './polyfill'
@@ -22,6 +22,12 @@ const orpcHandler = new ORPCHandler(router, {
 })
 const compositeHandler = new CompositeHandler([openAPIHandler, orpcHandler])
 
+const openAPIGenerator = new OpenAPIGenerator({
+  schemaConverters: [
+    new ZodToJsonSchemaConverter(),
+  ],
+})
+
 const server = createServer(
   createServerAdapter(async (request: Request) => {
     const url = new URL(request.url)
@@ -38,8 +44,7 @@ const server = createServer(
     }
 
     if (url.pathname === '/spec.json') {
-      const spec = await generateOpenAPI({
-        router,
+      const spec = await openAPIGenerator.generate(router, {
         info: {
           title: 'ORPC Playground',
           version: '1.0.0',