diff --git a/packages/openapi-ts-tests/main/test/3.1.x.test.ts b/packages/openapi-ts-tests/main/test/3.1.x.test.ts
index 84e20de05..a169f622f 100644
--- a/packages/openapi-ts-tests/main/test/3.1.x.test.ts
+++ b/packages/openapi-ts-tests/main/test/3.1.x.test.ts
@@ -803,6 +803,22 @@ describe(`OpenAPI ${version}`, () => {
       }),
       description: 'transforms an array',
     },
+    {
+      config: createConfig({
+        input: 'transformers-array-date-ref.json',
+        output: 'transformers-array-date-ref',
+        plugins: [
+          '@hey-api/client-fetch',
+          {
+            name: '@hey-api/sdk',
+            transformer: true,
+          },
+          '@hey-api/transformers',
+        ],
+      }),
+      description:
+        'transforms array of dates with $ref and collection endpoints',
+    },
     {
       config: createConfig({
         input: 'transformers-recursive.json',
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client.gen.ts
new file mode 100644
index 000000000..cab3c7019
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client.gen.ts
@@ -0,0 +1,16 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import { type ClientOptions, type Config, createClient, createConfig } from './client';
+import type { ClientOptions as ClientOptions2 } from './types.gen';
+
+/**
+ * The `createClientConfig()` function will be called on client initialization
+ * and the returned object will become the client's initial configuration.
+ *
+ * You may want to initialize your client this way instead of calling
+ * `setConfig()`. This is useful for example if you're using Next.js
+ * to ensure your client always has the correct values.
+ */
+export type CreateClientConfig<T extends ClientOptions = ClientOptions2> = (override?: Config<ClientOptions & T>) => Config<Required<ClientOptions> & T>;
+
+export const client = createClient(createConfig<ClientOptions2>());
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client/client.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client/client.gen.ts
new file mode 100644
index 000000000..a439d2748
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client/client.gen.ts
@@ -0,0 +1,268 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import { createSseClient } from '../core/serverSentEvents.gen';
+import type { HttpMethod } from '../core/types.gen';
+import { getValidRequestBody } from '../core/utils.gen';
+import type {
+  Client,
+  Config,
+  RequestOptions,
+  ResolvedRequestOptions,
+} from './types.gen';
+import {
+  buildUrl,
+  createConfig,
+  createInterceptors,
+  getParseAs,
+  mergeConfigs,
+  mergeHeaders,
+  setAuthParams,
+} from './utils.gen';
+
+type ReqInit = Omit<RequestInit, 'body' | 'headers'> & {
+  body?: any;
+  headers: ReturnType<typeof mergeHeaders>;
+};
+
+export const createClient = (config: Config = {}): Client => {
+  let _config = mergeConfigs(createConfig(), config);
+
+  const getConfig = (): Config => ({ ..._config });
+
+  const setConfig = (config: Config): Config => {
+    _config = mergeConfigs(_config, config);
+    return getConfig();
+  };
+
+  const interceptors = createInterceptors<
+    Request,
+    Response,
+    unknown,
+    ResolvedRequestOptions
+  >();
+
+  const beforeRequest = async (options: RequestOptions) => {
+    const opts = {
+      ..._config,
+      ...options,
+      fetch: options.fetch ?? _config.fetch ?? globalThis.fetch,
+      headers: mergeHeaders(_config.headers, options.headers),
+      serializedBody: undefined,
+    };
+
+    if (opts.security) {
+      await setAuthParams({
+        ...opts,
+        security: opts.security,
+      });
+    }
+
+    if (opts.requestValidator) {
+      await opts.requestValidator(opts);
+    }
+
+    if (opts.body !== undefined && opts.bodySerializer) {
+      opts.serializedBody = opts.bodySerializer(opts.body);
+    }
+
+    // remove Content-Type header if body is empty to avoid sending invalid requests
+    if (opts.body === undefined || opts.serializedBody === '') {
+      opts.headers.delete('Content-Type');
+    }
+
+    const url = buildUrl(opts);
+
+    return { opts, url };
+  };
+
+  const request: Client['request'] = async (options) => {
+    // @ts-expect-error
+    const { opts, url } = await beforeRequest(options);
+    const requestInit: ReqInit = {
+      redirect: 'follow',
+      ...opts,
+      body: getValidRequestBody(opts),
+    };
+
+    let request = new Request(url, requestInit);
+
+    for (const fn of interceptors.request.fns) {
+      if (fn) {
+        request = await fn(request, opts);
+      }
+    }
+
+    // fetch must be assigned here, otherwise it would throw the error:
+    // TypeError: Failed to execute 'fetch' on 'Window': Illegal invocation
+    const _fetch = opts.fetch!;
+    let response = await _fetch(request);
+
+    for (const fn of interceptors.response.fns) {
+      if (fn) {
+        response = await fn(response, request, opts);
+      }
+    }
+
+    const result = {
+      request,
+      response,
+    };
+
+    if (response.ok) {
+      const parseAs =
+        (opts.parseAs === 'auto'
+          ? getParseAs(response.headers.get('Content-Type'))
+          : opts.parseAs) ?? 'json';
+
+      if (
+        response.status === 204 ||
+        response.headers.get('Content-Length') === '0'
+      ) {
+        let emptyData: any;
+        switch (parseAs) {
+          case 'arrayBuffer':
+          case 'blob':
+          case 'text':
+            emptyData = await response[parseAs]();
+            break;
+          case 'formData':
+            emptyData = new FormData();
+            break;
+          case 'stream':
+            emptyData = response.body;
+            break;
+          case 'json':
+          default:
+            emptyData = {};
+            break;
+        }
+        return opts.responseStyle === 'data'
+          ? emptyData
+          : {
+              data: emptyData,
+              ...result,
+            };
+      }
+
+      let data: any;
+      switch (parseAs) {
+        case 'arrayBuffer':
+        case 'blob':
+        case 'formData':
+        case 'json':
+        case 'text':
+          data = await response[parseAs]();
+          break;
+        case 'stream':
+          return opts.responseStyle === 'data'
+            ? response.body
+            : {
+                data: response.body,
+                ...result,
+              };
+      }
+
+      if (parseAs === 'json') {
+        if (opts.responseValidator) {
+          await opts.responseValidator(data);
+        }
+
+        if (opts.responseTransformer) {
+          data = await opts.responseTransformer(data);
+        }
+      }
+
+      return opts.responseStyle === 'data'
+        ? data
+        : {
+            data,
+            ...result,
+          };
+    }
+
+    const textError = await response.text();
+    let jsonError: unknown;
+
+    try {
+      jsonError = JSON.parse(textError);
+    } catch {
+      // noop
+    }
+
+    const error = jsonError ?? textError;
+    let finalError = error;
+
+    for (const fn of interceptors.error.fns) {
+      if (fn) {
+        finalError = (await fn(error, response, request, opts)) as string;
+      }
+    }
+
+    finalError = finalError || ({} as string);
+
+    if (opts.throwOnError) {
+      throw finalError;
+    }
+
+    // TODO: we probably want to return error and improve types
+    return opts.responseStyle === 'data'
+      ? undefined
+      : {
+          error: finalError,
+          ...result,
+        };
+  };
+
+  const makeMethodFn =
+    (method: Uppercase<HttpMethod>) => (options: RequestOptions) =>
+      request({ ...options, method });
+
+  const makeSseFn =
+    (method: Uppercase<HttpMethod>) => async (options: RequestOptions) => {
+      const { opts, url } = await beforeRequest(options);
+      return createSseClient({
+        ...opts,
+        body: opts.body as BodyInit | null | undefined,
+        headers: opts.headers as unknown as Record<string, string>,
+        method,
+        onRequest: async (url, init) => {
+          let request = new Request(url, init);
+          for (const fn of interceptors.request.fns) {
+            if (fn) {
+              request = await fn(request, opts);
+            }
+          }
+          return request;
+        },
+        url,
+      });
+    };
+
+  return {
+    buildUrl,
+    connect: makeMethodFn('CONNECT'),
+    delete: makeMethodFn('DELETE'),
+    get: makeMethodFn('GET'),
+    getConfig,
+    head: makeMethodFn('HEAD'),
+    interceptors,
+    options: makeMethodFn('OPTIONS'),
+    patch: makeMethodFn('PATCH'),
+    post: makeMethodFn('POST'),
+    put: makeMethodFn('PUT'),
+    request,
+    setConfig,
+    sse: {
+      connect: makeSseFn('CONNECT'),
+      delete: makeSseFn('DELETE'),
+      get: makeSseFn('GET'),
+      head: makeSseFn('HEAD'),
+      options: makeSseFn('OPTIONS'),
+      patch: makeSseFn('PATCH'),
+      post: makeSseFn('POST'),
+      put: makeSseFn('PUT'),
+      trace: makeSseFn('TRACE'),
+    },
+    trace: makeMethodFn('TRACE'),
+  } as Client;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client/index.ts
new file mode 100644
index 000000000..cbf8dfeed
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client/index.ts
@@ -0,0 +1,26 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+export type { Auth } from '../core/auth.gen';
+export type { QuerySerializerOptions } from '../core/bodySerializer.gen';
+export {
+  formDataBodySerializer,
+  jsonBodySerializer,
+  urlSearchParamsBodySerializer,
+} from '../core/bodySerializer.gen';
+export { buildClientParams } from '../core/params.gen';
+export { serializeQueryKeyValue } from '../core/queryKeySerializer.gen';
+export { createClient } from './client.gen';
+export type {
+  Client,
+  ClientOptions,
+  Config,
+  CreateClientConfig,
+  Options,
+  OptionsLegacyParser,
+  RequestOptions,
+  RequestResult,
+  ResolvedRequestOptions,
+  ResponseStyle,
+  TDataShape,
+} from './types.gen';
+export { createConfig, mergeHeaders } from './utils.gen';
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client/types.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client/types.gen.ts
new file mode 100644
index 000000000..1a005b51e
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client/types.gen.ts
@@ -0,0 +1,268 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import type { Auth } from '../core/auth.gen';
+import type {
+  ServerSentEventsOptions,
+  ServerSentEventsResult,
+} from '../core/serverSentEvents.gen';
+import type {
+  Client as CoreClient,
+  Config as CoreConfig,
+} from '../core/types.gen';
+import type { Middleware } from './utils.gen';
+
+export type ResponseStyle = 'data' | 'fields';
+
+export interface Config<T extends ClientOptions = ClientOptions>
+  extends Omit<RequestInit, 'body' | 'headers' | 'method'>,
+    CoreConfig {
+  /**
+   * Base URL for all requests made by this client.
+   */
+  baseUrl?: T['baseUrl'];
+  /**
+   * Fetch API implementation. You can use this option to provide a custom
+   * fetch instance.
+   *
+   * @default globalThis.fetch
+   */
+  fetch?: typeof fetch;
+  /**
+   * Please don't use the Fetch client for Next.js applications. The `next`
+   * options won't have any effect.
+   *
+   * Install {@link https://www.npmjs.com/package/@hey-api/client-next `@hey-api/client-next`} instead.
+   */
+  next?: never;
+  /**
+   * Return the response data parsed in a specified format. By default, `auto`
+   * will infer the appropriate method from the `Content-Type` response header.
+   * You can override this behavior with any of the {@link Body} methods.
+   * Select `stream` if you don't want to parse response data at all.
+   *
+   * @default 'auto'
+   */
+  parseAs?:
+    | 'arrayBuffer'
+    | 'auto'
+    | 'blob'
+    | 'formData'
+    | 'json'
+    | 'stream'
+    | 'text';
+  /**
+   * Should we return only data or multiple fields (data, error, response, etc.)?
+   *
+   * @default 'fields'
+   */
+  responseStyle?: ResponseStyle;
+  /**
+   * Throw an error instead of returning it in the response?
+   *
+   * @default false
+   */
+  throwOnError?: T['throwOnError'];
+}
+
+export interface RequestOptions<
+  TData = unknown,
+  TResponseStyle extends ResponseStyle = 'fields',
+  ThrowOnError extends boolean = boolean,
+  Url extends string = string,
+> extends Config<{
+      responseStyle: TResponseStyle;
+      throwOnError: ThrowOnError;
+    }>,
+    Pick<
+      ServerSentEventsOptions<TData>,
+      | 'onSseError'
+      | 'onSseEvent'
+      | 'sseDefaultRetryDelay'
+      | 'sseMaxRetryAttempts'
+      | 'sseMaxRetryDelay'
+    > {
+  /**
+   * Any body that you want to add to your request.
+   *
+   * {@link https://developer.mozilla.org/docs/Web/API/fetch#body}
+   */
+  body?: unknown;
+  path?: Record<string, unknown>;
+  query?: Record<string, unknown>;
+  /**
+   * Security mechanism(s) to use for the request.
+   */
+  security?: ReadonlyArray<Auth>;
+  url: Url;
+}
+
+export interface ResolvedRequestOptions<
+  TResponseStyle extends ResponseStyle = 'fields',
+  ThrowOnError extends boolean = boolean,
+  Url extends string = string,
+> extends RequestOptions<unknown, TResponseStyle, ThrowOnError, Url> {
+  serializedBody?: string;
+}
+
+export type RequestResult<
+  TData = unknown,
+  TError = unknown,
+  ThrowOnError extends boolean = boolean,
+  TResponseStyle extends ResponseStyle = 'fields',
+> = ThrowOnError extends true
+  ? Promise<
+      TResponseStyle extends 'data'
+        ? TData extends Record<string, unknown>
+          ? TData[keyof TData]
+          : TData
+        : {
+            data: TData extends Record<string, unknown>
+              ? TData[keyof TData]
+              : TData;
+            request: Request;
+            response: Response;
+          }
+    >
+  : Promise<
+      TResponseStyle extends 'data'
+        ?
+            | (TData extends Record<string, unknown>
+                ? TData[keyof TData]
+                : TData)
+            | undefined
+        : (
+            | {
+                data: TData extends Record<string, unknown>
+                  ? TData[keyof TData]
+                  : TData;
+                error: undefined;
+              }
+            | {
+                data: undefined;
+                error: TError extends Record<string, unknown>
+                  ? TError[keyof TError]
+                  : TError;
+              }
+          ) & {
+            request: Request;
+            response: Response;
+          }
+    >;
+
+export interface ClientOptions {
+  baseUrl?: string;
+  responseStyle?: ResponseStyle;
+  throwOnError?: boolean;
+}
+
+type MethodFn = <
+  TData = unknown,
+  TError = unknown,
+  ThrowOnError extends boolean = false,
+  TResponseStyle extends ResponseStyle = 'fields',
+>(
+  options: Omit<RequestOptions<TData, TResponseStyle, ThrowOnError>, 'method'>,
+) => RequestResult<TData, TError, ThrowOnError, TResponseStyle>;
+
+type SseFn = <
+  TData = unknown,
+  TError = unknown,
+  ThrowOnError extends boolean = false,
+  TResponseStyle extends ResponseStyle = 'fields',
+>(
+  options: Omit<RequestOptions<TData, TResponseStyle, ThrowOnError>, 'method'>,
+) => Promise<ServerSentEventsResult<TData, TError>>;
+
+type RequestFn = <
+  TData = unknown,
+  TError = unknown,
+  ThrowOnError extends boolean = false,
+  TResponseStyle extends ResponseStyle = 'fields',
+>(
+  options: Omit<RequestOptions<TData, TResponseStyle, ThrowOnError>, 'method'> &
+    Pick<
+      Required<RequestOptions<TData, TResponseStyle, ThrowOnError>>,
+      'method'
+    >,
+) => RequestResult<TData, TError, ThrowOnError, TResponseStyle>;
+
+type BuildUrlFn = <
+  TData extends {
+    body?: unknown;
+    path?: Record<string, unknown>;
+    query?: Record<string, unknown>;
+    url: string;
+  },
+>(
+  options: Pick<TData, 'url'> & Options<TData>,
+) => string;
+
+export type Client = CoreClient<
+  RequestFn,
+  Config,
+  MethodFn,
+  BuildUrlFn,
+  SseFn
+> & {
+  interceptors: Middleware<Request, Response, unknown, ResolvedRequestOptions>;
+};
+
+/**
+ * The `createClientConfig()` function will be called on client initialization
+ * and the returned object will become the client's initial configuration.
+ *
+ * You may want to initialize your client this way instead of calling
+ * `setConfig()`. This is useful for example if you're using Next.js
+ * to ensure your client always has the correct values.
+ */
+export type CreateClientConfig<T extends ClientOptions = ClientOptions> = (
+  override?: Config<ClientOptions & T>,
+) => Config<Required<ClientOptions> & T>;
+
+export interface TDataShape {
+  body?: unknown;
+  headers?: unknown;
+  path?: unknown;
+  query?: unknown;
+  url: string;
+}
+
+type OmitKeys<T, K> = Pick<T, Exclude<keyof T, K>>;
+
+export type Options<
+  TData extends TDataShape = TDataShape,
+  ThrowOnError extends boolean = boolean,
+  TResponse = unknown,
+  TResponseStyle extends ResponseStyle = 'fields',
+> = OmitKeys<
+  RequestOptions<TResponse, TResponseStyle, ThrowOnError>,
+  'body' | 'path' | 'query' | 'url'
+> &
+  Omit<TData, 'url'>;
+
+export type OptionsLegacyParser<
+  TData = unknown,
+  ThrowOnError extends boolean = boolean,
+  TResponseStyle extends ResponseStyle = 'fields',
+> = TData extends { body?: any }
+  ? TData extends { headers?: any }
+    ? OmitKeys<
+        RequestOptions<unknown, TResponseStyle, ThrowOnError>,
+        'body' | 'headers' | 'url'
+      > &
+        TData
+    : OmitKeys<
+        RequestOptions<unknown, TResponseStyle, ThrowOnError>,
+        'body' | 'url'
+      > &
+        TData &
+        Pick<RequestOptions<unknown, TResponseStyle, ThrowOnError>, 'headers'>
+  : TData extends { headers?: any }
+    ? OmitKeys<
+        RequestOptions<unknown, TResponseStyle, ThrowOnError>,
+        'headers' | 'url'
+      > &
+        TData &
+        Pick<RequestOptions<unknown, TResponseStyle, ThrowOnError>, 'body'>
+    : OmitKeys<RequestOptions<unknown, TResponseStyle, ThrowOnError>, 'url'> &
+        TData;
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client/utils.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client/utils.gen.ts
new file mode 100644
index 000000000..4c48a9ee1
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/client/utils.gen.ts
@@ -0,0 +1,332 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import { getAuthToken } from '../core/auth.gen';
+import type { QuerySerializerOptions } from '../core/bodySerializer.gen';
+import { jsonBodySerializer } from '../core/bodySerializer.gen';
+import {
+  serializeArrayParam,
+  serializeObjectParam,
+  serializePrimitiveParam,
+} from '../core/pathSerializer.gen';
+import { getUrl } from '../core/utils.gen';
+import type { Client, ClientOptions, Config, RequestOptions } from './types.gen';
+
+export const createQuerySerializer = <T = unknown>({
+  parameters = {},
+  ...args
+}: QuerySerializerOptions = {}) => {
+  const querySerializer = (queryParams: T) => {
+    const search: string[] = [];
+    if (queryParams && typeof queryParams === 'object') {
+      for (const name in queryParams) {
+        const value = queryParams[name];
+
+        if (value === undefined || value === null) {
+          continue;
+        }
+
+        const options = parameters[name] || args;
+
+        if (Array.isArray(value)) {
+          const serializedArray = serializeArrayParam({
+            allowReserved: options.allowReserved,
+            explode: true,
+            name,
+            style: 'form',
+            value,
+            ...options.array,
+          });
+          if (serializedArray) search.push(serializedArray);
+        } else if (typeof value === 'object') {
+          const serializedObject = serializeObjectParam({
+            allowReserved: options.allowReserved,
+            explode: true,
+            name,
+            style: 'deepObject',
+            value: value as Record<string, unknown>,
+            ...options.object,
+          });
+          if (serializedObject) search.push(serializedObject);
+        } else {
+          const serializedPrimitive = serializePrimitiveParam({
+            allowReserved: options.allowReserved,
+            name,
+            value: value as string,
+          });
+          if (serializedPrimitive) search.push(serializedPrimitive);
+        }
+      }
+    }
+    return search.join('&');
+  };
+  return querySerializer;
+};
+
+/**
+ * Infers parseAs value from provided Content-Type header.
+ */
+export const getParseAs = (
+  contentType: string | null,
+): Exclude<Config['parseAs'], 'auto'> => {
+  if (!contentType) {
+    // If no Content-Type header is provided, the best we can do is return the raw response body,
+    // which is effectively the same as the 'stream' option.
+    return 'stream';
+  }
+
+  const cleanContent = contentType.split(';')[0]?.trim();
+
+  if (!cleanContent) {
+    return;
+  }
+
+  if (
+    cleanContent.startsWith('application/json') ||
+    cleanContent.endsWith('+json')
+  ) {
+    return 'json';
+  }
+
+  if (cleanContent === 'multipart/form-data') {
+    return 'formData';
+  }
+
+  if (
+    ['application/', 'audio/', 'image/', 'video/'].some((type) =>
+      cleanContent.startsWith(type),
+    )
+  ) {
+    return 'blob';
+  }
+
+  if (cleanContent.startsWith('text/')) {
+    return 'text';
+  }
+
+  return;
+};
+
+const checkForExistence = (
+  options: Pick<RequestOptions, 'auth' | 'query'> & {
+    headers: Headers;
+  },
+  name?: string,
+): boolean => {
+  if (!name) {
+    return false;
+  }
+  if (
+    options.headers.has(name) ||
+    options.query?.[name] ||
+    options.headers.get('Cookie')?.includes(`${name}=`)
+  ) {
+    return true;
+  }
+  return false;
+};
+
+export const setAuthParams = async ({
+  security,
+  ...options
+}: Pick<Required<RequestOptions>, 'security'> &
+  Pick<RequestOptions, 'auth' | 'query'> & {
+    headers: Headers;
+  }) => {
+  for (const auth of security) {
+    if (checkForExistence(options, auth.name)) {
+      continue;
+    }
+
+    const token = await getAuthToken(auth, options.auth);
+
+    if (!token) {
+      continue;
+    }
+
+    const name = auth.name ?? 'Authorization';
+
+    switch (auth.in) {
+      case 'query':
+        if (!options.query) {
+          options.query = {};
+        }
+        options.query[name] = token;
+        break;
+      case 'cookie':
+        options.headers.append('Cookie', `${name}=${token}`);
+        break;
+      case 'header':
+      default:
+        options.headers.set(name, token);
+        break;
+    }
+  }
+};
+
+export const buildUrl: Client['buildUrl'] = (options) =>
+  getUrl({
+    baseUrl: options.baseUrl as string,
+    path: options.path,
+    query: options.query,
+    querySerializer:
+      typeof options.querySerializer === 'function'
+        ? options.querySerializer
+        : createQuerySerializer(options.querySerializer),
+    url: options.url,
+  });
+
+export const mergeConfigs = (a: Config, b: Config): Config => {
+  const config = { ...a, ...b };
+  if (config.baseUrl?.endsWith('/')) {
+    config.baseUrl = config.baseUrl.substring(0, config.baseUrl.length - 1);
+  }
+  config.headers = mergeHeaders(a.headers, b.headers);
+  return config;
+};
+
+const headersEntries = (headers: Headers): Array<[string, string]> => {
+  const entries: Array<[string, string]> = [];
+  headers.forEach((value, key) => {
+    entries.push([key, value]);
+  });
+  return entries;
+};
+
+export const mergeHeaders = (
+  ...headers: Array<Required<Config>['headers'] | undefined>
+): Headers => {
+  const mergedHeaders = new Headers();
+  for (const header of headers) {
+    if (!header) {
+      continue;
+    }
+
+    const iterator =
+      header instanceof Headers
+        ? headersEntries(header)
+        : Object.entries(header);
+
+    for (const [key, value] of iterator) {
+      if (value === null) {
+        mergedHeaders.delete(key);
+      } else if (Array.isArray(value)) {
+        for (const v of value) {
+          mergedHeaders.append(key, v as string);
+        }
+      } else if (value !== undefined) {
+        // assume object headers are meant to be JSON stringified, i.e. their
+        // content value in OpenAPI specification is 'application/json'
+        mergedHeaders.set(
+          key,
+          typeof value === 'object' ? JSON.stringify(value) : (value as string),
+        );
+      }
+    }
+  }
+  return mergedHeaders;
+};
+
+type ErrInterceptor<Err, Res, Req, Options> = (
+  error: Err,
+  response: Res,
+  request: Req,
+  options: Options,
+) => Err | Promise<Err>;
+
+type ReqInterceptor<Req, Options> = (
+  request: Req,
+  options: Options,
+) => Req | Promise<Req>;
+
+type ResInterceptor<Res, Req, Options> = (
+  response: Res,
+  request: Req,
+  options: Options,
+) => Res | Promise<Res>;
+
+class Interceptors<Interceptor> {
+  fns: Array<Interceptor | null> = [];
+
+  clear(): void {
+    this.fns = [];
+  }
+
+  eject(id: number | Interceptor): void {
+    const index = this.getInterceptorIndex(id);
+    if (this.fns[index]) {
+      this.fns[index] = null;
+    }
+  }
+
+  exists(id: number | Interceptor): boolean {
+    const index = this.getInterceptorIndex(id);
+    return Boolean(this.fns[index]);
+  }
+
+  getInterceptorIndex(id: number | Interceptor): number {
+    if (typeof id === 'number') {
+      return this.fns[id] ? id : -1;
+    }
+    return this.fns.indexOf(id);
+  }
+
+  update(
+    id: number | Interceptor,
+    fn: Interceptor,
+  ): number | Interceptor | false {
+    const index = this.getInterceptorIndex(id);
+    if (this.fns[index]) {
+      this.fns[index] = fn;
+      return id;
+    }
+    return false;
+  }
+
+  use(fn: Interceptor): number {
+    this.fns.push(fn);
+    return this.fns.length - 1;
+  }
+}
+
+export interface Middleware<Req, Res, Err, Options> {
+  error: Interceptors<ErrInterceptor<Err, Res, Req, Options>>;
+  request: Interceptors<ReqInterceptor<Req, Options>>;
+  response: Interceptors<ResInterceptor<Res, Req, Options>>;
+}
+
+export const createInterceptors = <Req, Res, Err, Options>(): Middleware<
+  Req,
+  Res,
+  Err,
+  Options
+> => ({
+  error: new Interceptors<ErrInterceptor<Err, Res, Req, Options>>(),
+  request: new Interceptors<ReqInterceptor<Req, Options>>(),
+  response: new Interceptors<ResInterceptor<Res, Req, Options>>(),
+});
+
+const defaultQuerySerializer = createQuerySerializer({
+  allowReserved: false,
+  array: {
+    explode: true,
+    style: 'form',
+  },
+  object: {
+    explode: true,
+    style: 'deepObject',
+  },
+});
+
+const defaultHeaders = {
+  'Content-Type': 'application/json',
+};
+
+export const createConfig = <T extends ClientOptions = ClientOptions>(
+  override: Config<Omit<ClientOptions, keyof T> & T> = {},
+): Config<Omit<ClientOptions, keyof T> & T> => ({
+  ...jsonBodySerializer,
+  headers: defaultHeaders,
+  parseAs: 'auto',
+  querySerializer: defaultQuerySerializer,
+  ...override,
+});
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/auth.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/auth.gen.ts
new file mode 100644
index 000000000..f8a73266f
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/auth.gen.ts
@@ -0,0 +1,42 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+export type AuthToken = string | undefined;
+
+export interface Auth {
+  /**
+   * Which part of the request do we use to send the auth?
+   *
+   * @default 'header'
+   */
+  in?: 'header' | 'query' | 'cookie';
+  /**
+   * Header or query parameter name.
+   *
+   * @default 'Authorization'
+   */
+  name?: string;
+  scheme?: 'basic' | 'bearer';
+  type: 'apiKey' | 'http';
+}
+
+export const getAuthToken = async (
+  auth: Auth,
+  callback: ((auth: Auth) => Promise<AuthToken> | AuthToken) | AuthToken,
+): Promise<string | undefined> => {
+  const token =
+    typeof callback === 'function' ? await callback(auth) : callback;
+
+  if (!token) {
+    return;
+  }
+
+  if (auth.scheme === 'bearer') {
+    return `Bearer ${token}`;
+  }
+
+  if (auth.scheme === 'basic') {
+    return `Basic ${btoa(token)}`;
+  }
+
+  return token;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/bodySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/bodySerializer.gen.ts
new file mode 100644
index 000000000..552b50f7c
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/bodySerializer.gen.ts
@@ -0,0 +1,100 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import type {
+  ArrayStyle,
+  ObjectStyle,
+  SerializerOptions,
+} from './pathSerializer.gen';
+
+export type QuerySerializer = (query: Record<string, unknown>) => string;
+
+export type BodySerializer = (body: any) => any;
+
+type QuerySerializerOptionsObject = {
+  allowReserved?: boolean;
+  array?: Partial<SerializerOptions<ArrayStyle>>;
+  object?: Partial<SerializerOptions<ObjectStyle>>;
+};
+
+export type QuerySerializerOptions = QuerySerializerOptionsObject & {
+  /**
+   * Per-parameter serialization overrides. When provided, these settings
+   * override the global array/object settings for specific parameter names.
+   */
+  parameters?: Record<string, QuerySerializerOptionsObject>;
+};
+
+const serializeFormDataPair = (
+  data: FormData,
+  key: string,
+  value: unknown,
+): void => {
+  if (typeof value === 'string' || value instanceof Blob) {
+    data.append(key, value);
+  } else if (value instanceof Date) {
+    data.append(key, value.toISOString());
+  } else {
+    data.append(key, JSON.stringify(value));
+  }
+};
+
+const serializeUrlSearchParamsPair = (
+  data: URLSearchParams,
+  key: string,
+  value: unknown,
+): void => {
+  if (typeof value === 'string') {
+    data.append(key, value);
+  } else {
+    data.append(key, JSON.stringify(value));
+  }
+};
+
+export const formDataBodySerializer = {
+  bodySerializer: <T extends Record<string, any> | Array<Record<string, any>>>(
+    body: T,
+  ): FormData => {
+    const data = new FormData();
+
+    Object.entries(body).forEach(([key, value]) => {
+      if (value === undefined || value === null) {
+        return;
+      }
+      if (Array.isArray(value)) {
+        value.forEach((v) => serializeFormDataPair(data, key, v));
+      } else {
+        serializeFormDataPair(data, key, value);
+      }
+    });
+
+    return data;
+  },
+};
+
+export const jsonBodySerializer = {
+  bodySerializer: <T>(body: T): string =>
+    JSON.stringify(body, (_key, value) =>
+      typeof value === 'bigint' ? value.toString() : value,
+    ),
+};
+
+export const urlSearchParamsBodySerializer = {
+  bodySerializer: <T extends Record<string, any> | Array<Record<string, any>>>(
+    body: T,
+  ): string => {
+    const data = new URLSearchParams();
+
+    Object.entries(body).forEach(([key, value]) => {
+      if (value === undefined || value === null) {
+        return;
+      }
+      if (Array.isArray(value)) {
+        value.forEach((v) => serializeUrlSearchParamsPair(data, key, v));
+      } else {
+        serializeUrlSearchParamsPair(data, key, value);
+      }
+    });
+
+    return data.toString();
+  },
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/params.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/params.gen.ts
new file mode 100644
index 000000000..71c88e852
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/params.gen.ts
@@ -0,0 +1,153 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+type Slot = 'body' | 'headers' | 'path' | 'query';
+
+export type Field =
+  | {
+      in: Exclude<Slot, 'body'>;
+      /**
+       * Field name. This is the name we want the user to see and use.
+       */
+      key: string;
+      /**
+       * Field mapped name. This is the name we want to use in the request.
+       * If omitted, we use the same value as `key`.
+       */
+      map?: string;
+    }
+  | {
+      in: Extract<Slot, 'body'>;
+      /**
+       * Key isn't required for bodies.
+       */
+      key?: string;
+      map?: string;
+    };
+
+export interface Fields {
+  allowExtra?: Partial<Record<Slot, boolean>>;
+  args?: ReadonlyArray<Field>;
+}
+
+export type FieldsConfig = ReadonlyArray<Field | Fields>;
+
+const extraPrefixesMap: Record<string, Slot> = {
+  $body_: 'body',
+  $headers_: 'headers',
+  $path_: 'path',
+  $query_: 'query',
+};
+const extraPrefixes = Object.entries(extraPrefixesMap);
+
+type KeyMap = Map<
+  string,
+  {
+    in: Slot;
+    map?: string;
+  }
+>;
+
+const buildKeyMap = (fields: FieldsConfig, map?: KeyMap): KeyMap => {
+  if (!map) {
+    map = new Map();
+  }
+
+  for (const config of fields) {
+    if ('in' in config) {
+      if (config.key) {
+        map.set(config.key, {
+          in: config.in,
+          map: config.map,
+        });
+      }
+    } else if (config.args) {
+      buildKeyMap(config.args, map);
+    }
+  }
+
+  return map;
+};
+
+interface Params {
+  body: unknown;
+  headers: Record<string, unknown>;
+  path: Record<string, unknown>;
+  query: Record<string, unknown>;
+}
+
+const stripEmptySlots = (params: Params) => {
+  for (const [slot, value] of Object.entries(params)) {
+    if (value && typeof value === 'object' && !Object.keys(value).length) {
+      delete params[slot as Slot];
+    }
+  }
+};
+
+export const buildClientParams = (
+  args: ReadonlyArray<unknown>,
+  fields: FieldsConfig,
+) => {
+  const params: Params = {
+    body: {},
+    headers: {},
+    path: {},
+    query: {},
+  };
+
+  const map = buildKeyMap(fields);
+
+  let config: FieldsConfig[number] | undefined;
+
+  for (const [index, arg] of args.entries()) {
+    if (fields[index]) {
+      config = fields[index];
+    }
+
+    if (!config) {
+      continue;
+    }
+
+    if ('in' in config) {
+      if (config.key) {
+        const field = map.get(config.key)!;
+        const name = field.map || config.key;
+        (params[field.in] as Record<string, unknown>)[name] = arg;
+      } else {
+        params.body = arg;
+      }
+    } else {
+      for (const [key, value] of Object.entries(arg ?? {})) {
+        const field = map.get(key);
+
+        if (field) {
+          const name = field.map || key;
+          (params[field.in] as Record<string, unknown>)[name] = value;
+        } else {
+          const extra = extraPrefixes.find(([prefix]) =>
+            key.startsWith(prefix),
+          );
+
+          if (extra) {
+            const [prefix, slot] = extra;
+            (params[slot] as Record<string, unknown>)[
+              key.slice(prefix.length)
+            ] = value;
+          } else {
+            for (const [slot, allowed] of Object.entries(
+              config.allowExtra ?? {},
+            )) {
+              if (allowed) {
+                (params[slot as Slot] as Record<string, unknown>)[key] = value;
+                break;
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+
+  stripEmptySlots(params);
+
+  return params;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/pathSerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/pathSerializer.gen.ts
new file mode 100644
index 000000000..8d9993104
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/pathSerializer.gen.ts
@@ -0,0 +1,181 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+interface SerializeOptions<T>
+  extends SerializePrimitiveOptions,
+    SerializerOptions<T> {}
+
+interface SerializePrimitiveOptions {
+  allowReserved?: boolean;
+  name: string;
+}
+
+export interface SerializerOptions<T> {
+  /**
+   * @default true
+   */
+  explode: boolean;
+  style: T;
+}
+
+export type ArrayStyle = 'form' | 'spaceDelimited' | 'pipeDelimited';
+export type ArraySeparatorStyle = ArrayStyle | MatrixStyle;
+type MatrixStyle = 'label' | 'matrix' | 'simple';
+export type ObjectStyle = 'form' | 'deepObject';
+type ObjectSeparatorStyle = ObjectStyle | MatrixStyle;
+
+interface SerializePrimitiveParam extends SerializePrimitiveOptions {
+  value: string;
+}
+
+export const separatorArrayExplode = (style: ArraySeparatorStyle) => {
+  switch (style) {
+    case 'label':
+      return '.';
+    case 'matrix':
+      return ';';
+    case 'simple':
+      return ',';
+    default:
+      return '&';
+  }
+};
+
+export const separatorArrayNoExplode = (style: ArraySeparatorStyle) => {
+  switch (style) {
+    case 'form':
+      return ',';
+    case 'pipeDelimited':
+      return '|';
+    case 'spaceDelimited':
+      return '%20';
+    default:
+      return ',';
+  }
+};
+
+export const separatorObjectExplode = (style: ObjectSeparatorStyle) => {
+  switch (style) {
+    case 'label':
+      return '.';
+    case 'matrix':
+      return ';';
+    case 'simple':
+      return ',';
+    default:
+      return '&';
+  }
+};
+
+export const serializeArrayParam = ({
+  allowReserved,
+  explode,
+  name,
+  style,
+  value,
+}: SerializeOptions<ArraySeparatorStyle> & {
+  value: unknown[];
+}) => {
+  if (!explode) {
+    const joinedValues = (
+      allowReserved ? value : value.map((v) => encodeURIComponent(v as string))
+    ).join(separatorArrayNoExplode(style));
+    switch (style) {
+      case 'label':
+        return `.${joinedValues}`;
+      case 'matrix':
+        return `;${name}=${joinedValues}`;
+      case 'simple':
+        return joinedValues;
+      default:
+        return `${name}=${joinedValues}`;
+    }
+  }
+
+  const separator = separatorArrayExplode(style);
+  const joinedValues = value
+    .map((v) => {
+      if (style === 'label' || style === 'simple') {
+        return allowReserved ? v : encodeURIComponent(v as string);
+      }
+
+      return serializePrimitiveParam({
+        allowReserved,
+        name,
+        value: v as string,
+      });
+    })
+    .join(separator);
+  return style === 'label' || style === 'matrix'
+    ? separator + joinedValues
+    : joinedValues;
+};
+
+export const serializePrimitiveParam = ({
+  allowReserved,
+  name,
+  value,
+}: SerializePrimitiveParam) => {
+  if (value === undefined || value === null) {
+    return '';
+  }
+
+  if (typeof value === 'object') {
+    throw new Error(
+      'Deeply-nested arrays/objects aren’t supported. Provide your own `querySerializer()` to handle these.',
+    );
+  }
+
+  return `${name}=${allowReserved ? value : encodeURIComponent(value)}`;
+};
+
+export const serializeObjectParam = ({
+  allowReserved,
+  explode,
+  name,
+  style,
+  value,
+  valueOnly,
+}: SerializeOptions<ObjectSeparatorStyle> & {
+  value: Record<string, unknown> | Date;
+  valueOnly?: boolean;
+}) => {
+  if (value instanceof Date) {
+    return valueOnly ? value.toISOString() : `${name}=${value.toISOString()}`;
+  }
+
+  if (style !== 'deepObject' && !explode) {
+    let values: string[] = [];
+    Object.entries(value).forEach(([key, v]) => {
+      values = [
+        ...values,
+        key,
+        allowReserved ? (v as string) : encodeURIComponent(v as string),
+      ];
+    });
+    const joinedValues = values.join(',');
+    switch (style) {
+      case 'form':
+        return `${name}=${joinedValues}`;
+      case 'label':
+        return `.${joinedValues}`;
+      case 'matrix':
+        return `;${name}=${joinedValues}`;
+      default:
+        return joinedValues;
+    }
+  }
+
+  const separator = separatorObjectExplode(style);
+  const joinedValues = Object.entries(value)
+    .map(([key, v]) =>
+      serializePrimitiveParam({
+        allowReserved,
+        name: style === 'deepObject' ? `${name}[${key}]` : key,
+        value: v as string,
+      }),
+    )
+    .join(separator);
+  return style === 'label' || style === 'matrix'
+    ? separator + joinedValues
+    : joinedValues;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/queryKeySerializer.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/queryKeySerializer.gen.ts
new file mode 100644
index 000000000..d3bb68396
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/queryKeySerializer.gen.ts
@@ -0,0 +1,136 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+/**
+ * JSON-friendly union that mirrors what Pinia Colada can hash.
+ */
+export type JsonValue =
+  | null
+  | string
+  | number
+  | boolean
+  | JsonValue[]
+  | { [key: string]: JsonValue };
+
+/**
+ * Replacer that converts non-JSON values (bigint, Date, etc.) to safe substitutes.
+ */
+export const queryKeyJsonReplacer = (_key: string, value: unknown) => {
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+  return value;
+};
+
+/**
+ * Safely stringifies a value and parses it back into a JsonValue.
+ */
+export const stringifyToJsonValue = (input: unknown): JsonValue | undefined => {
+  try {
+    const json = JSON.stringify(input, queryKeyJsonReplacer);
+    if (json === undefined) {
+      return undefined;
+    }
+    return JSON.parse(json) as JsonValue;
+  } catch {
+    return undefined;
+  }
+};
+
+/**
+ * Detects plain objects (including objects with a null prototype).
+ */
+const isPlainObject = (value: unknown): value is Record<string, unknown> => {
+  if (value === null || typeof value !== 'object') {
+    return false;
+  }
+  const prototype = Object.getPrototypeOf(value as object);
+  return prototype === Object.prototype || prototype === null;
+};
+
+/**
+ * Turns URLSearchParams into a sorted JSON object for deterministic keys.
+ */
+const serializeSearchParams = (params: URLSearchParams): JsonValue => {
+  const entries = Array.from(params.entries()).sort(([a], [b]) =>
+    a.localeCompare(b),
+  );
+  const result: Record<string, JsonValue> = {};
+
+  for (const [key, value] of entries) {
+    const existing = result[key];
+    if (existing === undefined) {
+      result[key] = value;
+      continue;
+    }
+
+    if (Array.isArray(existing)) {
+      (existing as string[]).push(value);
+    } else {
+      result[key] = [existing, value];
+    }
+  }
+
+  return result;
+};
+
+/**
+ * Normalizes any accepted value into a JSON-friendly shape for query keys.
+ */
+export const serializeQueryKeyValue = (
+  value: unknown,
+): JsonValue | undefined => {
+  if (value === null) {
+    return null;
+  }
+
+  if (
+    typeof value === 'string' ||
+    typeof value === 'number' ||
+    typeof value === 'boolean'
+  ) {
+    return value;
+  }
+
+  if (
+    value === undefined ||
+    typeof value === 'function' ||
+    typeof value === 'symbol'
+  ) {
+    return undefined;
+  }
+
+  if (typeof value === 'bigint') {
+    return value.toString();
+  }
+
+  if (value instanceof Date) {
+    return value.toISOString();
+  }
+
+  if (Array.isArray(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  if (
+    typeof URLSearchParams !== 'undefined' &&
+    value instanceof URLSearchParams
+  ) {
+    return serializeSearchParams(value);
+  }
+
+  if (isPlainObject(value)) {
+    return stringifyToJsonValue(value);
+  }
+
+  return undefined;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/serverSentEvents.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/serverSentEvents.gen.ts
new file mode 100644
index 000000000..f8fd78e28
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/serverSentEvents.gen.ts
@@ -0,0 +1,264 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import type { Config } from './types.gen';
+
+export type ServerSentEventsOptions<TData = unknown> = Omit<
+  RequestInit,
+  'method'
+> &
+  Pick<Config, 'method' | 'responseTransformer' | 'responseValidator'> & {
+    /**
+     * Fetch API implementation. You can use this option to provide a custom
+     * fetch instance.
+     *
+     * @default globalThis.fetch
+     */
+    fetch?: typeof fetch;
+    /**
+     * Implementing clients can call request interceptors inside this hook.
+     */
+    onRequest?: (url: string, init: RequestInit) => Promise<Request>;
+    /**
+     * Callback invoked when a network or parsing error occurs during streaming.
+     *
+     * This option applies only if the endpoint returns a stream of events.
+     *
+     * @param error The error that occurred.
+     */
+    onSseError?: (error: unknown) => void;
+    /**
+     * Callback invoked when an event is streamed from the server.
+     *
+     * This option applies only if the endpoint returns a stream of events.
+     *
+     * @param event Event streamed from the server.
+     * @returns Nothing (void).
+     */
+    onSseEvent?: (event: StreamEvent<TData>) => void;
+    serializedBody?: RequestInit['body'];
+    /**
+     * Default retry delay in milliseconds.
+     *
+     * This option applies only if the endpoint returns a stream of events.
+     *
+     * @default 3000
+     */
+    sseDefaultRetryDelay?: number;
+    /**
+     * Maximum number of retry attempts before giving up.
+     */
+    sseMaxRetryAttempts?: number;
+    /**
+     * Maximum retry delay in milliseconds.
+     *
+     * Applies only when exponential backoff is used.
+     *
+     * This option applies only if the endpoint returns a stream of events.
+     *
+     * @default 30000
+     */
+    sseMaxRetryDelay?: number;
+    /**
+     * Optional sleep function for retry backoff.
+     *
+     * Defaults to using `setTimeout`.
+     */
+    sseSleepFn?: (ms: number) => Promise<void>;
+    url: string;
+  };
+
+export interface StreamEvent<TData = unknown> {
+  data: TData;
+  event?: string;
+  id?: string;
+  retry?: number;
+}
+
+export type ServerSentEventsResult<
+  TData = unknown,
+  TReturn = void,
+  TNext = unknown,
+> = {
+  stream: AsyncGenerator<
+    TData extends Record<string, unknown> ? TData[keyof TData] : TData,
+    TReturn,
+    TNext
+  >;
+};
+
+export const createSseClient = <TData = unknown>({
+  onRequest,
+  onSseError,
+  onSseEvent,
+  responseTransformer,
+  responseValidator,
+  sseDefaultRetryDelay,
+  sseMaxRetryAttempts,
+  sseMaxRetryDelay,
+  sseSleepFn,
+  url,
+  ...options
+}: ServerSentEventsOptions): ServerSentEventsResult<TData> => {
+  let lastEventId: string | undefined;
+
+  const sleep =
+    sseSleepFn ??
+    ((ms: number) => new Promise((resolve) => setTimeout(resolve, ms)));
+
+  const createStream = async function* () {
+    let retryDelay: number = sseDefaultRetryDelay ?? 3000;
+    let attempt = 0;
+    const signal = options.signal ?? new AbortController().signal;
+
+    while (true) {
+      if (signal.aborted) break;
+
+      attempt++;
+
+      const headers =
+        options.headers instanceof Headers
+          ? options.headers
+          : new Headers(options.headers as Record<string, string> | undefined);
+
+      if (lastEventId !== undefined) {
+        headers.set('Last-Event-ID', lastEventId);
+      }
+
+      try {
+        const requestInit: RequestInit = {
+          redirect: 'follow',
+          ...options,
+          body: options.serializedBody,
+          headers,
+          signal,
+        };
+        let request = new Request(url, requestInit);
+        if (onRequest) {
+          request = await onRequest(url, requestInit);
+        }
+        // fetch must be assigned here, otherwise it would throw the error:
+        // TypeError: Failed to execute 'fetch' on 'Window': Illegal invocation
+        const _fetch = options.fetch ?? globalThis.fetch;
+        const response = await _fetch(request);
+
+        if (!response.ok)
+          throw new Error(
+            `SSE failed: ${response.status} ${response.statusText}`,
+          );
+
+        if (!response.body) throw new Error('No body in SSE response');
+
+        const reader = response.body
+          .pipeThrough(new TextDecoderStream())
+          .getReader();
+
+        let buffer = '';
+
+        const abortHandler = () => {
+          try {
+            reader.cancel();
+          } catch {
+            // noop
+          }
+        };
+
+        signal.addEventListener('abort', abortHandler);
+
+        try {
+          while (true) {
+            const { done, value } = await reader.read();
+            if (done) break;
+            buffer += value;
+
+            const chunks = buffer.split('\n\n');
+            buffer = chunks.pop() ?? '';
+
+            for (const chunk of chunks) {
+              const lines = chunk.split('\n');
+              const dataLines: Array<string> = [];
+              let eventName: string | undefined;
+
+              for (const line of lines) {
+                if (line.startsWith('data:')) {
+                  dataLines.push(line.replace(/^data:\s*/, ''));
+                } else if (line.startsWith('event:')) {
+                  eventName = line.replace(/^event:\s*/, '');
+                } else if (line.startsWith('id:')) {
+                  lastEventId = line.replace(/^id:\s*/, '');
+                } else if (line.startsWith('retry:')) {
+                  const parsed = Number.parseInt(
+                    line.replace(/^retry:\s*/, ''),
+                    10,
+                  );
+                  if (!Number.isNaN(parsed)) {
+                    retryDelay = parsed;
+                  }
+                }
+              }
+
+              let data: unknown;
+              let parsedJson = false;
+
+              if (dataLines.length) {
+                const rawData = dataLines.join('\n');
+                try {
+                  data = JSON.parse(rawData);
+                  parsedJson = true;
+                } catch {
+                  data = rawData;
+                }
+              }
+
+              if (parsedJson) {
+                if (responseValidator) {
+                  await responseValidator(data);
+                }
+
+                if (responseTransformer) {
+                  data = await responseTransformer(data);
+                }
+              }
+
+              onSseEvent?.({
+                data,
+                event: eventName,
+                id: lastEventId,
+                retry: retryDelay,
+              });
+
+              if (dataLines.length) {
+                yield data as any;
+              }
+            }
+          }
+        } finally {
+          signal.removeEventListener('abort', abortHandler);
+          reader.releaseLock();
+        }
+
+        break; // exit loop on normal completion
+      } catch (error) {
+        // connection failed or aborted; retry after delay
+        onSseError?.(error);
+
+        if (
+          sseMaxRetryAttempts !== undefined &&
+          attempt >= sseMaxRetryAttempts
+        ) {
+          break; // stop after firing error
+        }
+
+        // exponential backoff: double retry each attempt, cap at 30s
+        const backoff = Math.min(
+          retryDelay * 2 ** (attempt - 1),
+          sseMaxRetryDelay ?? 30000,
+        );
+        await sleep(backoff);
+      }
+    }
+  };
+
+  const stream = createStream();
+
+  return { stream };
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/types.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/types.gen.ts
new file mode 100644
index 000000000..643c070c9
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/types.gen.ts
@@ -0,0 +1,118 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import type { Auth, AuthToken } from './auth.gen';
+import type {
+  BodySerializer,
+  QuerySerializer,
+  QuerySerializerOptions,
+} from './bodySerializer.gen';
+
+export type HttpMethod =
+  | 'connect'
+  | 'delete'
+  | 'get'
+  | 'head'
+  | 'options'
+  | 'patch'
+  | 'post'
+  | 'put'
+  | 'trace';
+
+export type Client<
+  RequestFn = never,
+  Config = unknown,
+  MethodFn = never,
+  BuildUrlFn = never,
+  SseFn = never,
+> = {
+  /**
+   * Returns the final request URL.
+   */
+  buildUrl: BuildUrlFn;
+  getConfig: () => Config;
+  request: RequestFn;
+  setConfig: (config: Config) => Config;
+} & {
+  [K in HttpMethod]: MethodFn;
+} & ([SseFn] extends [never]
+    ? { sse?: never }
+    : { sse: { [K in HttpMethod]: SseFn } });
+
+export interface Config {
+  /**
+   * Auth token or a function returning auth token. The resolved value will be
+   * added to the request payload as defined by its `security` array.
+   */
+  auth?: ((auth: Auth) => Promise<AuthToken> | AuthToken) | AuthToken;
+  /**
+   * A function for serializing request body parameter. By default,
+   * {@link JSON.stringify()} will be used.
+   */
+  bodySerializer?: BodySerializer | null;
+  /**
+   * An object containing any HTTP headers that you want to pre-populate your
+   * `Headers` object with.
+   *
+   * {@link https://developer.mozilla.org/docs/Web/API/Headers/Headers#init See more}
+   */
+  headers?:
+    | RequestInit['headers']
+    | Record<
+        string,
+        | string
+        | number
+        | boolean
+        | (string | number | boolean)[]
+        | null
+        | undefined
+        | unknown
+      >;
+  /**
+   * The request method.
+   *
+   * {@link https://developer.mozilla.org/docs/Web/API/fetch#method See more}
+   */
+  method?: Uppercase<HttpMethod>;
+  /**
+   * A function for serializing request query parameters. By default, arrays
+   * will be exploded in form style, objects will be exploded in deepObject
+   * style, and reserved characters are percent-encoded.
+   *
+   * This method will have no effect if the native `paramsSerializer()` Axios
+   * API function is used.
+   *
+   * {@link https://swagger.io/docs/specification/serialization/#query View examples}
+   */
+  querySerializer?: QuerySerializer | QuerySerializerOptions;
+  /**
+   * A function validating request data. This is useful if you want to ensure
+   * the request conforms to the desired shape, so it can be safely sent to
+   * the server.
+   */
+  requestValidator?: (data: unknown) => Promise<unknown>;
+  /**
+   * A function transforming response data before it's returned. This is useful
+   * for post-processing data, e.g. converting ISO strings into Date objects.
+   */
+  responseTransformer?: (data: unknown) => Promise<unknown>;
+  /**
+   * A function validating response data. This is useful if you want to ensure
+   * the response conforms to the desired shape, so it can be safely passed to
+   * the transformers and returned to the user.
+   */
+  responseValidator?: (data: unknown) => Promise<unknown>;
+}
+
+type IsExactlyNeverOrNeverUndefined<T> = [T] extends [never]
+  ? true
+  : [T] extends [never | undefined]
+    ? [undefined] extends [T]
+      ? false
+      : true
+    : false;
+
+export type OmitNever<T extends Record<string, unknown>> = {
+  [K in keyof T as IsExactlyNeverOrNeverUndefined<T[K]> extends true
+    ? never
+    : K]: T[K];
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/utils.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/utils.gen.ts
new file mode 100644
index 000000000..0b5389d08
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/core/utils.gen.ts
@@ -0,0 +1,143 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import type { BodySerializer, QuerySerializer } from './bodySerializer.gen';
+import {
+  type ArraySeparatorStyle,
+  serializeArrayParam,
+  serializeObjectParam,
+  serializePrimitiveParam,
+} from './pathSerializer.gen';
+
+export interface PathSerializer {
+  path: Record<string, unknown>;
+  url: string;
+}
+
+export const PATH_PARAM_RE = /\{[^{}]+\}/g;
+
+export const defaultPathSerializer = ({ path, url: _url }: PathSerializer) => {
+  let url = _url;
+  const matches = _url.match(PATH_PARAM_RE);
+  if (matches) {
+    for (const match of matches) {
+      let explode = false;
+      let name = match.substring(1, match.length - 1);
+      let style: ArraySeparatorStyle = 'simple';
+
+      if (name.endsWith('*')) {
+        explode = true;
+        name = name.substring(0, name.length - 1);
+      }
+
+      if (name.startsWith('.')) {
+        name = name.substring(1);
+        style = 'label';
+      } else if (name.startsWith(';')) {
+        name = name.substring(1);
+        style = 'matrix';
+      }
+
+      const value = path[name];
+
+      if (value === undefined || value === null) {
+        continue;
+      }
+
+      if (Array.isArray(value)) {
+        url = url.replace(
+          match,
+          serializeArrayParam({ explode, name, style, value }),
+        );
+        continue;
+      }
+
+      if (typeof value === 'object') {
+        url = url.replace(
+          match,
+          serializeObjectParam({
+            explode,
+            name,
+            style,
+            value: value as Record<string, unknown>,
+            valueOnly: true,
+          }),
+        );
+        continue;
+      }
+
+      if (style === 'matrix') {
+        url = url.replace(
+          match,
+          `;${serializePrimitiveParam({
+            name,
+            value: value as string,
+          })}`,
+        );
+        continue;
+      }
+
+      const replaceValue = encodeURIComponent(
+        style === 'label' ? `.${value as string}` : (value as string),
+      );
+      url = url.replace(match, replaceValue);
+    }
+  }
+  return url;
+};
+
+export const getUrl = ({
+  baseUrl,
+  path,
+  query,
+  querySerializer,
+  url: _url,
+}: {
+  baseUrl?: string;
+  path?: Record<string, unknown>;
+  query?: Record<string, unknown>;
+  querySerializer: QuerySerializer;
+  url: string;
+}) => {
+  const pathUrl = _url.startsWith('/') ? _url : `/${_url}`;
+  let url = (baseUrl ?? '') + pathUrl;
+  if (path) {
+    url = defaultPathSerializer({ path, url });
+  }
+  let search = query ? querySerializer(query) : '';
+  if (search.startsWith('?')) {
+    search = search.substring(1);
+  }
+  if (search) {
+    url += `?${search}`;
+  }
+  return url;
+};
+
+export function getValidRequestBody(options: {
+  body?: unknown;
+  bodySerializer?: BodySerializer | null;
+  serializedBody?: unknown;
+}) {
+  const hasBody = options.body !== undefined;
+  const isSerializedBody = hasBody && options.bodySerializer;
+
+  if (isSerializedBody) {
+    if ('serializedBody' in options) {
+      const hasSerializedBody =
+        options.serializedBody !== undefined && options.serializedBody !== '';
+
+      return hasSerializedBody ? options.serializedBody : null;
+    }
+
+    // not all clients implement a serializedBody property (i.e. client-axios)
+    return options.body !== '' ? options.body : null;
+  }
+
+  // plain/text body
+  if (hasBody) {
+    return options.body;
+  }
+
+  // no body was provided
+  return undefined;
+}
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/index.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/index.ts
new file mode 100644
index 000000000..c352c1047
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/index.ts
@@ -0,0 +1,4 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+export type * from './types.gen';
+export * from './sdk.gen';
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/sdk.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/sdk.gen.ts
new file mode 100644
index 000000000..ad0aa0830
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/sdk.gen.ts
@@ -0,0 +1,44 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import type { Client, Options as Options2, TDataShape } from './client';
+import { client } from './client.gen';
+import { getUserResponseTransformer, listDatesResponseTransformer, listUsersResponseTransformer } from './transformers.gen';
+import type { GetUserData, GetUserResponses, ListDatesData, ListDatesResponses, ListUsersData, ListUsersResponses } from './types.gen';
+
+export type Options<TData extends TDataShape = TDataShape, ThrowOnError extends boolean = boolean> = Options2<TData, ThrowOnError> & {
+    /**
+     * You can provide a client instance returned by `createClient()` instead of
+     * individual options. This might be also useful if you want to implement a
+     * custom client.
+     */
+    client?: Client;
+    /**
+     * You can pass arbitrary values through the `meta` object. This can be
+     * used to access values that aren't defined as part of the SDK function.
+     */
+    meta?: Record<string, unknown>;
+};
+
+export const getUser = <ThrowOnError extends boolean = false>(options: Options<GetUserData, ThrowOnError>) => {
+    return (options.client ?? client).get<GetUserResponses, unknown, ThrowOnError>({
+        responseTransformer: getUserResponseTransformer,
+        url: '/users/{id}',
+        ...options
+    });
+};
+
+export const listUsers = <ThrowOnError extends boolean = false>(options?: Options<ListUsersData, ThrowOnError>) => {
+    return (options?.client ?? client).get<ListUsersResponses, unknown, ThrowOnError>({
+        responseTransformer: listUsersResponseTransformer,
+        url: '/users',
+        ...options
+    });
+};
+
+export const listDates = <ThrowOnError extends boolean = false>(options?: Options<ListDatesData, ThrowOnError>) => {
+    return (options?.client ?? client).get<ListDatesResponses, unknown, ThrowOnError>({
+        responseTransformer: listDatesResponseTransformer,
+        url: '/dates',
+        ...options
+    });
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/transformers.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/transformers.gen.ts
new file mode 100644
index 000000000..4017878ac
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/transformers.gen.ts
@@ -0,0 +1,34 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+import type { GetUserResponse, ListDatesResponse, ListUsersResponse } from './types.gen';
+
+const userSchemaResponseTransformer = (data: any) => {
+    if (data.createdAt) {
+        data.createdAt = new Date(data.createdAt);
+    }
+    return data;
+};
+
+export const getUserResponseTransformer = async (data: any): Promise<GetUserResponse> => {
+    data = userSchemaResponseTransformer(data);
+    return data;
+};
+
+const userCollectionSchemaResponseTransformer = (data: any) => {
+    data = data.map((item: any) => {
+        return userSchemaResponseTransformer(item);
+    });
+    return data;
+};
+
+export const listUsersResponseTransformer = async (data: any): Promise<ListUsersResponse> => {
+    data = userCollectionSchemaResponseTransformer(data);
+    return data;
+};
+
+export const listDatesResponseTransformer = async (data: any): Promise<ListDatesResponse> => {
+    data = data.map((item: any) => {
+        return new Date(item);
+    });
+    return data;
+};
diff --git a/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/types.gen.ts b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/types.gen.ts
new file mode 100644
index 000000000..573443f90
--- /dev/null
+++ b/packages/openapi-ts-tests/main/test/__snapshots__/3.1.x/transformers-array-date-ref/types.gen.ts
@@ -0,0 +1,63 @@
+// This file is auto-generated by @hey-api/openapi-ts
+
+export type ClientOptions = {
+    baseUrl: `${string}://${string}` | (string & {});
+};
+
+export type User = {
+    id: string;
+    name: string;
+    createdAt?: Date;
+};
+
+export type UserCollection = Array<User>;
+
+export type GetUserData = {
+    body?: never;
+    path: {
+        id: string;
+    };
+    query?: never;
+    url: '/users/{id}';
+};
+
+export type GetUserResponses = {
+    /**
+     * Success
+     */
+    200: User;
+};
+
+export type GetUserResponse = GetUserResponses[keyof GetUserResponses];
+
+export type ListUsersData = {
+    body?: never;
+    path?: never;
+    query?: never;
+    url: '/users';
+};
+
+export type ListUsersResponses = {
+    /**
+     * Success
+     */
+    200: UserCollection;
+};
+
+export type ListUsersResponse = ListUsersResponses[keyof ListUsersResponses];
+
+export type ListDatesData = {
+    body?: never;
+    path?: never;
+    query?: never;
+    url: '/dates';
+};
+
+export type ListDatesResponses = {
+    /**
+     * Array of date strings
+     */
+    200: Array<Date>;
+};
+
+export type ListDatesResponse = ListDatesResponses[keyof ListDatesResponses];
diff --git a/packages/openapi-ts/src/plugins/@hey-api/transformers/expressions.ts b/packages/openapi-ts/src/plugins/@hey-api/transformers/expressions.ts
index 070bd06a9..fc3de4da2 100644
--- a/packages/openapi-ts/src/plugins/@hey-api/transformers/expressions.ts
+++ b/packages/openapi-ts/src/plugins/@hey-api/transformers/expressions.ts
@@ -40,7 +40,13 @@ export const bigIntExpressions: ExpressionTransformer = ({
 
   if (bigIntCallExpression) {
     if (typeof dataExpression === 'string') {
-      return [bigIntCallExpression];
+      // When dataExpression is a string (e.g., 'item' in a map callback),
+      // return a return statement with the transformed value
+      return [
+        tsc.returnStatement({
+          expression: bigIntCallExpression,
+        }),
+      ];
     }
 
     if (dataExpression) {
@@ -70,10 +76,14 @@ export const dateExpressions: ExpressionTransformer = ({
   const identifierDate = tsc.identifier({ text: 'Date' });
 
   if (typeof dataExpression === 'string') {
+    // When dataExpression is a string (e.g., 'item' in a map callback),
+    // return a return statement with the transformed value
     return [
-      tsc.newExpression({
-        argumentsArray: [tsc.identifier({ text: dataExpression })],
-        expression: identifierDate,
+      tsc.returnStatement({
+        expression: tsc.newExpression({
+          argumentsArray: [tsc.identifier({ text: dataExpression })],
+          expression: identifierDate,
+        }),
       }),
     ];
   }
diff --git a/specs/3.1.x/transformers-array-date-ref.json b/specs/3.1.x/transformers-array-date-ref.json
new file mode 100644
index 000000000..4a5f3224e
--- /dev/null
+++ b/specs/3.1.x/transformers-array-date-ref.json
@@ -0,0 +1,100 @@
+{
+  "openapi": "3.1.0",
+  "info": {
+    "title": "Test array date transformation with $ref",
+    "version": "1.0.0"
+  },
+  "paths": {
+    "/users/{id}": {
+      "get": {
+        "operationId": "getUser",
+        "parameters": [
+          {
+            "name": "id",
+            "in": "path",
+            "required": true,
+            "schema": {
+              "type": "string"
+            }
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "Success",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/User"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
+    "/users": {
+      "get": {
+        "operationId": "listUsers",
+        "responses": {
+          "200": {
+            "description": "Success",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/UserCollection"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
+    "/dates": {
+      "get": {
+        "operationId": "listDates",
+        "responses": {
+          "200": {
+            "description": "Array of date strings",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "type": "array",
+                  "items": {
+                    "type": "string",
+                    "format": "date-time"
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  },
+  "components": {
+    "schemas": {
+      "User": {
+        "type": "object",
+        "properties": {
+          "id": {
+            "type": "string"
+          },
+          "name": {
+            "type": "string"
+          },
+          "createdAt": {
+            "type": "string",
+            "format": "date-time"
+          }
+        },
+        "required": ["id", "name"]
+      },
+      "UserCollection": {
+        "type": "array",
+        "items": {
+          "$ref": "#/components/schemas/User"
+        }
+      }
+    }
+  }
+}