diff --git a/.changeset/slick-dancers-think.md b/.changeset/slick-dancers-think.md
new file mode 100644
index 000000000..ae20ca202
--- /dev/null
+++ b/.changeset/slick-dancers-think.md
@@ -0,0 +1,5 @@
+---
+'@hey-api/openapi-ts': patch
+---
+
+fix(client-axios): revert return error when axios request fails
diff --git a/examples/openapi-ts-axios/src/client/client.gen.ts b/examples/openapi-ts-axios/src/client/client.gen.ts
index 102ab4bfb..c8bfd460b 100644
--- a/examples/openapi-ts-axios/src/client/client.gen.ts
+++ b/examples/openapi-ts-axios/src/client/client.gen.ts
@@ -1,12 +1,12 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
 import {
-  type ClientOptions as DefaultClientOptions,
+  type ClientOptions,
   type Config,
   createClient,
   createConfig,
 } from './client';
-import type { ClientOptions } from './types.gen';
+import type { ClientOptions as ClientOptions2 } from './types.gen';
 
 /**
  * The `createClientConfig()` function will be called on client initialization
@@ -16,13 +16,12 @@ import type { ClientOptions } from './types.gen';
  * `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 DefaultClientOptions = ClientOptions> =
-  (
-    override?: Config<DefaultClientOptions & T>,
-  ) => Config<Required<DefaultClientOptions> & T>;
+export type CreateClientConfig<T extends ClientOptions = ClientOptions2> = (
+  override?: Config<ClientOptions & T>,
+) => Config<Required<ClientOptions> & T>;
 
 export const client = createClient(
-  createConfig<ClientOptions>({
+  createConfig<ClientOptions2>({
     baseURL: 'https://petstore3.swagger.io/api/v3',
   }),
 );
diff --git a/examples/openapi-ts-axios/src/client/client/client.gen.ts b/examples/openapi-ts-axios/src/client/client/client.gen.ts
index b2f7b118f..f81a9e786 100644
--- a/examples/openapi-ts-axios/src/client/client/client.gen.ts
+++ b/examples/openapi-ts-axios/src/client/client/client.gen.ts
@@ -3,7 +3,10 @@
 import type { AxiosError, AxiosInstance, RawAxiosRequestHeaders } from 'axios';
 import axios from 'axios';
 
-import type { Client, Config } from './types.gen';
+import { createSseClient } from '../core/serverSentEvents.gen';
+import type { HttpMethod } from '../core/types.gen';
+import { getValidRequestBody } from '../core/utils.gen';
+import type { Client, Config, RequestOptions } from './types.gen';
 import {
   buildUrl,
   createConfig,
@@ -38,8 +41,7 @@ export const createClient = (config: Config = {}): Client => {
     return getConfig();
   };
 
-  // @ts-expect-error
-  const request: Client['request'] = async (options) => {
+  const beforeRequest = async (options: RequestOptions) => {
     const opts = {
       ..._config,
       ...options,
@@ -58,12 +60,19 @@ export const createClient = (config: Config = {}): Client => {
       await opts.requestValidator(opts);
     }
 
-    if (opts.body && opts.bodySerializer) {
+    if (opts.body !== undefined && opts.bodySerializer) {
       opts.body = opts.bodySerializer(opts.body);
     }
 
     const url = buildUrl(opts);
 
+    return { opts, url };
+  };
+
+  // @ts-expect-error
+  const request: Client['request'] = async (options) => {
+    // @ts-expect-error
+    const { opts, url } = await beforeRequest(options);
     try {
       // assign Axios here for consistency with fetch
       const _axios = opts.axios!;
@@ -71,8 +80,8 @@ export const createClient = (config: Config = {}): Client => {
       const { auth, ...optsWithoutAuth } = opts;
       const response = await _axios({
         ...optsWithoutAuth,
-        baseURL: opts.baseURL as string,
-        data: opts.body,
+        baseURL: '', // the baseURL is already included in `url`
+        data: getValidRequestBody(opts),
         headers: opts.headers as RawAxiosRequestHeaders,
         // let `paramsSerializer()` handle query params if it exists
         params: opts.paramsSerializer ? opts.query : undefined,
@@ -106,18 +115,49 @@ export const createClient = (config: Config = {}): Client => {
     }
   };
 
+  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 Record<string, string>,
+        method,
+        // @ts-expect-error
+        signal: opts.signal,
+        url,
+      });
+    };
+
   return {
     buildUrl,
-    delete: (options) => request({ ...options, method: 'DELETE' }),
-    get: (options) => request({ ...options, method: 'GET' }),
+    connect: makeMethodFn('CONNECT'),
+    delete: makeMethodFn('DELETE'),
+    get: makeMethodFn('GET'),
     getConfig,
-    head: (options) => request({ ...options, method: 'HEAD' }),
+    head: makeMethodFn('HEAD'),
     instance,
-    options: (options) => request({ ...options, method: 'OPTIONS' }),
-    patch: (options) => request({ ...options, method: 'PATCH' }),
-    post: (options) => request({ ...options, method: 'POST' }),
-    put: (options) => request({ ...options, method: 'PUT' }),
+    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/examples/openapi-ts-axios/src/client/client/index.ts b/examples/openapi-ts-axios/src/client/client/index.ts
index 8ddc04f42..cff1d39c9 100644
--- a/examples/openapi-ts-axios/src/client/client/index.ts
+++ b/examples/openapi-ts-axios/src/client/client/index.ts
@@ -8,6 +8,7 @@ export {
   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,
diff --git a/examples/openapi-ts-axios/src/client/client/types.gen.ts b/examples/openapi-ts-axios/src/client/client/types.gen.ts
index b28841acc..d59239b9a 100644
--- a/examples/openapi-ts-axios/src/client/client/types.gen.ts
+++ b/examples/openapi-ts-axios/src/client/client/types.gen.ts
@@ -10,6 +10,10 @@ import type {
 } from 'axios';
 
 import type { Auth } from '../core/auth.gen';
+import type {
+  ServerSentEventsOptions,
+  ServerSentEventsResult,
+} from '../core/serverSentEvents.gen';
 import type {
   Client as CoreClient,
   Config as CoreConfig,
@@ -56,11 +60,20 @@ export interface Config<T extends ClientOptions = ClientOptions>
 }
 
 export interface RequestOptions<
+  TData = unknown,
   ThrowOnError extends boolean = boolean,
   Url extends string = string,
 > extends Config<{
-    throwOnError: ThrowOnError;
-  }> {
+      throwOnError: ThrowOnError;
+    }>,
+    Pick<
+      ServerSentEventsOptions<TData>,
+      | 'onSseError'
+      | 'onSseEvent'
+      | 'sseDefaultRetryDelay'
+      | 'sseMaxRetryAttempts'
+      | 'sseMaxRetryDelay'
+    > {
   /**
    * Any body that you want to add to your request.
    *
@@ -76,6 +89,11 @@ export interface RequestOptions<
   url: Url;
 }
 
+export interface ClientOptions {
+  baseURL?: string;
+  throwOnError?: boolean;
+}
+
 export type RequestResult<
   TData = unknown,
   TError = unknown,
@@ -100,26 +118,29 @@ export type RequestResult<
         })
     >;
 
-export interface ClientOptions {
-  baseURL?: string;
-  throwOnError?: boolean;
-}
-
 type MethodFn = <
   TData = unknown,
   TError = unknown,
   ThrowOnError extends boolean = false,
 >(
-  options: Omit<RequestOptions<ThrowOnError>, 'method'>,
+  options: Omit<RequestOptions<TData, ThrowOnError>, 'method'>,
 ) => RequestResult<TData, TError, ThrowOnError>;
 
+type SseFn = <
+  TData = unknown,
+  TError = unknown,
+  ThrowOnError extends boolean = false,
+>(
+  options: Omit<RequestOptions<TData, ThrowOnError>, 'method'>,
+) => Promise<ServerSentEventsResult<TData, TError>>;
+
 type RequestFn = <
   TData = unknown,
   TError = unknown,
   ThrowOnError extends boolean = false,
 >(
-  options: Omit<RequestOptions<ThrowOnError>, 'method'> &
-    Pick<Required<RequestOptions<ThrowOnError>>, 'method'>,
+  options: Omit<RequestOptions<TData, ThrowOnError>, 'method'> &
+    Pick<Required<RequestOptions<TData, ThrowOnError>>, 'method'>,
 ) => RequestResult<TData, TError, ThrowOnError>;
 
 type BuildUrlFn = <
@@ -130,10 +151,16 @@ type BuildUrlFn = <
     url: string;
   },
 >(
-  options: Pick<TData, 'url'> & Omit<Options<TData>, 'axios'>,
+  options: Pick<TData, 'url'> & Options<TData>,
 ) => string;
 
-export type Client = CoreClient<RequestFn, Config, MethodFn, BuildUrlFn> & {
+export type Client = CoreClient<
+  RequestFn,
+  Config,
+  MethodFn,
+  BuildUrlFn,
+  SseFn
+> & {
   instance: AxiosInstance;
 };
 
@@ -162,7 +189,11 @@ type OmitKeys<T, K> = Pick<T, Exclude<keyof T, K>>;
 export type Options<
   TData extends TDataShape = TDataShape,
   ThrowOnError extends boolean = boolean,
-> = OmitKeys<RequestOptions<ThrowOnError>, 'body' | 'path' | 'query' | 'url'> &
+  TResponse = unknown,
+> = OmitKeys<
+  RequestOptions<TResponse, ThrowOnError>,
+  'body' | 'path' | 'query' | 'url'
+> &
   Omit<TData, 'url'>;
 
 export type OptionsLegacyParser<
@@ -170,12 +201,16 @@ export type OptionsLegacyParser<
   ThrowOnError extends boolean = boolean,
 > = TData extends { body?: any }
   ? TData extends { headers?: any }
-    ? OmitKeys<RequestOptions<ThrowOnError>, 'body' | 'headers' | 'url'> & TData
-    : OmitKeys<RequestOptions<ThrowOnError>, 'body' | 'url'> &
+    ? OmitKeys<
+        RequestOptions<unknown, ThrowOnError>,
+        'body' | 'headers' | 'url'
+      > &
+        TData
+    : OmitKeys<RequestOptions<unknown, ThrowOnError>, 'body' | 'url'> &
         TData &
-        Pick<RequestOptions<ThrowOnError>, 'headers'>
+        Pick<RequestOptions<unknown, ThrowOnError>, 'headers'>
   : TData extends { headers?: any }
-    ? OmitKeys<RequestOptions<ThrowOnError>, 'headers' | 'url'> &
+    ? OmitKeys<RequestOptions<unknown, ThrowOnError>, 'headers' | 'url'> &
         TData &
-        Pick<RequestOptions<ThrowOnError>, 'body'>
-    : OmitKeys<RequestOptions<ThrowOnError>, 'url'> & TData;
+        Pick<RequestOptions<unknown, ThrowOnError>, 'body'>
+    : OmitKeys<RequestOptions<unknown, ThrowOnError>, 'url'> & TData;
diff --git a/examples/openapi-ts-axios/src/client/client/utils.gen.ts b/examples/openapi-ts-axios/src/client/client/utils.gen.ts
index 8f20fa853..c87309246 100644
--- a/examples/openapi-ts-axios/src/client/client/utils.gen.ts
+++ b/examples/openapi-ts-axios/src/client/client/utils.gen.ts
@@ -1,16 +1,13 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
 import { getAuthToken } from '../core/auth.gen';
-import type {
-  QuerySerializer,
-  QuerySerializerOptions,
-} from '../core/bodySerializer.gen';
-import type { ArraySeparatorStyle } from '../core/pathSerializer.gen';
+import type { QuerySerializerOptions } from '../core/bodySerializer.gen';
 import {
   serializeArrayParam,
   serializeObjectParam,
   serializePrimitiveParam,
 } from '../core/pathSerializer.gen';
+import { getUrl } from '../core/utils.gen';
 import type {
   Client,
   ClientOptions,
@@ -18,83 +15,6 @@ import type {
   RequestOptions,
 } from './types.gen';
 
-interface PathSerializer {
-  path: Record<string, unknown>;
-  url: string;
-}
-
-const PATH_PARAM_RE = /\{[^{}]+\}/g;
-
-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 createQuerySerializer = <T = unknown>({
   allowReserved,
   array,
@@ -211,7 +131,15 @@ export const setAuthParams = async ({
 };
 
 export const buildUrl: Client['buildUrl'] = (options) => {
-  const url = getUrl({
+  const instanceBaseUrl = options.axios?.defaults?.baseURL;
+
+  const baseUrl =
+    !!options.baseURL && typeof options.baseURL === 'string'
+      ? options.baseURL
+      : instanceBaseUrl;
+
+  return getUrl({
+    baseUrl: baseUrl as string,
     path: options.path,
     // let `paramsSerializer()` handle query params if it exists
     query: !options.paramsSerializer ? options.query : undefined,
@@ -221,33 +149,6 @@ export const buildUrl: Client['buildUrl'] = (options) => {
         : createQuerySerializer(options.querySerializer),
     url: options.url,
   });
-  return url;
-};
-
-export const getUrl = ({
-  path,
-  query,
-  querySerializer,
-  url: _url,
-}: {
-  path?: Record<string, unknown>;
-  query?: Record<string, unknown>;
-  querySerializer: QuerySerializer;
-  url: string;
-}) => {
-  const pathUrl = _url.startsWith('/') ? _url : `/${_url}`;
-  let url = pathUrl;
-  if (path) {
-    url = defaultPathSerializer({ path, url });
-  }
-  let search = query ? querySerializer(query) : '';
-  if (search.startsWith('?')) {
-    search = search.substring(1);
-  }
-  if (search) {
-    url += `?${search}`;
-  }
-  return url;
 };
 
 export const mergeConfigs = (a: Config, b: Config): Config => {
diff --git a/examples/openapi-ts-axios/src/client/core/queryKeySerializer.gen.ts b/examples/openapi-ts-axios/src/client/core/queryKeySerializer.gen.ts
new file mode 100644
index 000000000..d3bb68396
--- /dev/null
+++ b/examples/openapi-ts-axios/src/client/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/examples/openapi-ts-axios/src/client/core/serverSentEvents.gen.ts b/examples/openapi-ts-axios/src/client/core/serverSentEvents.gen.ts
new file mode 100644
index 000000000..f8fd78e28
--- /dev/null
+++ b/examples/openapi-ts-axios/src/client/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/examples/openapi-ts-axios/src/client/core/types.gen.ts b/examples/openapi-ts-axios/src/client/core/types.gen.ts
index 5bfae35c0..643c070c9 100644
--- a/examples/openapi-ts-axios/src/client/core/types.gen.ts
+++ b/examples/openapi-ts-axios/src/client/core/types.gen.ts
@@ -7,29 +7,36 @@ import type {
   QuerySerializerOptions,
 } from './bodySerializer.gen';
 
-export interface Client<
+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;
-  connect: MethodFn;
-  delete: MethodFn;
-  get: MethodFn;
   getConfig: () => Config;
-  head: MethodFn;
-  options: MethodFn;
-  patch: MethodFn;
-  post: MethodFn;
-  put: MethodFn;
   request: RequestFn;
   setConfig: (config: Config) => Config;
-  trace: MethodFn;
-}
+} & {
+  [K in HttpMethod]: MethodFn;
+} & ([SseFn] extends [never]
+    ? { sse?: never }
+    : { sse: { [K in HttpMethod]: SseFn } });
 
 export interface Config {
   /**
@@ -65,16 +72,7 @@ export interface Config {
    *
    * {@link https://developer.mozilla.org/docs/Web/API/fetch#method See more}
    */
-  method?:
-    | 'CONNECT'
-    | 'DELETE'
-    | 'GET'
-    | 'HEAD'
-    | 'OPTIONS'
-    | 'PATCH'
-    | 'POST'
-    | 'PUT'
-    | 'TRACE';
+  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
diff --git a/examples/openapi-ts-axios/src/client/core/utils.gen.ts b/examples/openapi-ts-axios/src/client/core/utils.gen.ts
new file mode 100644
index 000000000..0b5389d08
--- /dev/null
+++ b/examples/openapi-ts-axios/src/client/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/examples/openapi-ts-axios/src/client/index.ts b/examples/openapi-ts-axios/src/client/index.ts
index 688e3c912..57ed02bf5 100644
--- a/examples/openapi-ts-axios/src/client/index.ts
+++ b/examples/openapi-ts-axios/src/client/index.ts
@@ -1,3 +1,4 @@
 // This file is auto-generated by @hey-api/openapi-ts
+
 export * from './sdk.gen';
-export * from './types.gen';
+export type * from './types.gen';
diff --git a/examples/openapi-ts-axios/src/client/sdk.gen.ts b/examples/openapi-ts-axios/src/client/sdk.gen.ts
index 59074a4f4..bb7cee4ba 100644
--- a/examples/openapi-ts-axios/src/client/sdk.gen.ts
+++ b/examples/openapi-ts-axios/src/client/sdk.gen.ts
@@ -1,7 +1,7 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
-import type { Client, Options as ClientOptions, TDataShape } from './client';
-import { client as _heyApiClient } from './client.gen';
+import type { Client, Options as Options2, TDataShape } from './client';
+import { client } from './client.gen';
 import type {
   AddPetData,
   AddPetErrors,
@@ -65,7 +65,7 @@ import type {
 export type Options<
   TData extends TDataShape = TDataShape,
   ThrowOnError extends boolean = boolean,
-> = ClientOptions<TData, ThrowOnError> & {
+> = 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
@@ -81,16 +81,13 @@ export type Options<
 
 /**
  * Add a new pet to the store.
+ *
  * Add a new pet to the store.
  */
 export const addPet = <ThrowOnError extends boolean = false>(
   options: Options<AddPetData, ThrowOnError>,
 ) =>
-  (options.client ?? _heyApiClient).post<
-    AddPetResponses,
-    AddPetErrors,
-    ThrowOnError
-  >({
+  (options.client ?? client).post<AddPetResponses, AddPetErrors, ThrowOnError>({
     responseType: 'json',
     security: [
       {
@@ -108,12 +105,13 @@ export const addPet = <ThrowOnError extends boolean = false>(
 
 /**
  * Update an existing pet.
+ *
  * Update an existing pet by Id.
  */
 export const updatePet = <ThrowOnError extends boolean = false>(
   options: Options<UpdatePetData, ThrowOnError>,
 ) =>
-  (options.client ?? _heyApiClient).put<
+  (options.client ?? client).put<
     UpdatePetResponses,
     UpdatePetErrors,
     ThrowOnError
@@ -135,12 +133,13 @@ export const updatePet = <ThrowOnError extends boolean = false>(
 
 /**
  * Finds Pets by status.
+ *
  * Multiple status values can be provided with comma separated strings.
  */
 export const findPetsByStatus = <ThrowOnError extends boolean = false>(
   options: Options<FindPetsByStatusData, ThrowOnError>,
 ) =>
-  (options.client ?? _heyApiClient).get<
+  (options.client ?? client).get<
     FindPetsByStatusResponses,
     FindPetsByStatusErrors,
     ThrowOnError
@@ -158,12 +157,13 @@ export const findPetsByStatus = <ThrowOnError extends boolean = false>(
 
 /**
  * Finds Pets by tags.
+ *
  * Multiple tags can be provided with comma separated strings. Use tag1, tag2, tag3 for testing.
  */
 export const findPetsByTags = <ThrowOnError extends boolean = false>(
   options: Options<FindPetsByTagsData, ThrowOnError>,
 ) =>
-  (options.client ?? _heyApiClient).get<
+  (options.client ?? client).get<
     FindPetsByTagsResponses,
     FindPetsByTagsErrors,
     ThrowOnError
@@ -181,12 +181,13 @@ export const findPetsByTags = <ThrowOnError extends boolean = false>(
 
 /**
  * Deletes a pet.
+ *
  * Delete a pet.
  */
 export const deletePet = <ThrowOnError extends boolean = false>(
   options: Options<DeletePetData, ThrowOnError>,
 ) =>
-  (options.client ?? _heyApiClient).delete<
+  (options.client ?? client).delete<
     DeletePetResponses,
     DeletePetErrors,
     ThrowOnError
@@ -203,12 +204,13 @@ export const deletePet = <ThrowOnError extends boolean = false>(
 
 /**
  * Find pet by ID.
+ *
  * Returns a single pet.
  */
 export const getPetById = <ThrowOnError extends boolean = false>(
   options: Options<GetPetByIdData, ThrowOnError>,
 ) =>
-  (options.client ?? _heyApiClient).get<
+  (options.client ?? client).get<
     GetPetByIdResponses,
     GetPetByIdErrors,
     ThrowOnError
@@ -230,12 +232,13 @@ export const getPetById = <ThrowOnError extends boolean = false>(
 
 /**
  * Updates a pet in the store with form data.
+ *
  * Updates a pet resource based on the form data.
  */
 export const updatePetWithForm = <ThrowOnError extends boolean = false>(
   options: Options<UpdatePetWithFormData, ThrowOnError>,
 ) =>
-  (options.client ?? _heyApiClient).post<
+  (options.client ?? client).post<
     UpdatePetWithFormResponses,
     UpdatePetWithFormErrors,
     ThrowOnError
@@ -253,12 +256,13 @@ export const updatePetWithForm = <ThrowOnError extends boolean = false>(
 
 /**
  * Uploads an image.
+ *
  * Upload image of the pet.
  */
 export const uploadFile = <ThrowOnError extends boolean = false>(
   options: Options<UploadFileData, ThrowOnError>,
 ) =>
-  (options.client ?? _heyApiClient).post<
+  (options.client ?? client).post<
     UploadFileResponses,
     UploadFileErrors,
     ThrowOnError
@@ -281,12 +285,13 @@ export const uploadFile = <ThrowOnError extends boolean = false>(
 
 /**
  * Returns pet inventories by status.
+ *
  * Returns a map of status codes to quantities.
  */
 export const getInventory = <ThrowOnError extends boolean = false>(
   options?: Options<GetInventoryData, ThrowOnError>,
 ) =>
-  (options?.client ?? _heyApiClient).get<
+  (options?.client ?? client).get<
     GetInventoryResponses,
     GetInventoryErrors,
     ThrowOnError
@@ -304,12 +309,13 @@ export const getInventory = <ThrowOnError extends boolean = false>(
 
 /**
  * Place an order for a pet.
+ *
  * Place a new order in the store.
  */
 export const placeOrder = <ThrowOnError extends boolean = false>(
   options?: Options<PlaceOrderData, ThrowOnError>,
 ) =>
-  (options?.client ?? _heyApiClient).post<
+  (options?.client ?? client).post<
     PlaceOrderResponses,
     PlaceOrderErrors,
     ThrowOnError
@@ -325,12 +331,13 @@ export const placeOrder = <ThrowOnError extends boolean = false>(
 
 /**
  * Delete purchase order by identifier.
+ *
  * For valid response try integer IDs with value < 1000. Anything above 1000 or non-integers will generate API errors.
  */
 export const deleteOrder = <ThrowOnError extends boolean = false>(
   options: Options<DeleteOrderData, ThrowOnError>,
 ) =>
-  (options.client ?? _heyApiClient).delete<
+  (options.client ?? client).delete<
     DeleteOrderResponses,
     DeleteOrderErrors,
     ThrowOnError
@@ -341,12 +348,13 @@ export const deleteOrder = <ThrowOnError extends boolean = false>(
 
 /**
  * Find purchase order by ID.
+ *
  * For valid response try integer IDs with value <= 5 or > 10. Other values will generate exceptions.
  */
 export const getOrderById = <ThrowOnError extends boolean = false>(
   options: Options<GetOrderByIdData, ThrowOnError>,
 ) =>
-  (options.client ?? _heyApiClient).get<
+  (options.client ?? client).get<
     GetOrderByIdResponses,
     GetOrderByIdErrors,
     ThrowOnError
@@ -358,12 +366,13 @@ export const getOrderById = <ThrowOnError extends boolean = false>(
 
 /**
  * Create user.
+ *
  * This can only be done by the logged in user.
  */
 export const createUser = <ThrowOnError extends boolean = false>(
   options?: Options<CreateUserData, ThrowOnError>,
 ) =>
-  (options?.client ?? _heyApiClient).post<
+  (options?.client ?? client).post<
     CreateUserResponses,
     CreateUserErrors,
     ThrowOnError
@@ -379,12 +388,13 @@ export const createUser = <ThrowOnError extends boolean = false>(
 
 /**
  * Creates list of users with given input array.
+ *
  * Creates list of users with given input array.
  */
 export const createUsersWithListInput = <ThrowOnError extends boolean = false>(
   options?: Options<CreateUsersWithListInputData, ThrowOnError>,
 ) =>
-  (options?.client ?? _heyApiClient).post<
+  (options?.client ?? client).post<
     CreateUsersWithListInputResponses,
     CreateUsersWithListInputErrors,
     ThrowOnError
@@ -400,12 +410,13 @@ export const createUsersWithListInput = <ThrowOnError extends boolean = false>(
 
 /**
  * Logs user into the system.
+ *
  * Log into the system.
  */
 export const loginUser = <ThrowOnError extends boolean = false>(
   options?: Options<LoginUserData, ThrowOnError>,
 ) =>
-  (options?.client ?? _heyApiClient).get<
+  (options?.client ?? client).get<
     LoginUserResponses,
     LoginUserErrors,
     ThrowOnError
@@ -417,12 +428,13 @@ export const loginUser = <ThrowOnError extends boolean = false>(
 
 /**
  * Logs out current logged in user session.
+ *
  * Log user out of the system.
  */
 export const logoutUser = <ThrowOnError extends boolean = false>(
   options?: Options<LogoutUserData, ThrowOnError>,
 ) =>
-  (options?.client ?? _heyApiClient).get<
+  (options?.client ?? client).get<
     LogoutUserResponses,
     LogoutUserErrors,
     ThrowOnError
@@ -433,12 +445,13 @@ export const logoutUser = <ThrowOnError extends boolean = false>(
 
 /**
  * Delete user resource.
+ *
  * This can only be done by the logged in user.
  */
 export const deleteUser = <ThrowOnError extends boolean = false>(
   options: Options<DeleteUserData, ThrowOnError>,
 ) =>
-  (options.client ?? _heyApiClient).delete<
+  (options.client ?? client).delete<
     DeleteUserResponses,
     DeleteUserErrors,
     ThrowOnError
@@ -449,12 +462,13 @@ export const deleteUser = <ThrowOnError extends boolean = false>(
 
 /**
  * Get user by user name.
+ *
  * Get user detail based on username.
  */
 export const getUserByName = <ThrowOnError extends boolean = false>(
   options: Options<GetUserByNameData, ThrowOnError>,
 ) =>
-  (options.client ?? _heyApiClient).get<
+  (options.client ?? client).get<
     GetUserByNameResponses,
     GetUserByNameErrors,
     ThrowOnError
@@ -466,12 +480,13 @@ export const getUserByName = <ThrowOnError extends boolean = false>(
 
 /**
  * Update user resource.
+ *
  * This can only be done by the logged in user.
  */
 export const updateUser = <ThrowOnError extends boolean = false>(
   options: Options<UpdateUserData, ThrowOnError>,
 ) =>
-  (options.client ?? _heyApiClient).put<
+  (options.client ?? client).put<
     UpdateUserResponses,
     UpdateUserErrors,
     ThrowOnError
diff --git a/examples/openapi-ts-axios/src/client/types.gen.ts b/examples/openapi-ts-axios/src/client/types.gen.ts
index 257d5446a..48da19d87 100644
--- a/examples/openapi-ts-axios/src/client/types.gen.ts
+++ b/examples/openapi-ts-axios/src/client/types.gen.ts
@@ -1,5 +1,9 @@
 // This file is auto-generated by @hey-api/openapi-ts
 
+export type ClientOptions = {
+  baseURL: 'https://petstore3.swagger.io/api/v3' | (string & {});
+};
+
 export type Order = {
   complete?: boolean;
   id?: number;
@@ -693,7 +697,3 @@ export type UpdateUserResponses = {
    */
   200: unknown;
 };
-
-export type ClientOptions = {
-  baseURL: 'https://petstore3.swagger.io/api/v3' | (string & {});
-};