diff --git a/codegen/src/api.ts b/codegen/src/api.ts
index aa63db35..9302ccec 100644
--- a/codegen/src/api.ts
+++ b/codegen/src/api.ts
@@ -27,7 +27,7 @@ export async function generateIndex(
 
   export type { APIConfig } from './client'
   export { APIError, SumUpError } from './core'
-  export type { FetchParams } from './core'
+  export type { RequestOptions } from './core'
   export * from './types'
   `);
 
diff --git a/codegen/src/core.ts b/codegen/src/core.ts
index 6a788f0c..ba31029a 100644
--- a/codegen/src/core.ts
+++ b/codegen/src/core.ts
@@ -33,20 +33,31 @@ export class APIResource {
 // biome-ignore lint/suspicious/noExplicitAny: any, but only for tests
 type QueryParams = Record<string, any>;
 
+type HTTPMethod = "GET" | "POST" | "PUT" | "PATCH" | "DELETE";
+
 /**
- * Params that get passed to \`fetch\`. This ends up as an optional second
- * argument to each generated request method. Properties are a subset of
- * \`RequestInit\`.
+ * SDK-specific options that can be passed to any generated request method.
  */
-export type FetchParams = Omit<RequestInit, "body" | "method">;
+export type RequestOptions = {
+  /**
+   * Optional bearer authorization value to apply to the request, for example
+   * \`Bearer <access-token>\`. When provided, it overrides any default
+   * Authorization header configured on the client.
+   */
+  authorization?: string;
+  headers?: HeadersInit;
+  host?: string;
+  maxRetries?: number;
+  signal?: AbortSignal | null;
+  timeout?: number;
+};
 
 /** All arguments to \`request()\` */
-export type FullParams = FetchParams & {
+export type FullRequestOptions = RequestOptions & {
   path: string;
   query?: QueryParams;
   body?: unknown;
-  host?: string;
-  method?: string;
+  method?: HTTPMethod;
 };
 
 export class SumUpError extends Error {}
diff --git a/codegen/src/resource.ts b/codegen/src/resource.ts
index 1f6c67cf..1e5e0608 100644
--- a/codegen/src/resource.ts
+++ b/codegen/src/resource.ts
@@ -9,7 +9,6 @@ import {
   iterPathConfig,
   responseSchema,
 } from "./base";
-import type { FileWriter } from "./io";
 import { fileWriter } from "./io";
 import { schemaNameToTypeName, schemaToTypes } from "./schema";
 import {
@@ -66,7 +65,7 @@ export async function generateResource(
   const collectorWriter = {
     w() {},
     w0() {},
-  } as unknown as FileWriter;
+  };
 
   const resolveResponseObject = (
     response: OpenAPIV3_1.ResponseObject | OpenAPIV3_1.ReferenceObject,
@@ -180,11 +179,10 @@ export async function generateResource(
       );
   }
 
-  writer.w(`
-// Code generated by @sumup/sumup-ts-codegen. DO NOT EDIT.
-
-import { APIResource, type APIPromise, type FetchParams } from "../../core";
-`);
+  writer.w("// Code generated by @sumup/sumup-ts-codegen. DO NOT EDIT.\n");
+  writer.w(
+    'import { APIResource, type APIPromise, type RequestOptions } from "../../core";',
+  );
 
   const sortedSharedTypes = [...usedSharedTypes].sort((a, b) =>
     a > b ? 1 : -1,
@@ -316,6 +314,7 @@ export class ${resourceClassName} extends APIResource {`);
       writer.w(comment);
     }
 
+    const body = getRequestBody(opId, methodSpec);
     writer.w0(`${methodName}(`);
 
     if (pathParams.length > 0) {
@@ -327,7 +326,6 @@ export class ${resourceClassName} extends APIResource {`);
       }
     }
 
-    const body = getRequestBody(opId, methodSpec);
     if (body) {
       writer.w0(`body${body.required ? "" : "?"}: ${body.typeName}, `);
     }
@@ -338,7 +336,7 @@ export class ${resourceClassName} extends APIResource {`);
       writer.w0(`: ${queryParamsType(methodNameType)}, `);
     }
 
-    writer.w(`params?: FetchParams): APIPromise<${successType}, ${errorTypeName}> {
+    writer.w(`options?: RequestOptions): APIPromise<${successType}, ${errorTypeName}> {
          return this._client.${method}<${successType}, ${errorTypeName}>({
            path: ${pathToTemplateStr(path)},`);
     if (methodSpec.requestBody) {
@@ -347,7 +345,7 @@ export class ${resourceClassName} extends APIResource {`);
     if (queryParams.length > 0) {
       writer.w("  query,");
     }
-    writer.w(`  ...params,
+    writer.w(`  ...options,
          })
       }\n`);
   }
diff --git a/examples/checkout/index.ts b/examples/checkout/index.ts
index 3b74bae4..fdaa8e1c 100644
--- a/examples/checkout/index.ts
+++ b/examples/checkout/index.ts
@@ -5,12 +5,6 @@ const client = new SumUp({
 });
 
 async function main() {
-  const merchant = await client.merchant.get();
-  console.info({ merchant });
-
-  const merchant2 = await client.merchant.get().withResponse();
-  console.info({ merchant2 });
-
   const merchantCode = process.env.SUMUP_MERCHANT_CODE;
   if (!merchantCode) {
     console.warn(
@@ -19,6 +13,12 @@ async function main() {
     return;
   }
 
+  const merchant = await client.merchants.get(merchantCode);
+  console.info({ merchant });
+
+  const merchant2 = await client.merchants.get(merchantCode).withResponse();
+  console.info({ merchant2 });
+
   const request: CheckoutCreateRequest = {
     amount: 19,
     checkout_reference: "CO746453",
diff --git a/sdk/README.md b/sdk/README.md
index 4fa2ad00..3db44b4a 100644
--- a/sdk/README.md
+++ b/sdk/README.md
@@ -46,8 +46,8 @@ const sumup = require('@sumup/sdk')({
   apiKey: 'sup_sk_MvxmLOl0...'
 });
 
-sumup.merchant.get()
-  .then(merchant => console.info(merchant))
+sumup.checkouts.list()
+  .then(checkouts => console.info(checkouts))
   .catch(error => console.error(error));
 ```
 
@@ -60,10 +60,29 @@ const client = new SumUp({
   apiKey: 'sup_sk_MvxmLOl0...',
 });
 
-const merchant = await client.merchant.get();
+const merchantCode = process.env.SUMUP_MERCHANT_CODE!;
+const merchant = await client.merchants.get(merchantCode);
 console.info(merchant);
 ```
 
+Per-request options are available as the last argument to any SDK call. For
+example, you can override authorization, timeout, retries, or headers for a
+single request:
+
+```ts
+await client.checkouts.list(undefined, {
+  timeout: 5_000,
+});
+
+await client.merchants.get(merchantCode, {
+  authorization: `Bearer ${accessToken}`,
+  headers: {
+    "x-request-id": "req_123",
+  },
+  maxRetries: 1,
+});
+```
+
 ## Examples
 
 Examples require an API key and your merchant code. You can run the examples using:
diff --git a/sdk/src/client.ts b/sdk/src/client.ts
index f6b7723e..90df6e96 100644
--- a/sdk/src/client.ts
+++ b/sdk/src/client.ts
@@ -6,19 +6,23 @@ import { VERSION } from "./version";
 
 export type APIConfig = {
   apiKey?: string;
-  baseParams?: Core.FetchParams;
   host?: string;
+  baseParams?: Core.RequestOptions;
+  maxRetries?: number;
+  timeout?: number;
 };
 
 export class HTTPClient {
   host: string;
   apiKey?: string;
-  baseParams: Core.FetchParams;
+  baseParams: Core.RequestOptions;
 
   constructor({
     apiKey,
     host = "https://api.sumup.com",
     baseParams = {},
+    maxRetries = 0,
+    timeout,
   }: APIConfig = {}) {
     this.host = host;
     this.apiKey = apiKey;
@@ -32,12 +36,12 @@ export class HTTPClient {
     if (apiKey) {
       headers.append("Authorization", `Bearer ${apiKey}`);
     }
-    this.baseParams = mergeParams({ headers }, baseParams);
+    this.baseParams = mergeParams({ headers, maxRetries, timeout }, baseParams);
   }
 
   public get<R, E = Core.APIError<unknown>>({
     ...params
-  }: Omit<Core.FullParams, "method">): Core.APIPromise<R, E> {
+  }: Omit<Core.FullRequestOptions, "method">): Core.APIPromise<R, E> {
     return this.request<R, E>({
       method: "GET",
       ...params,
@@ -46,7 +50,7 @@ export class HTTPClient {
 
   public post<R, E = Core.APIError<unknown>>({
     ...params
-  }: Omit<Core.FullParams, "method">): Core.APIPromise<R, E> {
+  }: Omit<Core.FullRequestOptions, "method">): Core.APIPromise<R, E> {
     return this.request<R, E>({
       method: "POST",
       ...params,
@@ -55,16 +59,16 @@ export class HTTPClient {
 
   public put<R, E = Core.APIError<unknown>>({
     ...params
-  }: Omit<Core.FullParams, "method">): Core.APIPromise<R, E> {
+  }: Omit<Core.FullRequestOptions, "method">): Core.APIPromise<R, E> {
     return this.request<R, E>({
-      method: "put",
+      method: "PUT",
       ...params,
     });
   }
 
   public patch<R, E = Core.APIError<unknown>>({
     ...params
-  }: Omit<Core.FullParams, "method">): Core.APIPromise<R, E> {
+  }: Omit<Core.FullRequestOptions, "method">): Core.APIPromise<R, E> {
     return this.request<R, E>({
       method: "PATCH",
       ...params,
@@ -73,7 +77,7 @@ export class HTTPClient {
 
   public delete<R, E = Core.APIError<unknown>>({
     ...params
-  }: Omit<Core.FullParams, "method">): Core.APIPromise<R, E> {
+  }: Omit<Core.FullRequestOptions, "method">): Core.APIPromise<R, E> {
     return this.request<R, E>({
       method: "DELETE",
       ...params,
@@ -85,8 +89,8 @@ export class HTTPClient {
     path,
     query,
     host: hostOverride,
-    ...fetchParams
-  }: Core.FullParams): Core.APIPromise<T, E> {
+    ...requestOptions
+  }: Core.FullRequestOptions): Core.APIPromise<T, E> {
     const host = hostOverride || this.host;
     const url = new URL(
       host +
@@ -95,27 +99,70 @@ export class HTTPClient {
     if (typeof query === "object" && query && !Array.isArray(query)) {
       url.search = this.stringifyQuery(query as Record<string, unknown>);
     }
+    const mergedOptions = mergeParams(this.baseParams, requestOptions);
+    const { maxRetries, timeout, ...fetchParams } = mergedOptions;
     const init = {
-      ...mergeParams(this.baseParams, fetchParams),
+      ...fetchParams,
       body: JSON.stringify(body),
     };
-    return new Core.APIPromise<T, E>(this.do<E>(url, init));
+    return new Core.APIPromise<T, E>(
+      this.do<E>(url, init, {
+        maxRetries,
+        signal: fetchParams.signal,
+        timeout,
+      }),
+    );
   }
 
-  protected async do<E>(input: URL, init: RequestInit): Promise<Response> {
-    const res = await fetch(input, init);
+  protected async do<E>(
+    input: URL,
+    init: RequestInit,
+    options: {
+      maxRetries?: number;
+      signal?: AbortSignal | null;
+      timeout?: number;
+    },
+  ): Promise<Response> {
+    const maxRetries = options.maxRetries ?? 0;
 
-    if (!res.ok) {
-      const contentType = res.headers.get("content-type");
-      const isJSON = contentType?.includes("json");
-      throw new Core.APIError(
-        res.status,
-        isJSON ? ((await res.json()) as E) : await res.text(),
-        res,
+    for (let attempt = 0; ; attempt++) {
+      const { cleanup, didTimeout, signal } = withTimeoutSignal(
+        options.signal,
+        options.timeout,
       );
-    }
 
-    return res;
+      try {
+        const res = await fetch(input, { ...init, signal });
+
+        if (!res.ok) {
+          if (attempt < maxRetries && isRetryableStatus(res.status)) {
+            continue;
+          }
+
+          const contentType = res.headers.get("content-type");
+          const isJSON = contentType?.includes("json");
+          throw new Core.APIError(
+            res.status,
+            isJSON ? ((await res.json()) as E) : await res.text(),
+            res,
+          );
+        }
+
+        return res;
+      } catch (error) {
+        if (attempt < maxRetries && isRetryableError(error, options.signal)) {
+          continue;
+        }
+        if (didTimeout()) {
+          throw new Core.SumUpError(
+            `Request timed out after ${options.timeout}ms.`,
+          );
+        }
+        throw error;
+      } finally {
+        cleanup();
+      }
+    }
   }
 
   protected stringifyQuery(query: Record<string, unknown>): string {
@@ -146,14 +193,102 @@ export class HTTPClient {
 }
 
 export function mergeParams(
-  a: Core.FetchParams,
-  b: Core.FetchParams,
-): Core.FetchParams {
+  a: Core.RequestOptions,
+  b: Core.RequestOptions,
+): Core.RequestOptions {
+  const {
+    authorization: defaultAuthorization,
+    headers: defaultHeaders,
+    ...defaultParams
+  } = a;
+  const {
+    authorization: overrideAuthorization,
+    headers: overrideHeaders,
+    ...overrideParams
+  } = b;
   // calling `new Headers()` normalizes `HeadersInit`, which could be a Headers
   // object, a plain object, or an array of tuples
-  const headers = new Headers(a.headers);
-  for (const [key, value] of new Headers(b.headers).entries()) {
+  const headers = new Headers(defaultHeaders);
+  for (const [key, value] of new Headers(overrideHeaders).entries()) {
     headers.set(key, value);
   }
-  return { ...a, ...b, headers };
+  const authorization = overrideAuthorization ?? defaultAuthorization;
+  if (authorization) {
+    headers.set("Authorization", authorization);
+  }
+
+  return { ...defaultParams, ...overrideParams, headers };
+}
+
+function isRetryableStatus(status: number): boolean {
+  return status === 408 || status === 409 || status === 429 || status >= 500;
+}
+
+function isRetryableError(
+  error: unknown,
+  signal?: AbortSignal | null,
+): boolean {
+  if (signal?.aborted) {
+    return false;
+  }
+  return error instanceof TypeError || isAbortError(error);
+}
+
+function isAbortError(error: unknown): boolean {
+  return error instanceof DOMException
+    ? error.name === "AbortError"
+    : error instanceof Error && error.name === "AbortError";
+}
+
+function withTimeoutSignal(
+  signal?: AbortSignal | null,
+  timeout?: number,
+): {
+  cleanup: () => void;
+  didTimeout: () => boolean;
+  signal: AbortSignal | undefined;
+} {
+  if (!signal && typeof timeout === "undefined") {
+    return {
+      cleanup: () => {},
+      didTimeout: () => false,
+      signal: undefined,
+    };
+  }
+
+  const controller = new AbortController();
+  let timedOut = false;
+
+  const onAbort = () => {
+    controller.abort(signal?.reason);
+  };
+
+  if (signal) {
+    if (signal.aborted) {
+      onAbort();
+    } else {
+      signal.addEventListener("abort", onAbort, { once: true });
+    }
+  }
+
+  const timeoutId =
+    typeof timeout === "number"
+      ? setTimeout(() => {
+          timedOut = true;
+          controller.abort(
+            new Core.SumUpError(`Request timed out after ${timeout}ms.`),
+          );
+        }, timeout)
+      : undefined;
+
+  return {
+    cleanup: () => {
+      if (typeof timeoutId !== "undefined") {
+        clearTimeout(timeoutId);
+      }
+      signal?.removeEventListener("abort", onAbort);
+    },
+    didTimeout: () => timedOut,
+    signal: controller.signal,
+  };
 }
diff --git a/sdk/src/core.ts b/sdk/src/core.ts
index 7eee2b1f..a56c7727 100644
--- a/sdk/src/core.ts
+++ b/sdk/src/core.ts
@@ -14,20 +14,31 @@ export class APIResource {
 // biome-ignore lint/suspicious/noExplicitAny: any, but only for tests
 type QueryParams = Record<string, any>;
 
+type HTTPMethod = "GET" | "POST" | "PUT" | "PATCH" | "DELETE";
+
 /**
- * Params that get passed to `fetch`. This ends up as an optional second
- * argument to each generated request method. Properties are a subset of
- * `RequestInit`.
+ * SDK-specific options that can be passed to any generated request method.
  */
-export type FetchParams = Omit<RequestInit, "body" | "method">;
+export type RequestOptions = {
+  /**
+   * Optional bearer authorization value to apply to the request, for example
+   * `Bearer <access-token>`. When provided, it overrides any default
+   * Authorization header configured on the client.
+   */
+  authorization?: string;
+  headers?: HeadersInit;
+  host?: string;
+  maxRetries?: number;
+  signal?: AbortSignal | null;
+  timeout?: number;
+};
 
 /** All arguments to `request()` */
-export type FullParams = FetchParams & {
+export type FullRequestOptions = RequestOptions & {
   path: string;
   query?: QueryParams;
   body?: unknown;
-  host?: string;
-  method?: string;
+  method?: HTTPMethod;
 };
 
 export class SumUpError extends Error {}
diff --git a/sdk/src/index.ts b/sdk/src/index.ts
index 894693e5..3f6f5e8e 100644
--- a/sdk/src/index.ts
+++ b/sdk/src/index.ts
@@ -3,7 +3,7 @@
 import { HTTPClient } from "./client";
 
 export type { APIConfig } from "./client";
-export type { FetchParams } from "./core";
+export type { RequestOptions } from "./core";
 export { APIError, SumUpError } from "./core";
 export * from "./resources/checkouts";
 export * from "./types";
diff --git a/sdk/src/resources/checkouts/index.ts b/sdk/src/resources/checkouts/index.ts
index 762e3642..acfb170d 100644
--- a/sdk/src/resources/checkouts/index.ts
+++ b/sdk/src/resources/checkouts/index.ts
@@ -1,7 +1,6 @@
 // Code generated by @sumup/sumup-ts-codegen. DO NOT EDIT.
 
-import { type APIPromise, APIResource, type FetchParams } from "../../core";
-
+import { type APIPromise, APIResource, type RequestOptions } from "../../core";
 import type {
   Checkout,
   CheckoutAccepted,
@@ -47,12 +46,12 @@ export class Checkouts extends APIResource {
   listAvailablePaymentMethods(
     merchantCode: string,
     query?: GetPaymentMethodsQueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<GetPaymentMethodsResponse, DetailsError> {
     return this._client.get<GetPaymentMethodsResponse, DetailsError>({
       path: `/v0.1/merchants/${merchantCode}/payment-methods`,
       query,
-      ...params,
+      ...options,
     });
   }
 
@@ -61,12 +60,12 @@ export class Checkouts extends APIResource {
    */
   list(
     query?: ListCheckoutsQueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<CheckoutSuccess[], Problem> {
     return this._client.get<CheckoutSuccess[], Problem>({
       path: `/v0.1/checkouts`,
       query,
-      ...params,
+      ...options,
     });
   }
 
@@ -80,7 +79,7 @@ export class Checkouts extends APIResource {
    */
   create(
     body: CheckoutCreateRequest,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<
     Checkout,
     ErrorExtended | Problem | ErrorForbidden | ErrorBody
@@ -91,7 +90,7 @@ export class Checkouts extends APIResource {
     >({
       path: `/v0.1/checkouts`,
       body,
-      ...params,
+      ...options,
     });
   }
 
@@ -100,11 +99,11 @@ export class Checkouts extends APIResource {
    */
   get(
     id: string,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<CheckoutSuccess, Problem | ErrorBody> {
     return this._client.get<CheckoutSuccess, Problem | ErrorBody>({
       path: `/v0.1/checkouts/${id}`,
-      ...params,
+      ...options,
     });
   }
 
@@ -117,7 +116,7 @@ export class Checkouts extends APIResource {
   process(
     id: string,
     body: ProcessCheckout,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<
     CheckoutSuccess | CheckoutAccepted,
     ProcessCheckoutError | Problem | ErrorBody
@@ -128,7 +127,7 @@ export class Checkouts extends APIResource {
     >({
       path: `/v0.1/checkouts/${id}`,
       body,
-      ...params,
+      ...options,
     });
   }
 
@@ -137,11 +136,11 @@ export class Checkouts extends APIResource {
    */
   deactivate(
     id: string,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Checkout, Problem | ErrorBody> {
     return this._client.delete<Checkout, Problem | ErrorBody>({
       path: `/v0.1/checkouts/${id}`,
-      ...params,
+      ...options,
     });
   }
 }
diff --git a/sdk/src/resources/customers/index.ts b/sdk/src/resources/customers/index.ts
index 9c111d26..933e9b75 100644
--- a/sdk/src/resources/customers/index.ts
+++ b/sdk/src/resources/customers/index.ts
@@ -1,7 +1,6 @@
 // Code generated by @sumup/sumup-ts-codegen. DO NOT EDIT.
 
-import { type APIPromise, APIResource, type FetchParams } from "../../core";
-
+import { type APIPromise, APIResource, type RequestOptions } from "../../core";
 import type {
   Customer,
   ErrorBody,
@@ -25,7 +24,7 @@ export class Customers extends APIResource {
    */
   create(
     body: Customer,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<
     Customer,
     CreateCustomerError | Problem | ErrorForbidden | ErrorBody
@@ -36,7 +35,7 @@ export class Customers extends APIResource {
     >({
       path: `/v0.1/customers`,
       body,
-      ...params,
+      ...options,
     });
   }
 
@@ -45,11 +44,11 @@ export class Customers extends APIResource {
    */
   get(
     customerId: string,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Customer, Problem | ErrorForbidden | ErrorBody> {
     return this._client.get<Customer, Problem | ErrorForbidden | ErrorBody>({
       path: `/v0.1/customers/${customerId}`,
-      ...params,
+      ...options,
     });
   }
 
@@ -62,12 +61,12 @@ export class Customers extends APIResource {
   update(
     customerId: string,
     body: UpdateCustomerParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Customer, Problem | ErrorForbidden | ErrorBody> {
     return this._client.put<Customer, Problem | ErrorForbidden | ErrorBody>({
       path: `/v0.1/customers/${customerId}`,
       body,
-      ...params,
+      ...options,
     });
   }
 
@@ -76,7 +75,7 @@ export class Customers extends APIResource {
    */
   listPaymentInstruments(
     customerId: string,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<
     PaymentInstrumentResponse[],
     Problem | ErrorForbidden | ErrorBody
@@ -86,7 +85,7 @@ export class Customers extends APIResource {
       Problem | ErrorForbidden | ErrorBody
     >({
       path: `/v0.1/customers/${customerId}/payment-instruments`,
-      ...params,
+      ...options,
     });
   }
 
@@ -96,11 +95,11 @@ export class Customers extends APIResource {
   deactivatePaymentInstrument(
     customerId: string,
     token: string,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<void, ErrorBody | Problem | ErrorForbidden> {
     return this._client.delete<void, ErrorBody | Problem | ErrorForbidden>({
       path: `/v0.1/customers/${customerId}/payment-instruments/${token}`,
-      ...params,
+      ...options,
     });
   }
 }
diff --git a/sdk/src/resources/members/index.ts b/sdk/src/resources/members/index.ts
index 918fa94d..10eca8ef 100644
--- a/sdk/src/resources/members/index.ts
+++ b/sdk/src/resources/members/index.ts
@@ -1,7 +1,6 @@
 // Code generated by @sumup/sumup-ts-codegen. DO NOT EDIT.
 
-import { type APIPromise, APIResource, type FetchParams } from "../../core";
-
+import { type APIPromise, APIResource, type RequestOptions } from "../../core";
 import type {
   Attributes,
   Member,
@@ -75,12 +74,12 @@ export class Members extends APIResource {
   list(
     merchantCode: string,
     query?: ListMerchantMembersQueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<ListMerchantMembersResponse, Problem> {
     return this._client.get<ListMerchantMembersResponse, Problem>({
       path: `/v0.1/merchants/${merchantCode}/members`,
       query,
-      ...params,
+      ...options,
     });
   }
 
@@ -90,12 +89,12 @@ export class Members extends APIResource {
   create(
     merchantCode: string,
     body: CreateMerchantMemberParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Member, Problem> {
     return this._client.post<Member, Problem>({
       path: `/v0.1/merchants/${merchantCode}/members`,
       body,
-      ...params,
+      ...options,
     });
   }
 
@@ -105,11 +104,11 @@ export class Members extends APIResource {
   get(
     merchantCode: string,
     memberId: string,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Member, Problem> {
     return this._client.get<Member, Problem>({
       path: `/v0.1/merchants/${merchantCode}/members/${memberId}`,
-      ...params,
+      ...options,
     });
   }
 
@@ -120,12 +119,12 @@ export class Members extends APIResource {
     merchantCode: string,
     memberId: string,
     body: UpdateMerchantMemberParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Member, Problem> {
     return this._client.put<Member, Problem>({
       path: `/v0.1/merchants/${merchantCode}/members/${memberId}`,
       body,
-      ...params,
+      ...options,
     });
   }
 
@@ -135,11 +134,11 @@ export class Members extends APIResource {
   delete(
     merchantCode: string,
     memberId: string,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<void, Problem> {
     return this._client.delete<void, Problem>({
       path: `/v0.1/merchants/${merchantCode}/members/${memberId}`,
-      ...params,
+      ...options,
     });
   }
 }
diff --git a/sdk/src/resources/memberships/index.ts b/sdk/src/resources/memberships/index.ts
index 38e40392..f2f8c8d9 100644
--- a/sdk/src/resources/memberships/index.ts
+++ b/sdk/src/resources/memberships/index.ts
@@ -1,7 +1,6 @@
 // Code generated by @sumup/sumup-ts-codegen. DO NOT EDIT.
 
-import { type APIPromise, APIResource, type FetchParams } from "../../core";
-
+import { type APIPromise, APIResource, type RequestOptions } from "../../core";
 import type { Membership, MembershipStatus, ResourceType } from "../../types";
 export type ListMembershipsQueryParams = {
   offset?: number;
@@ -27,12 +26,12 @@ export class Memberships extends APIResource {
    */
   list(
     query?: ListMembershipsQueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<ListMembershipsResponse, unknown> {
     return this._client.get<ListMembershipsResponse, unknown>({
       path: `/v0.1/memberships`,
       query,
-      ...params,
+      ...options,
     });
   }
 }
diff --git a/sdk/src/resources/merchants/index.ts b/sdk/src/resources/merchants/index.ts
index 091803fa..cdbf5077 100644
--- a/sdk/src/resources/merchants/index.ts
+++ b/sdk/src/resources/merchants/index.ts
@@ -1,7 +1,6 @@
 // Code generated by @sumup/sumup-ts-codegen. DO NOT EDIT.
 
-import { type APIPromise, APIResource, type FetchParams } from "../../core";
-
+import { type APIPromise, APIResource, type RequestOptions } from "../../core";
 import type {
   ListPersonsResponseBody,
   Merchant,
@@ -27,12 +26,12 @@ export class Merchants extends APIResource {
   get(
     merchantCode: string,
     query?: GetMerchantQueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Merchant, Problem> {
     return this._client.get<Merchant, Problem>({
       path: `/v1/merchants/${merchantCode}`,
       query,
-      ...params,
+      ...options,
     });
   }
 
@@ -42,12 +41,12 @@ export class Merchants extends APIResource {
   listPersons(
     merchantCode: string,
     query?: ListPersonsQueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<ListPersonsResponseBody, Problem> {
     return this._client.get<ListPersonsResponseBody, Problem>({
       path: `/v1/merchants/${merchantCode}/persons`,
       query,
-      ...params,
+      ...options,
     });
   }
 
@@ -58,12 +57,12 @@ export class Merchants extends APIResource {
     merchantCode: string,
     personId: string,
     query?: GetPersonQueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Person, Problem> {
     return this._client.get<Person, Problem>({
       path: `/v1/merchants/${merchantCode}/persons/${personId}`,
       query,
-      ...params,
+      ...options,
     });
   }
 }
diff --git a/sdk/src/resources/payouts/index.ts b/sdk/src/resources/payouts/index.ts
index 24b030fe..0b32ef89 100644
--- a/sdk/src/resources/payouts/index.ts
+++ b/sdk/src/resources/payouts/index.ts
@@ -1,7 +1,6 @@
 // Code generated by @sumup/sumup-ts-codegen. DO NOT EDIT.
 
-import { type APIPromise, APIResource, type FetchParams } from "../../core";
-
+import { type APIPromise, APIResource, type RequestOptions } from "../../core";
 import type { ErrorExtended, FinancialPayouts, Problem } from "../../types";
 export type ListPayoutsV1QueryParams = {
   start_date: string;
@@ -30,12 +29,12 @@ export class Payouts extends APIResource {
   list(
     merchantCode: string,
     query: ListPayoutsV1QueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<FinancialPayouts, ErrorExtended[] | Problem> {
     return this._client.get<FinancialPayouts, ErrorExtended[] | Problem>({
       path: `/v1.0/merchants/${merchantCode}/payouts`,
       query,
-      ...params,
+      ...options,
     });
   }
 
@@ -44,12 +43,12 @@ export class Payouts extends APIResource {
    */
   listDeprecated(
     query: ListPayoutsQueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<FinancialPayouts, ErrorExtended[] | Problem> {
     return this._client.get<FinancialPayouts, ErrorExtended[] | Problem>({
       path: `/v0.1/me/financials/payouts`,
       query,
-      ...params,
+      ...options,
     });
   }
 }
diff --git a/sdk/src/resources/readers/index.ts b/sdk/src/resources/readers/index.ts
index 0a225fb4..47f67f1d 100644
--- a/sdk/src/resources/readers/index.ts
+++ b/sdk/src/resources/readers/index.ts
@@ -1,7 +1,6 @@
 // Code generated by @sumup/sumup-ts-codegen. DO NOT EDIT.
 
-import { type APIPromise, APIResource, type FetchParams } from "../../core";
-
+import { type APIPromise, APIResource, type RequestOptions } from "../../core";
 import type {
   CreateReaderCheckoutRequest,
   CreateReaderCheckoutResponse,
@@ -31,11 +30,11 @@ export class Readers extends APIResource {
    */
   list(
     merchantCode: string,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<ListReadersResponse, unknown> {
     return this._client.get<ListReadersResponse, unknown>({
       path: `/v0.1/merchants/${merchantCode}/readers`,
-      ...params,
+      ...options,
     });
   }
 
@@ -45,12 +44,12 @@ export class Readers extends APIResource {
   create(
     merchantCode: string,
     body: CreateReaderParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Reader, Problem> {
     return this._client.post<Reader, Problem>({
       path: `/v0.1/merchants/${merchantCode}/readers`,
       body,
-      ...params,
+      ...options,
     });
   }
 
@@ -60,11 +59,11 @@ export class Readers extends APIResource {
   get(
     merchantCode: string,
     id: ReaderID,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Reader, Problem> {
     return this._client.get<Reader, Problem>({
       path: `/v0.1/merchants/${merchantCode}/readers/${id}`,
-      ...params,
+      ...options,
     });
   }
 
@@ -74,11 +73,11 @@ export class Readers extends APIResource {
   delete(
     merchantCode: string,
     id: ReaderID,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<void, Problem> {
     return this._client.delete<void, Problem>({
       path: `/v0.1/merchants/${merchantCode}/readers/${id}`,
-      ...params,
+      ...options,
     });
   }
 
@@ -89,12 +88,12 @@ export class Readers extends APIResource {
     merchantCode: string,
     id: ReaderID,
     body: UpdateReaderParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Reader, Problem> {
     return this._client.patch<Reader, Problem>({
       path: `/v0.1/merchants/${merchantCode}/readers/${id}`,
       body,
-      ...params,
+      ...options,
     });
   }
 
@@ -116,12 +115,12 @@ export class Readers extends APIResource {
     merchantCode: string,
     readerId: string,
     body: CreateReaderCheckoutRequest,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<CreateReaderCheckoutResponse, Problem> {
     return this._client.post<CreateReaderCheckoutResponse, Problem>({
       path: `/v0.1/merchants/${merchantCode}/readers/${readerId}/checkout`,
       body,
-      ...params,
+      ...options,
     });
   }
 
@@ -150,11 +149,11 @@ export class Readers extends APIResource {
   getStatus(
     merchantCode: string,
     readerId: string,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<StatusResponse, Problem> {
     return this._client.get<StatusResponse, Problem>({
       path: `/v0.1/merchants/${merchantCode}/readers/${readerId}/status`,
-      ...params,
+      ...options,
     });
   }
 
@@ -179,12 +178,12 @@ export class Readers extends APIResource {
     merchantCode: string,
     readerId: string,
     body?: CreateReaderTerminateParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<void, Problem> {
     return this._client.post<void, Problem>({
       path: `/v0.1/merchants/${merchantCode}/readers/${readerId}/terminate`,
       body,
-      ...params,
+      ...options,
     });
   }
 }
diff --git a/sdk/src/resources/receipts/index.ts b/sdk/src/resources/receipts/index.ts
index fa2b14f9..c1a55bba 100644
--- a/sdk/src/resources/receipts/index.ts
+++ b/sdk/src/resources/receipts/index.ts
@@ -1,7 +1,6 @@
 // Code generated by @sumup/sumup-ts-codegen. DO NOT EDIT.
 
-import { type APIPromise, APIResource, type FetchParams } from "../../core";
-
+import { type APIPromise, APIResource, type RequestOptions } from "../../core";
 import type { ErrorBody, Problem, Receipt } from "../../types";
 export type GetReceiptQueryParams = {
   mid: string;
@@ -15,12 +14,12 @@ export class Receipts extends APIResource {
   get(
     id: string,
     query: GetReceiptQueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Receipt, ErrorBody | Problem> {
     return this._client.get<Receipt, ErrorBody | Problem>({
       path: `/v1.1/receipts/${id}`,
       query,
-      ...params,
+      ...options,
     });
   }
 }
diff --git a/sdk/src/resources/roles/index.ts b/sdk/src/resources/roles/index.ts
index c721a524..42356c92 100644
--- a/sdk/src/resources/roles/index.ts
+++ b/sdk/src/resources/roles/index.ts
@@ -1,7 +1,6 @@
 // Code generated by @sumup/sumup-ts-codegen. DO NOT EDIT.
 
-import { type APIPromise, APIResource, type FetchParams } from "../../core";
-
+import { type APIPromise, APIResource, type RequestOptions } from "../../core";
 import type { Metadata, Problem, Role } from "../../types";
 export type ListMerchantRolesResponse = { items: Role[] };
 
@@ -42,11 +41,11 @@ export class Roles extends APIResource {
    */
   list(
     merchantCode: string,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<ListMerchantRolesResponse, Problem> {
     return this._client.get<ListMerchantRolesResponse, Problem>({
       path: `/v0.1/merchants/${merchantCode}/roles`,
-      ...params,
+      ...options,
     });
   }
 
@@ -56,12 +55,12 @@ export class Roles extends APIResource {
   create(
     merchantCode: string,
     body: CreateMerchantRoleParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Role, Problem> {
     return this._client.post<Role, Problem>({
       path: `/v0.1/merchants/${merchantCode}/roles`,
       body,
-      ...params,
+      ...options,
     });
   }
 
@@ -71,11 +70,11 @@ export class Roles extends APIResource {
   get(
     merchantCode: string,
     roleId: string,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Role, Problem> {
     return this._client.get<Role, Problem>({
       path: `/v0.1/merchants/${merchantCode}/roles/${roleId}`,
-      ...params,
+      ...options,
     });
   }
 
@@ -85,11 +84,11 @@ export class Roles extends APIResource {
   delete(
     merchantCode: string,
     roleId: string,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<void, Problem> {
     return this._client.delete<void, Problem>({
       path: `/v0.1/merchants/${merchantCode}/roles/${roleId}`,
-      ...params,
+      ...options,
     });
   }
 
@@ -100,12 +99,12 @@ export class Roles extends APIResource {
     merchantCode: string,
     roleId: string,
     body: UpdateMerchantRoleParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Role, Problem> {
     return this._client.patch<Role, Problem>({
       path: `/v0.1/merchants/${merchantCode}/roles/${roleId}`,
       body,
-      ...params,
+      ...options,
     });
   }
 }
diff --git a/sdk/src/resources/subaccounts/index.ts b/sdk/src/resources/subaccounts/index.ts
index 817bcc3a..2f318197 100644
--- a/sdk/src/resources/subaccounts/index.ts
+++ b/sdk/src/resources/subaccounts/index.ts
@@ -1,7 +1,6 @@
 // Code generated by @sumup/sumup-ts-codegen. DO NOT EDIT.
 
-import { type APIPromise, APIResource, type FetchParams } from "../../core";
-
+import { type APIPromise, APIResource, type RequestOptions } from "../../core";
 import type { Operator, Problem } from "../../types";
 export type ListSubAccountsQueryParams = {
   query?: string;
@@ -41,12 +40,12 @@ export class Subaccounts extends APIResource {
    */
   listSubAccounts(
     query?: ListSubAccountsQueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Operator[], unknown> {
     return this._client.get<Operator[], unknown>({
       path: `/v0.1/me/accounts`,
       query,
-      ...params,
+      ...options,
     });
   }
 
@@ -55,12 +54,12 @@ export class Subaccounts extends APIResource {
    */
   createSubAccount(
     body: CreateSubAccountParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Operator, Problem> {
     return this._client.post<Operator, Problem>({
       path: `/v0.1/me/accounts`,
       body,
-      ...params,
+      ...options,
     });
   }
 
@@ -69,11 +68,11 @@ export class Subaccounts extends APIResource {
    */
   compatGetOperator(
     operatorId: number,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Operator, unknown> {
     return this._client.get<Operator, unknown>({
       path: `/v0.1/me/accounts/${operatorId}`,
-      ...params,
+      ...options,
     });
   }
 
@@ -83,12 +82,12 @@ export class Subaccounts extends APIResource {
   updateSubAccount(
     operatorId: number,
     body: UpdateSubAccountParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<Operator, Problem> {
     return this._client.put<Operator, Problem>({
       path: `/v0.1/me/accounts/${operatorId}`,
       body,
-      ...params,
+      ...options,
     });
   }
 }
diff --git a/sdk/src/resources/transactions/index.ts b/sdk/src/resources/transactions/index.ts
index be0899dc..48c5f0a8 100644
--- a/sdk/src/resources/transactions/index.ts
+++ b/sdk/src/resources/transactions/index.ts
@@ -1,7 +1,6 @@
 // Code generated by @sumup/sumup-ts-codegen. DO NOT EDIT.
 
-import { type APIPromise, APIResource, type FetchParams } from "../../core";
-
+import { type APIPromise, APIResource, type RequestOptions } from "../../core";
 import type {
   EntryModeFilter,
   ErrorBody,
@@ -92,12 +91,12 @@ export class Transactions extends APIResource {
   refund(
     txnId: string,
     body?: RefundTransactionParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<void, ErrorBody> {
     return this._client.post<void, ErrorBody>({
       path: `/v0.1/me/refund/${txnId}`,
       body,
-      ...params,
+      ...options,
     });
   }
 
@@ -114,12 +113,12 @@ export class Transactions extends APIResource {
   get(
     merchantCode: string,
     query?: GetTransactionV2_1QueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<TransactionFull, Problem | ErrorBody> {
     return this._client.get<TransactionFull, Problem | ErrorBody>({
       path: `/v2.1/merchants/${merchantCode}/transactions`,
       query,
-      ...params,
+      ...options,
     });
   }
 
@@ -135,12 +134,12 @@ export class Transactions extends APIResource {
    */
   getDeprecated(
     query?: GetTransactionQueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<TransactionFull, Problem | ErrorBody> {
     return this._client.get<TransactionFull, Problem | ErrorBody>({
       path: `/v0.1/me/transactions`,
       query,
-      ...params,
+      ...options,
     });
   }
 
@@ -150,12 +149,12 @@ export class Transactions extends APIResource {
   list(
     merchantCode: string,
     query?: ListTransactionsV2_1QueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<ListTransactionsV2_1Response, ErrorBody | Problem> {
     return this._client.get<ListTransactionsV2_1Response, ErrorBody | Problem>({
       path: `/v2.1/merchants/${merchantCode}/transactions/history`,
       query,
-      ...params,
+      ...options,
     });
   }
 
@@ -164,12 +163,12 @@ export class Transactions extends APIResource {
    */
   listDeprecated(
     query?: ListTransactionsQueryParams,
-    params?: FetchParams,
+    options?: RequestOptions,
   ): APIPromise<ListTransactionsResponse, ErrorBody | Problem> {
     return this._client.get<ListTransactionsResponse, ErrorBody | Problem>({
       path: `/v0.1/me/transactions/history`,
       query,
-      ...params,
+      ...options,
     });
   }
 }
diff --git a/sdk/tests/client.test.ts b/sdk/tests/client.test.ts
index d44221eb..4607684f 100644
--- a/sdk/tests/client.test.ts
+++ b/sdk/tests/client.test.ts
@@ -1,7 +1,8 @@
-import { describe, expect, it } from "vitest";
+import { afterEach, describe, expect, it, vi } from "vitest";
 
 import { SumUp } from "../src";
 import { API_VERSION } from "../src/api-version";
+import { mergeParams } from "../src/client";
 import { buildRuntimeHeaders } from "../src/runtime";
 import { VERSION } from "../src/version";
 
@@ -43,3 +44,95 @@ describe("query string", () => {
     ).toEqual("a=b&foo=false&x=&include=1&include=2");
   });
 });
+
+describe("merge params", () => {
+  it("allows per-request authorization to override the default client header", () => {
+    const params = mergeParams(
+      {
+        headers: {
+          Authorization: "Bearer default-token",
+        },
+      },
+      {
+        authorization: "Bearer request-token",
+      },
+    );
+
+    const headers = new Headers(params.headers);
+    expect(headers.get("authorization")).toBe("Bearer request-token");
+  });
+});
+
+afterEach(() => {
+  vi.restoreAllMocks();
+  vi.useRealTimers();
+});
+
+describe("request options", () => {
+  it("retries a request when the per-call override allows it", async () => {
+    const fetchMock = vi
+      .fn()
+      .mockRejectedValueOnce(new TypeError("network"))
+      .mockResolvedValueOnce(
+        new Response(JSON.stringify({ id: "checkout-id" }), {
+          headers: {
+            "content-type": "application/json",
+          },
+          status: 200,
+        }),
+      );
+    vi.stubGlobal("fetch", fetchMock);
+
+    const client = new SumUp({ maxRetries: 0 });
+    const data = await client.checkouts.get("checkout-id", { maxRetries: 1 });
+
+    expect(data).toEqual({ id: "checkout-id" });
+    expect(fetchMock).toHaveBeenCalledTimes(2);
+  });
+
+  it("aborts a request when the per-call timeout is exceeded", async () => {
+    vi.useFakeTimers();
+
+    const fetchMock = vi.fn((_input: URL | RequestInfo, init?: RequestInit) => {
+      return new Promise<Response>((_resolve, reject) => {
+        const signal = init?.signal;
+        signal?.addEventListener(
+          "abort",
+          () => {
+            reject(signal.reason ?? new DOMException("Aborted", "AbortError"));
+          },
+          { once: true },
+        );
+      });
+    });
+    vi.stubGlobal("fetch", fetchMock);
+
+    const client = new SumUp();
+    const request = client.checkouts.get("checkout-id", { timeout: 10 });
+    const assertion = expect(request).rejects.toThrow(
+      "Request timed out after 10ms.",
+    );
+
+    await vi.advanceTimersByTimeAsync(10);
+
+    await assertion;
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+  });
+});
+
+describe("generated signatures", () => {
+  it("keeps request options in the final argument position", () => {
+    const client = new SumUp();
+    const getSpy = vi
+      .spyOn(client, "get")
+      .mockReturnValue({} as ReturnType<typeof client.get>);
+
+    client.checkouts.list(undefined, { timeout: 25 });
+
+    expect(getSpy).toHaveBeenCalledWith({
+      path: "/v0.1/checkouts",
+      query: undefined,
+      timeout: 25,
+    });
+  });
+});