diff --git a/src/common.ts b/src/common.ts
index eae37f2..9db4988 100644
--- a/src/common.ts
+++ b/src/common.ts
@@ -77,7 +77,7 @@ export class GaxiosError<T = any> extends Error {
 
   constructor(
     message: string,
-    public config: GaxiosOptions,
+    public config: GaxiosOptionsPrepared,
     public response?: GaxiosResponse<T>,
     public error?: Error | NodeJS.ErrnoException
   ) {
@@ -111,7 +111,7 @@ export class GaxiosError<T = any> extends Error {
     }
 
     if (config.errorRedactor) {
-      config.errorRedactor<T>({
+      config.errorRedactor({
         config: this.config,
         response: this.response,
       });
@@ -119,37 +119,35 @@ export class GaxiosError<T = any> extends Error {
   }
 }
 
-/**
- * @deprecated use native {@link globalThis.Headers}.
- */
-export interface Headers {
-  [index: string]: any;
-}
-export type GaxiosPromise<T = any> = Promise<GaxiosResponse<T>>;
+type GaxiosResponseData =
+  | ReturnType<JSON['parse']>
+  | GaxiosOptionsPrepared['data'];
+
+export type GaxiosPromise<T = GaxiosResponseData> = Promise<GaxiosResponse<T>>;
 
-export interface GaxiosResponse<T = any> extends Response {
-  config: GaxiosOptions;
+export interface GaxiosResponse<T = GaxiosResponseData> extends Response {
+  config: GaxiosOptionsPrepared;
   data: T;
 }
 
 export interface GaxiosMultipartOptions {
-  headers: Headers;
+  headers: HeadersInit;
   content: string | Readable;
 }
 
 /**
  * Request options that are used to form the request.
  */
-export interface GaxiosOptions extends Omit<RequestInit, 'headers'> {
+export interface GaxiosOptions extends RequestInit {
   /**
    * Optional method to override making the actual HTTP request. Useful
    * for writing tests.
    *
    * @deprecated Use {@link GaxiosOptions.fetchImplementation} instead.
    */
-  adapter?: <T = any>(
-    options: GaxiosOptions,
-    defaultAdapter: (options: GaxiosOptions) => GaxiosPromise<T>
+  adapter?: <T = GaxiosResponseData>(
+    options: GaxiosOptionsPrepared,
+    defaultAdapter: (options: GaxiosOptionsPrepared) => GaxiosPromise<T>
   ) => GaxiosPromise<T>;
   url?: string | URL;
   /**
@@ -167,16 +165,6 @@ export interface GaxiosOptions extends Omit<RequestInit, 'headers'> {
     | 'OPTIONS'
     | 'TRACE'
     | 'PATCH';
-  /**
-   * Recommended: Provide a native {@link globalThis.Headers Headers} object.
-   *
-   * @privateRemarks
-   *
-   * This type does not have the native {@link globalThis.Headers Headers} in
-   * its signature as it would break customers looking to modify headers before
-   * providing to this library (new, unnecessary type checks/guards).
-   */
-  headers?: Headers;
   /**
    * The data to send in the {@link RequestInit.body} of the request. Objects will be
    * serialized as JSON, except for:
@@ -308,24 +296,11 @@ export interface GaxiosOptions extends Omit<RequestInit, 'headers'> {
    */
   errorRedactor?: typeof defaultErrorRedactor | false;
 }
-/**
- * A partial object of `GaxiosOptions` with only redactable keys
- *
- * @experimental
- */
-export type RedactableGaxiosOptions = Pick<
-  GaxiosOptions,
-  'body' | 'data' | 'headers' | 'url'
->;
-/**
- * A partial object of `GaxiosResponse` with only redactable keys
- *
- * @experimental
- */
-export type RedactableGaxiosResponse<T = any> = Pick<
-  GaxiosResponse<T>,
-  'config' | 'data' | 'headers'
->;
+
+export interface GaxiosOptionsPrepared extends GaxiosOptions {
+  headers: globalThis.Headers;
+  url: URL;
+}
 
 /**
  * Configuration for the Gaxios `request` method.
@@ -381,7 +356,10 @@ export interface RetryConfig {
   retryBackoff?: (err: GaxiosError, defaultBackoffMs: number) => Promise<void>;
 }
 
-function translateData(responseType: string | undefined, data: any) {
+function translateData(
+  responseType: string | undefined,
+  data: GaxiosResponseData
+) {
   switch (responseType) {
     case 'stream':
       return data;
@@ -404,51 +382,30 @@ function translateData(responseType: string | undefined, data: any) {
  *
  * @experimental
  */
-export function defaultErrorRedactor<T = any>(data: {
-  config?: RedactableGaxiosOptions;
-  response?: RedactableGaxiosResponse<T>;
-}) {
+export function defaultErrorRedactor<
+  O extends GaxiosOptionsPrepared,
+  R extends GaxiosResponse<GaxiosResponseData>,
+>(data: {config?: O; response?: R}) {
   const REDACT =
     '<<REDACTED> - See `errorRedactor` option in `gaxios` for configuration>.';
 
-  function redactHeaders(headers?: Headers | globalThis.Headers) {
+  function redactHeaders(headers?: Headers) {
     if (!headers) return;
 
-    function check(key: string) {
+    headers.forEach((_, key) => {
       // any casing of `Authentication`
       // any casing of `Authorization`
       // anything containing secret, such as 'client secret'
-      return (
+      if (
         /^authentication$/i.test(key) ||
         /^authorization$/i.test(key) ||
         /secret/i.test(key)
-      );
-    }
-
-    function redactHeadersObject(headers: Headers) {
-      for (const key of Object.keys(headers)) {
-        if (check(key)) headers[key] = REDACT;
-      }
-    }
-
-    function redactHeadersHeaders(headers: globalThis.Headers) {
-      headers.forEach((value, key) => {
-        if (check(key)) headers.set(key, REDACT);
-      });
-    }
-
-    // support `node-fetch` Headers and other third-parties
-    if (headers instanceof Headers || 'set' in headers) {
-      redactHeadersHeaders(headers as globalThis.Headers);
-    } else {
-      redactHeadersObject(headers);
-    }
+      )
+        headers.set(key, REDACT);
+    });
   }
 
-  function redactString<T extends GaxiosOptions | RedactableGaxiosResponse>(
-    obj: T,
-    key: keyof T
-  ) {
+  function redactString<T extends O | R>(obj: T, key: keyof T) {
     if (
       typeof obj === 'object' &&
       obj !== null &&
@@ -466,9 +423,7 @@ export function defaultErrorRedactor<T = any>(data: {
     }
   }
 
-  function redactObject<T extends GaxiosOptions['data'] | GaxiosResponse>(
-    obj: T | null
-  ) {
+  function redactObject<T extends O['data'] | R>(obj: T | null) {
     if (!obj) {
       return;
     } else if (
@@ -507,7 +462,7 @@ export function defaultErrorRedactor<T = any>(data: {
     redactObject(data.config.body);
 
     try {
-      const url = new URL('', data.config.url);
+      const url = data.config.url;
 
       if (url.searchParams.has('token')) {
         url.searchParams.set('token', REDACT);
@@ -517,7 +472,7 @@ export function defaultErrorRedactor<T = any>(data: {
         url.searchParams.set('client_secret', REDACT);
       }
 
-      data.config.url = url.toString();
+      data.config.url = url;
     } catch {
       // ignore error - no need to parse an invalid URL
     }
diff --git a/src/gaxios.ts b/src/gaxios.ts
index 0e19c29..e857d1b 100644
--- a/src/gaxios.ts
+++ b/src/gaxios.ts
@@ -20,9 +20,9 @@ import {
   GaxiosMultipartOptions,
   GaxiosError,
   GaxiosOptions,
+  GaxiosOptionsPrepared,
   GaxiosPromise,
   GaxiosResponse,
-  Headers,
   defaultErrorRedactor,
 } from './common';
 import {getRetryConfig} from './retry';
@@ -49,7 +49,7 @@ export class Gaxios {
    * Interceptors
    */
   interceptors: {
-    request: GaxiosInterceptorManager<GaxiosOptions>;
+    request: GaxiosInterceptorManager<GaxiosOptionsPrepared>;
     response: GaxiosInterceptorManager<GaxiosResponse>;
   };
 
@@ -76,11 +76,11 @@ export class Gaxios {
   }
 
   private async _defaultAdapter<T>(
-    config: GaxiosOptions
+    config: GaxiosOptionsPrepared
   ): Promise<GaxiosResponse<T>> {
     const fetchImpl = config.fetchImplementation || fetch;
 
-    const res = await fetchImpl(config.url!, config);
+    const res = await fetchImpl(config.url, config);
     const data = await this.getResponseData(config, res);
 
     return Object.assign(res, {config, data}) as GaxiosResponse<T>;
@@ -91,7 +91,7 @@ export class Gaxios {
    * @param opts Set of HTTP options that will be used for this HTTP request.
    */
   protected async _request<T = any>(
-    opts: GaxiosOptions = {}
+    opts: GaxiosOptionsPrepared
   ): GaxiosPromise<T> {
     try {
       let translatedResponse: GaxiosResponse<T>;
@@ -143,7 +143,7 @@ export class Gaxios {
   }
 
   private async getResponseData(
-    opts: GaxiosOptions,
+    opts: GaxiosOptionsPrepared,
     res: Response
   ): Promise<any> {
     if (
@@ -177,7 +177,7 @@ export class Gaxios {
 
   #urlMayUseProxy(
     url: string | URL,
-    noProxy: GaxiosOptions['noProxy'] = []
+    noProxy: GaxiosOptionsPrepared['noProxy'] = []
   ): boolean {
     const candidate = new URL(url);
     const noProxyList = [...noProxy];
@@ -225,13 +225,13 @@ export class Gaxios {
    * Applies the request interceptors. The request interceptors are applied after the
    * call to prepareRequest is completed.
    *
-   * @param {GaxiosOptions} options The current set of options.
+   * @param {GaxiosOptionsPrepared} options The current set of options.
    *
-   * @returns {Promise<GaxiosOptions>} Promise that resolves to the set of options or response after interceptors are applied.
+   * @returns {Promise<GaxiosOptionsPrepared>} Promise that resolves to the set of options or response after interceptors are applied.
    */
   async #applyRequestInterceptors(
-    options: GaxiosOptions
-  ): Promise<GaxiosOptions> {
+    options: GaxiosOptionsPrepared
+  ): Promise<GaxiosOptionsPrepared> {
     let promiseChain = Promise.resolve(options);
 
     for (const interceptor of this.interceptors.request.values()) {
@@ -239,7 +239,7 @@ export class Gaxios {
         promiseChain = promiseChain.then(
           interceptor.resolved,
           interceptor.rejected
-        ) as Promise<GaxiosOptions>;
+        ) as Promise<GaxiosOptionsPrepared>;
       }
     }
 
@@ -250,9 +250,9 @@ export class Gaxios {
    * Applies the response interceptors. The response interceptors are applied after the
    * call to request is made.
    *
-   * @param {GaxiosOptions} options The current set of options.
+   * @param {GaxiosOptionsPrepared} options The current set of options.
    *
-   * @returns {Promise<GaxiosOptions>} Promise that resolves to the set of options or response after interceptors are applied.
+   * @returns {Promise<GaxiosOptionsPrepared>} Promise that resolves to the set of options or response after interceptors are applied.
    */
   async #applyResponseInterceptors(
     response: GaxiosResponse | Promise<GaxiosResponse>
@@ -277,8 +277,10 @@ export class Gaxios {
    * @param options The original options passed from the client.
    * @returns Prepared options, ready to make a request
    */
-  async #prepareRequest(options: GaxiosOptions): Promise<GaxiosOptions> {
-    const opts: GaxiosOptions = extend(true, {}, this.defaults, options);
+  async #prepareRequest(
+    options: GaxiosOptions
+  ): Promise<GaxiosOptionsPrepared> {
+    const opts = extend(true, {}, this.defaults, options);
     if (!opts.url) {
       throw new Error('URL is required.');
     }
@@ -432,18 +434,10 @@ export class Gaxios {
       (opts as {duplex: string}).duplex = 'half';
     }
 
-    // preserve the original type for auditing later
-    if (opts.headers instanceof Headers) {
-      opts.headers = preparedHeaders;
-    } else {
-      const headers: Headers = {};
-      preparedHeaders.forEach((value, key) => {
-        headers[key] = value;
-      });
-      opts.headers = headers;
-    }
-
-    return opts;
+    return Object.assign(opts, {
+      headers: preparedHeaders,
+      url: opts.url instanceof URL ? opts.url : new URL(opts.url),
+    });
   }
 
   /**
@@ -498,8 +492,12 @@ export class Gaxios {
   ) {
     const finale = `--${boundary}--`;
     for (const currentPart of multipartOptions) {
+      const headers =
+        currentPart.headers instanceof Headers
+          ? currentPart.headers
+          : new Headers(currentPart.headers);
       const partContentType =
-        currentPart.headers['Content-Type'] || 'application/octet-stream';
+        headers.get('Content-Type') || 'application/octet-stream';
       const preamble = `--${boundary}\r\nContent-Type: ${partContentType}\r\n\r\n`;
       yield preamble;
       if (typeof currentPart.content === 'string') {
diff --git a/src/index.ts b/src/index.ts
index a18ddef..c563eac 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -18,7 +18,7 @@ export {
   GaxiosError,
   GaxiosPromise,
   GaxiosResponse,
-  Headers,
+  GaxiosOptionsPrepared,
   RetryConfig,
 } from './common';
 export {Gaxios, GaxiosOptions};
diff --git a/src/interceptor.ts b/src/interceptor.ts
index d52aacb..9ccfad8 100644
--- a/src/interceptor.ts
+++ b/src/interceptor.ts
@@ -11,12 +11,14 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-import {GaxiosError, GaxiosOptions, GaxiosResponse} from './common';
+import {GaxiosError, GaxiosOptionsPrepared, GaxiosResponse} from './common';
 
 /**
  * Interceptors that can be run for requests or responses. These interceptors run asynchronously.
  */
-export interface GaxiosInterceptor<T extends GaxiosOptions | GaxiosResponse> {
+export interface GaxiosInterceptor<
+  T extends GaxiosOptionsPrepared | GaxiosResponse,
+> {
   /**
    * Function to be run when applying an interceptor.
    *
@@ -37,5 +39,5 @@ export interface GaxiosInterceptor<T extends GaxiosOptions | GaxiosResponse> {
  * Class to manage collections of GaxiosInterceptors for both requests and responses.
  */
 export class GaxiosInterceptorManager<
-  T extends GaxiosOptions | GaxiosResponse,
+  T extends GaxiosOptionsPrepared | GaxiosResponse,
 > extends Set<GaxiosInterceptor<T> | null> {}
diff --git a/test/test.getch.ts b/test/test.getch.ts
index bdd0e53..0203204 100644
--- a/test/test.getch.ts
+++ b/test/test.getch.ts
@@ -25,7 +25,7 @@ import {
   GaxiosResponse,
   GaxiosPromise,
 } from '../src';
-import {GAXIOS_ERROR_SYMBOL, Headers} from '../src/common';
+import {GAXIOS_ERROR_SYMBOL, GaxiosOptionsPrepared} from '../src/common';
 import {pkg} from '../src/util';
 import fs from 'fs';
 
@@ -113,7 +113,11 @@ describe('🚙 error handling', () => {
       headers: {},
     } as GaxiosResponse;
 
-    const error = new GaxiosError('translation test', {}, response);
+    const error = new GaxiosError(
+      'translation test',
+      {} as GaxiosOptionsPrepared,
+      response
+    );
 
     assert(error.response);
     assert.equal(error.response.data, notJSON);
@@ -124,7 +128,7 @@ describe('🚙 error handling', () => {
 
     const wrongVersion = {[GAXIOS_ERROR_SYMBOL]: '0.0.0'};
     const correctVersion = {[GAXIOS_ERROR_SYMBOL]: pkg.version};
-    const child = new A('', {});
+    const child = new A('', {} as GaxiosOptionsPrepared);
 
     assert.equal(wrongVersion instanceof GaxiosError, false);
     assert.equal(correctVersion instanceof GaxiosError, true);
@@ -153,8 +157,8 @@ describe('🥁 configuration options', () => {
     const inst = new Gaxios({headers: {apple: 'juice'}});
     const res = await inst.request({url, headers: {figgy: 'pudding'}});
     scope.done();
-    assert.strictEqual(res.config.headers!.apple, 'juice');
-    assert.strictEqual(res.config.headers!.figgy, 'pudding');
+    assert.strictEqual(res.config.headers.get('apple'), 'juice');
+    assert.strictEqual(res.config.headers.get('figgy'), 'pudding');
   });
 
   it('should allow setting a base url in the options', async () => {
@@ -1093,7 +1097,7 @@ describe('🍂 defaults & instances', () => {
       }
       // eslint-disable-next-line @typescript-eslint/no-explicit-any
       protected async _request<T = any>(
-        opts: GaxiosOptions = {}
+        opts: GaxiosOptionsPrepared
       ): GaxiosPromise<T> {
         assert(opts.agent);
         return super._request(opts);
@@ -1109,8 +1113,8 @@ describe('🍂 defaults & instances', () => {
       });
       const res = await inst.request({url, headers: {figgy: 'pudding'}});
       scope.done();
-      assert.strictEqual(res.config.headers!.apple, 'juice');
-      assert.strictEqual(res.config.headers!.figgy, 'pudding');
+      assert.strictEqual(res.config.headers.get('apple'), 'juice');
+      assert.strictEqual(res.config.headers.get('figgy'), 'pudding');
       const agentCache = inst.getAgentCache();
       assert(agentCache.get(key));
     });
@@ -1141,7 +1145,7 @@ describe('interceptors', () => {
       const instance = new Gaxios();
       instance.interceptors.request.add({
         resolved: config => {
-          config.headers = {hello: 'world'};
+          config.headers.set('hello', 'world');
           return Promise.resolve(config);
         },
       });
@@ -1158,7 +1162,7 @@ describe('interceptors', () => {
             validateStatus: () => {
               return true;
             },
-          }) as unknown as Promise<GaxiosOptions>
+          }) as unknown as Promise<GaxiosOptionsPrepared>
       );
       const instance = new Gaxios();
       const interceptor = {resolved: spyFunc};
@@ -1180,22 +1184,22 @@ describe('interceptors', () => {
       const instance = new Gaxios();
       instance.interceptors.request.add({
         resolved: config => {
-          config.headers!['foo'] = 'bar';
+          config.headers.set('foo', 'bar');
           return Promise.resolve(config);
         },
       });
       instance.interceptors.request.add({
         resolved: config => {
-          assert.strictEqual(config.headers!['foo'], 'bar');
-          config.headers!['bar'] = 'baz';
+          assert.strictEqual(config.headers.get('foo'), 'bar');
+          config.headers.set('bar', 'baz');
           return Promise.resolve(config);
         },
       });
       instance.interceptors.request.add({
         resolved: config => {
-          assert.strictEqual(config.headers!['foo'], 'bar');
-          assert.strictEqual(config.headers!['bar'], 'baz');
-          config.headers!['baz'] = 'buzz';
+          assert.strictEqual(config.headers.get('foo'), 'bar');
+          assert.strictEqual(config.headers.get('bar'), 'baz');
+          config.headers.set('baz', 'buzz');
           return Promise.resolve(config);
         },
       });
@@ -1212,7 +1216,7 @@ describe('interceptors', () => {
             validateStatus: () => {
               return true;
             },
-          }) as unknown as Promise<GaxiosOptions>
+          }) as unknown as Promise<GaxiosOptionsPrepared>
       );
       const instance = new Gaxios();
       instance.interceptors.request.add({
@@ -1240,7 +1244,7 @@ describe('interceptors', () => {
       });
       instance.interceptors.request.add({
         resolved: config => {
-          config.headers = {hello: 'world'};
+          config.headers.set('hello', 'world');
           return Promise.resolve(config);
         },
         rejected: err => {