diff --git a/src/index.ts b/src/index.ts
index 76f464c..a65da26 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -17,7 +17,7 @@ export interface ClientOptions {
   /**
    * Defaults to process.env['HONCHO_AUTH_TOKEN'].
    */
-  apiKey?: string | undefined;
+  apiKey?: string | null | undefined;
 
   /**
    * Specifies the environment to use for the API.
@@ -87,14 +87,14 @@ export interface ClientOptions {
 
 /** API Client for interfacing with the Honcho API. */
 export class Honcho extends Core.APIClient {
-  apiKey: string;
+  apiKey: string | null;
 
   private _options: ClientOptions;
 
   /**
    * API Client for interfacing with the Honcho API.
    *
-   * @param {string | undefined} [opts.apiKey=process.env['HONCHO_AUTH_TOKEN'] ?? undefined]
+   * @param {string | null | undefined} [opts.apiKey=process.env['HONCHO_AUTH_TOKEN'] ?? null]
    * @param {Environment} [opts.environment=local] - Specifies the environment URL to use for the API.
    * @param {string} [opts.baseURL=process.env['HONCHO_BASE_URL'] ?? http://localhost:8000] - Override the default base URL for the API.
    * @param {number} [opts.timeout=1 minute] - The maximum amount of time (in milliseconds) the client will wait for a response before timing out.
@@ -106,15 +106,9 @@ export class Honcho extends Core.APIClient {
    */
   constructor({
     baseURL = Core.readEnv('HONCHO_BASE_URL'),
-    apiKey = Core.readEnv('HONCHO_AUTH_TOKEN'),
+    apiKey = Core.readEnv('HONCHO_AUTH_TOKEN') ?? null,
     ...opts
   }: ClientOptions = {}) {
-    if (apiKey === undefined) {
-      throw new Errors.HonchoError(
-        "The HONCHO_AUTH_TOKEN environment variable is missing or empty; either provide it, or instantiate the Honcho client with an apiKey option, like new Honcho({ apiKey: 'My API Key' }).",
-      );
-    }
-
     const options: ClientOptions = {
       apiKey,
       ...opts,
@@ -153,7 +147,23 @@ export class Honcho extends Core.APIClient {
     };
   }
 
+  protected override validateHeaders(headers: Core.Headers, customHeaders: Core.Headers) {
+    if (this.apiKey && headers['authorization']) {
+      return;
+    }
+    if (customHeaders['authorization'] === null) {
+      return;
+    }
+
+    throw new Error(
+      'Could not resolve authentication method. Expected the apiKey to be set. Or for the "Authorization" headers to be explicitly omitted',
+    );
+  }
+
   protected override authHeaders(opts: Core.FinalRequestOptions): Core.Headers {
+    if (this.apiKey == null) {
+      return {};
+    }
     return { Authorization: `Bearer ${this.apiKey}` };
   }