diff --git a/examples/mixture-of-agents/index.html b/examples/mixture-of-agents/index.html
index a35d275..e971b73 100644
--- a/examples/mixture-of-agents/index.html
+++ b/examples/mixture-of-agents/index.html
@@ -165,7 +165,7 @@
         "GPT-4o Mini",
         "Llama 3.1 8B",
         "Mixtral 8x7B",
-      ]
+      ];
       const individualResults = "{{ individual }}";
       const aggResults = "{{ summaries }}";
 
@@ -190,7 +190,7 @@
           contentArea.textContent =
             individualResults[currentLayer][currentIndex].trim();
 
-          cardTitle.textContent = `${modelNames[currentIndex]} - Layer ${ currentLayer + 1 }`;
+          cardTitle.textContent = `${modelNames[currentIndex]} - Layer ${currentLayer + 1}`;
         } else {
           contentArea.textContent = aggResults[currentLayer].trim();
           cardTitle.textContent = `MoA Layer ${currentLayer + 1}`;
diff --git a/src/Substrate.ts b/src/Substrate.ts
index e123c9f..4ecb6cc 100644
--- a/src/Substrate.ts
+++ b/src/Substrate.ts
@@ -27,12 +27,22 @@ type Configuration = {
    */
   timeout?: number;
 
+  /**
+   * Secrets for third party services.
+   */
+  secrets?: Secrets;
+
   /**
    * Add additional headers to each request. These may override headers set by the Substrate client.
    */
   additionalHeaders?: Record<string, string>;
 };
 
+export type Secrets = {
+  openai?: string;
+  anthropic?: string;
+};
+
 /**
  * [docs/introduction](https://docs.substrate.run)
  */
@@ -51,6 +61,7 @@ export class Substrate {
     baseUrl,
     apiVersion,
     timeout,
+    secrets,
     additionalHeaders,
   }: Configuration) {
     if (!apiKey) {
@@ -63,6 +74,15 @@ export class Substrate {
     this.apiVersion = apiVersion ?? OpenAPIjson["info"]["version"];
     this.timeout = timeout ?? 300_000;
     this.additionalHeaders = additionalHeaders ?? {};
+    if (secrets) {
+      if (secrets.openai) {
+        this.additionalHeaders["x-substrate-openai-api-key"] = secrets.openai;
+      }
+      if (secrets.anthropic) {
+        this.additionalHeaders["x-substrate-anthropic-api-key"] =
+          secrets.anthropic;
+      }
+    }
   }
 
   /**