diff --git a/README.md b/README.md
index 5906af1..b5f69fd 100644
--- a/README.md
+++ b/README.md
@@ -32,6 +32,10 @@ First, install the SDK in your project
 npm install @anam-ai/js-sdk
 ```
 
+## Deprecation Notice
+
+**Important**: The `brainType` field in `PersonaConfig` is deprecated and will be removed in a future version. Please use `llmId` instead. If you are currently using `brainType`, you will see a deprecation warning in the console. Both fields are supported during the transition period.
+
 ## Local development
 
 The quickest way to start testing the SDK is to use your API key directly with our SDK and the example persona config shown below.
@@ -84,7 +88,7 @@ const response = await fetch(`https://api.anam.ai/v1/auth/session-token`, {
       name: 'Cara',
       avatarId: '30fa96d0-26c4-4e55-94a0-517025942e18',
       voiceId: '6bfbe25a-979d-40f3-a92b-5394170af54b',
-      brainType: 'ANAM_GPT_4O_MINI_V1',
+      llmId: '<LLM ID HERE>',
       systemPrompt:
         "[STYLE] Reply in natural speech without formatting. Add pauses using '...' and very occasionally a disfluency. [PERSONALITY] You are Cara, a helpful assistant.",
     },
diff --git a/src/modules/CoreApiRestClient.ts b/src/modules/CoreApiRestClient.ts
index 33844f8..59bc82c 100644
--- a/src/modules/CoreApiRestClient.ts
+++ b/src/modules/CoreApiRestClient.ts
@@ -47,6 +47,13 @@ export class CoreApiRestClient {
       this.sessionToken = await this.unsafe_getSessionToken(personaConfig);
     }
 
+    // Check if brainType is being used and log deprecation warning
+    if (personaConfig && 'brainType' in personaConfig) {
+      console.warn(
+        'Warning: brainType is deprecated and will be removed in a future version. Please use llmId instead.',
+      );
+    }
+
     try {
       const response = await fetch(`${this.getApiUrl()}/engine/session`, {
         method: 'POST',
@@ -139,6 +146,14 @@ export class CoreApiRestClient {
     if (!this.apiKey) {
       throw new Error('No apiKey provided');
     }
+
+    // Check if brainType is being used and log deprecation warning
+    if (personaConfig && 'brainType' in personaConfig) {
+      console.warn(
+        'Warning: brainType is deprecated and will be removed in a future version. Please use llmId instead.',
+      );
+    }
+
     let body: { clientLabel: string; personaConfig?: PersonaConfig } = {
       clientLabel: 'js-sdk-api-key',
     };
diff --git a/src/types/PersonaConfig.ts b/src/types/PersonaConfig.ts
index c022863..ca49f23 100644
--- a/src/types/PersonaConfig.ts
+++ b/src/types/PersonaConfig.ts
@@ -5,7 +5,7 @@ export interface CustomPersonaConfig {
   name: string;
   avatarId: string;
   voiceId: string;
-  brainType: string;
+  llmId?: string;
   systemPrompt?: string;
   maxSessionLengthSeconds?: number;
   languageCode?: string;
@@ -14,5 +14,5 @@ export interface CustomPersonaConfig {
 export function isCustomPersonaConfig(
   personaConfig: PersonaConfig,
 ): personaConfig is CustomPersonaConfig {
-  return 'brainType' in personaConfig;
+  return 'brainType' in personaConfig || 'llmId' in personaConfig;
 }