diff --git a/src/models/types.ts b/src/models/types.ts
index 731e803..95badf3 100644
--- a/src/models/types.ts
+++ b/src/models/types.ts
@@ -12,12 +12,26 @@ export interface ChatRequest {
 export interface ChatResponse {
   content: string;
   stopReason: 'end_turn' | 'max_tokens' | 'stop_sequence' | string;
-  usage: {
-    inputTokens: number;
-    outputTokens: number;
-  };
+  usage: TokenUsage;
+}
+
+export interface TokenUsage {
+  inputTokens: number;
+  outputTokens: number;
+}
+
+export interface ChatStreamEvent {
+  type: 'content' | 'done' | 'error';
+  content?: string;
+  usage?: TokenUsage;
+  error?: Error;
+}
+
+export interface StreamingModelClient {
+  chatStream(request: ChatRequest): AsyncIterable<ChatStreamEvent>;
 }
 
 export interface ModelClient {
   chat(request: ChatRequest): Promise<ChatResponse>;
+  chatStream?(request: ChatRequest): AsyncIterable<ChatStreamEvent>;
 }