diff --git a/packages/core/src/core/geminiChat.ts b/packages/core/src/core/geminiChat.ts
index 87d0c235f40..ae5f46db37c 100644
--- a/packages/core/src/core/geminiChat.ts
+++ b/packages/core/src/core/geminiChat.ts
@@ -691,9 +691,13 @@ export class GeminiChat {
     const history = curated
       ? extractCuratedHistory(this.history)
       : this.history;
-    // Deep copy the history to avoid mutating the history outside of the
-    // chat session.
-    return structuredClone(history);
+    // Return a shallow copy of the array to prevent callers from mutating
+    // the internal history array (push/pop/splice). Content objects are
+    // shared references — callers MUST NOT mutate them in place.
+    // This replaces a prior structuredClone() which deep-copied the entire
+    // conversation on every call, causing O(n) memory pressure per turn
+    // that compounded into OOM crashes in long-running sessions.
+    return [...history];
   }
 
   /**
diff --git a/packages/core/src/core/turn.ts b/packages/core/src/core/turn.ts
index 4fd6af2185b..9c0e536c48d 100644
--- a/packages/core/src/core/turn.ts
+++ b/packages/core/src/core/turn.ts
@@ -241,6 +241,7 @@ export class Turn {
   readonly pendingToolCalls: ToolCallRequestInfo[] = [];
   private debugResponses: GenerateContentResponse[] = [];
   private pendingCitations = new Set<string>();
+  private cachedResponseText: string | undefined = undefined;
   finishReason: FinishReason | undefined = undefined;
 
   constructor(
@@ -432,11 +433,15 @@ export class Turn {
   /**
    * Get the concatenated response text from all responses in this turn.
    * This extracts and joins all text content from the model's responses.
+   * The result is cached since this is called multiple times per turn.
    */
   getResponseText(): string {
-    return this.debugResponses
-      .map((response) => getResponseText(response))
-      .filter((text): text is string => text !== null)
-      .join(' ');
+    if (this.cachedResponseText === undefined) {
+      this.cachedResponseText = this.debugResponses
+        .map((response) => getResponseText(response))
+        .filter((text): text is string => text !== null)
+        .join(' ');
+    }
+    return this.cachedResponseText;
   }
 }