diff --git a/apps/web/src/components/chat/AssistantCitationSource.tsx b/apps/web/src/components/chat/AssistantCitationSource.tsx
index cf2e950e96abd..789ce6ebe4746 100644
--- a/apps/web/src/components/chat/AssistantCitationSource.tsx
+++ b/apps/web/src/components/chat/AssistantCitationSource.tsx
@@ -338,6 +338,7 @@ export function AssistantCitationSource({
   itemKey,
   request,
   listRef,
+  quotable,
   children,
 }: {
   messageId: MessageId;
@@ -345,6 +346,7 @@ export function AssistantCitationSource({
   itemKey: string;
   request: AssistantCitationTarget | null;
   listRef: RefObject<LegendListRef | null>;
+  quotable: boolean;
   children: ReactNode;
 }) {
   const rootRef = useRef<HTMLDivElement>(null);
@@ -362,6 +364,7 @@ export function AssistantCitationSource({
       data-assistant-citation-source={messageId}
       data-assistant-citation-environment={threadRef?.environmentId}
       data-assistant-citation-thread={threadRef?.threadId}
+      data-assistant-citation-quotable={quotable}
     >
       {children}
     </div>
diff --git a/apps/web/src/components/chat/MessagesTimeline.logic.test.ts b/apps/web/src/components/chat/MessagesTimeline.logic.test.ts
index 6c209d78d6ba3..5890330a98b55 100644
--- a/apps/web/src/components/chat/MessagesTimeline.logic.test.ts
+++ b/apps/web/src/components/chat/MessagesTimeline.logic.test.ts
@@ -32,6 +32,7 @@ import {
   timelineTurnFoldRunIdsByEntryId,
   liveAnswerPreview,
   deriveMessagesTimelineRowsWithState,
+  isQuotableAssistantMessage,
   resolveAssistantMessageCopyState,
   type MessagesTimelineRow,
   workEntryDisplayLabel,
@@ -57,6 +58,20 @@ describe("resolveAssistantMessageCopyState", () => {
   });
 });
 
+describe("isQuotableAssistantMessage", () => {
+  it("does not offer quotes on Claude thinking shown as a reply", () => {
+    const ref = (driver: string, nativeId: string) => ({
+      driver: ProviderDriverKind.make(driver),
+      nativeId,
+      strength: "strong" as const,
+    });
+    expect(isQuotableAssistantMessage(ref("claudeAgent", "msg_01:thinking:1"))).toBe(false);
+    expect(isQuotableAssistantMessage(ref("claudeAgent", "6b1f0c2e-uuid"))).toBe(true);
+    expect(isQuotableAssistantMessage(ref("codex", "msg_01:thinking:1"))).toBe(true);
+    expect(isQuotableAssistantMessage(null)).toBe(true);
+  });
+});
+
 describe("deriveMessagesTimelineRows", () => {
   it.each([
     ["html-render", "reply-run", true],
diff --git a/apps/web/src/components/chat/MessagesTimeline.logic.ts b/apps/web/src/components/chat/MessagesTimeline.logic.ts
index 9208e409ba205..1789575fa1076 100644
--- a/apps/web/src/components/chat/MessagesTimeline.logic.ts
+++ b/apps/web/src/components/chat/MessagesTimeline.logic.ts
@@ -57,6 +57,7 @@ import {
   type OrchestrationV2IdleCompaction,
   type WorktreeSetupSnapshot,
   type OrchestrationV2ProjectedTurnItem,
+  type OrchestrationV2ProviderRef,
   type RunAttemptId,
   type RuntimeRequestId,
   RunId,
@@ -708,6 +709,16 @@ export function resolveAssistantMessageCopyState({
   };
 }
 
+// Claude 5.1+ shows a thinking block before a tool call as a reply. It is still reasoning,
+// which no provider lets users quote, and quoting it trips Claude's reasoning_extraction refusal.
+export function isQuotableAssistantMessage(
+  nativeItemRef: OrchestrationV2ProviderRef | null | undefined,
+) {
+  return !(
+    nativeItemRef?.driver === "claudeAgent" && /:thinking:\d+$/u.test(nativeItemRef.nativeId ?? "")
+  );
+}
+
 function deriveTerminalAssistantMessageIds(timelineEntries: ReadonlyArray<TimelineEntry>) {
   const lastAssistantMessageIdByResponseKey = new Map<string, string>();
   let nullTurnResponseIndex = 0;
diff --git a/apps/web/src/components/chat/TimelineAssistantRows.tsx b/apps/web/src/components/chat/TimelineAssistantRows.tsx
index d508e0071dadf..fd7fabd04350e 100644
--- a/apps/web/src/components/chat/TimelineAssistantRows.tsx
+++ b/apps/web/src/components/chat/TimelineAssistantRows.tsx
@@ -23,7 +23,10 @@ import {
 } from "../../state/entities";
 import { MessageCopyButton } from "./MessageCopyButton";
 import { AssistantCitationSource } from "./AssistantCitationSource";
-import { resolveAssistantMessageCopyState } from "./MessagesTimeline.logic";
+import {
+  isQuotableAssistantMessage,
+  resolveAssistantMessageCopyState,
+} from "./MessagesTimeline.logic";
 import { Tooltip, TooltipPopup, TooltipTrigger } from "../ui/tooltip";
 import { cn } from "~/lib/utils";
 import { useUiStateStore } from "~/uiStateStore";
@@ -55,6 +58,7 @@ export function AssistantTimelineRow({ row }: { row: Extract<TimelineRow, { kind
             itemKey={row.id}
             request={ctx.citationRequest}
             listRef={ctx.listRef}
+            quotable={isQuotableAssistantMessage(row.projectedItem?.item.nativeItemRef)}
           >
             <ChatMarkdown
               text={messageText}
@@ -233,7 +237,9 @@ function AssistantMessageMeta({
       {projectedItem?.item.type === "assistant_message" ? (
         <AssistantForkButton projectedItem={projectedItem} />
       ) : null}
-      {!message.streaming && projectedItem ? (
+      {!message.streaming &&
+      projectedItem &&
+      isQuotableAssistantMessage(projectedItem.item.nativeItemRef) ? (
         <AssistantReplyButton message={message} itemId={projectedItem.sourceItemId} />
       ) : null}
       {!message.streaming && (
diff --git a/apps/web/src/lib/assistantTextSelection.test.ts b/apps/web/src/lib/assistantTextSelection.test.ts
index d06261cb856aa..154d543bebd9d 100644
--- a/apps/web/src/lib/assistantTextSelection.test.ts
+++ b/apps/web/src/lib/assistantTextSelection.test.ts
@@ -310,6 +310,15 @@ describe("captureAssistantTextSelection", () => {
     expect(capture(source, nativeSelection([quote, 0], [control, 1]))).toBeNull();
   });
 
+  it("does not quote a response marked unquotable", () => {
+    const quote = textNode("Reasoning shown as a reply.");
+    const source = new SelectionNode("DIV", "", {
+      "data-assistant-citation-source": "assistant",
+      "data-assistant-citation-quotable": "false",
+    }).append(quote);
+    expect(capture(source, nativeSelection([quote, 0], [quote, quote.length]))).toBeNull();
+  });
+
   it.each([
     new SelectionNode("BUTTON"),
     new SelectionNode("SPAN", "", { role: "button" }),
diff --git a/apps/web/src/lib/assistantTextSelection.ts b/apps/web/src/lib/assistantTextSelection.ts
index 9f83cd829eed0..c18a4c89e64b8 100644
--- a/apps/web/src/lib/assistantTextSelection.ts
+++ b/apps/web/src/lib/assistantTextSelection.ts
@@ -219,7 +219,13 @@ export function captureAssistantTextSelection(
   const last = selectedTextBoundary(range, range.commonAncestorContainer, true);
   if (first === null || last === null) return null;
   const source = first.parentElement?.closest<HTMLElement>("[data-assistant-citation-source]");
-  if (!source || !viewport.contains(source)) return null;
+  if (
+    !source ||
+    !viewport.contains(source) ||
+    source.matches("[data-assistant-citation-quotable=false]")
+  ) {
+    return null;
+  }
 
   // Paragraph selection can end at the next block's offset 0 or a parent
   // boundary. Validate the text actually selected, not that empty endpoint.