diff --git a/packages/ui/src/components/session-turn.tsx b/packages/ui/src/components/session-turn.tsx
index ae1321bac14..a8eb61dc71c 100644
--- a/packages/ui/src/components/session-turn.tsx
+++ b/packages/ui/src/components/session-turn.tsx
@@ -271,6 +271,17 @@ export function SessionTurn(
 
   const isShellMode = createMemo(() => !!shellModePart())
 
+  const hasReasoningParts = createMemo(() => {
+    for (const m of assistantMessages()) {
+      const msgParts = data.store.part[m.id]
+      if (!msgParts) continue
+      for (const p of msgParts) {
+        if (p?.type === "reasoning") return true
+      }
+    }
+    return false
+  })
+
   const rawStatus = createMemo(() => {
     const msgs = assistantMessages()
     let last: PartType | undefined
@@ -376,6 +387,8 @@ export function SessionTurn(
     diffLimit: diffInit,
     status: rawStatus(),
     duration: duration(),
+    userMessageHovered: false,
+    showReasoning: false,
   })
 
   createEffect(
@@ -564,7 +577,7 @@ export function SessionTurn(
                               message={assistantMessage}
                               responsePartId={responsePartId()}
                               hideResponsePart={hideResponsePart()}
-                              hideReasoning={!working()}
+                              hideReasoning={!working() && !store.showReasoning}
                             />
                           )}
                         </For>
@@ -596,6 +609,17 @@ export function SessionTurn(
                         </div>
                         <div data-slot="session-turn-summary-header">
                           <h2 data-slot="session-turn-summary-title">Response</h2>
+                          <Show when={hasReasoningParts()}>
+                            <Button
+                              data-slot="session-turn-reasoning-toggle"
+                              variant="ghost"
+                              size="small"
+                              onClick={() => setStore("showReasoning", (prev) => !prev)}
+                            >
+                              <Icon name="eye" size="small" />
+                              <span>{store.showReasoning ? "Hide" : "Show"} thinking</span>
+                            </Button>
+                          </Show>
                           <Markdown
                             data-slot="session-turn-markdown"
                             data-diffs={hasDiffs()}
@@ -675,6 +699,20 @@ export function SessionTurn(
                             Show more changes ({(msg().summary?.diffs?.length ?? 0) - store.diffLimit})
                           </Button>
                         </Show>
+                        <Show when={store.showReasoning && hasReasoningParts()}>
+                          <div data-slot="session-turn-reasoning-section">
+                            <For each={assistantMessages()}>
+                              {(assistantMessage) => (
+                                <AssistantMessageItem
+                                  message={assistantMessage}
+                                  responsePartId={responsePartId()}
+                                  hideResponsePart={true}
+                                  hideReasoning={false}
+                                />
+                              )}
+                            </For>
+                          </div>
+                        </Show>
                       </div>
                     </Show>
                     <Show when={error() && !props.stepsExpanded}>