diff --git a/packages/server/src/server/agent/providers/claude/agent.test.ts b/packages/server/src/server/agent/providers/claude/agent.test.ts
index dbd10aea4d..d28ac910ac 100644
--- a/packages/server/src/server/agent/providers/claude/agent.test.ts
+++ b/packages/server/src/server/agent/providers/claude/agent.test.ts
@@ -1009,7 +1009,7 @@ describe("ClaudeAgentSession features", () => {
 
     expect(queryFactory.mock.calls[0]?.[0].options).toMatchObject({
       effort: "xhigh",
-      thinking: { type: "adaptive" },
+      thinking: { type: "adaptive", display: "summarized" },
       settings: { ultracode: true },
     });
 
@@ -1223,7 +1223,7 @@ describe("ClaudeAgentSession features", () => {
 
   test.each([
     ["supported model", "claude-opus-4-8", { type: "disabled" }, undefined],
-    ["unsupported model", "claude-fable-5", { type: "adaptive" }, "high"],
+    ["unsupported model", "claude-fable-5", { type: "adaptive", display: "summarized" }, "high"],
     ["custom model", "openrouter/anthropic/claude-opus-4-8", undefined, undefined],
     ["provider default", null, undefined, undefined],
   ])("reconciles Off when switching to a %s", async (_label, modelId, thinking, effort) => {
diff --git a/packages/server/src/server/agent/providers/claude/agent.ts b/packages/server/src/server/agent/providers/claude/agent.ts
index 15eeb1500a..36f991d019 100644
--- a/packages/server/src/server/agent/providers/claude/agent.ts
+++ b/packages/server/src/server/agent/providers/claude/agent.ts
@@ -3244,10 +3244,18 @@ class ClaudeAgentSession implements AgentSession {
       return { thinking: { type: "disabled" }, effort: undefined, ultracode: false };
     }
     if (thinkingOptionId === CLAUDE_ULTRACODE_THINKING_OPTION_ID) {
-      return { thinking: { type: "adaptive" }, effort: "xhigh", ultracode: true };
+      return {
+        thinking: { type: "adaptive", display: "summarized" },
+        effort: "xhigh",
+        ultracode: true,
+      };
     }
     if (thinkingOptionId && isClaudeThinkingEffort(thinkingOptionId)) {
-      return { thinking: { type: "adaptive" }, effort: thinkingOptionId, ultracode: false };
+      return {
+        thinking: { type: "adaptive", display: "summarized" },
+        effort: thinkingOptionId,
+        ultracode: false,
+      };
     }
     return { thinking: undefined, effort: undefined, ultracode: false };
   }