diff --git a/apps/shared/OpenClawKit/Sources/OpenClawProtocol/GatewayModels.swift b/apps/shared/OpenClawKit/Sources/OpenClawProtocol/GatewayModels.swift
index 59511dddf28..10fd84d7584 100644
--- a/apps/shared/OpenClawKit/Sources/OpenClawProtocol/GatewayModels.swift
+++ b/apps/shared/OpenClawKit/Sources/OpenClawProtocol/GatewayModels.swift
@@ -6251,6 +6251,7 @@ public struct ChatEvent: Codable, Sendable {
     public let seq: Int
     public let state: AnyCodable
     public let message: AnyCodable?
+    public let deltatext: String?
     public let errormessage: String?
     public let errorkind: AnyCodable?
     public let usage: AnyCodable?
@@ -6263,6 +6264,7 @@ public struct ChatEvent: Codable, Sendable {
         seq: Int,
         state: AnyCodable,
         message: AnyCodable?,
+        deltatext: String?,
         errormessage: String?,
         errorkind: AnyCodable?,
         usage: AnyCodable?,
@@ -6274,6 +6276,7 @@ public struct ChatEvent: Codable, Sendable {
         self.seq = seq
         self.state = state
         self.message = message
+        self.deltatext = deltatext
         self.errormessage = errormessage
         self.errorkind = errorkind
         self.usage = usage
@@ -6287,6 +6290,7 @@ public struct ChatEvent: Codable, Sendable {
         case seq
         case state
         case message
+        case deltatext = "deltaText"
         case errormessage = "errorMessage"
         case errorkind = "errorKind"
         case usage
diff --git a/packages/sdk/src/client.ts b/packages/sdk/src/client.ts
index d1b770ce824..6666c8a9f35 100644
--- a/packages/sdk/src/client.ts
+++ b/packages/sdk/src/client.ts
@@ -264,6 +264,7 @@ function normalizeChatProjectionEvent(
 ): OpenClawEvent {
   const text = readChatProjectionText(projection.payload);
   const deltaText = readChatProjectionDeltaText(projection.payload);
+  const hasPreviousText = previousText !== undefined;
   const isReplacement = Boolean(
     deltaText === undefined && previousText && text !== undefined && !text.startsWith(previousText),
   );
@@ -275,7 +276,12 @@ function normalizeChatProjectionEvent(
         ? text !== undefined
           ? {
               text,
-              delta: deltaText ?? (isReplacement ? text : text.slice(previousText?.length ?? 0)),
+              delta:
+                deltaText !== undefined && hasPreviousText
+                  ? deltaText
+                  : isReplacement
+                    ? text
+                    : text.slice(previousText?.length ?? 0),
               ...(isReplacement ? { replace: true } : {}),
             }
           : event.data
diff --git a/packages/sdk/src/index.test.ts b/packages/sdk/src/index.test.ts
index a239c090e70..a0bfbc03dd3 100644
--- a/packages/sdk/src/index.test.ts
+++ b/packages/sdk/src/index.test.ts
@@ -847,6 +847,60 @@ describe("OpenClaw SDK", () => {
     }
   });
 
+  it("uses cumulative text for the first replayed chat projection", async () => {
+    const transport = new FakeTransport({});
+    const oc = new OpenClaw({ transport });
+    const runId = "run_chat_delta_text_replay";
+    let text = "";
+    let iterator: AsyncIterator<OpenClawEvent> | undefined;
+
+    try {
+      await oc.connect();
+      const observedLast = (async () => {
+        for await (const event of oc.events(
+          (event) => event.raw?.event === "chat" && event.raw.seq === 501,
+        )) {
+          return event;
+        }
+        throw new Error("expected final replay setup event");
+      })();
+
+      for (let index = 0; index <= 500; index += 1) {
+        const deltaText = index === 0 ? "hello" : ` ${index}`;
+        text += deltaText;
+        transport.emit({
+          event: "chat",
+          seq: index + 1,
+          payload: {
+            runId,
+            sessionKey: "chat-delta-text-replay",
+            state: "delta",
+            deltaText,
+            message: {
+              role: "assistant",
+              content: [{ type: "text", text }],
+              timestamp: 1_777_000_000_300 + index,
+            },
+          },
+        });
+      }
+
+      await observedLast;
+      const run = await oc.runs.get(runId);
+      iterator = run.events()[Symbol.asyncIterator]();
+      const first = await iterator.next();
+      expect(first.done).toBe(false);
+      if (first.done !== false) {
+        throw new Error("expected first replayed chat projection event");
+      }
+      expect(first.value.type).toBe("assistant.delta");
+      expect(first.value.data).toEqual({ text: "hello 1", delta: "hello 1" });
+    } finally {
+      await iterator?.return?.();
+      await oc.close();
+    }
+  });
+
   it("creates a session and sends a message as a run", async () => {
     const transport = new FakeTransport({
       "sessions.create": { key: "session-main", label: "Main" },