diff --git a/studio/backend/routes/research_runs.py b/studio/backend/routes/research_runs.py
index 62ee3cce4c..1880936ff6 100644
--- a/studio/backend/routes/research_runs.py
+++ b/studio/backend/routes/research_runs.py
@@ -24,6 +24,7 @@ from storage.studio_db import get_chat_message, get_chat_thread, upsert_chat_mes
 router = APIRouter()
 _SENSITIVE_KEY = re.compile(r"^(?:api.?key|secret|token|authorization|password)$", re.IGNORECASE)
 _MAX_PLAN_STEPS = 30
+_DELTA_ONLY_EVENTS = {"reasoning.updated", "report.updated"}
 
 
 class CreateResearchRun(BaseModel):
@@ -389,7 +390,8 @@ async def research_events(
                 cursor = int(event["seq"])
                 event_data = dict(event["data"])
                 event_data["createdAt"] = event["createdAt"]
-                event_data["run"] = snapshot
+                if event["type"] not in _DELTA_ONLY_EVENTS:
+                    event_data["run"] = snapshot
                 data = json.dumps(event_data, separators = (",", ":"), ensure_ascii = False)
                 yield f"id: {cursor}\nevent: {event['type']}\ndata: {data}\n\n"
             if snapshot["status"] in db.TERMINAL_STATUSES and cursor >= int(
diff --git a/studio/backend/tests/test_research_runs_storage.py b/studio/backend/tests/test_research_runs_storage.py
index 530cf556f4..accb29a297 100644
--- a/studio/backend/tests/test_research_runs_storage.py
+++ b/studio/backend/tests/test_research_runs_storage.py
@@ -1498,6 +1498,11 @@ def test_terminal_sse_event_contains_report_and_complete_snapshot(research_home)
     research_db.upsert_source(
         "run-1", 0, "https://example.com/final", "Final source", "Final evidence"
     )
+    research_db.append_event(
+        "run-1",
+        "report.updated",
+        {"delta": "Draft chunk", "offset": 0, "length": 11},
+    )
     report = "# Durable report\n\nFinal markdown."
     assert (
         research_db.finish("run-1", "worker-1", "completed", event_payload = {"report": report})
@@ -1525,6 +1530,11 @@ def test_terminal_sse_event_contains_report_and_complete_snapshot(research_home)
         return "".join(chunks)
 
     stream = asyncio.run(consume())
+    delta = next(block for block in stream.split("\n\n") if "event: report.updated" in block)
+    delta_line = next(line for line in delta.splitlines() if line.startswith("data: "))
+    delta_payload = json.loads(delta_line[6:])
+    assert delta_payload["delta"] == "Draft chunk"
+    assert "run" not in delta_payload
     terminal = next(block for block in stream.split("\n\n") if "event: run.completed" in block)
     data_line = next(line for line in terminal.splitlines() if line.startswith("data: "))
     payload = json.loads(data_line[6:])
diff --git a/studio/frontend/src/features/chat/api/research-api.ts b/studio/frontend/src/features/chat/api/research-api.ts
index 278f414733..c56377b23b 100644
--- a/studio/frontend/src/features/chat/api/research-api.ts
+++ b/studio/frontend/src/features/chat/api/research-api.ts
@@ -8,6 +8,11 @@ import type {
   ResearchRun,
 } from "../types/research";
 
+type StreamResearchEvent = Omit<ResearchEvent, "data" | "run"> & {
+  data: Omit<ResearchEvent["data"], "run">;
+  run?: ResearchRun;
+};
+
 type JsonObject = Record<string, unknown>;
 const TERMINAL_RESEARCH_STATUSES = new Set([
   "completed",
@@ -139,7 +144,7 @@ export async function* streamResearchEvents(
   id: string,
   after: number,
   signal?: AbortSignal,
-): AsyncGenerator<ResearchEvent> {
+): AsyncGenerator<StreamResearchEvent> {
   const response = await authFetch(
     `/api/chat/research-runs/${id}/events?after=${Math.max(0, after)}`,
     { headers: { accept: "text/event-stream" }, signal },
@@ -176,18 +181,16 @@ export async function* streamResearchEvents(
         if (data.length > 0) {
           const parsed = camelize(JSON.parse(data.join("\n"))) as JsonObject;
           const candidate = parsed.run as ResearchRun | undefined;
-          if (candidate?.id && candidate.status) {
-            yield {
-              id: eventId,
-              event: event as ResearchEvent["event"],
-              createdAt:
-                typeof parsed.createdAt === "number"
-                  ? parsed.createdAt
-                  : candidate.updatedAt,
-              data: parsed as unknown as ResearchEvent["data"],
-              run: candidate,
-            };
-          }
+          yield {
+            id: eventId,
+            event: event as ResearchEvent["event"],
+            createdAt:
+              typeof parsed.createdAt === "number"
+                ? parsed.createdAt
+                : (candidate?.updatedAt ?? Date.now()),
+            data: parsed as unknown as StreamResearchEvent["data"],
+            ...(candidate?.id && candidate.status ? { run: candidate } : {}),
+          };
         }
         boundary = buffer.indexOf("\n\n");
       }
@@ -272,20 +275,31 @@ export async function* followResearchRun(
   ) {
     return;
   }
+  let currentRun: ResearchRun = run;
   let cursor = replayFrom ?? run.lastEventSeq;
   while (!signal?.aborted) {
     try {
       for await (const event of streamResearchEvents(id, cursor, signal)) {
         cursor = Math.max(cursor, event.id);
-        run = event.run;
+        const eventRun: ResearchRun = event.run ?? {
+          ...currentRun,
+          lastEventSeq: Math.max(currentRun.lastEventSeq, event.id),
+          updatedAt: Math.max(currentRun.updatedAt, event.createdAt),
+        };
+        const hydratedEvent: ResearchEvent = {
+          ...event,
+          data: { ...event.data, run: eventRun },
+          run: eventRun,
+        };
+        currentRun = eventRun;
         failures = 0;
-        yield { run, event, source: "event" };
+        yield { run: currentRun, event: hydratedEvent, source: "event" };
         if (
-          (event.event === "run.completed" ||
-            event.event === "run.failed" ||
-            event.event === "run.cancelled") &&
-          TERMINAL_RESEARCH_STATUSES.has(event.run.status) &&
-          (event.data.attempt ?? 0) === (event.run.retryCount ?? 0)
+          (hydratedEvent.event === "run.completed" ||
+            hydratedEvent.event === "run.failed" ||
+            hydratedEvent.event === "run.cancelled") &&
+          TERMINAL_RESEARCH_STATUSES.has(eventRun.status) &&
+          (hydratedEvent.data.attempt ?? 0) === (eventRun.retryCount ?? 0)
         ) {
           return;
         }
@@ -306,21 +320,21 @@ export async function* followResearchRun(
     try {
       const fresh = await getResearchRun(id, signal);
       const changed =
-        fresh.lastEventSeq !== run.lastEventSeq ||
-        fresh.updatedAt !== run.updatedAt ||
-        fresh.status !== run.status ||
-        fresh.report !== run.report;
+        fresh.lastEventSeq !== currentRun.lastEventSeq ||
+        fresh.updatedAt !== currentRun.updatedAt ||
+        fresh.status !== currentRun.status ||
+        fresh.report !== currentRun.report;
       const needsCatchup = cursor < fresh.lastEventSeq;
-      run = fresh;
+      currentRun = fresh;
       if (replayFrom === undefined) {
         cursor = Math.max(cursor, fresh.lastEventSeq);
       }
       if (changed || needsCatchup) {
-        yield { run, source: "snapshot" };
+        yield { run: currentRun, source: "snapshot" };
       }
       if (
-        TERMINAL_RESEARCH_STATUSES.has(run.status) &&
-        cursor >= run.lastEventSeq
+        TERMINAL_RESEARCH_STATUSES.has(currentRun.status) &&
+        cursor >= currentRun.lastEventSeq
       ) {
         return;
       }
diff --git a/studio/frontend/src/features/chat/stores/research-run-store.ts b/studio/frontend/src/features/chat/stores/research-run-store.ts
index bf239803ce..021f21736d 100644
--- a/studio/frontend/src/features/chat/stores/research-run-store.ts
+++ b/studio/frontend/src/features/chat/stores/research-run-store.ts
@@ -706,6 +706,9 @@ export function ingestResearchUpdate(
   }
 
   const pending = pendingStreamEvents.get(run.id);
+  if (pending && event.id <= pending.event.id) {
+    return;
+  }
   if (pending && canCoalesceStreamEvent(pending.event, event)) {
     const reasoningDelta =
       event.event === "reasoning.updated"
diff --git a/tests/studio/test_deep_research_frontend_contract.py b/tests/studio/test_deep_research_frontend_contract.py
index e6ba96ff80..767f3589a2 100644
--- a/tests/studio/test_deep_research_frontend_contract.py
+++ b/tests/studio/test_deep_research_frontend_contract.py
@@ -11,6 +11,7 @@ def source(path: str) -> str:
 
 def test_research_api_is_isolated_and_cursor_based() -> None:
     api = source("features/chat/api/research-api.ts")
+    store = source("features/chat/stores/research-run-store.ts")
     assert 'authFetch("/api/chat/research-runs"' in api
     assert "authFetch(`/api/chat/research-runs/active?${query}`)" in api
     assert "const { runs, hasRun }" in api
@@ -22,11 +23,12 @@ def test_research_api_is_isolated_and_cursor_based() -> None:
     assert "Math.min(8_000, 500 * 2 ** (failures - 1))" in api
     assert "for await (const event of streamResearchEvents" in api
     assert 'source: "event"' in api
-    assert "fresh.report !== run.report" in api
+    assert "fresh.report !== currentRun.report" in api
     assert "await waitForReconnect(" in api
     assert "while (!(run || signal?.aborted))" in api
     assert "isPermanentResearchError(error)" in api
     assert 'yield { run, source: "snapshot" }' in api
+    assert "event.id <= pending.event.id" in store
     for action in ("cancel", "retry"):
         assert f'mutate(id, "{action}")' in api
     assert 'mutate(id, "approve", { planRevision, planHash })' in api