diff --git a/ui/src/api/issues.ts b/ui/src/api/issues.ts
index 2ac3744f828..e0d8ec05d0d 100644
--- a/ui/src/api/issues.ts
+++ b/ui/src/api/issues.ts
@@ -97,6 +97,8 @@ export const issuesApi = {
     const qs = params.toString();
     return api.get<IssueComment[]>(`/issues/${id}/comments${qs ? `?${qs}` : ""}`);
   },
+  getComment: (id: string, commentId: string) =>
+    api.get<IssueComment>(`/issues/${id}/comments/${commentId}`),
   listFeedbackVotes: (id: string) => api.get<FeedbackVote[]>(`/issues/${id}/feedback-votes`),
   listFeedbackTraces: (id: string, filters?: Record<string, string | boolean | undefined>) => {
     const params = new URLSearchParams();
diff --git a/ui/src/context/LiveUpdatesProvider.test.ts b/ui/src/context/LiveUpdatesProvider.test.ts
index ad0c02bcc14..559f80df1e9 100644
--- a/ui/src/context/LiveUpdatesProvider.test.ts
+++ b/ui/src/context/LiveUpdatesProvider.test.ts
@@ -1,5 +1,15 @@
 // @vitest-environment node
 
+const { getCommentMock } = vi.hoisted(() => ({
+  getCommentMock: vi.fn(),
+}));
+
+vi.mock("../api/issues", () => ({
+  issuesApi: {
+    getComment: getCommentMock,
+  },
+}));
+
 import { describe, expect, it, vi } from "vitest";
 import { __liveUpdatesTestUtils } from "./LiveUpdatesProvider";
 import { queryKeys } from "../lib/queryKeys";
@@ -257,6 +267,150 @@ describe("LiveUpdatesProvider issue invalidation", () => {
       refetchType: "inactive",
     });
   });
+
+  it("keeps visible issue comment updates inactive-only instead of active refetching", () => {
+    const invalidations: unknown[] = [];
+    const queryClient = {
+      invalidateQueries: (input: unknown) => {
+        invalidations.push(input);
+      },
+      getQueryData: (key: unknown) => {
+        if (JSON.stringify(key) === JSON.stringify(queryKeys.issues.detail("PAP-759"))) {
+          return {
+            id: "issue-1",
+            identifier: "PAP-759",
+            assigneeAgentId: "agent-1",
+          };
+        }
+        return undefined;
+      },
+    };
+
+    __liveUpdatesTestUtils.invalidateActivityQueries(
+      queryClient as never,
+      "company-1",
+      {
+        entityType: "issue",
+        entityId: "issue-1",
+        action: "issue.comment_added",
+        actorType: "agent",
+        actorId: "agent-1",
+        details: {
+          identifier: "PAP-759",
+          commentId: "comment-1",
+          bodySnippet: "New agent comment",
+        },
+      },
+      { userId: null, agentId: null },
+      { pathname: "/PAP/issues/PAP-759", isForegrounded: true },
+    );
+
+    expect(invalidations).toContainEqual({
+      queryKey: queryKeys.issues.detail("issue-1"),
+      refetchType: "inactive",
+    });
+    expect(invalidations).toContainEqual({
+      queryKey: queryKeys.issues.activity("issue-1"),
+      refetchType: "inactive",
+    });
+    expect(invalidations).toContainEqual({
+      queryKey: queryKeys.issues.comments("issue-1"),
+      refetchType: "inactive",
+    });
+  });
+});
+
+describe("LiveUpdatesProvider visible issue comment hydration", () => {
+  it("hydrates the visible issue comments cache with only the new comment", async () => {
+    getCommentMock.mockResolvedValueOnce({
+      id: "comment-2",
+      companyId: "company-1",
+      issueId: "issue-1",
+      authorAgentId: "agent-1",
+      authorUserId: null,
+      body: "Second comment",
+      createdAt: "2026-04-13T15:00:00.000Z",
+      updatedAt: "2026-04-13T15:00:00.000Z",
+    });
+
+    const setCalls: Array<{ key: unknown; value: unknown }> = [];
+    const queryClient = {
+      getQueryData: (key: unknown) => {
+        if (JSON.stringify(key) === JSON.stringify(queryKeys.issues.detail("PAP-759"))) {
+          return {
+            id: "issue-1",
+            identifier: "PAP-759",
+            assigneeAgentId: "agent-1",
+          };
+        }
+        if (JSON.stringify(key) === JSON.stringify(queryKeys.issues.comments("PAP-759"))) {
+          return {
+            pages: [[{
+              id: "comment-1",
+              companyId: "company-1",
+              issueId: "issue-1",
+              authorAgentId: null,
+              authorUserId: "user-1",
+              body: "First comment",
+              createdAt: "2026-04-13T14:00:00.000Z",
+              updatedAt: "2026-04-13T14:00:00.000Z",
+            }]],
+            pageParams: [null],
+          };
+        }
+        return undefined;
+      },
+      setQueryData: (key: unknown, updater: (value: unknown) => unknown) => {
+        const current = queryClient.getQueryData(key);
+        setCalls.push({ key, value: updater(current) });
+      },
+      invalidateQueries: vi.fn(),
+    };
+
+    await __liveUpdatesTestUtils.hydrateVisibleIssueComment(
+      queryClient as never,
+      "/PAP/issues/PAP-759",
+      {
+        entityType: "issue",
+        entityId: "issue-1",
+        action: "issue.comment_added",
+        details: {
+          identifier: "PAP-759",
+          commentId: "comment-2",
+        },
+      },
+      { isForegrounded: true },
+    );
+
+    expect(getCommentMock).toHaveBeenCalledWith("PAP-759", "comment-2");
+    expect(setCalls).toHaveLength(1);
+    expect(setCalls[0]?.key).toEqual(queryKeys.issues.comments("PAP-759"));
+    expect(setCalls[0]?.value).toEqual({
+      pages: [[
+        {
+          id: "comment-2",
+          companyId: "company-1",
+          issueId: "issue-1",
+          authorAgentId: "agent-1",
+          authorUserId: null,
+          body: "Second comment",
+          createdAt: "2026-04-13T15:00:00.000Z",
+          updatedAt: "2026-04-13T15:00:00.000Z",
+        },
+        {
+          id: "comment-1",
+          companyId: "company-1",
+          issueId: "issue-1",
+          authorAgentId: null,
+          authorUserId: "user-1",
+          body: "First comment",
+          createdAt: "2026-04-13T14:00:00.000Z",
+          updatedAt: "2026-04-13T14:00:00.000Z",
+        },
+      ]],
+      pageParams: [null],
+    });
+  });
 });
 
 describe("LiveUpdatesProvider visible issue toast suppression", () => {
diff --git a/ui/src/context/LiveUpdatesProvider.tsx b/ui/src/context/LiveUpdatesProvider.tsx
index 33efd5238dd..c26df965ad6 100644
--- a/ui/src/context/LiveUpdatesProvider.tsx
+++ b/ui/src/context/LiveUpdatesProvider.tsx
@@ -1,12 +1,14 @@
 import { useEffect, useRef, type ReactNode } from "react";
-import { useQuery, useQueryClient, type QueryClient } from "@tanstack/react-query";
-import type { Agent, Issue, LiveEvent } from "@paperclipai/shared";
+import { useQuery, useQueryClient, type InfiniteData, type QueryClient } from "@tanstack/react-query";
+import type { Agent, Issue, IssueComment, LiveEvent } from "@paperclipai/shared";
 import type { RunForIssue } from "../api/activity";
 import type { ActiveRunForIssue, LiveRunForIssue } from "../api/heartbeats";
+import { issuesApi } from "../api/issues";
 import { authApi } from "../api/auth";
 import { useCompany } from "./CompanyContext";
 import type { ToastInput } from "./ToastContext";
 import { useToast } from "./ToastContext";
+import { upsertIssueCommentInPages } from "../lib/optimistic-issue-comments";
 import { queryKeys } from "../lib/queryKeys";
 import { toCompanyRelativePath } from "../lib/company-routes";
 import { useLocation } from "../lib/router";
@@ -83,6 +85,7 @@ interface VisibleRouteOptions {
 }
 
 interface VisibleIssueRouteContext {
+  routeIssueRef: string;
   issueRefs: Set<string>;
   assigneeAgentId: string | null;
   runIds: Set<string>;
@@ -189,6 +192,7 @@ function resolveVisibleIssueRouteContext(
   }
 
   return {
+    routeIssueRef: issueRef,
     issueRefs,
     assigneeAgentId: issue?.assigneeAgentId ?? null,
     runIds,
@@ -277,6 +281,72 @@ function shouldDeferIssueRefetchForVisibleAgentActivity(
   return overlaps(context.issueRefs, buildIssueRefsForPayload(entityId, details));
 }
 
+function shouldDeferVisibleIssueCommentActivity(
+  queryClient: QueryClient,
+  pathname: string,
+  payload: Record<string, unknown>,
+  options?: VisibleRouteOptions,
+): boolean {
+  const entityType = readString(payload.entityType);
+  const entityId = readString(payload.entityId);
+  const action = readString(payload.action);
+  const details = readRecord(payload.details);
+
+  if (entityType !== "issue" || !entityId) return false;
+  if (action !== "issue.comment_added") return false;
+
+  const context = resolveVisibleIssueRouteContext(queryClient, pathname, options);
+  if (!context) return false;
+
+  return overlaps(context.issueRefs, buildIssueRefsForPayload(entityId, details));
+}
+
+async function hydrateVisibleIssueComment(
+  queryClient: QueryClient,
+  pathname: string,
+  payload: Record<string, unknown>,
+  options?: VisibleRouteOptions,
+) {
+  const entityType = readString(payload.entityType);
+  const action = readString(payload.action);
+  const details = readRecord(payload.details);
+  const commentId = readString(details?.commentId);
+
+  if (entityType !== "issue" || action !== "issue.comment_added" || !commentId) return false;
+
+  const context = resolveVisibleIssueRouteContext(queryClient, pathname, options);
+  if (!context) return false;
+
+  const entityId = readString(payload.entityId);
+  if (!entityId || !overlaps(context.issueRefs, buildIssueRefsForPayload(entityId, details))) {
+    return false;
+  }
+
+  try {
+    const comment = await issuesApi.getComment(context.routeIssueRef, commentId);
+    queryClient.setQueryData<InfiniteData<IssueComment[], string | null> | undefined>(
+      queryKeys.issues.comments(context.routeIssueRef),
+      (current) => {
+        if (!current) {
+          return {
+            pages: [[comment]],
+            pageParams: [null],
+          };
+        }
+
+        return {
+          ...current,
+          pages: upsertIssueCommentInPages(current.pages, comment),
+        };
+      },
+    );
+    return true;
+  } catch {
+    queryClient.invalidateQueries({ queryKey: queryKeys.issues.comments(context.routeIssueRef) });
+    return false;
+  }
+}
+
 const ISSUE_TOAST_ACTIONS = new Set(["issue.created", "issue.updated", "issue.comment_added"]);
 const AGENT_TOAST_STATUSES = new Set(["error"]);
 const RUN_TOAST_STATUSES = new Set(["failed", "timed_out", "cancelled"]);
@@ -536,10 +606,18 @@ function invalidateActivityQueries(
           payload,
           { isForegrounded: options.isForegrounded },
         );
+      const visibleIssueCommentActivity =
+        !!options?.pathname &&
+        shouldDeferVisibleIssueCommentActivity(
+          queryClient,
+          options.pathname,
+          payload,
+          { isForegrounded: options.isForegrounded },
+        );
       const issueRefs = resolveIssueQueryRefs(queryClient, companyId, entityId, details);
       for (const ref of issueRefs) {
         const invalidationOptions =
-          (selfCommentActivity || visibleIssueAgentActivity)
+          (selfCommentActivity || visibleIssueAgentActivity || visibleIssueCommentActivity)
             ? { refetchType: "inactive" as const }
             : undefined;
         queryClient.invalidateQueries({ queryKey: queryKeys.issues.detail(ref), ...invalidationOptions });
@@ -691,6 +769,9 @@ function handleLiveEvent(
 
   if (event.type === "activity.logged") {
     invalidateActivityQueries(queryClient, expectedCompanyId, payload, currentActor, { pathname });
+    if (shouldDeferVisibleIssueCommentActivity(queryClient, pathname, payload)) {
+      void hydrateVisibleIssueComment(queryClient, pathname, payload);
+    }
     const action = readString(payload.action);
     const toast =
       buildActivityToast(queryClient, expectedCompanyId, payload, currentActor) ??
@@ -747,9 +828,11 @@ export const __liveUpdatesTestUtils = {
   buildAgentStatusToast,
   buildRunStatusToast,
   closeSocketQuietly,
+  hydrateVisibleIssueComment,
   invalidateActivityQueries,
   resolveLiveCompanyId,
   shouldDeferIssueRefetchForVisibleAgentActivity,
+  shouldDeferVisibleIssueCommentActivity,
   shouldSuppressActivityToastForVisibleIssue,
   shouldSuppressRunStatusToastForVisibleIssue,
   shouldSuppressAgentStatusToastForVisibleIssue,