diff --git a/services/hackbot-api/alembic/versions/7f3a9d21b6c4_add_notify_email_to_runs.py b/services/hackbot-api/alembic/versions/7f3a9d21b6c4_add_notify_email_to_runs.py
new file mode 100644
index 0000000000..ddc76b0056
--- /dev/null
+++ b/services/hackbot-api/alembic/versions/7f3a9d21b6c4_add_notify_email_to_runs.py
@@ -0,0 +1,28 @@
+"""Add notify_email to runs.
+
+Revision ID: 7f3a9d21b6c4
+Revises: b5b896e1ce12
+Create Date: 2026-07-01 00:00:00.000000
+
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "7f3a9d21b6c4"
+down_revision: Union[str, Sequence[str], None] = "b5b896e1ce12"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Upgrade schema."""
+    op.add_column("runs", sa.Column("notify_email", sa.String(), nullable=True))
+
+
+def downgrade() -> None:
+    """Downgrade schema."""
+    op.drop_column("runs", "notify_email")
diff --git a/services/hackbot-api/app/config.py b/services/hackbot-api/app/config.py
index 8975be89d1..ceb1737e3a 100644
--- a/services/hackbot-api/app/config.py
+++ b/services/hackbot-api/app/config.py
@@ -21,6 +21,11 @@ class Settings(BaseSettings):
     # API auth
     external_api_key: str = ""
 
+    # Email notifications (optional; notifications are skipped if unset)
+    sendgrid_api_key: str = ""
+    notification_sender_email: str = ""
+    hackbot_ui_base_url: str = ""
+
     # Server
     port: int = 8080
     environment: str = "development"
diff --git a/services/hackbot-api/app/database/models.py b/services/hackbot-api/app/database/models.py
index 0f566fb035..a470552659 100644
--- a/services/hackbot-api/app/database/models.py
+++ b/services/hackbot-api/app/database/models.py
@@ -20,6 +20,7 @@ class Run(Base):
     agent: Mapped[str] = mapped_column(String, nullable=False, index=True)
     status: Mapped[str] = mapped_column(String, nullable=False, index=True)
     inputs: Mapped[dict] = mapped_column(JSONB, nullable=False)
+    notify_email: Mapped[str | None] = mapped_column(String, nullable=True)
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),
         server_default=func.now(),
diff --git a/services/hackbot-api/app/notifications.py b/services/hackbot-api/app/notifications.py
new file mode 100644
index 0000000000..dd831bfe47
--- /dev/null
+++ b/services/hackbot-api/app/notifications.py
@@ -0,0 +1,118 @@
+"""Email notifications for completed agent runs.
+
+Sends a best-effort email via SendGrid when a run reaches a terminal
+status (succeeded / failed / timed_out), so a developer doesn't have to
+keep polling ``GET /runs/{run_id}`` to find out an agent finished.
+
+This is entirely optional: if ``SENDGRID_API_KEY`` or
+``NOTIFICATION_SENDER_EMAIL`` aren't configured, or a run was created
+without a ``notify_email``, this module is a no-op. Any failure to
+send (bad API key, SendGrid outage, etc.) is logged and swallowed --
+a broken notification must never fail run reconciliation.
+"""
+
+import asyncio
+import html
+import logging
+import re
+from functools import lru_cache
+from uuid import UUID
+
+import sendgrid
+from sendgrid.helpers.mail import Content, From, HtmlContent, Mail, Subject, To
+
+from app.config import settings
+from app.database.models import Run
+
+log = logging.getLogger(__name__)
+
+# Deliberately permissive: this only guards against obviously malformed
+# input at run-creation time. SendGrid itself validates deliverability.
+_EMAIL_RE = re.compile(r"^[^@\s]+@[^@\s]+\.[^@\s]+$")
+
+_STATUS_VERBS = {
+    "succeeded": "finished successfully",
+    "failed": "failed",
+    "timed_out": "timed out",
+}
+
+
+def is_valid_email(value: str) -> bool:
+    """Return whether ``value`` looks like a plausible email address."""
+    return bool(_EMAIL_RE.match(value))
+
+
+def build_run_url(run_id: UUID) -> str | None:
+    """Build a link to the run's results page, or None if unconfigured."""
+    base_url = settings.hackbot_ui_base_url.rstrip("/")
+    if not base_url:
+        return None
+    return f"{base_url}/runs/{run_id}"
+
+
+@lru_cache(maxsize=1)
+def _client() -> sendgrid.SendGridAPIClient:
+    return sendgrid.SendGridAPIClient(api_key=settings.sendgrid_api_key)
+
+
+def _status_verb(status: str) -> str:
+    return _STATUS_VERBS.get(status, status)
+
+
+def _build_lines(run: Run) -> list[str]:
+    lines = [
+        f"Agent: {run.agent}",
+        f"Run ID: {run.run_id}",
+        f"Status: {run.status}",
+    ]
+    if run.error:
+        lines.append(f"Error: {run.error}")
+    run_url = build_run_url(run.run_id)
+    if run_url:
+        lines.append(f"Results: {run_url}")
+    return lines
+
+
+def _build_message(run: Run) -> Mail:
+    lines = _build_lines(run)
+    plain_text = "\n".join(lines)
+    html_text = "<br>".join(html.escape(line) for line in lines)
+
+    return Mail(
+        From(settings.notification_sender_email),
+        To(run.notify_email),
+        Subject(f"[hackbot] {run.agent} run {_status_verb(run.status)}"),
+        Content("text/plain", plain_text),
+        HtmlContent(f"<p>{html_text}</p>"),
+    )
+
+
+def _send_sync(run: Run) -> None:
+    message = _build_message(run)
+    response = _client().send(message=message)
+    log.info(
+        "Sent run-completion email for run %s to %s (status code %s)",
+        run.run_id,
+        run.notify_email,
+        response.status_code,
+    )
+
+
+async def notify_run_complete(run: Run) -> None:
+    """Best-effort email notification for a run that just went terminal."""
+    if not settings.sendgrid_api_key:
+        return
+    if not run.notify_email:
+        return
+    if not settings.notification_sender_email:
+        log.warning(
+            "SENDGRID_API_KEY is set but NOTIFICATION_SENDER_EMAIL is not; "
+            "skipping notification for run %s",
+            run.run_id,
+        )
+        return
+
+    try:
+        await asyncio.to_thread(_send_sync, run)
+    except Exception:
+        log.exception("Failed to send completion email for run %s", run.run_id)
diff --git a/services/hackbot-api/app/routers/runs.py b/services/hackbot-api/app/routers/runs.py
index ff55d466e8..fe5ee7dcc6 100644
--- a/services/hackbot-api/app/routers/runs.py
+++ b/services/hackbot-api/app/routers/runs.py
@@ -6,7 +6,7 @@
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from app import gcs, jobs
+from app import gcs, jobs, notifications
 from app.agents import AGENT_REGISTRY, AgentSpec, model_to_env
 from app.auth import require_api_key
 from app.config import settings
@@ -53,6 +53,10 @@ async def list_agents() -> list[AgentDescriptor]:
 async def create_run(
     agent_name: str,
     payload: dict,
+    notify_email: str | None = Query(
+        default=None,
+        description="Optional email address to notify when this run finishes.",
+    ),
     db: AsyncSession = Depends(get_db),
 ) -> RunRef:
     agent = _lookup_agent(agent_name)
@@ -61,6 +65,11 @@ async def create_run(
     except ValueError as exc:
         raise HTTPException(status_code=422, detail=str(exc)) from exc
 
+    if notify_email is not None and not notifications.is_valid_email(notify_email):
+        raise HTTPException(
+            status_code=422, detail=f"Invalid notify_email: {notify_email!r}"
+        )
+
     run_id = uuid.uuid4()
     results_prefix = gcs.run_prefix(str(run_id))
 
@@ -71,6 +80,7 @@ async def create_run(
         agent=agent.name,
         status=RunStatus.pending.value,
         inputs=inputs.model_dump(mode="json"),
+        notify_email=notify_email,
         results_prefix=results_prefix,
         artifacts=[],
     )
@@ -192,6 +202,7 @@ async def _reconcile(db: AsyncSession, run: Run) -> None:
         run.error = error
 
     await db.commit()
+    await notifications.notify_run_complete(run)
 
 
 def _terminal_status(
diff --git a/services/hackbot-api/app/schemas.py b/services/hackbot-api/app/schemas.py
index 3b01e033cf..b4ea6f49ea 100644
--- a/services/hackbot-api/app/schemas.py
+++ b/services/hackbot-api/app/schemas.py
@@ -50,6 +50,7 @@ class RunDoc(BaseModel):
     agent: str
     status: RunStatus
     inputs: dict[str, Any]
+    notify_email: str | None = None
     created_at: datetime
     updated_at: datetime
     execution_name: str | None = None
diff --git a/services/hackbot-api/pyproject.toml b/services/hackbot-api/pyproject.toml
index 69f555c7e1..3896962443 100644
--- a/services/hackbot-api/pyproject.toml
+++ b/services/hackbot-api/pyproject.toml
@@ -15,6 +15,7 @@ dependencies = [
     "google-cloud-storage>=2.16.0",
     "google-cloud-run>=0.10.0",
     "sentry-sdk>=2.51.0",
+    "sendgrid>=6.12.5",
 ]
 
 [project.optional-dependencies]
diff --git a/services/hackbot-api/tests/test_notifications.py b/services/hackbot-api/tests/test_notifications.py
new file mode 100644
index 0000000000..b6c88c63b8
--- /dev/null
+++ b/services/hackbot-api/tests/test_notifications.py
@@ -0,0 +1,136 @@
+"""Tests for the email-notification module."""
+
+import uuid
+from unittest.mock import patch
+
+import pytest
+from app import notifications
+from app.config import settings
+from app.database.models import Run
+
+
+def make_run(**overrides) -> Run:
+    run = Run(
+        run_id=uuid.uuid4(),
+        agent="bug-fix",
+        status="succeeded",
+        inputs={},
+        results_prefix="runs/x/",
+        artifacts=[],
+    )
+    for key, value in overrides.items():
+        setattr(run, key, value)
+    return run
+
+
+@pytest.mark.parametrize(
+    "value,expected",
+    [
+        ("dev@example.com", True),
+        ("dev+tag@example.co.uk", True),
+        ("not-an-email", False),
+        ("missing-domain@", False),
+        ("@missing-local.com", False),
+        ("has space@example.com", False),
+        ("", False),
+    ],
+)
+def test_is_valid_email(value, expected):
+    assert notifications.is_valid_email(value) is expected
+
+
+def test_build_run_url_none_when_unconfigured(monkeypatch):
+    monkeypatch.setattr(settings, "hackbot_ui_base_url", "")
+    assert notifications.build_run_url(uuid.uuid4()) is None
+
+
+def test_build_run_url_strips_trailing_slash(monkeypatch):
+    monkeypatch.setattr(settings, "hackbot_ui_base_url", "https://hackbot.example/")
+    run_id = uuid.uuid4()
+    assert (
+        notifications.build_run_url(run_id) == f"https://hackbot.example/runs/{run_id}"
+    )
+
+
+def test_build_lines_includes_error_and_run_url(monkeypatch):
+    monkeypatch.setattr(settings, "hackbot_ui_base_url", "https://hackbot.example")
+    run = make_run(notify_email="dev@example.com", status="failed", error="boom")
+
+    lines = notifications._build_lines(run)
+
+    assert "Status: failed" in lines
+    assert "Error: boom" in lines
+    assert f"Results: https://hackbot.example/runs/{run.run_id}" in lines
+
+
+def test_build_lines_omits_error_and_url_when_absent(monkeypatch):
+    monkeypatch.setattr(settings, "hackbot_ui_base_url", "")
+    run = make_run(notify_email="dev@example.com", status="succeeded", error=None)
+
+    lines = notifications._build_lines(run)
+
+    assert not any(line.startswith("Error:") for line in lines)
+    assert not any(line.startswith("Results:") for line in lines)
+
+
+def test_build_message_smoke(monkeypatch):
+    monkeypatch.setattr(settings, "notification_sender_email", "hackbot@example.com")
+    run = make_run(notify_email="dev@example.com")
+
+    # Must not raise -- exercises the sendgrid Mail() construction path.
+    message = notifications._build_message(run)
+
+    assert message is not None
+
+
+async def test_notify_run_complete_noop_without_api_key(monkeypatch):
+    monkeypatch.setattr(settings, "sendgrid_api_key", "")
+    run = make_run(notify_email="dev@example.com")
+
+    with patch.object(notifications, "_send_sync") as send:
+        await notifications.notify_run_complete(run)
+
+    send.assert_not_called()
+
+
+async def test_notify_run_complete_noop_without_notify_email(monkeypatch):
+    monkeypatch.setattr(settings, "sendgrid_api_key", "SG.fake")
+    monkeypatch.setattr(settings, "notification_sender_email", "hackbot@example.com")
+    run = make_run(notify_email=None)
+
+    with patch.object(notifications, "_send_sync") as send:
+        await notifications.notify_run_complete(run)
+
+    send.assert_not_called()
+
+
+async def test_notify_run_complete_noop_without_sender(monkeypatch):
+    monkeypatch.setattr(settings, "sendgrid_api_key", "SG.fake")
+    monkeypatch.setattr(settings, "notification_sender_email", "")
+    run = make_run(notify_email="dev@example.com")
+
+    with patch.object(notifications, "_send_sync") as send:
+        await notifications.notify_run_complete(run)
+
+    send.assert_not_called()
+
+
+async def test_notify_run_complete_sends_when_configured(monkeypatch):
+    monkeypatch.setattr(settings, "sendgrid_api_key", "SG.fake")
+    monkeypatch.setattr(settings, "notification_sender_email", "hackbot@example.com")
+    run = make_run(notify_email="dev@example.com", status="failed", error="boom")
+
+    with patch.object(notifications, "_send_sync") as send:
+        await notifications.notify_run_complete(run)
+
+    send.assert_called_once_with(run)
+
+
+async def test_notify_run_complete_swallows_send_errors(monkeypatch):
+    monkeypatch.setattr(settings, "sendgrid_api_key", "SG.fake")
+    monkeypatch.setattr(settings, "notification_sender_email", "hackbot@example.com")
+    run = make_run(notify_email="dev@example.com")
+
+    with patch.object(notifications, "_send_sync", side_effect=RuntimeError("boom")):
+        # Must not raise -- a broken notification must never break reconciliation.
+        await notifications.notify_run_complete(run)