diff --git a/backend/alembic/versions/c6cbfc534fad_subscriptions_pilot_complimentary_.py b/backend/alembic/versions/c6cbfc534fad_subscriptions_pilot_complimentary_.py
new file mode 100644
index 00000000..647fd085
--- /dev/null
+++ b/backend/alembic/versions/c6cbfc534fad_subscriptions_pilot_complimentary_.py
@@ -0,0 +1,47 @@
+"""subscriptions pilot complimentary backfill
+
+This migration converts existing pilot/dev accounts to permanent complimentary
+Pro per the self-serve signup spec section 5. Forward-only; downgrade is
+prohibited because original status is not preserved.
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision: str = "c6cbfc534fad"
+down_revision: Union[str, None] = "c982a3fc4bf1"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    """Set status='complimentary' and plan='pro' for all existing accounts that
+    don't have a canceled or past_due subscription. Pilot users transition to
+    permanent complimentary Pro per spec section 5.
+
+    Forward-only — does not preserve original status values."""
+    conn = op.get_bind()
+    # Update existing rows
+    conn.execute(sa.text("""
+        UPDATE subscriptions
+        SET status = 'complimentary', plan = 'pro',
+            current_period_end = NULL, current_period_start = NULL,
+            updated_at = now()
+        WHERE status NOT IN ('canceled', 'past_due')
+    """))
+    # Backfill: any account without a Subscription row gets one
+    conn.execute(sa.text("""
+        INSERT INTO subscriptions (id, account_id, plan, status, cancel_at_period_end, created_at, updated_at)
+        SELECT gen_random_uuid(), a.id, 'pro', 'complimentary', false, now(), now()
+        FROM accounts a
+        WHERE NOT EXISTS (SELECT 1 FROM subscriptions s WHERE s.account_id = a.id)
+    """))
+
+
+def downgrade() -> None:
+    raise RuntimeError(
+        "Cannot downgrade: original subscription state is not preserved. "
+        "Restore from backup if needed."
+    )
diff --git a/backend/tests/test_pilot_complimentary_backfill.py b/backend/tests/test_pilot_complimentary_backfill.py
new file mode 100644
index 00000000..70deb48d
--- /dev/null
+++ b/backend/tests/test_pilot_complimentary_backfill.py
@@ -0,0 +1,85 @@
+"""Smoke test for the complimentary backfill: assertions about the post-state.
+The actual migration runs at deploy time; tests use create_all so the
+migration body isn't executed automatically. We invoke the SQL inline to
+exercise the same effect."""
+import uuid
+import pytest
+from sqlalchemy import select, text, delete
+from app.models.account import Account
+from app.models.subscription import Subscription
+
+
+@pytest.mark.asyncio
+async def test_complimentary_backfill_sets_status_and_inserts_missing_rows(test_db):
+    """Inline-run the backfill SQL and assert post-state."""
+    # Seed a fresh account with no subscription
+    no_sub_account = Account(name="NoSub", display_code="NOSUB001")
+    test_db.add(no_sub_account)
+    await test_db.flush()
+
+    # Seed an account with a trialing subscription (should become complimentary)
+    trial_account = Account(name="Trial", display_code="TRIAL001")
+    test_db.add(trial_account)
+    await test_db.flush()
+    test_db.add(Subscription(
+        account_id=trial_account.id, plan="free", status="trialing",
+    ))
+
+    # Seed an account with a canceled subscription (should be preserved)
+    canceled_account = Account(name="Cancel", display_code="CANCL001")
+    test_db.add(canceled_account)
+    await test_db.flush()
+    test_db.add(Subscription(
+        account_id=canceled_account.id, plan="pro", status="canceled",
+    ))
+    await test_db.commit()
+
+    # Run the same SQL the migration runs
+    await test_db.execute(text("""
+        UPDATE subscriptions
+        SET status = 'complimentary', plan = 'pro',
+            current_period_end = NULL, current_period_start = NULL,
+            updated_at = now()
+        WHERE status NOT IN ('canceled', 'past_due')
+    """))
+    await test_db.execute(text("""
+        INSERT INTO subscriptions (id, account_id, plan, status, cancel_at_period_end, created_at, updated_at)
+        SELECT gen_random_uuid(), a.id, 'pro', 'complimentary', false, now(), now()
+        FROM accounts a
+        WHERE NOT EXISTS (SELECT 1 FROM subscriptions s WHERE s.account_id = a.id)
+    """))
+    await test_db.commit()
+
+    # All three accounts now have a Subscription
+    no_sub_row = (await test_db.execute(
+        select(Subscription).where(Subscription.account_id == no_sub_account.id)
+    )).scalar_one()
+    assert no_sub_row.status == "complimentary"
+    assert no_sub_row.plan == "pro"
+
+    trial_row = (await test_db.execute(
+        select(Subscription).where(Subscription.account_id == trial_account.id)
+    )).scalar_one()
+    assert trial_row.status == "complimentary"
+    assert trial_row.plan == "pro"
+
+    canceled_row = (await test_db.execute(
+        select(Subscription).where(Subscription.account_id == canceled_account.id)
+    )).scalar_one()
+    # Canceled is preserved
+    assert canceled_row.status == "canceled"
+    assert canceled_row.plan == "pro"
+
+
+@pytest.mark.asyncio
+async def test_complimentary_subscription_passes_active_subscription_guard(
+    client, test_db, test_user, auth_headers
+):
+    """The require_active_subscription guard accepts complimentary status."""
+    account_id = uuid.UUID(test_user["user_data"]["account_id"])
+    await test_db.execute(delete(Subscription).where(Subscription.account_id == account_id))
+    test_db.add(Subscription(account_id=account_id, plan="pro", status="complimentary"))
+    await test_db.commit()
+
+    response = await client.get("/api/v1/trees", headers=auth_headers)
+    assert response.status_code != 402