fix(budget): recompute budget_reset_at when budget_duration changes on /budget/update (#30555)

POST /budget/update did not recompute budget_reset_at when budget_duration
changed and no explicit budget_reset_at was supplied, leaving shortened
budgets pinned to the old (longer) schedule. The same defect reached
POST /team/update via team_member_budget_duration, which delegates to
update_budget.

update_budget now recomputes budget_reset_at = get_budget_reset_time(duration)
when the caller sets budget_duration without pinning budget_reset_at,
mirroring /budget/new. Explicit budget_reset_at is preserved and updates
that omit budget_duration leave the reset untouched. get_budget_reset_time
now declares its datetime return type so the recomputed value stays concretely
typed.

Resolves LIT-3362

litellm/proxy/common_utils/timezone_utils.py

@@ -15,7 +15,7 @@ def get_budget_reset_timezone():
     return getattr(litellm, "timezone", None) or "UTC"
 
 
-def get_budget_reset_time(budget_duration: str):
+def get_budget_reset_time(budget_duration: str) -> datetime:
     """
     Get the budget reset time based on the configured timezone.
     Falls back to UTC if not specified.

litellm/proxy/management_endpoints/budget_management_endpoints.py

@@ -183,10 +183,23 @@ async def update_budget(
         except ValueError as e:
             raise HTTPException(status_code=400, detail={"error": str(e)})
 
+    # recompute budget_reset_at when the duration changes, unless the caller pinned a reset time explicitly
+    recomputed_reset_at = (
+        {
+            "budget_reset_at": get_budget_reset_time(
+                budget_duration=budget_obj.budget_duration
+            )
+        }
+        if budget_obj.budget_duration is not None
+        and "budget_reset_at" not in budget_obj.model_fields_set
+        else {}
+    )
+
     response = await BudgetRepository(prisma_client).table.update(
         where={"budget_id": budget_obj.budget_id},
         data={
             **budget_obj.model_dump(exclude_unset=True),  # type: ignore
+            **recomputed_reset_at,
             "updated_by": user_api_key_dict.user_id or litellm_proxy_admin_name,
         },  # type: ignore
     )

tests/test_litellm/proxy/management_endpoints/test_budget_endpoints.py

@@ -3,6 +3,7 @@
 import os
 import sys
 import types
+from datetime import datetime, timedelta, timezone
 import pytest
 from unittest.mock import AsyncMock, MagicMock
 from fastapi.testclient import TestClient
@@ -11,7 +12,6 @@ import litellm.proxy.proxy_server as ps
 from litellm.proxy.proxy_server import app
 from litellm.proxy._types import UserAPIKeyAuth, LitellmUserRoles, CommonProxyErrors
 
-
 sys.path.insert(
     0, os.path.abspath("../../../")
 )  # Adds the parent directory to the system path
@@ -265,3 +265,98 @@ async def test_new_budget_invalid_model_max_budget(client_and_mocks, monkeypatch
     assert resp.status_code in (400, 422), resp.text
     detail = resp.json()["detail"]
     assert "model_max_budget" in str(detail) or "dictionary" in str(detail).lower()
+
+
+def _capture_update_data(mock_table):
+    captured = {}
+
+    async def capture(*, where, data):
+        captured.update(data)
+        return {**where, **data}
+
+    mock_table.update = AsyncMock(side_effect=capture)
+    return captured
+
+
+@pytest.mark.asyncio
+async def test_update_budget_recomputes_reset_at_when_duration_changes(
+    client_and_mocks,
+):
+    """
+    Regression for LIT-3362: shortening budget_duration without an explicit
+    budget_reset_at must bring the reset forward instead of leaving it pinned
+    to the previous (longer) schedule.
+    """
+    client, _, mock_table = client_and_mocks
+    captured = _capture_update_data(mock_table)
+
+    before = datetime.now(timezone.utc)
+    resp = client.post(
+        "/budget/update",
+        json={"budget_id": "budget_reset_recompute", "budget_duration": "1d"},
+    )
+    assert resp.status_code == 200, resp.text
+
+    assert (
+        "budget_reset_at" in captured
+    ), "duration change must recompute budget_reset_at"
+    reset_at = captured["budget_reset_at"]
+    assert isinstance(reset_at, datetime)
+    assert reset_at > before, "recomputed reset must be in the future"
+    # "1d" resets at the next standardized day boundary, always within ~24h
+    assert reset_at <= before + timedelta(days=1, hours=1), reset_at
+    # and it must be far closer than a stale 30d schedule would have left it
+    assert reset_at < before + timedelta(days=29)
+
+
+@pytest.mark.asyncio
+async def test_update_budget_preserves_explicit_reset_at(client_and_mocks):
+    """An explicit budget_reset_at from the caller always wins over recompute."""
+    client, _, mock_table = client_and_mocks
+    captured = _capture_update_data(mock_table)
+
+    explicit = datetime(2027, 1, 1, tzinfo=timezone.utc)
+    resp = client.post(
+        "/budget/update",
+        json={
+            "budget_id": "budget_explicit_reset",
+            "budget_duration": "1d",
+            "budget_reset_at": explicit.isoformat(),
+        },
+    )
+    assert resp.status_code == 200, resp.text
+
+    assert captured["budget_reset_at"] == explicit
+
+
+@pytest.mark.asyncio
+async def test_update_budget_without_duration_leaves_reset_at_untouched(
+    client_and_mocks,
+):
+    """Updates that do not touch budget_duration must not introduce budget_reset_at."""
+    client, _, mock_table = client_and_mocks
+    captured = _capture_update_data(mock_table)
+
+    resp = client.post(
+        "/budget/update",
+        json={"budget_id": "budget_other_field", "max_budget": 200.0},
+    )
+    assert resp.status_code == 200, resp.text
+
+    assert "budget_reset_at" not in captured
+
+
+@pytest.mark.asyncio
+async def test_update_budget_duration_none_does_not_recompute(client_and_mocks):
+    """Clearing budget_duration (explicit null) must not recompute against a None duration."""
+    client, _, mock_table = client_and_mocks
+    captured = _capture_update_data(mock_table)
+
+    resp = client.post(
+        "/budget/update",
+        json={"budget_id": "budget_clear_duration", "budget_duration": None},
+    )
+    assert resp.status_code == 200, resp.text
+
+    assert "budget_duration" in captured and captured["budget_duration"] is None
+    assert "budget_reset_at" not in captured