jgoedeke opened a new issue, #55410:
URL: https://github.com/apache/airflow/issues/55410
### Apache Airflow version
3.0.6
### If "Other Airflow 2 version" selected, which one?
_No response_
### What happened?
In Airflow 3 (TaskFlow), returning a dict from a `@task` where one of the
dict KEYS contains a "/" causes the task to fail at the end during XCom push
with:
AirflowRuntimeError: `API_SERVER_ERROR: {'status_code': 404, 'message': 'Not
Found', 'detail': {'detail': 'Not Found'}}`.
The same code works when the dict keys do NOT contain "/".
It looks like when `@task` returns a dict and Airflow treats it as multiple
outputs, it creates one XCom per dictionary key. Those per-key XCom writes go
through the Execution API and the XCom KEY is placed in the URL path. If the
key contains "/", the path is split and the route doesn't match, yielding a
404/4xx.
### What you think should happen instead?
The task should succeed and XComs should be written even when dictionary
keys contain "/" (either by accepting "/" in the server route, or by
safe-encoding/sanitizing keys on client/server consistently). At minimum, the
behavior should be documented or validated early with a clear error if "/" in
keys is unsupported.
### How to reproduce
````python
from airflow.decorators import dag, task
@dag(schedule=None)
def xcom_slash_key_bug():
@task
def this_works() -> dict[str, str]:
return {"Some Key": "Some Value"}
@task
def this_works_as_well() -> str:
return "/some/path/like/key"
@task
def this_does_not_work() -> dict[str, str]:
return {"key with slash /": "Some Value"}
this_works() >> this_works_as_well() >> this_does_not_work()
dag = xcom_slash_key_bug()
````
### Operating System
Docker image
### Versions of Apache Airflow Providers
_No response_
### Deployment
Other Docker-based deployment
### Deployment details
_No response_
### Anything else?
Log output:
````
[2025-09-09, 08:33:14] INFO - Done. Returned value was:
{'/some/path/like/key': 'Some Value'}:
source="airflow.task.operators.airflow.providers.standard.decorators.python._PythonDecoratedOperator"
[2025-09-09, 08:33:14] INFO - Pushing xcom:
ti="RuntimeTaskInstance(id=UUID('01992d2d-836b-716c-b17d-03be4ec4c67a'),
task_id='this_does_not_work', dag_id='testing',
run_id='manual__2025-09-09T06:33:01.531829+00:00', try_number=1, map_index=-1,
hostname='e7e821981d6d', context_carrier={},
task=<Task(_PythonDecoratedOperator): this_does_not_work>,
bundle_instance=LocalDagBundle(name=dags-folder), max_tries=0,
start_date=datetime.datetime(2025, 9, 9, 6, 33, 11, 94959, tzinfo=TzInfo(UTC)),
end_date=None, state=<TaskInstanceState.RUNNING: 'running'>, is_mapped=False,
rendered_map_index=None,
log_url='https://airflow.damas.pilatus-aircraft.com/dags/testing/runs/manual__2025-09-09T06%3A33%3A01.531829%2B00%3A00/tasks/this_does_not_work?try_number=1')":
source="task"
[2025-09-09, 08:33:14] ERROR - Task failed with exception: source="task"
AirflowRuntimeError: API_SERVER_ERROR: {'status_code': 404, 'message': 'Not
Found', 'detail': {'detail': 'Not Found'}}
File
"/home/airflow/.local/lib/python3.11/site-packages/airflow/sdk/execution_time/task_runner.py",
line 931 in run
File
"/home/airflow/.local/lib/python3.11/site-packages/airflow/sdk/execution_time/task_runner.py",
line 1275 in _push_xcom_if_needed
File
"/home/airflow/.local/lib/python3.11/site-packages/airflow/sdk/execution_time/task_runner.py",
line 414 in xcom_push
File
"/home/airflow/.local/lib/python3.11/site-packages/airflow/sdk/execution_time/task_runner.py",
line 561 in _xcom_push
File
"/home/airflow/.local/lib/python3.11/site-packages/airflow/sdk/bases/xcom.py",
line 84 in set
File
"/home/airflow/.local/lib/python3.11/site-packages/airflow/sdk/execution_time/comms.py",
line 204 in send
File
"/home/airflow/.local/lib/python3.11/site-packages/airflow/sdk/execution_time/comms.py",
line 264 in _get_response
File
"/home/airflow/.local/lib/python3.11/site-packages/airflow/sdk/execution_time/comms.py",
line 251 in _from_frame
````
### Are you willing to submit PR?
- [ ] Yes I am willing to submit a PR!
### Code of Conduct
- [x] I agree to follow this project's [Code of
Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)
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