Short answer: In Prefect 3.x, the default logging level is INFO. That means DEBUG logs are filtered out before they’re sent to the API/UI. Raise the logging level to DEBUG and they’ll appear. How to enable DEBUG logs - One-off for a single run - Run your script with:

PREFECT_LOGGING_LEVEL=DEBUG python your_flow.py

- Persistently (profile) - Save to your active Prefect profile:

prefect config set logging.level=DEBUG

- Only bump flow/task loggers (keep everything else at INFO) - Set just these:

export PREFECT_LOGGING_LOGGERS_PREFECT_FLOW_RUNS_LEVEL=DEBUG
    export PREFECT_LOGGING_LOGGERS_PREFECT_TASK_RUNS_LEVEL=DEBUG

Notes - Make sure the UI’s log level filter includes Debug. - API logging is on by default, but if you’ve changed it, ensure:

PREFECT_LOGGING_TO_API_ENABLED=true

POC (copy/paste) 1) Local run POC (shows DEBUG in UI when enabled) Save as flow_debug_poc.py:

from prefect import flow, task
from prefect.logging import get_run_logger

@task
def my_task():
    logger = get_run_logger()
    logger.debug("Task DEBUG appears when level=DEBUG")
    <http://logger.info|logger.info>("Task INFO")
    logger.warning("Task WARNING")
    logger.error("Task ERROR")
    logger.critical("Task CRITICAL")

@flow(name="debug-demo")
def debug_demo():
    logger = get_run_logger()
    logger.debug("Flow DEBUG appears when level=DEBUG")
    <http://logger.info|logger.info>("Flow INFO")
    logger.warning("Flow WARNING")
    logger.error("Flow ERROR")
    logger.critical("Flow CRITICAL")
    my_task()

if __name__ == "__main__":
    debug_demo()

Run it with DEBUG enabled:

PREFECT_LOGGING_LEVEL=DEBUG python flow_debug_poc.py

2) Deployment/worker POC (two ways) Option A: Set DEBUG at the worker - Create a process work pool (once):

prefect work-pool create "process-pool" --type process

- Start a worker with DEBUG in the environment:

PREFECT_LOGGING_LEVEL=DEBUG prefect worker start --pool process-pool

- Deploy the flow (from the same directory as flow_debug_poc.py):

python -c "from prefect.flows import Flow; Flow.from_source('.', 'flow_debug_poc.py:debug_demo').deploy(name='debug-demo', work_pool_name='process-pool')"

- Run the deployment:

prefect deployment run debug-demo --watch

Option B: Set DEBUG on the deployment (no special worker env needed) - Deploy with an env override:

python -c "from prefect.flows import Flow; Flow.from_source('.', 'flow_debug_poc.py:debug_demo').deploy(name='debug-demo', work_pool_name='process-pool', job_variables={'env': {'PREFECT_LOGGING_LEVEL':'DEBUG'}})"

- Start a normal worker:

prefect worker start --pool process-pool

- Run the deployment:

prefect deployment run debug-demo --watch

If you still don’t see DEBUG logs: - Double-check the UI filter for Debug - Confirm the process actually has

PREFECT_LOGGING_LEVEL=DEBUG

- For targeted control, try:

PREFECT_LOGGING_LOGGERS_PREFECT_FLOW_RUNS_LEVEL=DEBUG
  PREFECT_LOGGING_LOGGERS_PREFECT_TASK_RUNS_LEVEL=DEBUG