Consider this DAG for a dbt project.

The --fail-fast flag changes dbt’s execution behavior by immediately stopping the scheduling of any further models as soon as the first failure occurs. This is true regardless of the number of threads; in this case, the environment uses one thread, meaning models run strictly in sequence based on dependency order.

In the DAG provided, model_d is downstream of model_b, and model_f depends on model_d. The execution sequence when using a single thread would be something like:

model_a runs

model_c runs

model_e runs

model_b runs

model_d runs → fails

Once model_d fails:

With normal dbt run, dbt would attempt to continue running any unrelated models (though in this DAG, there are no more independent nodes left anyway).

With --fail-fast, dbt immediately stops scheduling any additional work, halting the run.

Therefore, no further models—including model_f or any other—will run. dbt does not drop models, retry them, or attempt related branches. It simply stops.