## TL;DR

Ephemeral models compile into downstream queries as CTEs, so a syntax error in the ephemeral model breaks every model that references it. Compile the downstream model, read the CTE dbt generated, fix the ephemeral model's SQL, and rebuild the chain.

## Error

```text
dbt ephemeral model broken: downstream ref chain failing
```

## Steps

1. Run `dbt compile --select [DOWNSTREAM MODEL]` and open the compiled SQL. Expected: you see the ephemeral model inlined as a CTE.
2. Read the CTE carefully for the syntax error (it is the ephemeral model's SQL, transplanted). Expected: you find the defect in the CTE body.
3. Fix the ephemeral model's source file (not the compiled output). Expected: the source SQL is now valid.
4. Check the whole ref chain for disabled models: an ephemeral model referencing a disabled node breaks the same way. Expected: every node in the chain is enabled.
5. Run `dbt run --select [EPHEMERAL MODEL]+` to rebuild the chain. Expected: all downstream models succeed.

## When to use

- Downstream models fail and an ephemeral model is in their ancestry.
- The error points at SQL you did not write in the downstream model (it came from the CTE).

## When not to use

- The downstream model's own SQL is broken (fix that file).
- No ephemeral models are involved (a normal dependency problem).

## Variant phrasings

### CTE syntax error naming a model you did not write

The CTE came from an ephemeral model; fix it at its source file.

### Ephemeral model works alone but breaks downstream

"Alone" is misleading: ephemeral models never build alone; always test via a downstream compile.

## Tool compatibility

- dbt Core 1.0 and later, all adapters. Ephemeral materialization is adapter-independent.

## Why it happens

Ephemeral models are never created as relations; dbt injects their SQL as CTEs into every downstream query. An error in the ephemeral SQL therefore multiplies across all its descendants.

## Edge cases

- Deeply nested ephemeral chains produce enormous compiled SQL; compile one downstream model at a time when debugging.
- An ephemeral model cannot be referenced from a test's `ref` the way tables can; test through a downstream model.
- Converting a broken ephemeral model to a view temporarily makes it independently testable.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_9-JnaCAx92yY3Ee3M8zVYA