diff --git a/src/conclave/adapters/base.py b/src/conclave/adapters/base.py
index b92bcd6..2bfc7a2 100644
--- a/src/conclave/adapters/base.py
+++ b/src/conclave/adapters/base.py
@@ -15,8 +15,9 @@
   malformed payloads. Its message is ALREADY scrubbed via :func:`redact` so it
   is safe to surface in ``ModelAnswer.error``.
 * :func:`redact` -- key-leak hardening. Strips bearer tokens, ``sk-`` style
-  keys, ``x-api-key`` echoes, and any value of the env vars we hold names for,
-  before an error string can ever escape the call path.
+  keys, ``x-api-key`` echoes, and any value of the env vars we hold names for --
+  built-in providers AND custom-endpoint ``api_key_env`` names declared in
+  config -- before an error string can ever escape the call path.
 """
 
 from __future__ import annotations
@@ -38,10 +39,29 @@
 _REDACTED = "[REDACTED]"
 
 
+def _custom_endpoint_env_vars() -> list[str]:
+    """Return the env-var NAMES declared by custom endpoints, or [] on any error.
+
+    Custom OpenAI-compatible endpoints (``config.endpoints[*].env_var``) name a
+    key var that is NOT in :data:`PROVIDER_ENV_VARS`, so :func:`redact` would not
+    otherwise know to mask its value -- the BYO-keys leak class. We load config
+    here (lazily, to avoid an import cycle) purely to learn those names; failures
+    must never break redaction, so any error yields an empty list and we fall
+    back to pattern-based scrubbing only.
+    """
+    try:
+        from ..config import load_config
+
+        return [ep.env_var for ep in load_config().endpoints.values() if ep.env_var]
+    except Exception:  # noqa: BLE001 -- redaction must never raise
+        return []
+
+
 def redact(text: str) -> str:
     """Scrub anything key-shaped from a string before it can be surfaced.
 
-    Removes, in order: any live value of an env var we know a name for,
+    Removes, in order: any live value of an env var we know a name for --
+    including custom-endpoint ``api_key_env`` names declared in config --
     ``Bearer <token>`` auth headers, ``x-api-key``/``x-goog-api-key`` header
     echoes, and standalone provider-style key tokens (``sk-``, ``xai-``,
     ``pplx-``, ``AIza...``). Idempotent and safe on already-clean text.
@@ -55,13 +75,15 @@ def redact(text: str) -> str:
     if not text:
         return text
     cleaned = text
-    # 1) Redact concrete env-var values first (most authoritative). We only read
-    # values here to mask them; the masked result never contains the value.
-    for names in PROVIDER_ENV_VARS.values():
-        for name in names:
-            value = os.environ.get(name, "").strip()
-            if value:
-                cleaned = cleaned.replace(value, _REDACTED)
+    # 1) Redact concrete env-var values first (most authoritative). This covers
+    # the built-in providers AND any custom-endpoint key var declared in config,
+    # so a BYO custom key with an unrecognized shape is still masked. We only
+    # read values here to mask them; the masked result never contains the value.
+    builtin_names = [name for names in PROVIDER_ENV_VARS.values() for name in names]
+    for name in builtin_names + _custom_endpoint_env_vars():
+        value = os.environ.get(name, "").strip()
+        if value:
+            cleaned = cleaned.replace(value, _REDACTED)
     # 2) Header-shaped echoes.
     cleaned = _HEADER_KEY_RE.sub(rf"\1: {_REDACTED}", cleaned)
     # 3) Bearer auth headers.
diff --git a/tests/test_providers.py b/tests/test_providers.py
index 1d8beba..001b3a1 100644
--- a/tests/test_providers.py
+++ b/tests/test_providers.py
@@ -144,6 +144,47 @@ async def test_call_model_unknown_provider_is_error(monkeypatch):
     assert "unknown provider 'mystery'" in answer.error
 
 
+async def test_call_model_custom_endpoint_key_not_leaked_in_error(monkeypatch, tmp_path):
+    """A custom-endpoint key value echoed in a provider error is scrubbed (issue #14).
+
+    Repro: declare a custom OpenAI-compatible endpoint whose api_key_env is NOT
+    in PROVIDER_ENV_VARS and whose value has no recognized prefix, then have the
+    mocked transport return a 401 whose error message echoes that key. The
+    resulting ModelAnswer.error must not contain the key value anywhere.
+    """
+    # Obviously-synthetic, unprefixed fake key -- no sk-/xai-/pplx-/AIza shape,
+    # so pattern-based scrubbing alone would miss it; only name-based scrubbing
+    # via the custom endpoint's env var saves it.
+    fake_key = "togetherFAKEsecret_unprefixed_0123456789"
+    monkeypatch.setenv("TOGETHER_API_KEY", fake_key)
+
+    config_file = tmp_path / "conclave.yml"
+    config_file.write_text(
+        "endpoints:\n"
+        "  together:\n"
+        "    completions_url: https://api.together.xyz/v1/chat/completions\n"
+        "    env_var: TOGETHER_API_KEY\n",
+        encoding="utf-8",
+    )
+    monkeypatch.setenv("CONCLAVE_CONFIG", str(config_file))
+
+    async def echoing_401(url, headers, json_body, timeout):
+        # Simulate a gateway that echoes the submitted credential on auth failure.
+        return 401, {"error": {"message": f"invalid api key: {fake_key}"}}
+
+    monkeypatch.setattr("conclave.transport.post_json", echoing_401)
+
+    answer = await call_model(
+        "together",
+        "together/some-model",
+        [{"role": "user", "content": "hi"}],
+    )
+    assert not answer.ok
+    assert answer.error is not None
+    assert fake_key not in answer.error
+    assert "[REDACTED]" in answer.error
+
+
 # --------------------------------------------------------------------------- #
 # Redaction
 # --------------------------------------------------------------------------- #
@@ -175,3 +216,27 @@ def test_provider_error_message_is_pre_redacted():
     err = ProviderError("openai: HTTP 401: Bearer sk-leakedTOKEN12345")
     assert "sk-leakedTOKEN12345" not in str(err)
     assert "[REDACTED]" in str(err)
+
+
+def test_redact_scrubs_custom_endpoint_env_var_value(monkeypatch, tmp_path):
+    """An unprefixed custom-endpoint key value is scrubbed via config (issue #14).
+
+    The key has no recognized provider prefix, so only name-based scrubbing
+    sourced from config.endpoints[*].env_var can catch it.
+    """
+    fake_key = "togetherFAKEsecret_unprefixed_0123456789"
+    monkeypatch.setenv("TOGETHER_API_KEY", fake_key)
+
+    config_file = tmp_path / "conclave.yml"
+    config_file.write_text(
+        "endpoints:\n"
+        "  together:\n"
+        "    completions_url: https://api.together.xyz/v1/chat/completions\n"
+        "    env_var: TOGETHER_API_KEY\n",
+        encoding="utf-8",
+    )
+    monkeypatch.setenv("CONCLAVE_CONFIG", str(config_file))
+
+    cleaned = redact(f"auth failed: invalid api key: {fake_key}")
+    assert fake_key not in cleaned
+    assert "[REDACTED]" in cleaned