diff --git a/tests/e2e/claude_code/_compat_models.py b/tests/e2e/claude_code/_compat_models.py
new file mode 100644
index 00000000000..89239ca9716
--- /dev/null
+++ b/tests/e2e/claude_code/_compat_models.py
@@ -0,0 +1,67 @@
+"""Load Claude Code matrix deployments from test_config.yaml for /model/new."""
+
+from __future__ import annotations
+
+from collections.abc import Callable, Mapping
+from dataclasses import dataclass
+from pathlib import Path
+from typing import cast
+
+import yaml
+
+from models import LiteLLMParamsBody
+
+CONFIG_PATH = Path(__file__).resolve().parent / "test_config.yaml"
+
+_YAML_TO_PYDANTIC_ALIASES = {
+    "vertex_ai_project": "vertex_project",
+    "vertex_ai_location": "vertex_location",
+    "vertex_ai_credentials": "vertex_credentials",
+}
+
+
+@dataclass(frozen=True, slots=True)
+class CompatDeployment:
+    model_name: str
+    litellm_params: LiteLLMParamsBody
+
+
+def _normalize_params(raw: Mapping[str, object]) -> dict[str, object]:
+    return {_YAML_TO_PYDANTIC_ALIASES.get(key, key): value for key, value in raw.items()}
+
+
+ConfigReader = Callable[[Path], str]
+
+
+def _default_reader(path: Path) -> str:
+    return path.read_text()
+
+
+def load_all_deployments(
+    config_path: Path = CONFIG_PATH,
+    reader: ConfigReader = _default_reader,
+) -> tuple[CompatDeployment, ...]:
+    doc = yaml.safe_load(reader(config_path))
+    if not isinstance(doc, dict):
+        return ()
+    model_list = doc.get("model_list") or []
+    if not isinstance(model_list, list):
+        return ()
+    return tuple(
+        CompatDeployment(
+            model_name=str(entry["model_name"]),
+            litellm_params=LiteLLMParamsBody(
+                **_normalize_params(cast(Mapping[str, object], entry["litellm_params"]))
+            ),
+        )
+        for entry in model_list
+        if isinstance(entry, dict) and "model_name" in entry and "litellm_params" in entry
+    )
+
+
+def all_expected_model_names(
+    *,
+    config_path: Path = CONFIG_PATH,
+    reader: ConfigReader = _default_reader,
+) -> frozenset[str]:
+    return frozenset(d.model_name for d in load_all_deployments(config_path, reader))
diff --git a/tests/e2e/claude_code/_pr_gate_unit_tests/test_compat_models.py b/tests/e2e/claude_code/_pr_gate_unit_tests/test_compat_models.py
new file mode 100644
index 00000000000..2da981782fe
--- /dev/null
+++ b/tests/e2e/claude_code/_pr_gate_unit_tests/test_compat_models.py
@@ -0,0 +1,75 @@
+"""Unit tests for the compat matrix deployment loader and yaml drift checks."""
+
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+import pytest
+
+from claude_code._compat_models import (
+    all_expected_model_names,
+    load_all_deployments,
+)
+
+CLAUDE_CODE_DIR = Path(__file__).resolve().parents[1]
+
+
+def _cell_declared_model_names() -> frozenset[str]:
+    pattern = re.compile(r'"(claude-[a-zA-Z0-9._-]+)"')
+    found: set[str] = set()
+    for path in CLAUDE_CODE_DIR.glob("*/test_*.py"):
+        if path.parent.name.startswith("_"):
+            continue
+        for match in pattern.finditer(path.read_text()):
+            name = match.group(1)
+            if "/" in name or "@" in name:
+                continue
+            found.add(name)
+    return frozenset(found)
+
+
+def test_yaml_covers_every_cell_declared_model_name() -> None:
+    yaml_names = all_expected_model_names()
+    cell_names = _cell_declared_model_names()
+    missing = cell_names - yaml_names
+    assert not missing, (
+        f"compat cells reference model names not declared in "
+        f"test_config.yaml: {sorted(missing)}. Add a matching "
+        f"model_list entry so the session fixture can register them."
+    )
+
+
+def test_yaml_has_no_unused_declarations() -> None:
+    yaml_names = all_expected_model_names()
+    cell_names = _cell_declared_model_names()
+    unused = yaml_names - cell_names
+    assert not unused, (
+        f"test_config.yaml declares model names no cell references: "
+        f"{sorted(unused)}. Delete them or add the cell."
+    )
+
+
+def test_load_returns_fifteen_deployments() -> None:
+    assert len(load_all_deployments()) == 15
+
+
+def test_deployments_are_hashable_and_frozen() -> None:
+    d = load_all_deployments()[0]
+    with pytest.raises((AttributeError, TypeError)):
+        d.model_name = "mutated"  # type: ignore[misc]
+
+
+def test_vertex_yaml_keys_populate_pydantic_body() -> None:
+    vertex = tuple(d for d in load_all_deployments() if d.model_name.endswith("-vertex"))
+    assert vertex, "no vertex deployments found in yaml"
+    for d in vertex:
+        assert d.litellm_params.vertex_project, (
+            f"{d.model_name} lost its vertex_project after normalization"
+        )
+        assert d.litellm_params.vertex_location, (
+            f"{d.model_name} lost its vertex_location after normalization"
+        )
+        assert d.litellm_params.use_in_pass_through is True, (
+            f"{d.model_name} must set use_in_pass_through for the passthrough row"
+        )
diff --git a/tests/e2e/claude_code/conftest.py b/tests/e2e/claude_code/conftest.py
index d2bfa1a54bf..7454cba8871 100644
--- a/tests/e2e/claude_code/conftest.py
+++ b/tests/e2e/claude_code/conftest.py
@@ -43,6 +43,8 @@ from typing import Any, Dict, FrozenSet, List, Optional, Tuple
 import pytest
 import yaml
 
+from claude_code._compat_models import CompatDeployment, load_all_deployments
+
 VALID_STATUSES = {"pass", "fail", "not_applicable", "not_tested"}
 RESULTS_ARTIFACT_ENV = "COMPAT_RESULTS_PATH"
 DEFAULT_ARTIFACT_PATH = "compat-results.json"
@@ -548,3 +550,69 @@ def pytest_sessionfinish(session, exitstatus):
     )
     summary_path.write_text(json.dumps(summary, indent=2, sort_keys=True))
     _print_rate_limit_summary(summary)
+
+
+def _proxy_env_configured() -> bool:
+    has_url = bool(os.environ.get("LITELLM_PROXY_URL") or os.environ.get("LITELLM_PROXY_BASE_URL"))
+    has_key = bool(os.environ.get("LITELLM_MASTER_KEY") or os.environ.get("LITELLM_PROXY_API_KEY"))
+    return has_url and has_key
+
+
+def _build_control_gateway():
+    from e2e_gateway import build_gateway
+
+    return build_gateway()
+
+
+def _register_deployment(gateway: Any, deployment: CompatDeployment) -> str:
+    return gateway.create_model(deployment.model_name, deployment.litellm_params)
+
+
+def _try_register(
+    gateway: Any, deployment: CompatDeployment
+) -> tuple[str | None, tuple[str, str] | None]:
+    from requests import RequestException
+
+    try:
+        return _register_deployment(gateway, deployment), None
+    except (AssertionError, RequestException) as exc:
+        return None, (deployment.model_name, str(exc))
+
+
+@pytest.fixture(scope="session", autouse=True)
+def _compat_models_registered() -> Any:
+    """POST /model/new for every deployment in test_config.yaml; delete on exit.
+
+    No-ops when proxy env is unset so unit-test trees stay hermetic.
+    Per-deployment register failures are printed and skipped: cells that need
+    that alias fail with Invalid model name, which is the right signal when
+    the proxy lacks that provider's credentials.
+    """
+    if not _proxy_env_configured():
+        yield
+        return
+
+    from requests import RequestException
+
+    gateway = _build_control_gateway()
+    outcomes = tuple(_try_register(gateway, d) for d in load_all_deployments())
+    registered_ids = tuple(model_id for model_id, err in outcomes if model_id is not None)
+    failures = tuple(err for _model_id, err in outcomes if err is not None)
+    if failures:
+        summary = "\n".join(f"  - {name}: {reason}" for name, reason in failures)
+        print(
+            f"[compat fixture] {len(failures)} of "
+            f"{len(failures) + len(registered_ids)} deployments "
+            f"failed to register (proxy likely missing that provider's "
+            f"credentials); cells that target them will fail loudly:\n"
+            f"{summary}",
+            flush=True,
+        )
+    try:
+        yield
+    finally:
+        for model_id in registered_ids:
+            try:
+                gateway.delete_model(model_id)
+            except (AssertionError, RequestException):
+                pass
diff --git a/tests/e2e/claude_code/test_config.yaml b/tests/e2e/claude_code/test_config.yaml
index eec68d11dcf..5594c2884c8 100644
--- a/tests/e2e/claude_code/test_config.yaml
+++ b/tests/e2e/claude_code/test_config.yaml
@@ -59,21 +59,26 @@ model_list:
       aws_region_name: us-east-1
 
   # ---- Vertex AI ----
+  # use_in_pass_through registers project/location with the /vertex_ai
+  # passthrough router for the passthrough matrix row.
   - model_name: claude-haiku-4-5-vertex
     litellm_params:
       model: vertex_ai/claude-haiku-4-5
       vertex_ai_project: os.environ/VERTEXAI_PROJECT
       vertex_ai_location: os.environ/VERTEXAI_LOCATION
+      use_in_pass_through: true
   - model_name: claude-sonnet-4-6-vertex
     litellm_params:
       model: vertex_ai/claude-sonnet-4-6
       vertex_ai_project: os.environ/VERTEXAI_PROJECT
       vertex_ai_location: os.environ/VERTEXAI_LOCATION
+      use_in_pass_through: true
   - model_name: claude-opus-4-7-vertex
     litellm_params:
       model: vertex_ai/claude-opus-4-7
       vertex_ai_project: os.environ/VERTEXAI_PROJECT
       vertex_ai_location: os.environ/VERTEXAI_LOCATION
+      use_in_pass_through: true
 
   # ---- Microsoft Foundry (Anthropic deployments on Azure) ----
   - model_name: claude-haiku-4-5-azure
diff --git a/tests/e2e/models.py b/tests/e2e/models.py
index 4140967f3e0..5c3bc3bdd1d 100644
--- a/tests/e2e/models.py
+++ b/tests/e2e/models.py
@@ -431,6 +431,7 @@ class LiteLLMParamsBody(BaseModel):
     vertex_project: str | None = None
     vertex_location: str | None = None
     vertex_credentials: str | None = None
+    use_in_pass_through: bool | None = None
     gcs_bucket_name: str | None = None
     bucket_name: str | None = None
     s3_bucket_name: str | None = None