diff --git a/README.md b/README.md
index 1b4d83da..729f0bdb 100644
--- a/README.md
+++ b/README.md
@@ -151,7 +151,7 @@ uv run python examples/quickstart.py path/to/episode.mcap
 For the recommended first run on real egocentric footage, follow
 [Evaluate your first egocentric episode](./docs/tutorials/evaluate-an-egocentric-episode.md).
 It runs HFlow's local deterministic quality baseline and two hosted semantic
-checks together, without requiring an account, API key, or model server.
+checks together. Contact us to get access to the hosted API.
 
 Use `uv run hflow --help` to see the CLI. When you are ready to schedule the
 same pipeline, continue with the [runtime guide](https://github.com/Hebbian-Robotics/hflow/blob/main/docs/RUNTIME.md). Developers
diff --git a/docs/FAQ.md b/docs/FAQ.md
index dea7b57c..53e8c6b3 100644
--- a/docs/FAQ.md
+++ b/docs/FAQ.md
@@ -68,10 +68,10 @@ where in the recording each problem occurred.
 
 By default nothing leaves your infrastructure: the SDK, the catalog, and every
 built-in check run where you run them. The hosted checks are the exception and
-are opt-in. When you register one with `HFlowHostedExecution`, the SDK sends
-the sampled JPEG frames that check needs to `https://api.hflow.dev` and records
-the answers in your catalog alongside every other check. No API key is needed.
-Each hosted check version is frozen, so results stay comparable over time, and
+are opt-in. Contact us to get access to the hosted API. When you register a
+check with `HFlowHostedExecution(base_url=...)`, the SDK sends the sampled JPEG
+frames that check needs to that URL and records the answers in your catalog
+alongside every other check. Each hosted check version is frozen, so results stay comparable over time, and
 the service admits one request at a time per client.
 
 ## What does a run produce?
diff --git a/docs/how-to/run-build-ai-evaluation.md b/docs/how-to/run-build-ai-evaluation.md
index b9a8946e..0fd93962 100644
--- a/docs/how-to/run-build-ai-evaluation.md
+++ b/docs/how-to/run-build-ai-evaluation.md
@@ -24,8 +24,9 @@ deterministic quality checks, start with
 
 ## Run the methodology on an HFlow episode
 
-The example uses HFlow's fixed hosted implementation for both checks by
-default. It needs no model configuration, account, or API key.
+The example sends both checks to an OpenAI-compatible vision endpoint by
+default. HFlow's fixed hosted implementation is also available; contact us to
+get access to the hosted API.
 
 To try the checks without supplying your own recording, download a small
 egocentric MCAP from Lightwheel's
@@ -46,9 +47,12 @@ cp "$downloaded_sample_mcap_path" data/build-ai-evaluation/sample.mcap
 
 If Hugging Face requests access, accept the dataset's terms and run
 `hf auth login` before downloading. You can then run the pipeline against the
-sample:
+sample with an unauthenticated local OpenAI-compatible vision server:
 
 ```bash
+export OPENAI_BASE_URL="http://localhost:8000/v1"
+export OPENAI_MODEL="Qwen/Qwen3-VL-8B-Instruct"
+
 uv run --project examples/build_ai_evaluation \
     python -m examples.build_ai_evaluation.pipeline \
     data/build-ai-evaluation/sample.mcap
@@ -57,13 +61,12 @@ uv run --project examples/build_ai_evaluation \
 Replace that path with any MCAP containing meaningful egocentric footage to
 evaluate your own recording.
 
-To use an unauthenticated local OpenAI-compatible vision server instead, select
-that execution route and identify its model:
+To use HFlow's hosted checks instead, select that execution route and pass the
+hosted API URL you received:
 
 ```bash
-export BUILD_AI_EXECUTION="openai-compatible"
-export OPENAI_BASE_URL="http://localhost:8000/v1"
-export OPENAI_MODEL="Qwen/Qwen3-VL-8B-Instruct"
+export BUILD_AI_EXECUTION="hflow-hosted"
+export BUILD_AI_HOSTED_BASE_URL="$HFLOW_HOSTED_BASE_URL"
 
 uv run --project examples/build_ai_evaluation \
     python -m examples.build_ai_evaluation.pipeline \
@@ -107,8 +110,8 @@ different configurations do not claim comparable step versions.
 Each check can select its execution independently with
 `BUILD_AI_HAND_VISIBILITY_EXECUTION` and
 `BUILD_AI_ACTIVE_MANIPULATION_EXECUTION`; each defaults to `BUILD_AI_EXECUTION`
-and then to `hflow-hosted`. For example, one check can remain hosted while the
-other uses your model:
+and then to `openai-compatible`. For example, one check can use the hosted API
+while the other uses your model:
 
 ```bash
 export BUILD_AI_HAND_VISIBILITY_EXECUTION="hflow-hosted"
@@ -121,7 +124,8 @@ OpenAI-compatible checks can use different services through the
 `BUILD_AI_ACTIVE_MANIPULATION_*` overrides.
 
 `HFlowHostedExecution` owns the hosted base URL, check version, and request policy;
-its server owns every model setting. `request_timeout_seconds` defaults to 60,
+its server owns every model setting. `base_url` has no default: contact us to
+get access to the hosted API. `request_timeout_seconds` defaults to 60,
 `total_timeout_seconds` to 360, and `max_retries` to five additional attempts.
 Tenacity retries transport failures and HTTP 429/502/503/504, respecting numeric
 `Retry-After` delays (capped at 120 seconds) or exponential backoff. Authorization
@@ -165,7 +169,7 @@ per check, so the two checks may use different executions:
 ```python
 hflow.build_ai_vlm_checks.register_hand_visibility(
     app,
-    execution=hflow.build_ai_vlm_checks.HFlowHostedExecution(),
+    execution=hflow.build_ai_vlm_checks.HFlowHostedExecution(base_url=hosted_api_url),
 )
 hflow.build_ai_vlm_checks.register_active_manipulation(
     app,
@@ -191,7 +195,7 @@ the same prompt to every frame at that rate instead:
 ```python
 hflow.build_ai_vlm_checks.register_hand_visibility(
     app,
-    execution=hflow.build_ai_vlm_checks.HFlowHostedExecution(),
+    execution=hflow.build_ai_vlm_checks.HFlowHostedExecution(base_url=hosted_api_url),
     sampling=hflow.build_ai_vlm_checks.FrameSampling(fps=1.0, start_s=0.0, end_s=None),
 )
 ```
diff --git a/docs/tutorials/evaluate-an-egocentric-episode.md b/docs/tutorials/evaluate-an-egocentric-episode.md
index 58d38e0f..831eea0e 100644
--- a/docs/tutorials/evaluate-an-egocentric-episode.md
+++ b/docs/tutorials/evaluate-an-egocentric-episode.md
@@ -5,8 +5,8 @@ point for egocentric video: the default deterministic quality checks plus two
 hosted model checks. It demonstrates the useful split in one command:
 
 - HFlow measures recording integrity locally and deterministically.
-- HFlow's hosted checks add semantic evidence without requiring an account,
-  API key, or model server.
+- HFlow's hosted checks add semantic evidence without a model server of your
+  own. Contact us to get access to the hosted API.
 - Both kinds of evidence are versioned and recorded through the same pipeline.
 
 The hosted checks are registered explicitly rather than included in
@@ -50,11 +50,13 @@ The sample has two camera streams, so select its left head camera explicitly:
 ```bash
 uv run python examples/evaluate_episode.py \
     data/episode-evaluation/sample.mcap \
+    --hosted-base-url "$HFLOW_HOSTED_BASE_URL" \
     --camera /sensor/camera/head_left/video
 ```
 
-No model endpoint or API key is required. HFlow processes the episode locally;
-the two model checks send only the selected JPEG frame to `api.hflow.dev`.
+Set `HFLOW_HOSTED_BASE_URL` to the hosted API URL you received. HFlow
+processes the episode locally; the two model checks send only the selected
+JPEG frame to that URL.
 
 The first sample frame visibly contains two wearer hands manipulating material.
 The hosted results should therefore include:
@@ -87,6 +89,7 @@ one camera, or pass the desired camera topic when it contains several:
 
 ```bash
 uv run python examples/evaluate_episode.py path/to/episode.mcap \
+    --hosted-base-url "$HFLOW_HOSTED_BASE_URL" \
     --camera /your/egocentric/camera
 ```
 
diff --git a/examples/README.md b/examples/README.md
index fb5f7a47..40277b97 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -172,8 +172,9 @@ Code: [`measurement_distribution.py`](./measurement_distribution.py)
 **Use it for:** seeing HFlow's default deterministic checks and hosted semantic
 checks work together on real egocentric footage.
 
-**Prerequisites:** the normal development environment, the `hf` CLI, and
-network access. The hosted checks require no account, API key, or model server.
+**Prerequisites:** the normal development environment, the `hf` CLI, network
+access, and a hosted API URL in `HFLOW_HOSTED_BASE_URL`. Contact us to get
+access to the hosted API.
 
 ```bash
 mkdir -p data/episode-evaluation
@@ -187,6 +188,7 @@ cp "$downloaded_sample_mcap_path" data/episode-evaluation/sample.mcap
 
 uv run python examples/evaluate_episode.py \
     data/episode-evaluation/sample.mcap \
+    --hosted-base-url "$HFLOW_HOSTED_BASE_URL" \
     --camera /sensor/camera/head_left/video
 ```
 
@@ -229,9 +231,9 @@ Code: [`openai_vision/pipeline.py`](./openai_vision/pipeline.py)
 active-manipulation methodology as HFlow checks, then replaying their
 Egocentric-10K or Egocentric-100K inputs to compare models and prompts.
 
-**Prerequisites:** network access and the `hf` CLI for the sample recording.
-The default pipeline route uses HFlow's hosted checks without an account or API
-key. The pinned evaluation replay additionally needs sufficient disk for the
+**Prerequisites:** network access, the `hf` CLI for the sample recording, and an
+OpenAI-compatible vision endpoint (or access to HFlow's hosted API; contact us).
+The pinned evaluation replay additionally needs sufficient disk for the
 selected Parquet files. Each frame makes two external check calls; a configured
 model provider may charge for them.
 
@@ -245,6 +247,9 @@ downloaded_sample_mcap_path="$(
 )"
 cp "$downloaded_sample_mcap_path" data/build-ai-evaluation/sample.mcap
 
+export OPENAI_BASE_URL="http://localhost:8000/v1"
+export OPENAI_MODEL="Qwen/Qwen3-VL-8B-Instruct"
+
 uv run --project examples/build_ai_evaluation \
     python -m examples.build_ai_evaluation.pipeline \
     data/build-ai-evaluation/sample.mcap
@@ -256,12 +261,12 @@ identity, and any available model usage as `hflow.CheckResult`
 measurements. An episode path is required because generated test-pattern
 footage cannot meaningfully demonstrate either judgment.
 
-To use a local OpenAI-compatible model server instead of HFlow's hosted checks:
+To use HFlow's hosted checks instead (contact us to get access to the hosted
+API):
 
 ```bash
-export BUILD_AI_EXECUTION="openai-compatible"
-export OPENAI_BASE_URL="http://localhost:8000/v1"
-export OPENAI_MODEL="Qwen/Qwen3-VL-8B-Instruct"
+export BUILD_AI_EXECUTION="hflow-hosted"
+export BUILD_AI_HOSTED_BASE_URL="$HFLOW_HOSTED_BASE_URL"
 
 uv run --project examples/build_ai_evaluation \
     python -m examples.build_ai_evaluation.pipeline \
diff --git a/examples/build_ai_evaluation/pipeline.py b/examples/build_ai_evaluation/pipeline.py
index 103c0a54..4662e702 100644
--- a/examples/build_ai_evaluation/pipeline.py
+++ b/examples/build_ai_evaluation/pipeline.py
@@ -1,8 +1,9 @@
 """Run Build AI's published single-frame checks on HFlow episodes.
 
-The example uses HFlow's fixed hosted checks by default, without an API key.
-Set ``BUILD_AI_EXECUTION=openai-compatible`` to use a local or third-party
-OpenAI-compatible vision endpoint instead.
+The example sends each frame to an OpenAI-compatible vision endpoint, local or
+third-party. Set ``BUILD_AI_EXECUTION=hflow-hosted`` and
+``BUILD_AI_HOSTED_BASE_URL`` to use HFlow's hosted checks instead; contact us to
+get access to the hosted API.
 """
 
 from __future__ import annotations
@@ -18,8 +19,9 @@
 DEFAULT_HFLOW_DATA_ROOT = Path("data/build-ai-evaluation/hflow")
 DEFAULT_OPENAI_COMPATIBLE_BASE_URL = "http://localhost:8000/v1"
 DEFAULT_MODEL_NAME = "model-not-configured"
-DEFAULT_EXECUTION_NAME = "hflow-hosted"
+HFLOW_HOSTED_EXECUTION_NAME = "hflow-hosted"
 OPENAI_COMPATIBLE_EXECUTION_NAME = "openai-compatible"
+DEFAULT_EXECUTION_NAME = OPENAI_COMPATIBLE_EXECUTION_NAME
 
 
 def _optional_float_environment_variable(name: str, environment: Mapping[str, str]) -> float | None:
@@ -41,8 +43,10 @@ def _execution_from_environment(
         check_execution_environment_variable,
         environment.get("BUILD_AI_EXECUTION", DEFAULT_EXECUTION_NAME),
     )
-    if execution_name == DEFAULT_EXECUTION_NAME:
-        return hflow.build_ai_vlm_checks.HFlowHostedExecution()
+    if execution_name == HFLOW_HOSTED_EXECUTION_NAME:
+        return hflow.build_ai_vlm_checks.HFlowHostedExecution(
+            base_url=environment.get("BUILD_AI_HOSTED_BASE_URL")
+        )
     if execution_name == OPENAI_COMPATIBLE_EXECUTION_NAME:
         return hflow.build_ai_vlm_checks.OpenAICompatibleExecution(
             endpoint=environment.get(
@@ -69,7 +73,7 @@ def _execution_from_environment(
         )
     raise ValueError(
         f"{check_execution_environment_variable} (or BUILD_AI_EXECUTION) must be "
-        f"{DEFAULT_EXECUTION_NAME!r} or {OPENAI_COMPATIBLE_EXECUTION_NAME!r}, "
+        f"{HFLOW_HOSTED_EXECUTION_NAME!r} or {OPENAI_COMPATIBLE_EXECUTION_NAME!r}, "
         f"got {execution_name!r}"
     )
 
diff --git a/examples/build_ai_evaluation/tests/test_evaluation.py b/examples/build_ai_evaluation/tests/test_evaluation.py
index 69797700..04fddcf4 100644
--- a/examples/build_ai_evaluation/tests/test_evaluation.py
+++ b/examples/build_ai_evaluation/tests/test_evaluation.py
@@ -267,23 +267,36 @@ def test_build_ai_pipeline_registers_both_judgments_as_hflow_checks() -> None:
     assert all(check.requires == frozenset({"vision-model"}) for check in checks_by_name.values())
 
 
-def test_build_ai_pipeline_defaults_to_hosted_and_can_select_openai_compatible_execution() -> None:
-    hosted_execution = _execution_from_environment("BUILD_AI_HAND_VISIBILITY", {})
+def test_build_ai_pipeline_defaults_to_openai_compatible_and_can_select_hosted_execution() -> None:
     openai_compatible_execution = _execution_from_environment(
         "BUILD_AI_HAND_VISIBILITY",
         {
-            "BUILD_AI_EXECUTION": "hflow-hosted",
-            "BUILD_AI_HAND_VISIBILITY_EXECUTION": "openai-compatible",
             "BUILD_AI_HAND_VISIBILITY_BASE_URL": "http://localhost:8000/v1",
             "BUILD_AI_HAND_VISIBILITY_MODEL": "local-vision-model",
         },
     )
+    hosted_execution = _execution_from_environment(
+        "BUILD_AI_HAND_VISIBILITY",
+        {
+            "BUILD_AI_HAND_VISIBILITY_EXECUTION": "hflow-hosted",
+            "BUILD_AI_HOSTED_BASE_URL": "https://hosted.example",
+        },
+    )
 
-    assert hosted_execution == hflow.build_ai_vlm_checks.HFlowHostedExecution()
     assert openai_compatible_execution == hflow.build_ai_vlm_checks.OpenAICompatibleExecution(
         endpoint="http://localhost:8000/v1",
         model="local-vision-model",
     )
+    assert hosted_execution == hflow.build_ai_vlm_checks.HFlowHostedExecution(
+        base_url="https://hosted.example"
+    )
+
+
+def test_build_ai_pipeline_hosted_execution_without_a_url_asks_the_user_to_contact_us() -> None:
+    with pytest.raises(ValueError, match="contact us"):
+        _execution_from_environment(
+            "BUILD_AI_HAND_VISIBILITY", {"BUILD_AI_EXECUTION": "hflow-hosted"}
+        )
 
 
 def test_build_ai_pipeline_requires_an_episode_with_meaningful_footage() -> None:
diff --git a/examples/evaluate_episode.py b/examples/evaluate_episode.py
index 8174246b..49d75398 100644
--- a/examples/evaluate_episode.py
+++ b/examples/evaluate_episode.py
@@ -2,10 +2,12 @@
 
 The normal ``hflow.App`` baseline stays enabled. Two explicitly registered
 hosted checks add Build AI's hand-visibility and active-manipulation judgments.
+Contact us to get access to the hosted API.
 
 Run from the repository root::
 
-    uv run python examples/evaluate_episode.py episode.mcap [--camera TOPIC]
+    uv run python examples/evaluate_episode.py episode.mcap \\
+        --hosted-base-url URL [--camera TOPIC]
 """
 
 from __future__ import annotations
@@ -22,11 +24,12 @@
 def build_application(
     *,
     data_root: Path,
+    hosted_base_url: str,
     camera: str | None,
     frame_time_seconds: float,
 ) -> hflow.App:
     application = hflow.App("episode-evaluation", data_root=data_root)
-    hosted_execution = hflow.build_ai_vlm_checks.HFlowHostedExecution()
+    hosted_execution = hflow.build_ai_vlm_checks.HFlowHostedExecution(base_url=hosted_base_url)
     hflow.build_ai_vlm_checks.register_hand_visibility(
         application,
         execution=hosted_execution,
@@ -45,6 +48,11 @@ def build_application(
 def argument_parser() -> argparse.ArgumentParser:
     parser = argparse.ArgumentParser(description=__doc__)
     parser.add_argument("episode", type=Path, help="MCAP episode with egocentric video")
+    parser.add_argument(
+        "--hosted-base-url",
+        required=True,
+        help="HFlow hosted API URL; contact us to get access",
+    )
     parser.add_argument(
         "--camera",
         help="camera topic to evaluate; required when the episode has multiple cameras",
@@ -68,6 +76,7 @@ def main() -> None:
     arguments = argument_parser().parse_args()
     application = build_application(
         data_root=arguments.data_root,
+        hosted_base_url=arguments.hosted_base_url,
         camera=arguments.camera,
         frame_time_seconds=arguments.frame_time_seconds,
     )
diff --git a/src/hflow/build_ai_vlm_checks.py b/src/hflow/build_ai_vlm_checks.py
index 6ab575cc..292da780 100644
--- a/src/hflow/build_ai_vlm_checks.py
+++ b/src/hflow/build_ai_vlm_checks.py
@@ -125,7 +125,6 @@
 
 BUILD_AI_HAND_VISIBILITY_CHECK_NAME = "build_ai_hand_visibility"
 BUILD_AI_ACTIVE_MANIPULATION_CHECK_NAME = "build_ai_active_manipulation"
-DEFAULT_HFLOW_HOSTED_BASE_URL = "https://api.hflow.dev"
 
 _HFLOW_HOSTED_TRANSPORT_VERSION = 1
 _DEFAULT_HFLOW_HOSTED_CHECK_VERSION = 1
@@ -301,7 +300,8 @@ class HFlowHostedExecution:
     Build AI's prompts or results.
     """
 
-    base_url: str = DEFAULT_HFLOW_HOSTED_BASE_URL
+    # No default: access to the hosted service is granted on request.
+    base_url: str | None = None
     check_version: int = _DEFAULT_HFLOW_HOSTED_CHECK_VERSION
     request_timeout_seconds: float = 60.0
     total_timeout_seconds: float = 360.0
@@ -312,6 +312,10 @@ class HFlowHostedExecution:
     max_retries: int = 5
 
     def __post_init__(self) -> None:
+        if self.base_url is None:
+            raise ValueError(
+                "HFlowHostedExecution needs base_url: contact us to get access to the hosted API"
+            )
         _require_absolute_http_url(self.base_url, name="base_url")
         require_non_negative_int(self.max_retries, "max_retries")
         parsed_base_url = urlsplit(self.base_url)
@@ -806,6 +810,8 @@ def _check_name_for_task(task: EvaluationTask) -> str:
 
 def _hosted_check_endpoint(execution: HFlowHostedExecution, task: EvaluationTask) -> str:
     check_name = _check_name_for_task(task)
+    # __post_init__ refuses a missing base_url.
+    assert execution.base_url is not None
     return (
         f"{execution.base_url.rstrip('/')}/v{_HFLOW_HOSTED_TRANSPORT_VERSION}/checks/"
         f"{check_name}/versions/{execution.check_version}/evaluate"
diff --git a/tests/test_build_ai_sampled_checks.py b/tests/test_build_ai_sampled_checks.py
index 49d074f5..eadd13f0 100644
--- a/tests/test_build_ai_sampled_checks.py
+++ b/tests/test_build_ai_sampled_checks.py
@@ -23,6 +23,7 @@
 
 NANOSECONDS_PER_SECOND = 1_000_000_000
 CAMERA_TOPIC = "/head_camera/compressed"
+HOSTED_BASE_URL = "https://api.hflow.dev"
 
 
 def _scripted_hosted_answers(
@@ -67,7 +68,9 @@ def test_sampled_hand_visibility_folds_no_hand_frames_into_intervals(
     served = _scripted_hosted_answers(monkeypatch, [2, 0, 0, 1])
     application = hflow.App("sampled", data_root=tmp_path / "data", default_checks=())
     register_hand_visibility(
-        application, execution=HFlowHostedExecution(), sampling=FrameSampling(fps=1.0)
+        application,
+        execution=HFlowHostedExecution(base_url=HOSTED_BASE_URL),
+        sampling=FrameSampling(fps=1.0),
     )
 
     report = asyncio.run(application.test(_episode(tmp_path, duration_s=4.0), verbose=False))
@@ -106,7 +109,9 @@ def test_sampled_run_reaching_the_end_closes_one_period_after_the_last_frame(
     _scripted_hosted_answers(monkeypatch, ["yes", "no", "no"])
     application = hflow.App("sampled-end", data_root=tmp_path / "data", default_checks=())
     register_active_manipulation(
-        application, execution=HFlowHostedExecution(), sampling=FrameSampling(fps=1.0)
+        application,
+        execution=HFlowHostedExecution(base_url=HOSTED_BASE_URL),
+        sampling=FrameSampling(fps=1.0),
     )
 
     report = asyncio.run(application.test(_episode(tmp_path, duration_s=3.0), verbose=False))
@@ -129,7 +134,9 @@ def test_an_unparsed_answer_ends_a_run_without_counting_as_absence(
     _scripted_hosted_answers(monkeypatch, [0, "unparsed: three", 0, 2])
     application = hflow.App("sampled-unparsed", data_root=tmp_path / "data", default_checks=())
     register_hand_visibility(
-        application, execution=HFlowHostedExecution(), sampling=FrameSampling(fps=1.0)
+        application,
+        execution=HFlowHostedExecution(base_url=HOSTED_BASE_URL),
+        sampling=FrameSampling(fps=1.0),
     )
 
     report = asyncio.run(application.test(_episode(tmp_path, duration_s=4.0), verbose=False))
@@ -177,7 +184,9 @@ def hosted_response(method: str, url: str, **_request: object) -> StubHostedResp
     monkeypatch.setattr(httpx2.AsyncClient, "stream", staticmethod(hosted_response))
     application = hflow.App("sampled-retry", data_root=tmp_path / "data", default_checks=())
     register_hand_visibility(
-        application, execution=HFlowHostedExecution(), sampling=FrameSampling(fps=1.0)
+        application,
+        execution=HFlowHostedExecution(base_url=HOSTED_BASE_URL),
+        sampling=FrameSampling(fps=1.0),
     )
 
     report = asyncio.run(application.test(_episode(tmp_path, duration_s=3.0), verbose=False))
@@ -218,7 +227,7 @@ def hosted_response(method: str, url: str, **_request: object) -> StubHostedResp
     application = hflow.App("sampled-busy", data_root=tmp_path / "data", default_checks=())
     register_hand_visibility(
         application,
-        execution=HFlowHostedExecution(max_retries=2),
+        execution=HFlowHostedExecution(base_url=HOSTED_BASE_URL, max_retries=2),
         sampling=FrameSampling(fps=1.0),
     )
 
@@ -241,7 +250,9 @@ def test_black_frames_are_skipped_and_never_read_as_absence(
     served = _scripted_hosted_answers(monkeypatch, [0, 0, 2])
     application = hflow.App("sampled-black", data_root=tmp_path / "data", default_checks=())
     register_hand_visibility(
-        application, execution=HFlowHostedExecution(), sampling=FrameSampling(fps=1.0)
+        application,
+        execution=HFlowHostedExecution(base_url=HOSTED_BASE_URL),
+        sampling=FrameSampling(fps=1.0),
     )
     source = synthesize_episode(
         tmp_path / "episode.mcap",
@@ -287,6 +298,8 @@ def test_sampling_is_part_of_the_check_version(tmp_path: Path) -> None:
     versions: list[str] = []
     for sampling in (None, FrameSampling(fps=1.0), FrameSampling(fps=2.0)):
         application = hflow.App("versions", data_root=tmp_path / "data", default_checks=())
-        register_hand_visibility(application, execution=HFlowHostedExecution(), sampling=sampling)
+        register_hand_visibility(
+            application, execution=HFlowHostedExecution(base_url=HOSTED_BASE_URL), sampling=sampling
+        )
         versions.append(application.checks[0].version)
     assert len(set(versions)) == 3
diff --git a/tests/test_build_ai_vlm_checks.py b/tests/test_build_ai_vlm_checks.py
index efdfa2d6..66fe8edb 100644
--- a/tests/test_build_ai_vlm_checks.py
+++ b/tests/test_build_ai_vlm_checks.py
@@ -21,6 +21,8 @@
 import hflow
 from hflow.testing import SyntheticEpisodeSpec, synthesize_episode
 
+HOSTED_BASE_URL = "https://api.hflow.dev"
+
 
 def test_build_ai_vlm_checks_register_independent_execution_contracts(tmp_path: Path) -> None:
     application = hflow.App("model-checks", data_root=tmp_path, default_checks=())
@@ -260,11 +262,16 @@ def test_hosted_execution_refuses_custom_prompt(tmp_path: Path) -> None:
     with pytest.raises(ValueError, match="does not support prompt overrides"):
         hflow.build_ai_vlm_checks.register_hand_visibility(
             application,
-            execution=hflow.build_ai_vlm_checks.HFlowHostedExecution(),
+            execution=hflow.build_ai_vlm_checks.HFlowHostedExecution(base_url=HOSTED_BASE_URL),
             prompt="Use a different definition of visibility.",
         )
 
 
+def test_hosted_execution_requires_a_base_url() -> None:
+    with pytest.raises(ValueError, match="contact us to get access to the hosted API"):
+        hflow.build_ai_vlm_checks.HFlowHostedExecution()
+
+
 def test_hosted_execution_refuses_a_base_url_that_cannot_accept_check_paths() -> None:
     with pytest.raises(ValueError, match="query string or fragment"):
         hflow.build_ai_vlm_checks.HFlowHostedExecution(
@@ -410,10 +417,30 @@ def test_hosted_response_refuses_a_prediction_outside_the_check_contract(
             -1,
             0,
         ),
-        (hflow.build_ai_vlm_checks.HFlowHostedExecution, "max_retries", -1, 0),
-        (hflow.build_ai_vlm_checks.HFlowHostedExecution, "check_version", 0, 1),
-        (hflow.build_ai_vlm_checks.HFlowHostedExecution, "request_timeout_seconds", 0, 0.5),
-        (hflow.build_ai_vlm_checks.HFlowHostedExecution, "total_timeout_seconds", 0, 0.5),
+        (
+            partial(hflow.build_ai_vlm_checks.HFlowHostedExecution, base_url=HOSTED_BASE_URL),
+            "max_retries",
+            -1,
+            0,
+        ),
+        (
+            partial(hflow.build_ai_vlm_checks.HFlowHostedExecution, base_url=HOSTED_BASE_URL),
+            "check_version",
+            0,
+            1,
+        ),
+        (
+            partial(hflow.build_ai_vlm_checks.HFlowHostedExecution, base_url=HOSTED_BASE_URL),
+            "request_timeout_seconds",
+            0,
+            0.5,
+        ),
+        (
+            partial(hflow.build_ai_vlm_checks.HFlowHostedExecution, base_url=HOSTED_BASE_URL),
+            "total_timeout_seconds",
+            0,
+            0.5,
+        ),
         (hflow.build_ai_vlm_checks.FrameSampling, "fps", 0, 0.5),
         (hflow.build_ai_vlm_checks.FrameSampling, "start_s", -1, 0),
         (partial(hflow.build_ai_vlm_checks.FrameSampling, start_s=2), "end_s", 2, 3),
@@ -477,7 +504,7 @@ def test_registration_refuses_invalid_frame_times(tmp_path: Path, value: Any) ->
     with pytest.raises(ValueError, match="frame_time_seconds"):
         hflow.build_ai_vlm_checks.register_hand_visibility(
             application,
-            execution=hflow.build_ai_vlm_checks.HFlowHostedExecution(),
+            execution=hflow.build_ai_vlm_checks.HFlowHostedExecution(base_url=HOSTED_BASE_URL),
             frame_time_seconds=value,
         )
 
@@ -568,6 +595,7 @@ def test_check_version_is_pinned_for_a_fixed_hosted_configuration(tmp_path: Path
     hflow.build_ai_vlm_checks.register_hand_visibility(
         application,
         execution=hflow.build_ai_vlm_checks.HFlowHostedExecution(
+            base_url=HOSTED_BASE_URL,
             check_version=1,
             request_timeout_seconds=30.0,
         ),
@@ -598,7 +626,10 @@ def _openai_execution(**overrides: Any) -> hflow.build_ai_vlm_checks.OpenAICompa
 
 
 def _hosted_execution(**overrides: Any) -> hflow.build_ai_vlm_checks.HFlowHostedExecution:
-    return replace(hflow.build_ai_vlm_checks.HFlowHostedExecution(check_version=1), **overrides)
+    return replace(
+        hflow.build_ai_vlm_checks.HFlowHostedExecution(base_url=HOSTED_BASE_URL, check_version=1),
+        **overrides,
+    )
 
 
 @pytest.mark.parametrize(
@@ -770,6 +801,7 @@ def _evaluate_hosted_hand_count(
     **configuration: Any,
 ) -> hflow.build_ai_vlm_checks.VisionModelOutcome:
     checks = hflow.build_ai_vlm_checks
+    configuration.setdefault("base_url", HOSTED_BASE_URL)
     return asyncio.run(
         checks._evaluate_image_with_hflow_hosted_service(
             execution=checks.HFlowHostedExecution(**configuration),
diff --git a/tests/test_evaluate_episode_example.py b/tests/test_evaluate_episode_example.py
index af02dc1f..014c4110 100644
--- a/tests/test_evaluate_episode_example.py
+++ b/tests/test_evaluate_episode_example.py
@@ -11,6 +11,7 @@ def test_recommended_episode_evaluation_combines_default_and_hosted_checks(
 ) -> None:
     application = build_application(
         data_root=tmp_path,
+        hosted_base_url="https://hosted.example",
         camera="/head_camera",
         frame_time_seconds=0.0,
     )