diff --git a/apps/cloud-api/tests/test_cloud_planner_config.py b/apps/cloud-api/tests/test_cloud_planner_config.py
index 0ddc1ac..d71c13a 100644
--- a/apps/cloud-api/tests/test_cloud_planner_config.py
+++ b/apps/cloud-api/tests/test_cloud_planner_config.py
@@ -40,6 +40,15 @@ def test_build_cloud_planner_client_uses_managed_anthropic_key() -> None:
     assert client._api_key == "managed-api-key"
 
 
+def test_build_cloud_planner_client_uses_anthropic_base_url() -> None:
+    client = build_cloud_planner_client(
+        _resolved_profile("anthropic", base_url="https://anthropic-proxy.example")
+    )
+
+    assert isinstance(client, AnthropicToolCallingClient)
+    assert client._base_url == "https://anthropic-proxy.example"
+
+
 def test_build_cloud_planner_client_uses_openai_compatible_base_url() -> None:
     client = build_cloud_planner_client(
         _resolved_profile("openai-compatible", base_url="https://compat.example/v1")
diff --git a/apps/cloud-api/tests/test_llm_provider_management.py b/apps/cloud-api/tests/test_llm_provider_management.py
index bd4d126..3054cf7 100644
--- a/apps/cloud-api/tests/test_llm_provider_management.py
+++ b/apps/cloud-api/tests/test_llm_provider_management.py
@@ -136,6 +136,29 @@ def test_provider_profile_requires_admin_scope(monkeypatch) -> None:
         )
 
 
+def test_anthropic_profile_accepts_custom_base_url(monkeypatch) -> None:
+    from cryptography.fernet import Fernet
+
+    monkeypatch.setenv(
+        "CLOUD_LLM_PROVIDER_ENCRYPTION_KEY", Fernet.generate_key().decode()
+    )
+    app = create_app(config=CloudControlConfig(database_url="sqlite:///:memory:"))
+    with TestClient(app) as client:
+        _create_admin(client)
+        response = client.post(
+            "/v1/planner/providers",
+            headers=_csrf_headers(client),
+            json=_profile_payload(
+                name="Anthropic proxy",
+                provider_type="anthropic",
+                base_url="https://anthropic-proxy.example/",
+            ),
+        )
+
+    assert response.status_code == 201, response.text
+    assert response.json()["base_url"] == "https://anthropic-proxy.example"
+
+
 def test_profile_write_requires_encryption_key(monkeypatch) -> None:
     monkeypatch.delenv("CLOUD_LLM_PROVIDER_ENCRYPTION_KEY", raising=False)
     app = create_app(config=CloudControlConfig(database_url="sqlite:///:memory:"))
diff --git a/cloud-console/src/views/LlmProvidersView.vue b/cloud-console/src/views/LlmProvidersView.vue
index 127e299..c7fd25b 100644
--- a/cloud-console/src/views/LlmProvidersView.vue
+++ b/cloud-console/src/views/LlmProvidersView.vue
@@ -98,7 +98,7 @@ async function saveProfile() {
 
   saving.value = true;
   try {
-    const baseUrl = form.provider_type === "anthropic" ? null : form.base_url.trim() || null;
+    const baseUrl = form.base_url.trim() || null;
     if (editingId.value) {
       const existing = profiles.value.find((profile) => profile.id === editingId.value);
       if (!existing) throw new Error("Provider profile no longer exists");
@@ -195,8 +195,8 @@ onMounted(refresh);
           </label>
           <label>Model <input v-model="form.model" autocomplete="off" /></label>
           <label>Timeout seconds <input v-model="form.timeout_seconds" inputmode="decimal" /></label>
-          <label v-if="form.provider_type === 'openai-compatible'" class="field-full">Base URL
-            <input v-model="form.base_url" placeholder="Official OpenAI endpoint when blank" autocomplete="url" />
+          <label class="field-full">Base URL
+            <input v-model="form.base_url" placeholder="Official provider endpoint when blank" autocomplete="url" />
           </label>
           <label class="field-full">{{ editingId ? "Rotate API key" : "API key" }}
             <input v-model="form.api_key" type="password" autocomplete="new-password" />
diff --git a/docs/CLOUD_DEPLOYMENT.md b/docs/CLOUD_DEPLOYMENT.md
index 8adaad0..02b153d 100644
--- a/docs/CLOUD_DEPLOYMENT.md
+++ b/docs/CLOUD_DEPLOYMENT.md
@@ -387,9 +387,10 @@ mode:
   `AI_PLANNER_TIMEOUT_SECONDS`, `ANTHROPIC_API_KEY`, or `OPENAI_API_KEY`.
 - **Profile types:** choose **Anthropic** for native Anthropic tool use, or
   **OpenAI-compatible** for the OpenAI Chat Completions tool-calling protocol.
-  Leave its Base URL blank for official OpenAI, or provide the compatible
-  provider's absolute HTTP(S) `/v1` endpoint. Providers requiring another
-  request schema or custom authentication are not supported by this path.
+  Both accept an optional absolute HTTP(S) Base URL; leave it blank for the
+  official provider endpoint. The configured endpoint must accept the selected
+  provider's existing request schema and authentication; custom headers or
+  incompatible parameter dialects are not supported by this path.
 - **Activation is immediate:** a newly activated enabled profile becomes the
   Provider/model for the next Cloud-proxy planner decision. A Cloud-planner
   request fails closed until one enabled profile is active; it never falls back
diff --git a/openspec/changes/database-llm-provider-management/design.md b/openspec/changes/database-llm-provider-management/design.md
index b0da9a9..63d84ce 100644
--- a/openspec/changes/database-llm-provider-management/design.md
+++ b/openspec/changes/database-llm-provider-management/design.md
@@ -10,9 +10,9 @@ administrator Console, CSRF protection, and auth audit records that this
 change can reuse.
 
 The existing runtime clients instantiate provider SDKs with no arguments and
-therefore read keys from their environment. Database-backed credentials and
-an OpenAI-compatible base URL require those clients to accept explicit values
-while preserving the unchanged direct-transport default.
+therefore read keys from their environment. Database-backed credentials and a
+custom base URL require those clients to accept explicit values while
+preserving the unchanged direct-transport default.
 
 ## Goals / Non-Goals
 
@@ -22,8 +22,8 @@ while preserving the unchanged direct-transport default.
 - Encrypt every stored Provider API key and never return or log its plaintext.
 - Switch the provider/model used by all cloud-transport Host Agents without a
   Host configuration change, Cloud API restart, or local credential.
-- Support OpenAI-compatible endpoints through a configurable base URL and
-  API key using the existing Chat Completions tool-calling implementation.
+- Support custom base URLs for Anthropic native tool use and OpenAI-compatible
+  Chat Completions tool calling without changing their respective protocols.
 - Remove Cloud API environment-based planner Provider configuration so every
   cloud-transport decision is governed by the active database profile.
 
@@ -32,8 +32,8 @@ while preserving the unchanged direct-transport default.
 - Provider usage billing, connection-test endpoints, model discovery, or
   support for protocols other than Anthropic native tool use and OpenAI Chat
   Completions tool calling.
-- Arbitrary Anthropic-compatible endpoints, custom request headers, or
-  different OpenAI-compatible parameter dialects.
+- Custom request headers or different Anthropic/OpenAI-compatible parameter
+  dialects.
 - Automatic encryption-master-key rotation. Provider API key rotation is
   supported by updating a profile; master-key rotation remains an operational
   migration until a key-ring design is separately proposed.
@@ -103,16 +103,16 @@ backup or read access would expose external-provider credentials. Alternative
 considered: a database-held master key. Rejected because it does not create a
 separate protection boundary.
 
-### D4: Treat OpenAI-compatible as a concrete wire-protocol contract
+### D4: Treat each provider wire protocol as a concrete contract
 
-Profiles have `provider_type` of `anthropic` or `openai-compatible`. An
-`openai-compatible` profile may omit `base_url` to use the official OpenAI
-endpoint, or supply an absolute HTTP(S) base URL for a compatible service.
+Profiles have `provider_type` of `anthropic` or `openai-compatible`. Either
+profile may omit `base_url` to use its official provider endpoint, or supply
+an absolute HTTP(S) base URL for a compatible proxy or provider service.
 The runtime `OpenAIToolCallingClient` gains optional `api_key` and `base_url`
 constructor arguments and constructs `OpenAI` explicitly when supplied.
-`AnthropicToolCallingClient` gains an optional explicit API key for cloud-held
-credentials; absent optional arguments retain current SDK environment
-behavior for direct transport.
+`AnthropicToolCallingClient` gains optional explicit API key and `base_url`
+arguments and constructs `Anthropic` explicitly when supplied. Absent optional
+arguments retain current SDK environment behavior for direct transport.
 
 Compatibility means the endpoint accepts OpenAI Chat Completions requests
 with the tool/function-calling fields emitted by the existing client and
diff --git a/openspec/changes/database-llm-provider-management/proposal.md b/openspec/changes/database-llm-provider-management/proposal.md
index 730a912..ca02a1d 100644
--- a/openspec/changes/database-llm-provider-management/proposal.md
+++ b/openspec/changes/database-llm-provider-management/proposal.md
@@ -10,7 +10,7 @@ control plane for its planner decisions.
 
 - Add a durable, Cloud-wide catalog of planner Provider profiles. Each profile
   records its supported provider kind (`anthropic` or `openai-compatible`),
-  model, timeout, optional OpenAI-compatible base URL, enabled state, and an
+  model, timeout, optional base URL, enabled state, and an
   encrypted API key.
 - Add an administrator-only Cloud API and Cloud Console view to create, list,
   update, activate, disable, and retire Provider profiles. Read responses
@@ -25,10 +25,10 @@ control plane for its planner decisions.
   credential.
 - Add an encryption-key configuration for protecting Provider API keys at rest
   and document deployment, rotation, and migration behavior.
-- Extend the existing provider client construction so cloud-managed
-  OpenAI-compatible profiles pass their encrypted API key and configured base
-  URL explicitly to the OpenAI SDK, while Host Agent direct transport continues
-  to use its existing environment-based credentials.
+- Extend the existing provider client construction so cloud-managed profiles
+  pass their encrypted API key and configured base URL explicitly to the
+  Anthropic or OpenAI SDK, while Host Agent direct transport continues to use
+  its existing environment-based credentials.
 
 ## Capabilities
 
diff --git a/openspec/changes/database-llm-provider-management/specs/cloud-planner-proxy/spec.md b/openspec/changes/database-llm-provider-management/specs/cloud-planner-proxy/spec.md
index 70ea6af..859dbf0 100644
--- a/openspec/changes/database-llm-provider-management/specs/cloud-planner-proxy/spec.md
+++ b/openspec/changes/database-llm-provider-management/specs/cloud-planner-proxy/spec.md
@@ -6,7 +6,7 @@ credentials -- not any value supplied by the requesting Host Agent -- to
 resolve a planner-decision request to exactly one tool name and one arguments
 object, within the request's timeout. The endpoint SHALL resolve the active
 database-managed Provider profile for every request and use its provider,
-model, timeout, OpenAI-compatible base URL when applicable, and encrypted
+model, timeout, configured base URL, and encrypted
 cloud-held credential. It SHALL NOT read Cloud API planner Provider/model/
 timeout/API-key environment variables.
 
diff --git a/openspec/changes/database-llm-provider-management/specs/llm-provider-management/spec.md b/openspec/changes/database-llm-provider-management/specs/llm-provider-management/spec.md
index 31f8a79..e45343b 100644
--- a/openspec/changes/database-llm-provider-management/specs/llm-provider-management/spec.md
+++ b/openspec/changes/database-llm-provider-management/specs/llm-provider-management/spec.md
@@ -4,9 +4,8 @@
 The Cloud Control Plane SHALL persist administrator-managed LLM Provider
 profiles with a unique name, provider type, model, timeout, enabled state,
 revision, and timestamps. A profile's provider type SHALL be either
-`anthropic` or `openai-compatible`; an OpenAI-compatible profile MAY specify
-an absolute HTTP(S) base URL and SHALL use the official OpenAI endpoint when
-it does not.
+`anthropic` or `openai-compatible`; either profile MAY specify an absolute
+HTTP(S) base URL and SHALL use its official provider endpoint when it does not.
 
 #### Scenario: Administrator creates an OpenAI-compatible profile
 - **WHEN** an authorized administrator submits a unique profile name,
@@ -15,6 +14,13 @@ it does not.
 - **THEN** the Cloud Control Plane persists an enabled profile with a new
   revision and returns its non-secret metadata
 
+#### Scenario: Administrator creates an Anthropic profile with a custom base URL
+- **WHEN** an authorized administrator submits a unique profile name,
+  `anthropic` provider type, model, valid timeout, API key, and a valid
+  Anthropic-compatible base URL
+- **THEN** the Cloud Control Plane persists the normalized URL with the profile
+  and returns its non-secret metadata
+
 #### Scenario: Invalid profile configuration is rejected
 - **WHEN** an administrator submits an unsupported provider type, blank model,
   non-positive timeout, duplicate name, or invalid base URL
@@ -81,6 +87,12 @@ reconfiguration.
   tool-calling request to that base URL using the profile's decrypted API key
   and returns the resulting single tool-call decision
 
+#### Scenario: Active Anthropic profile is used with a custom base URL
+- **WHEN** the active profile is Anthropic and includes a base URL
+- **THEN** the Cloud Control Plane makes the existing Anthropic native
+  tool-calling request to that base URL using the profile's decrypted API key
+  and returns the resulting single tool-call decision
+
 ### Requirement: Cloud planner Provider configuration is database-only
 The Cloud Control Plane SHALL resolve Cloud planner Provider, model, timeout,
 base URL, and API key from the active database profile and SHALL NOT read
diff --git a/openspec/changes/database-llm-provider-management/tasks.md b/openspec/changes/database-llm-provider-management/tasks.md
index 899409b..b02c592 100644
--- a/openspec/changes/database-llm-provider-management/tasks.md
+++ b/openspec/changes/database-llm-provider-management/tasks.md
@@ -26,3 +26,9 @@
 
 - [x] 5.1 Document encryption-key provisioning, required active-profile cutover, OpenAI-compatible configuration, removed planner environment variables, and rollback in Cloud deployment documentation.
 - [x] 5.2 Run relevant backend tests, Console tests/build, format/lint, compile checks, and strict OpenSpec validation; resolve failures.
+
+## 6. Anthropic custom base URL
+
+- [x] 6.1 Allow Anthropic Provider profiles to validate and persist an optional custom base URL, and pass it to the Cloud planner client.
+- [x] 6.2 Extend `AnthropicToolCallingClient` to construct the Anthropic SDK with an explicit base URL while preserving direct-transport defaults.
+- [x] 6.3 Expose the Base URL field for Anthropic in the Cloud Console; add backend/runtime tests and update deployment/specification documentation.
diff --git a/packages/cloud-platform/cloud/llm_providers.py b/packages/cloud-platform/cloud/llm_providers.py
index bf321c0..53944d1 100644
--- a/packages/cloud-platform/cloud/llm_providers.py
+++ b/packages/cloud-platform/cloud/llm_providers.py
@@ -96,10 +96,6 @@ def validate_profile_input(
             "Timeout must be greater than zero and at most 120"
         )
     normalized_base_url = _normalize_base_url(base_url)
-    if provider_type == "anthropic" and normalized_base_url is not None:
-        raise LlmProviderValidationError(
-            "Anthropic profiles do not support a custom base URL"
-        )
     return LlmProviderProfileInput(
         name=display_name,
         name_normalized=normalized_name,
diff --git a/packages/cloud-platform/cloud/planner_config.py b/packages/cloud-platform/cloud/planner_config.py
index a5740b0..9cf7b51 100644
--- a/packages/cloud-platform/cloud/planner_config.py
+++ b/packages/cloud-platform/cloud/planner_config.py
@@ -21,4 +21,8 @@ def build_cloud_planner_client(
             api_key=resolved.api_key,
             base_url=profile.base_url,
         )
-    return AnthropicToolCallingClient(model=profile.model, api_key=resolved.api_key)
+    return AnthropicToolCallingClient(
+        model=profile.model,
+        api_key=resolved.api_key,
+        base_url=profile.base_url,
+    )
diff --git a/runtime/tool_calling_client.py b/runtime/tool_calling_client.py
index 2c45f99..931e5e6 100644
--- a/runtime/tool_calling_client.py
+++ b/runtime/tool_calling_client.py
@@ -47,11 +47,13 @@ class AnthropicToolCallingClient:
         transport: Any | None = None,
         max_tokens: int = 1024,
         api_key: str | None = None,
+        base_url: str | None = None,
     ) -> None:
         self.model = model
         self._transport = transport
         self.max_tokens = max_tokens
         self._api_key = api_key
+        self._base_url = base_url
 
     def decide(
         self,
@@ -120,11 +122,12 @@ class AnthropicToolCallingClient:
         except Exception as exc:
             raise ToolCallUnavailable("anthropic SDK is unavailable") from exc
 
-        self._transport = (
-            anthropic.Anthropic(api_key=self._api_key)
-            if self._api_key is not None
-            else anthropic.Anthropic()
-        )
+        client_kwargs: dict[str, str] = {}
+        if self._api_key is not None:
+            client_kwargs["api_key"] = self._api_key
+        if self._base_url is not None:
+            client_kwargs["base_url"] = self._base_url
+        self._transport = anthropic.Anthropic(**client_kwargs)
         return self._transport
 
 
diff --git a/tests/test_tool_calling_client.py b/tests/test_tool_calling_client.py
index 122701e..6d8816d 100644
--- a/tests/test_tool_calling_client.py
+++ b/tests/test_tool_calling_client.py
@@ -1,7 +1,9 @@
 from __future__ import annotations
 
 import base64
+import sys
 from typing import Any
+from types import SimpleNamespace
 
 import pytest
 
@@ -124,6 +126,35 @@ def test_anthropic_tool_calling_client_includes_image_block_when_screenshot_pres
     assert content[1] == {"type": "text", "text": "user"}
 
 
+def test_anthropic_tool_calling_client_passes_custom_base_url_to_sdk(
+    monkeypatch,
+) -> None:
+    constructed: list[dict[str, Any]] = []
+
+    class RecordingAnthropic:
+        def __init__(self, **kwargs: str) -> None:
+            constructed.append(kwargs)
+
+    monkeypatch.setitem(
+        sys.modules,
+        "anthropic",
+        SimpleNamespace(Anthropic=RecordingAnthropic),
+    )
+    client = AnthropicToolCallingClient(
+        model="test-model",
+        api_key="managed-api-key",
+        base_url="https://anthropic-proxy.example",
+    )
+
+    assert isinstance(client._client(), RecordingAnthropic)
+    assert constructed == [
+        {
+            "api_key": "managed-api-key",
+            "base_url": "https://anthropic-proxy.example",
+        }
+    ]
+
+
 def test_anthropic_tool_calling_client_wraps_transport_errors() -> None:
     messages = FakeMessages(error=TimeoutError("timed out"))
     client = AnthropicToolCallingClient(model="test-model", transport=FakeTransport(messages))