diff --git a/src/plyngent/config/models.py b/src/plyngent/config/models.py
index 1703d22..2f4fb1a 100644
--- a/src/plyngent/config/models.py
+++ b/src/plyngent/config/models.py
@@ -6,7 +6,8 @@ from msgspec import Struct, field
 # per-model ``ModelConfig.convention`` override).
 # - "" (default) / "openai" → OpenAI-compatible chat completions
 # - "responses"           → OpenAI Responses API (``POST /responses``)
-# - "anthropic"           → legacy value, ignored (still chat completions)
+# - "anthropic"           → Anthropic Messages API (``POST /messages`` on
+#                           ``https://api.deepseek.com/anthropic``)
 type DeepSeekConvention = Literal["", "openai", "anthropic", "responses"]
 
 # Built-in persona when ``[agent].system_prompt`` is omitted.
@@ -255,10 +256,11 @@ def _default_deepseek_models() -> dict[str, ModelConfig]:
 class DeepseekProvider(ProviderConfig, tag="deepseek"):
     """DeepSeek API provider.
 
-    ``convention`` selects the API surface on ``https://api.deepseek.com``:
+    ``convention`` selects the API surface on DeepSeek's endpoints:
     - ``""`` / ``"openai"`` → OpenAI-compatible chat completions (default)
     - ``"responses"`` → OpenAI Responses API (``POST /responses``)
-    - ``"anthropic"`` → legacy value, ignored (still chat completions)
+    - ``"anthropic"`` → Anthropic Messages API (``POST /messages`` on
+      ``https://api.deepseek.com/anthropic``)
 
     ``extras`` keeps arbitrary provider keys; the legacy ``extras.convention``
     key is parsed but ignored (prefer the typed ``convention`` field).
diff --git a/src/plyngent/config/routing.py b/src/plyngent/config/routing.py
index 46a9144..d7f7878 100644
--- a/src/plyngent/config/routing.py
+++ b/src/plyngent/config/routing.py
@@ -19,6 +19,9 @@ if TYPE_CHECKING:
 
 type ProviderPreset = Literal["openai", "openai-compatible", "anthropic", "deepseek"]
 
+DEFAULT_DEEPSEEK_BASE_URL = "https://api.deepseek.com"
+DEFAULT_DEEPSEEK_ANTHROPIC_BASE_URL = "https://api.deepseek.com/anthropic"
+
 
 @dataclass(frozen=True, slots=True)
 class EffectiveProvider:
@@ -54,11 +57,22 @@ def default_url_for_preset(preset: ProviderPreset) -> str:
     if preset == "anthropic":
         return "https://api.anthropic.com/v1"
     if preset == "deepseek":
-        return "https://api.deepseek.com"
+        return DEFAULT_DEEPSEEK_BASE_URL
     # Generic OpenAI-compatible providers usually require a host-specific URL.
     return ""
 
 
+def _default_url_for_deepseek_convention(convention: str) -> str:
+    """Default DeepSeek base URL for an API convention.
+
+    The Anthropic-convention endpoint lives under ``/anthropic``; chat and
+    Responses share the plain ``https://api.deepseek.com`` base.
+    """
+    if convention == "anthropic":
+        return DEFAULT_DEEPSEEK_ANTHROPIC_BASE_URL
+    return DEFAULT_DEEPSEEK_BASE_URL
+
+
 def validate_model_preset(preset: str) -> ProviderPreset:
     if preset in {"openai", "openai-compatible", "anthropic", "deepseek"}:
         return cast("ProviderPreset", preset)
@@ -77,9 +91,9 @@ def resolve_effective_provider(provider: Provider, *, model: str | None = None)
 
     ``preset`` always decides API conventions: ``openai`` means Responses,
     ``openai-compatible`` means Chat Completions, ``anthropic`` means Messages.
-    Exception: a ``deepseek`` preset may pick the Responses surface via the
-    ``convention`` field (``"responses"``); model-level ``convention`` wins
-    over the provider-level one.
+    Exception: a ``deepseek`` preset may pick the Responses or Anthropic
+    surface via the ``convention`` field (``"responses"`` / ``"anthropic"``);
+    model-level ``convention`` wins over the provider-level one.
     """
     parent_preset = provider_preset(provider)
     model_cfg = model_config_for(provider, model)
@@ -87,13 +101,6 @@ def resolve_effective_provider(provider: Provider, *, model: str | None = None)
         preset = validate_model_preset(model_cfg.preset.strip())
     else:
         preset = parent_preset
-    url = model_cfg.url.strip() if model_cfg is not None and model_cfg.url.strip() else provider.url.strip()
-    if not url:
-        url = default_url_for_preset(preset)
-
-    provider_tools: list[dict[str, object]] = []
-    if preset == "openai" and isinstance(provider, OpenAIProvider) and parent_preset == "openai":
-        provider_tools = [dict(item) for item in provider.provider_tools]
 
     # DeepSeek API surface: model override > provider convention > chat default.
     convention = ""
@@ -102,6 +109,17 @@ def resolve_effective_provider(provider: Provider, *, model: str | None = None)
         if model_cfg is not None and model_cfg.convention:
             convention = model_cfg.convention
 
+    url = model_cfg.url.strip() if model_cfg is not None and model_cfg.url.strip() else provider.url.strip()
+    if not url:
+        if preset == "deepseek":
+            url = _default_url_for_deepseek_convention(convention)
+        else:
+            url = default_url_for_preset(preset)
+
+    provider_tools: list[dict[str, object]] = []
+    if preset == "openai" and isinstance(provider, OpenAIProvider) and parent_preset == "openai":
+        provider_tools = [dict(item) for item in provider.provider_tools]
+
     return EffectiveProvider(
         preset=preset,
         access_key_or_token=provider.access_key_or_token,
diff --git a/tests/test_config/test_config.py b/tests/test_config/test_config.py
index b487500..942be5c 100644
--- a/tests/test_config/test_config.py
+++ b/tests/test_config/test_config.py
@@ -247,6 +247,45 @@ def test_deepseek_effective_convention_precedence() -> None:
     assert resolve_effective_provider(OpenAIProvider(access_key_or_token="sk")).convention == ""
 
 
+def test_deepseek_anthropic_convention_default_url() -> None:
+    from plyngent.config import resolve_effective_provider
+    from plyngent.config.routing import DEFAULT_DEEPSEEK_ANTHROPIC_BASE_URL, DEFAULT_DEEPSEEK_BASE_URL
+
+    provider = DeepseekProvider(access_key_or_token="sk-test", convention="anthropic")
+    effective = resolve_effective_provider(provider)
+    assert effective.convention == "anthropic"
+    assert effective.url == DEFAULT_DEEPSEEK_ANTHROPIC_BASE_URL
+
+    # Custom provider url wins over the convention default.
+    provider = DeepseekProvider(
+        access_key_or_token="sk-test",
+        url="https://gateway.example/anthropic",
+        convention="anthropic",
+    )
+    assert resolve_effective_provider(provider).url == "https://gateway.example/anthropic"
+
+    # Other conventions keep the plain deepseek base.
+    for convention in ("", "openai", "responses"):
+        provider = DeepseekProvider(access_key_or_token="sk-test", convention=convention)
+        assert resolve_effective_provider(provider).url == DEFAULT_DEEPSEEK_BASE_URL
+
+
+def test_deepseek_anthropic_model_convention_default_url() -> None:
+    from plyngent.config import ModelConfig, resolve_effective_provider
+    from plyngent.config.routing import DEFAULT_DEEPSEEK_ANTHROPIC_BASE_URL
+
+    provider = DeepseekProvider(
+        access_key_or_token="sk-test",
+        models={"claude-proxy": ModelConfig(convention="anthropic")},
+    )
+    effective = resolve_effective_provider(provider, model="claude-proxy")
+    assert effective.convention == "anthropic"
+    assert effective.url == DEFAULT_DEEPSEEK_ANTHROPIC_BASE_URL
+    # Provider default url for a model without convention stays the deepseek base.
+    other = resolve_effective_provider(provider, model=None)
+    assert other.url == "https://api.deepseek.com"
+
+
 def test_read_empty_config() -> None:
     config = plyngent.config.load(Path(__file__).parent / "plyngent-empty.toml")
     assert isinstance(config.providers, Mapping)