diff --git a/CUSTOMIZATION.md b/CUSTOMIZATION.md
index 6739a3b8..33037489 100644
--- a/CUSTOMIZATION.md
+++ b/CUSTOMIZATION.md
@@ -140,7 +140,7 @@ The model is configured in the `get_agent()` function in `agent/server.py`. By d
 
 ```bash
 # Set the model via environment variable (uses provider:model format)
-LLM_MODEL_ID="anthropic:claude-sonnet-4-6"
+LLM_MODEL_ID="anthropic:claude-sonnet-5"
 ```
 
 If `LLM_MODEL_ID` is not set, the default model (`openai:gpt-5.5`) is used.
@@ -153,7 +153,7 @@ Use the `provider:model` format:
 
 ```python
 # Anthropic
-model=make_model("anthropic:claude-sonnet-4-6", temperature=0, max_tokens=16_000)
+model=make_model("anthropic:claude-sonnet-5", temperature=0, max_tokens=16_000)
 
 # OpenAI (uses Responses API by default)
 model=make_model("openai:gpt-5.5", max_tokens=128_000, reasoning={"effort": "medium"})
@@ -167,7 +167,7 @@ The `make_model()` helper in `agent/utils/model.py` wraps `langchain.chat_models
 ```python
 from langchain_anthropic import ChatAnthropic
 
-model = ChatAnthropic(model_name="claude-sonnet-4-6", temperature=0, max_tokens=16_000)
+model = ChatAnthropic(model_name="claude-sonnet-5", temperature=0, max_tokens=16_000)
 
 return create_deep_agent(
     model=model,
@@ -185,7 +185,7 @@ async def get_agent(config: RunnableConfig) -> Pregel:
     
     if source == "slack":
         # Faster model for Slack Q&A
-        model = make_model("anthropic:claude-sonnet-4-6", temperature=0, max_tokens=16_000)
+        model = make_model("anthropic:claude-sonnet-5", temperature=0, max_tokens=16_000)
     else:
         # Full model for code changes from Linear
         model = make_model("openai:gpt-5.5", max_tokens=128_000, reasoning={"effort": "medium"})
diff --git a/agent/dashboard/options.py b/agent/dashboard/options.py
index ff7cb3e8..cc3c0048 100644
--- a/agent/dashboard/options.py
+++ b/agent/dashboard/options.py
@@ -21,6 +21,13 @@ SUPPORTED_MODELS: list[ModelOption] = [
         "default_effort": "high",
         "supports_images": True,
     },
+    {
+        "id": "anthropic:claude-sonnet-5",
+        "label": "Sonnet 5",
+        "efforts": ["low", "medium", "high", "xhigh", "max"],
+        "default_effort": "high",
+        "supports_images": True,
+    },
     {
         "id": "openai:gpt-5.5",
         "label": "GPT-5.5",
@@ -83,6 +90,16 @@ def _provider_of(model_id: str) -> str | None:
     return provider if rest else None
 
 
+def _claude_family_of(model_id: str) -> str | None:
+    provider, _, name = model_id.partition(":")
+    if provider != "anthropic" or not name.startswith("claude-"):
+        return None
+    parts = name.split("-")
+    if len(parts) < 2:
+        return None
+    return "-".join(parts[:2])
+
+
 def _fallback_effort_for(model: ModelOption, effort: object) -> str | None:
     if not isinstance(effort, str):
         return None
@@ -98,19 +115,25 @@ def _fallback_effort_for(model: ModelOption, effort: object) -> str | None:
 
 
 def provider_fallback_pair(model_id: object, effort: object = None) -> tuple[str, str] | None:
-    """Newest supported ``(model_id, effort)`` for the same provider as ``model_id``.
+    """Newest supported ``(model_id, effort)`` for the same provider/family.
 
     Keeps a stored selection on its original provider when its exact id has
-    dropped out of the supported set (e.g. an Opus minor-version bump), instead
-    of falling through to the cross-provider global default. Preserves ``effort``
-    when the fallback model supports it, otherwise uses that model's default
-    effort. Returns ``None`` when no supported model shares the provider.
+    dropped out of the supported set (e.g. an Opus minor-version bump), preferring
+    the same Claude family when available instead of falling through to the
+    cross-provider global default. Preserves ``effort`` when the fallback model
+    supports it, otherwise uses that model's default effort. Returns ``None`` when
+    no supported model shares the provider.
     """
     if not isinstance(model_id, str):
         return None
     provider = _provider_of(model_id)
     if provider is None:
         return None
+    family = _claude_family_of(model_id)
+    if family is not None:
+        for m in SUPPORTED_MODELS:
+            if _provider_of(m["id"]) == provider and _claude_family_of(m["id"]) == family:
+                return m["id"], _fallback_effort_for(m, effort) or m["default_effort"]
     for m in SUPPORTED_MODELS:
         if _provider_of(m["id"]) == provider:
             return m["id"], _fallback_effort_for(m, effort) or m["default_effort"]
diff --git a/tests/test_anthropic_model.py b/tests/test_anthropic_model.py
new file mode 100644
index 00000000..5257bdb3
--- /dev/null
+++ b/tests/test_anthropic_model.py
@@ -0,0 +1,36 @@
+import pytest
+
+from agent.dashboard.options import SUPPORTED_MODELS, provider_fallback_pair
+from agent.utils.model import provider_model_kwargs
+
+SONNET_5_ID = "anthropic:claude-sonnet-5"
+
+
+def test_sonnet_5_is_supported_with_documented_efforts() -> None:
+    sonnet = next(m for m in SUPPORTED_MODELS if m["id"] == SONNET_5_ID)
+    assert sonnet["label"] == "Sonnet 5"
+    assert sonnet["efforts"] == ["low", "medium", "high", "xhigh", "max"]
+    assert sonnet["default_effort"] == "high"
+    assert sonnet["supports_images"] is True
+
+
+@pytest.mark.parametrize("effort", ["low", "medium", "high", "xhigh", "max"])
+def test_sonnet_5_efforts_map_to_anthropic_kwargs(effort: str) -> None:
+    kwargs = provider_model_kwargs(SONNET_5_ID, effort, max_tokens=16_000)
+    assert kwargs["max_tokens"] == 16_000
+    assert kwargs["effort"] == effort
+    assert kwargs["thinking"] == {"type": "adaptive", "display": "summarized"}
+
+
+def test_sonnet_46_fallback_uses_sonnet_5() -> None:
+    assert provider_fallback_pair("anthropic:claude-sonnet-4-6", "xhigh") == (
+        SONNET_5_ID,
+        "xhigh",
+    )
+
+
+def test_opus_fallback_stays_on_opus_family() -> None:
+    assert provider_fallback_pair("anthropic:claude-opus-4-7", "xhigh") == (
+        "anthropic:claude-opus-4-8",
+        "xhigh",
+    )