diff --git a/tests/test_anthropic_effort.py b/tests/test_anthropic_effort.py
index d576f6aa6..7677eb936 100644
--- a/tests/test_anthropic_effort.py
+++ b/tests/test_anthropic_effort.py
@@ -28,6 +28,8 @@ class TestEffortGate:
             "claude-haiku-4-5", "claude-haiku-5-0", "claude-haiku-4-7-preview",
             # Sonnet 4.5 (and earlier) 400 on effort — only Sonnet 4.6+ supports it.
             "claude-sonnet-4-5", "claude-sonnet-4-0",
+            # A dated snapshot's date is not its minor version (#1585).
+            "claude-sonnet-4-20250514", "claude-opus-4-20250514", "claude-sonnet-4-5-20250929",
         ],
     )
     def test_unsupported_models_do_not_receive_effort(self, monkeypatch, model):
@@ -39,7 +41,7 @@ class TestEffortGate:
         "model",
         [
             "claude-opus-4-5", "claude-opus-4-6", "claude-opus-4-7",
-            "claude-sonnet-4-6",
+            "claude-sonnet-4-6", "claude-opus-4-5-20251101",
         ],
     )
     def test_current_opus_and_sonnet_receive_effort(self, monkeypatch, model):
diff --git a/tradingagents/llm_clients/anthropic_client.py b/tradingagents/llm_clients/anthropic_client.py
index 23772c65c..ab0a21c7c 100644
--- a/tradingagents/llm_clients/anthropic_client.py
+++ b/tradingagents/llm_clients/anthropic_client.py
@@ -15,12 +15,13 @@ _PASSTHROUGH_KWARGS = (
 # Sonnet 4.6+, and the Claude 5 family (Sonnet 5, Opus 5.5, Fable 5). Sonnet 4.5 and any
 # Haiku version 400 with ``"This model does not support the effort parameter"``
 # (#831). Versions may be dotted (``opus-4-8``) or single-number (``sonnet-5``,
-# ``fable-5``); the per-family minimum below is forward-compatible.
+# ``fable-5``), and a snapshot carries its date (``sonnet-4-20250514``), which is
+# not a minor version; the per-family minimum below is forward-compatible.
 _EFFORT_EXACT = {
     "claude-mythos-preview",  # non-standard preview name; effort-capable
     "claude-mythos-5",        # Fable 5 twin (Project Glasswing); effort-capable
 }
-_EFFORT_MODEL = re.compile(r"^claude-(opus|sonnet|fable)-(\d+)(?:-(\d+))?$")
+_EFFORT_MODEL = re.compile(r"^claude-(opus|sonnet|fable)-(\d+)(?:-(\d{1,2}))?(?:-\d{8})?$")
 _EFFORT_MIN_VERSION = {"opus": (4, 5), "sonnet": (4, 6), "fable": (5, 0)}