diff --git a/tests/test_capabilities.py b/tests/test_capabilities.py
index 2ab28dc2d..1cd396eaa 100644
--- a/tests/test_capabilities.py
+++ b/tests/test_capabilities.py
@@ -25,6 +25,17 @@ class TestExactIdMatches:
         assert caps.supports_tool_choice is False
         assert caps.requires_reasoning_content_roundtrip is True
 
+    def test_deepseek_flash_alias_rejects_tool_choice(self):
+        """``deepseek-flash`` is what the model picker offers for V4.1 Flash.
+
+        It was falling through to _DEFAULT (tool_choice on), so every
+        structured-output call 400'd with "Thinking mode does not support
+        this tool_choice" and burned a retry as free text.
+        """
+        caps = get_capabilities("deepseek-flash")
+        assert caps.supports_tool_choice is False
+        assert caps.requires_reasoning_content_roundtrip is True
+
     def test_deepseek_v4_pro_rejects_tool_choice(self):
         caps = get_capabilities("deepseek-v4-pro")
         assert caps.supports_tool_choice is False
@@ -48,6 +59,10 @@ class TestPatternMatches:
         caps = get_capabilities("deepseek-reasoner-pro")
         assert caps.supports_tool_choice is False
 
+    def test_future_flash_variant_inherits_thinking_quirks(self):
+        caps = get_capabilities("deepseek-flash-lite")
+        assert caps.supports_tool_choice is False
+
     def test_minimax_m3_inherits_thinking_quirks(self):
         caps = get_capabilities("MiniMax-M3")
         assert caps.supports_tool_choice is False
@@ -128,6 +143,9 @@ class TestOpenRouterDeepSeekNamespace:
     def test_prefixed_reasoner_suppresses_tool_choice(self):
         assert get_capabilities("deepseek/deepseek-reasoner").supports_tool_choice is False
 
+    def test_prefixed_flash_alias_suppresses_tool_choice(self):
+        assert get_capabilities("deepseek/deepseek-flash").supports_tool_choice is False
+
     def test_prefixed_chat_selects_deepseek_chat_not_default(self):
         # Must resolve to _DEEPSEEK_CHAT, not _DEFAULT: supports_json_schema=False
         # is what distinguishes them (both keep tool_choice).
diff --git a/tradingagents/llm_clients/capabilities.py b/tradingagents/llm_clients/capabilities.py
index a2df7100a..e693bb5df 100644
--- a/tradingagents/llm_clients/capabilities.py
+++ b/tradingagents/llm_clients/capabilities.py
@@ -94,6 +94,7 @@ _DEFAULT = ModelCapabilities(
 _BY_ID: dict[str, ModelCapabilities] = {
     "deepseek-chat": _DEEPSEEK_CHAT,
     "deepseek-reasoner": _DEEPSEEK_THINKING,
+    "deepseek-flash": _DEEPSEEK_THINKING,
     "deepseek-v4-flash": _DEEPSEEK_THINKING,
     "deepseek-v4-pro": _DEEPSEEK_THINKING,
     # MiniMax — full official model lineup per
@@ -108,10 +109,14 @@ _BY_ID: dict[str, ModelCapabilities] = {
 }
 
 # Forward-compat patterns. New ``deepseek-v5-*`` / ``deepseek-reasoner-*``
-# or ``MiniMax-M3*`` variants inherit the thinking-mode quirks automatically.
+# / ``deepseek-flash-*`` or ``MiniMax-M3*`` variants inherit the thinking-mode
+# quirks automatically. ``deepseek-flash`` is the unversioned alias the model
+# picker offers for V4.1 Flash; it serves thinking mode and so rejects
+# ``tool_choice`` exactly like the versioned ``deepseek-v4-flash`` ID does.
 _BY_PATTERN: list[tuple[re.Pattern[str], ModelCapabilities]] = [
     (re.compile(r"^deepseek-v\d"), _DEEPSEEK_THINKING),
     (re.compile(r"^deepseek-reasoner"), _DEEPSEEK_THINKING),
+    (re.compile(r"^deepseek-flash"), _DEEPSEEK_THINKING),
     (re.compile(r"^MiniMax-M\d"), _MINIMAX_THINKING),
 ]