diff --git a/app/openai_constants.py b/app/openai_constants.py
index c4a8cd6..a29f54a 100644
--- a/app/openai_constants.py
+++ b/app/openai_constants.py
@@ -33,6 +33,9 @@
 GPT_5_MODEL = "gpt-5"
 GPT_5_MINI_MODEL = "gpt-5-mini"
 GPT_5_NANO_MODEL = "gpt-5-nano"
+GPT_5_1_CHAT_LATEST_MODEL = "gpt-5.1-chat-latest"
+GPT_5_1_MODEL = "gpt-5.1"
+GPT_5_1_2025_11_13_MODEL = "gpt-5.1-2025-11-13"
 O3_MODEL = "o3"
 O4_MINI_MODEL = "o4-mini"
 GPT_5_2025_08_07_MODEL = "gpt-5-2025-08-07"
@@ -77,11 +80,13 @@
     GPT_4O_MINI_2024_07_18_MODEL: (3, 1),
     # GPT-5 chat latest
     GPT_5_CHAT_LATEST_MODEL: (3, 1),
+    GPT_5_1_CHAT_LATEST_MODEL: (3, 1),
     GPT_5_SEARCH_API_2025_10_14_MODEL: (3, 1),
     # GPT-5 family (dated)
     GPT_5_2025_08_07_MODEL: (3, 1),
     GPT_5_MINI_2025_08_07_MODEL: (3, 1),
     GPT_5_NANO_2025_08_07_MODEL: (3, 1),
+    GPT_5_1_2025_11_13_MODEL: (3, 1),
     # Reasoning models (dated)
     O3_2025_04_16_MODEL: (3, 1),
     O4_MINI_2025_04_16_MODEL: (3, 1),
@@ -103,6 +108,7 @@
     GPT_5_MODEL: GPT_5_2025_08_07_MODEL,
     GPT_5_MINI_MODEL: GPT_5_MINI_2025_08_07_MODEL,
     GPT_5_NANO_MODEL: GPT_5_NANO_2025_08_07_MODEL,
+    GPT_5_1_MODEL: GPT_5_1_2025_11_13_MODEL,
     GPT_5_SEARCH_API_MODEL: GPT_5_SEARCH_API_2025_10_14_MODEL,
     O3_MODEL: O3_2025_04_16_MODEL,
     O4_MINI_MODEL: O4_MINI_2025_04_16_MODEL,
@@ -134,11 +140,13 @@
     GPT_4_1_NANO_2025_04_14_MODEL: 1048576,
     # GPT-5 chat latest
     GPT_5_CHAT_LATEST_MODEL: 128000,
+    GPT_5_1_CHAT_LATEST_MODEL: 128000,
     GPT_5_SEARCH_API_2025_10_14_MODEL: 128000,
     # GPT-5 family (dated)
     GPT_5_2025_08_07_MODEL: 128000,
     GPT_5_MINI_2025_08_07_MODEL: 128000,
     GPT_5_NANO_2025_08_07_MODEL: 128000,
+    GPT_5_1_2025_11_13_MODEL: 128000,
     # Reasoning models (dated)
     O3_2025_04_16_MODEL: 128000,
     O4_MINI_2025_04_16_MODEL: 128000,
diff --git a/app/openai_ops.py b/app/openai_ops.py
index ae5d445..b9ef4b7 100644
--- a/app/openai_ops.py
+++ b/app/openai_ops.py
@@ -86,13 +86,15 @@ def messages_within_context_window(
 def _is_reasoning(model: str) -> bool:
     """Returns True if the model is a reasoning model under Chat Completions.
 
-    Excludes chat models like gpt-5-chat-latest and gpt-5-search-api. Matches o3*, o4*, and
-    non-chat gpt-5* families. Case-insensitive and safe with None/empty.
+    Excludes chat models like gpt-5-chat-latest, gpt-5.1-chat-latest, and gpt-5-search-api.
+    Matches o3*, o4*, and non-chat gpt-5* families. Case-insensitive and safe with None/empty.
     """
     if not model:
         return False
     ml = model.lower()
-    if ml.startswith("gpt-5-chat") or ml.startswith("gpt-5-search"):
+    # Treat any gpt-5 family chat/search variants (including numbered updates)
+    # as regular chat models so they keep sampling params.
+    if ml.startswith("gpt-5") and ("-chat" in ml or "-search" in ml):
         return False
     return (
         ml.startswith("o1")
diff --git a/app/slack_ui.py b/app/slack_ui.py
index 116aabd..f4a5019 100644
--- a/app/slack_ui.py
+++ b/app/slack_ui.py
@@ -8,6 +8,8 @@
     GPT_4O_MINI_MODEL,
     GPT_4_1_MODEL,
     GPT_4_1_MINI_MODEL,
+    GPT_5_1_CHAT_LATEST_MODEL,
+    GPT_5_1_MODEL,
     GPT_5_CHAT_LATEST_MODEL,
     GPT_5_MODEL,
     GPT_5_MINI_MODEL,
@@ -440,6 +442,14 @@ def build_configure_modal(context: BoltContext) -> dict:
         )
 
     options = [
+        {
+            "text": {"type": "plain_text", "text": "GPT-5.1-chat-latest"},
+            "value": GPT_5_1_CHAT_LATEST_MODEL,
+        },
+        {
+            "text": {"type": "plain_text", "text": "GPT-5.1"},
+            "value": GPT_5_1_MODEL,
+        },
         {
             "text": {"type": "plain_text", "text": "GPT-5-chat-latest"},
             "value": GPT_5_CHAT_LATEST_MODEL,
diff --git a/tests/model_constants_test.py b/tests/model_constants_test.py
index 85986f3..39d1771 100644
--- a/tests/model_constants_test.py
+++ b/tests/model_constants_test.py
@@ -6,12 +6,19 @@
     MODEL_CONTEXT_LENGTHS,
     GPT_4_MODEL,
     GPT_4_0613_MODEL,
+    GPT_5_1_MODEL,
+    GPT_5_1_2025_11_13_MODEL,
 )
 
 def test_alias_resolution():
     """Tests that a model alias resolves to its specific version."""
     assert resolve_model_alias(GPT_4_MODEL) == GPT_4_0613_MODEL
 
+
+def test_gpt_5_1_alias_resolution():
+    """Ensures the GPT-5.1 alias resolves to the dated release."""
+    assert resolve_model_alias(GPT_5_1_MODEL) == GPT_5_1_2025_11_13_MODEL
+
 def test_unregistered_model_fails():
     """Tests that resolving an unregistered model raises NotImplementedError."""
     # First, test the resolver
diff --git a/tests/openai_ops_test.py b/tests/openai_ops_test.py
index f138456..338a3cf 100755
--- a/tests/openai_ops_test.py
+++ b/tests/openai_ops_test.py
@@ -149,6 +149,24 @@ def fake_calculate_num_tokens(messages, model=None):  # type: ignore[no-redef]
     assert captured["model"] == GPT_4O_MODEL
 
 
+@pytest.mark.parametrize(
+    "model,expected",
+    [
+        ("gpt-5-chat-latest", False),
+        ("gpt-5.1-chat-latest", False),
+        ("gpt-5-search-api", False),
+        ("gpt-5.1-2025-11-13", True),
+        ("gpt-5-nano", True),
+        ("o3", True),
+        ("o4-mini", True),
+        ("o1-preview", True),
+        ("gpt-4o", False),
+    ],
+)
+def test_is_reasoning_heuristics(model, expected):
+    assert ops._is_reasoning(model) is expected
+
+
 @pytest.mark.parametrize("api_type", ["openai", "azure"])
 @pytest.mark.parametrize(
     "model,is_reasoning,temperature,timeout,user",