diff --git a/README.md b/README.md
index 4486dd2..acf410f 100644
--- a/README.md
+++ b/README.md
@@ -93,6 +93,7 @@ curl http://127.0.0.1:8000/v1/chat/completions \
 
 ## Supported Models
 
+- `gpt-5.5`
 - `gpt-5.4`
 - `gpt-5.4-mini`
 - `gpt-5.2`
diff --git a/chatmock/model_registry.py b/chatmock/model_registry.py
index 9bddbeb..1b97bc6 100644
--- a/chatmock/model_registry.py
+++ b/chatmock/model_registry.py
@@ -54,6 +54,13 @@ class ModelSpec:
         allowed_efforts=frozenset(("low", "medium", "high", "xhigh")),
         variant_efforts=("xhigh", "high", "medium", "low"),
     ),
+    ModelSpec(
+        public_id="gpt-5.5",
+        upstream_id="gpt-5.5",
+        aliases=("gpt5.5", "gpt-5.5-latest"),
+        allowed_efforts=frozenset(("none", "low", "medium", "high", "xhigh")),
+        variant_efforts=("xhigh", "high", "medium", "low", "none"),
+    ),
     ModelSpec(
         public_id="gpt-5.3-codex",
         upstream_id="gpt-5.3-codex",
diff --git a/tests/test_models.py b/tests/test_models.py
index e82b516..022cdd2 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -10,10 +10,12 @@ def test_normalizes_aliases(self) -> None:
         self.assertEqual(normalize_model_name("gpt5"), "gpt-5")
         self.assertEqual(normalize_model_name("gpt5.4"), "gpt-5.4")
         self.assertEqual(normalize_model_name("gpt5.4-mini"), "gpt-5.4-mini")
+        self.assertEqual(normalize_model_name("gpt5.5"), "gpt-5.5")
         self.assertEqual(normalize_model_name("gpt5.3-codex-spark"), "gpt-5.3-codex-spark")
         self.assertEqual(normalize_model_name("codex"), "codex-mini-latest")
 
     def test_strips_reasoning_suffixes(self) -> None:
+        self.assertEqual(normalize_model_name("gpt-5.5-high"), "gpt-5.5")
         self.assertEqual(normalize_model_name("gpt-5.4-high"), "gpt-5.4")
         self.assertEqual(normalize_model_name("gpt-5.4-mini-high"), "gpt-5.4-mini")
         self.assertEqual(normalize_model_name("gpt-5.2_codemirror"), "gpt-5.2_codemirror")
@@ -21,15 +23,18 @@ def test_strips_reasoning_suffixes(self) -> None:
         self.assertEqual(normalize_model_name("gpt-5.1-codex:high"), "gpt-5.1-codex")
 
     def test_allowed_efforts_follow_registry(self) -> None:
+        self.assertEqual(allowed_efforts_for_model("gpt-5.5"), frozenset(("none", "low", "medium", "high", "xhigh")))
         self.assertEqual(allowed_efforts_for_model("gpt-5.4"), frozenset(("none", "low", "medium", "high", "xhigh")))
         self.assertEqual(allowed_efforts_for_model("gpt-5.4-mini"), frozenset(("low", "medium", "high", "xhigh")))
         self.assertEqual(allowed_efforts_for_model("gpt-5.1-codex"), frozenset(("low", "medium", "high")))
 
     def test_public_models_include_variants(self) -> None:
         model_ids = list_public_models(expose_reasoning_models=True)
+        self.assertIn("gpt-5.5", model_ids)
         self.assertIn("gpt-5.4", model_ids)
         self.assertIn("gpt-5.4-mini", model_ids)
         self.assertIn("gpt-5.3-codex-spark", model_ids)
+        self.assertIn("gpt-5.5-none", model_ids)
         self.assertIn("gpt-5.4-none", model_ids)
         self.assertIn("gpt-5.4-mini-xhigh", model_ids)
         self.assertNotIn("gpt-5.4-mini-none", model_ids)