diff --git a/lm15/providers/openai.py b/lm15/providers/openai.py
index dad191e..f3d672c 100644
--- a/lm15/providers/openai.py
+++ b/lm15/providers/openai.py
@@ -167,7 +167,7 @@ def _attach_unmapped(provider_data: dict[str, Any], unmapped: list[dict[str, str
     return out
 
 
-_GPT_VERSION_RE = re.compile(r"^gpt-(\d+)\.(\d+)")
+_GPT_VERSION_RE = re.compile(r"^gpt-(?:(\d+)\.(\d+)|([1-9]))(?:-|$)")
 
 
 def openai_model_has_cache_options(model: str) -> bool:
@@ -177,12 +177,18 @@ def openai_model_has_cache_options(model: str) -> bool:
     that class accepts it (older models reject it with HTTP 400, and their
     writes are free anyway).  Deciding client-side needs a model check —
     a table that rots.  Stated trade-off: a future family whose name does
-    not match ``gpt-<major>.<minor>`` keeps the provider's implicit writes
-    on ``mode="off"``; ``extensions={"prompt_cache_options": ...}`` is the
-    override.
+    not match ``gpt-<major>`` or ``gpt-<major>.<minor>`` keeps the
+    provider's implicit writes on ``mode="off"``;
+    ``extensions={"prompt_cache_options": ...}`` is the override.
     """
     m = _GPT_VERSION_RE.match(model.lower())
-    return bool(m) and (int(m.group(1)), int(m.group(2))) >= (5, 6)
+    if not m:
+        return False
+    if m.group(1) is not None:
+        major, minor = int(m.group(1)), int(m.group(2))
+    else:
+        major, minor = int(m.group(3)), 0
+    return (major, minor) >= (5, 6)
 
 
 def _cache_breakpoint_index(request: Request, cache_control: str) -> int | None:
diff --git a/tests/test_cache_mapping.py b/tests/test_cache_mapping.py
index 7995757..530351f 100644
--- a/tests/test_cache_mapping.py
+++ b/tests/test_cache_mapping.py
@@ -34,11 +34,18 @@ def _body(lm, request: Request) -> dict:
 # ─── model class table ───────────────────────────────────────────────
 
 def test_openai_model_class_for_cache_options() -> None:
+    assert openai_model_has_cache_options("gpt-6")
     assert openai_model_has_cache_options("gpt-5.6-sol")
     assert openai_model_has_cache_options("gpt-6.0")
+    assert openai_model_has_cache_options("gpt-6-luna")
     assert openai_model_has_cache_options("GPT-5.10")
+    assert not openai_model_has_cache_options("gpt-5")
+    assert not openai_model_has_cache_options("gpt-5-mini")
     assert not openai_model_has_cache_options("gpt-5.5")
     assert not openai_model_has_cache_options("gpt-4.1-mini")
+    assert not openai_model_has_cache_options("gpt-3.5-turbo")
+    assert not openai_model_has_cache_options("gpt-35-turbo")
+    assert not openai_model_has_cache_options("gpt-35-turbo-16k")
     assert not openai_model_has_cache_options("o3")            # unknown pattern -> no switch (stated trade-off)
     assert not openai_model_has_cache_options("chat-latest")