diff --git a/src/httpx2/httpx2/_status_codes.py b/src/httpx2/httpx2/_status_codes.py
index 133a6231..8c645f16 100644
--- a/src/httpx2/httpx2/_status_codes.py
+++ b/src/httpx2/httpx2/_status_codes.py
@@ -1,21 +1,43 @@
 from __future__ import annotations
 
-from enum import IntEnum
+import warnings
+from enum import EnumMeta, IntEnum
 
 __all__ = ["codes"]
 
-
-class codes(IntEnum):
+# Constant names that were renamed by RFC 9110, kept as deprecated aliases
+# mapping each old name to its canonical replacement.
+_DEPRECATED_CODES = {
+    "REQUEST_ENTITY_TOO_LARGE": "CONTENT_TOO_LARGE",
+    "REQUEST_URI_TOO_LONG": "URI_TOO_LONG",
+    "REQUESTED_RANGE_NOT_SATISFIABLE": "RANGE_NOT_SATISFIABLE",
+    "UNPROCESSABLE_ENTITY": "UNPROCESSABLE_CONTENT",
+}
+
+
+class _CodesMeta(EnumMeta):
+    def __getattr__(cls, name: str) -> codes:
+        if name in _DEPRECATED_CODES:
+            new_name = _DEPRECATED_CODES[name]
+            warnings.warn(
+                f"'{name}' is deprecated. Use '{new_name}' instead.",
+                category=DeprecationWarning,
+                stacklevel=2,
+            )
+            return cls[new_name]
+        raise AttributeError(name)
+
+
+class codes(IntEnum, metaclass=_CodesMeta):
     """HTTP status codes and reason phrases
 
     Status codes from the following RFCs are all observed:
 
-        * RFC 7231: Hypertext Transfer Protocol (HTTP/1.1), obsoletes 2616
+        * RFC 9110: HTTP Semantics, obsoletes 7231 & 7238
         * RFC 6585: Additional HTTP Status Codes
         * RFC 3229: Delta encoding in HTTP
         * RFC 4918: HTTP Extensions for WebDAV, obsoletes 2518
         * RFC 5842: Binding Extensions to WebDAV
-        * RFC 7238: Permanent Redirect
         * RFC 2295: Transparent Content Negotiation in HTTP
         * RFC 2774: An HTTP Extension Framework
         * RFC 7540: Hypertext Transfer Protocol Version 2 (HTTP/2)
@@ -126,14 +148,14 @@ def is_error(cls, value: int) -> bool:
     GONE = 410, "Gone"
     LENGTH_REQUIRED = 411, "Length Required"
     PRECONDITION_FAILED = 412, "Precondition Failed"
-    REQUEST_ENTITY_TOO_LARGE = 413, "Request Entity Too Large"
-    REQUEST_URI_TOO_LONG = 414, "Request-URI Too Long"
+    CONTENT_TOO_LARGE = 413, "Content Too Large"
+    URI_TOO_LONG = 414, "URI Too Long"
     UNSUPPORTED_MEDIA_TYPE = 415, "Unsupported Media Type"
-    REQUESTED_RANGE_NOT_SATISFIABLE = 416, "Requested Range Not Satisfiable"
+    RANGE_NOT_SATISFIABLE = 416, "Range Not Satisfiable"
     EXPECTATION_FAILED = 417, "Expectation Failed"
     IM_A_TEAPOT = 418, "I'm a teapot"
     MISDIRECTED_REQUEST = 421, "Misdirected Request"
-    UNPROCESSABLE_ENTITY = 422, "Unprocessable Entity"
+    UNPROCESSABLE_CONTENT = 422, "Unprocessable Content"
     LOCKED = 423, "Locked"
     FAILED_DEPENDENCY = 424, "Failed Dependency"
     TOO_EARLY = 425, "Too Early"
diff --git a/tests/httpx2/test_status_codes.py b/tests/httpx2/test_status_codes.py
index 56dcafa3..d10daace 100644
--- a/tests/httpx2/test_status_codes.py
+++ b/tests/httpx2/test_status_codes.py
@@ -1,3 +1,5 @@
+import pytest
+
 import httpx2
 
 
@@ -16,7 +18,7 @@ def test_status_code_phrase_lookup() -> None:
 
 
 def test_lowercase_status_code() -> None:
-    assert httpx2.codes.not_found == 404  # type: ignore
+    assert httpx2.codes.not_found == 404
 
 
 def test_reason_phrase_for_status_code() -> None:
@@ -25,3 +27,32 @@ def test_reason_phrase_for_status_code() -> None:
 
 def test_reason_phrase_for_unknown_status_code() -> None:
     assert httpx2.codes.get_reason_phrase(499) == ""
+
+
+def test_rfc9110_status_texts() -> None:
+    assert httpx2.codes.get_reason_phrase(413) == "Content Too Large"
+    assert httpx2.codes.get_reason_phrase(414) == "URI Too Long"
+    assert httpx2.codes.get_reason_phrase(416) == "Range Not Satisfiable"
+    assert httpx2.codes.get_reason_phrase(422) == "Unprocessable Content"
+
+
+@pytest.mark.parametrize(
+    ("old_name", "new_name"),
+    [
+        ("REQUEST_ENTITY_TOO_LARGE", "CONTENT_TOO_LARGE"),
+        ("REQUEST_URI_TOO_LONG", "URI_TOO_LONG"),
+        ("REQUESTED_RANGE_NOT_SATISFIABLE", "RANGE_NOT_SATISFIABLE"),
+        ("UNPROCESSABLE_ENTITY", "UNPROCESSABLE_CONTENT"),
+    ],
+)
+def test_pre_rfc9110_aliases_are_deprecated(old_name: str, new_name: str) -> None:
+    # the pre-RFC 9110 constant names are kept as deprecated aliases
+    msg = f"'{old_name}' is deprecated. Use '{new_name}' instead."
+    with pytest.warns(DeprecationWarning, match=msg):
+        assert getattr(httpx2.codes, old_name) == httpx2.codes[new_name]
+
+
+def test_unknown_status_code_attribute_raises() -> None:
+    name = "NOT_A_REAL_CODE"
+    with pytest.raises(AttributeError):
+        getattr(httpx2.codes, name)