diff --git a/conformance/results/mypy/namedtuples_define_class.toml b/conformance/results/mypy/namedtuples_define_class.toml
index 575c5c0c..72785e42 100644
--- a/conformance/results/mypy/namedtuples_define_class.toml
+++ b/conformance/results/mypy/namedtuples_define_class.toml
@@ -1,29 +1,34 @@
 conformant = "Partial"
 notes = """
 Does not reject override of named tuple attribute in child class.
+Does not support version-conditional fields.
 """
 output = """
-namedtuples_define_class.py:32: error: Tuple index out of range  [misc]
 namedtuples_define_class.py:33: error: Tuple index out of range  [misc]
-namedtuples_define_class.py:44: error: Missing positional argument "y" in call to "Point"  [call-arg]
+namedtuples_define_class.py:34: error: Tuple index out of range  [misc]
 namedtuples_define_class.py:45: error: Missing positional argument "y" in call to "Point"  [call-arg]
-namedtuples_define_class.py:46: error: Argument 2 to "Point" has incompatible type "str"; expected "int"  [arg-type]
-namedtuples_define_class.py:47: error: Argument "units" to "Point" has incompatible type "int"; expected "str"  [arg-type]
-namedtuples_define_class.py:48: error: Too many arguments for "Point"  [call-arg]
-namedtuples_define_class.py:49: error: Unexpected keyword argument "other" for "Point"  [call-arg]
-namedtuples_define_class.py:59: error: Invalid statement in NamedTuple definition; expected "field_name: field_type [= default]"  [misc]
-namedtuples_define_class.py:65: error: Missing positional argument "units" in call to "Point2"  [call-arg]
-namedtuples_define_class.py:67: error: Too many values to unpack (2 expected, 3 provided)  [misc]
-namedtuples_define_class.py:76: error: NamedTuple field name cannot start with an underscore: _y  [misc]
-namedtuples_define_class.py:86: error: Non-default NamedTuple fields cannot follow default fields  [misc]
-namedtuples_define_class.py:125: error: Argument 2 to "Property" has incompatible type "float"; expected "str"  [arg-type]
-namedtuples_define_class.py:132: error: NamedTuple should be a single base  [misc]
+namedtuples_define_class.py:46: error: Missing positional argument "y" in call to "Point"  [call-arg]
+namedtuples_define_class.py:47: error: Argument 2 to "Point" has incompatible type "str"; expected "int"  [arg-type]
+namedtuples_define_class.py:48: error: Argument "units" to "Point" has incompatible type "int"; expected "str"  [arg-type]
+namedtuples_define_class.py:49: error: Too many arguments for "Point"  [call-arg]
+namedtuples_define_class.py:50: error: Unexpected keyword argument "other" for "Point"  [call-arg]
+namedtuples_define_class.py:60: error: Invalid statement in NamedTuple definition; expected "field_name: field_type [= default]"  [misc]
+namedtuples_define_class.py:66: error: Missing positional argument "units" in call to "Point2"  [call-arg]
+namedtuples_define_class.py:68: error: Too many values to unpack (2 expected, 3 provided)  [misc]
+namedtuples_define_class.py:77: error: NamedTuple field name cannot start with an underscore: _y  [misc]
+namedtuples_define_class.py:87: error: Non-default NamedTuple fields cannot follow default fields  [misc]
+namedtuples_define_class.py:114: error: Invalid statement in NamedTuple definition; expected "field_name: field_type [= default]"  [misc]
+namedtuples_define_class.py:118: error: Too many arguments for "ConditionalField"  [call-arg]
+namedtuples_define_class.py:137: error: Argument 2 to "Property" has incompatible type "float"; expected "str"  [arg-type]
+namedtuples_define_class.py:144: error: NamedTuple should be a single base  [misc]
 """
 conformance_automated = "Fail"
 errors_diff = """
-Line 69: Expected 1 errors
-Line 106: Expected 1 errors
-Line 59: Unexpected errors ['namedtuples_define_class.py:59: error: Invalid statement in NamedTuple definition; expected "field_name: field_type [= default]"  [misc]']
-Line 65: Unexpected errors ['namedtuples_define_class.py:65: error: Missing positional argument "units" in call to "Point2"  [call-arg]']
-Line 67: Unexpected errors ['namedtuples_define_class.py:67: error: Too many values to unpack (2 expected, 3 provided)  [misc]']
+Line 70: Expected 1 errors
+Line 107: Expected 1 errors
+Line 60: Unexpected errors ['namedtuples_define_class.py:60: error: Invalid statement in NamedTuple definition; expected "field_name: field_type [= default]"  [misc]']
+Line 66: Unexpected errors ['namedtuples_define_class.py:66: error: Missing positional argument "units" in call to "Point2"  [call-arg]']
+Line 68: Unexpected errors ['namedtuples_define_class.py:68: error: Too many values to unpack (2 expected, 3 provided)  [misc]']
+Line 114: Unexpected errors ['namedtuples_define_class.py:114: error: Invalid statement in NamedTuple definition; expected "field_name: field_type [= default]"  [misc]']
+Line 118: Unexpected errors ['namedtuples_define_class.py:118: error: Too many arguments for "ConditionalField"  [call-arg]']
 """
diff --git a/conformance/results/mypy/typeddicts_class_syntax.toml b/conformance/results/mypy/typeddicts_class_syntax.toml
index 76e44ef9..573c04e3 100644
--- a/conformance/results/mypy/typeddicts_class_syntax.toml
+++ b/conformance/results/mypy/typeddicts_class_syntax.toml
@@ -1,11 +1,18 @@
-conformant = "Pass"
+conformant = "Partial"
+notes = """
+Does not support version-conditional items in TypedDict definitions.
+"""
 output = """
-typeddicts_class_syntax.py:29: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]
-typeddicts_class_syntax.py:33: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]
-typeddicts_class_syntax.py:38: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]
-typeddicts_class_syntax.py:44: error: Unexpected keyword argument "metaclass" for "__init_subclass__" of "TypedDict"  [call-arg]
-typeddicts_class_syntax.py:49: error: Unexpected keyword argument "other" for "__init_subclass__" of "TypedDict"  [call-arg]
+typeddicts_class_syntax.py:30: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]
+typeddicts_class_syntax.py:34: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]
+typeddicts_class_syntax.py:39: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]
+typeddicts_class_syntax.py:45: error: Unexpected keyword argument "metaclass" for "__init_subclass__" of "TypedDict"  [call-arg]
+typeddicts_class_syntax.py:50: error: Unexpected keyword argument "other" for "__init_subclass__" of "TypedDict"  [call-arg]
+typeddicts_class_syntax.py:58: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]
+typeddicts_class_syntax.py:62: error: Extra key "y" for TypedDict "ConditionalField"  [typeddict-unknown-key]
 """
-conformance_automated = "Pass"
+conformance_automated = "Fail"
 errors_diff = """
+Line 58: Unexpected errors ['typeddicts_class_syntax.py:58: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]']
+Line 62: Unexpected errors ['typeddicts_class_syntax.py:62: error: Extra key "y" for TypedDict "ConditionalField"  [typeddict-unknown-key]']
 """
diff --git a/conformance/results/pyrefly/namedtuples_define_class.toml b/conformance/results/pyrefly/namedtuples_define_class.toml
index 706bce8f..67af61d9 100644
--- a/conformance/results/pyrefly/namedtuples_define_class.toml
+++ b/conformance/results/pyrefly/namedtuples_define_class.toml
@@ -3,18 +3,18 @@ conformance_automated = "Pass"
 errors_diff = """
 """
 output = """
-ERROR namedtuples_define_class.py:32:10-11: Index 3 out of range for tuple with 3 elements [bad-index]
-ERROR namedtuples_define_class.py:33:10-12: Index -4 out of range for tuple with 3 elements [bad-index]
-ERROR namedtuples_define_class.py:44:11-14: Missing argument `y` in function `Point.__new__` [missing-argument]
-ERROR namedtuples_define_class.py:45:11-16: Missing argument `y` in function `Point.__new__` [missing-argument]
-ERROR namedtuples_define_class.py:46:15-17: Argument `Literal['']` is not assignable to parameter `y` with type `int` in function `Point.__new__` [bad-argument-type]
-ERROR namedtuples_define_class.py:47:24-25: Argument `Literal[3]` is not assignable to parameter `units` with type `str` in function `Point.__new__` [bad-argument-type]
-ERROR namedtuples_define_class.py:48:22-24: Expected 3 positional arguments, got 4 in function `Point.__new__` [bad-argument-count]
-ERROR namedtuples_define_class.py:49:23-28: Unexpected keyword argument `other` in function `Point.__new__` [unexpected-keyword]
-ERROR namedtuples_define_class.py:69:20-22: Expected 2 positional arguments, got 3 in function `Point2.__new__` [bad-argument-count]
-ERROR namedtuples_define_class.py:76:5-7: NamedTuple field name may not start with an underscore: `_y` [bad-class-definition]
-ERROR namedtuples_define_class.py:86:5-13: NamedTuple field 'latitude' without a default may not follow NamedTuple field with a default [bad-class-definition]
-ERROR namedtuples_define_class.py:106:5-6: Cannot override named tuple element `x` [bad-override]
-ERROR namedtuples_define_class.py:125:19-22: Argument `float` is not assignable to parameter `value` with type `str` in function `Property.__new__` [bad-argument-type]
-ERROR namedtuples_define_class.py:132:7-11: Named tuples do not support multiple inheritance [invalid-inheritance]
+ERROR namedtuples_define_class.py:33:10-11: Index 3 out of range for tuple with 3 elements [bad-index]
+ERROR namedtuples_define_class.py:34:10-12: Index -4 out of range for tuple with 3 elements [bad-index]
+ERROR namedtuples_define_class.py:45:11-14: Missing argument `y` in function `Point.__new__` [missing-argument]
+ERROR namedtuples_define_class.py:46:11-16: Missing argument `y` in function `Point.__new__` [missing-argument]
+ERROR namedtuples_define_class.py:47:15-17: Argument `Literal['']` is not assignable to parameter `y` with type `int` in function `Point.__new__` [bad-argument-type]
+ERROR namedtuples_define_class.py:48:24-25: Argument `Literal[3]` is not assignable to parameter `units` with type `str` in function `Point.__new__` [bad-argument-type]
+ERROR namedtuples_define_class.py:49:22-24: Expected 3 positional arguments, got 4 in function `Point.__new__` [bad-argument-count]
+ERROR namedtuples_define_class.py:50:23-28: Unexpected keyword argument `other` in function `Point.__new__` [unexpected-keyword]
+ERROR namedtuples_define_class.py:70:20-22: Expected 2 positional arguments, got 3 in function `Point2.__new__` [bad-argument-count]
+ERROR namedtuples_define_class.py:77:5-7: NamedTuple field name may not start with an underscore: `_y` [bad-class-definition]
+ERROR namedtuples_define_class.py:87:5-13: NamedTuple field 'latitude' without a default may not follow NamedTuple field with a default [bad-class-definition]
+ERROR namedtuples_define_class.py:107:5-6: Cannot override named tuple element `x` [bad-override]
+ERROR namedtuples_define_class.py:137:19-22: Argument `float` is not assignable to parameter `value` with type `str` in function `Property.__new__` [bad-argument-type]
+ERROR namedtuples_define_class.py:144:7-11: Named tuples do not support multiple inheritance [invalid-inheritance]
 """
diff --git a/conformance/results/pyrefly/typeddicts_class_syntax.toml b/conformance/results/pyrefly/typeddicts_class_syntax.toml
index 6e367e6d..58e3bff5 100644
--- a/conformance/results/pyrefly/typeddicts_class_syntax.toml
+++ b/conformance/results/pyrefly/typeddicts_class_syntax.toml
@@ -3,9 +3,9 @@ conformance_automated = "Pass"
 errors_diff = """
 """
 output = """
-ERROR typeddicts_class_syntax.py:29:9-16: TypedDict members must be declared in the form `field: Annotation` with no assignment [bad-class-definition]
-ERROR typeddicts_class_syntax.py:34:9-16: TypedDict members must be declared in the form `field: Annotation` with no assignment [bad-class-definition]
-ERROR typeddicts_class_syntax.py:39:9-16: TypedDict members must be declared in the form `field: Annotation` with no assignment [bad-class-definition]
-ERROR typeddicts_class_syntax.py:44:7-20: Metaclass of `BadTypedDict2` has type `type[Any]` that is not a simple class type [invalid-inheritance]
-ERROR typeddicts_class_syntax.py:49:7-20: TypedDict does not support keyword argument `other` [bad-typed-dict]
+ERROR typeddicts_class_syntax.py:30:9-16: TypedDict members must be declared in the form `field: Annotation` with no assignment [bad-class-definition]
+ERROR typeddicts_class_syntax.py:35:9-16: TypedDict members must be declared in the form `field: Annotation` with no assignment [bad-class-definition]
+ERROR typeddicts_class_syntax.py:40:9-16: TypedDict members must be declared in the form `field: Annotation` with no assignment [bad-class-definition]
+ERROR typeddicts_class_syntax.py:45:7-20: Metaclass of `BadTypedDict2` has type `type[Any]` that is not a simple class type [invalid-inheritance]
+ERROR typeddicts_class_syntax.py:50:7-20: TypedDict does not support keyword argument `other` [bad-typed-dict]
 """
diff --git a/conformance/results/pyright/namedtuples_define_class.toml b/conformance/results/pyright/namedtuples_define_class.toml
index e04b26fc..b4cc632c 100644
--- a/conformance/results/pyright/namedtuples_define_class.toml
+++ b/conformance/results/pyright/namedtuples_define_class.toml
@@ -1,22 +1,22 @@
 conformant = "Pass"
 output = """
-namedtuples_define_class.py:32:7 - error: Index 3 is out of range for type Point (reportGeneralTypeIssues)
-namedtuples_define_class.py:33:7 - error: Index -4 is out of range for type Point (reportGeneralTypeIssues)
-namedtuples_define_class.py:44:6 - error: Argument missing for parameter "y" (reportCallIssue)
+namedtuples_define_class.py:33:7 - error: Index 3 is out of range for type Point (reportGeneralTypeIssues)
+namedtuples_define_class.py:34:7 - error: Index -4 is out of range for type Point (reportGeneralTypeIssues)
 namedtuples_define_class.py:45:6 - error: Argument missing for parameter "y" (reportCallIssue)
-namedtuples_define_class.py:46:15 - error: Argument of type "Literal['']" cannot be assigned to parameter "y" of type "int" in function "__new__"
+namedtuples_define_class.py:46:6 - error: Argument missing for parameter "y" (reportCallIssue)
+namedtuples_define_class.py:47:15 - error: Argument of type "Literal['']" cannot be assigned to parameter "y" of type "int" in function "__new__"
   "Literal['']" is not assignable to "int" (reportArgumentType)
-namedtuples_define_class.py:47:24 - error: Argument of type "Literal[3]" cannot be assigned to parameter "units" of type "str" in function "__new__"
+namedtuples_define_class.py:48:24 - error: Argument of type "Literal[3]" cannot be assigned to parameter "units" of type "str" in function "__new__"
   "Literal[3]" is not assignable to "str" (reportArgumentType)
-namedtuples_define_class.py:48:22 - error: Expected 3 positional arguments (reportCallIssue)
-namedtuples_define_class.py:49:23 - error: No parameter named "other" (reportCallIssue)
-namedtuples_define_class.py:69:20 - error: Expected 2 positional arguments (reportCallIssue)
-namedtuples_define_class.py:76:5 - error: Named tuple field names cannot start with an underscore (reportGeneralTypeIssues)
-namedtuples_define_class.py:86:5 - error: Fields without default values cannot appear after fields with default values (reportGeneralTypeIssues)
-namedtuples_define_class.py:106:5 - error: Cannot override "x" because parent class "Point" is a named tuple (reportIncompatibleVariableOverride)
-namedtuples_define_class.py:125:19 - error: Argument of type "float" cannot be assigned to parameter "value" of type "str" in function "__new__"
+namedtuples_define_class.py:49:22 - error: Expected 3 positional arguments (reportCallIssue)
+namedtuples_define_class.py:50:23 - error: No parameter named "other" (reportCallIssue)
+namedtuples_define_class.py:70:20 - error: Expected 2 positional arguments (reportCallIssue)
+namedtuples_define_class.py:77:5 - error: Named tuple field names cannot start with an underscore (reportGeneralTypeIssues)
+namedtuples_define_class.py:87:5 - error: Fields without default values cannot appear after fields with default values (reportGeneralTypeIssues)
+namedtuples_define_class.py:107:5 - error: Cannot override "x" because parent class "Point" is a named tuple (reportIncompatibleVariableOverride)
+namedtuples_define_class.py:137:19 - error: Argument of type "float" cannot be assigned to parameter "value" of type "str" in function "__new__"
   "float" is not assignable to "str" (reportArgumentType)
-namedtuples_define_class.py:132:7 - error: Multiple inheritance with NamedTuple is not supported (reportGeneralTypeIssues)
+namedtuples_define_class.py:144:7 - error: Multiple inheritance with NamedTuple is not supported (reportGeneralTypeIssues)
 """
 conformance_automated = "Pass"
 errors_diff = """
diff --git a/conformance/results/pyright/typeddicts_class_syntax.toml b/conformance/results/pyright/typeddicts_class_syntax.toml
index b518cd64..5558eb7c 100644
--- a/conformance/results/pyright/typeddicts_class_syntax.toml
+++ b/conformance/results/pyright/typeddicts_class_syntax.toml
@@ -1,11 +1,16 @@
-conformant = "Pass"
+conformant = "Partial"
+notes = """
+Does not support version-conditional items in TypedDict definitions.
+"""
 output = """
-typeddicts_class_syntax.py:29:5 - error: TypedDict classes can contain only type annotations (reportGeneralTypeIssues)
-typeddicts_class_syntax.py:33:5 - error: TypedDict classes can contain only type annotations (reportGeneralTypeIssues)
-typeddicts_class_syntax.py:38:5 - error: TypedDict classes can contain only type annotations (reportGeneralTypeIssues)
-typeddicts_class_syntax.py:44:32 - error: TypedDict does not support __init_subclass__ parameter "metaclass" (reportGeneralTypeIssues)
-typeddicts_class_syntax.py:49:32 - error: TypedDict does not support __init_subclass__ parameter "other" (reportGeneralTypeIssues)
+typeddicts_class_syntax.py:30:5 - error: TypedDict classes can contain only type annotations (reportGeneralTypeIssues)
+typeddicts_class_syntax.py:34:5 - error: TypedDict classes can contain only type annotations (reportGeneralTypeIssues)
+typeddicts_class_syntax.py:39:5 - error: TypedDict classes can contain only type annotations (reportGeneralTypeIssues)
+typeddicts_class_syntax.py:45:32 - error: TypedDict does not support __init_subclass__ parameter "metaclass" (reportGeneralTypeIssues)
+typeddicts_class_syntax.py:50:32 - error: TypedDict does not support __init_subclass__ parameter "other" (reportGeneralTypeIssues)
+typeddicts_class_syntax.py:58:5 - error: TypedDict classes can contain only type annotations (reportGeneralTypeIssues)
 """
-conformance_automated = "Pass"
+conformance_automated = "Fail"
 errors_diff = """
+Line 58: Unexpected errors ['typeddicts_class_syntax.py:58:5 - error: TypedDict classes can contain only type annotations (reportGeneralTypeIssues)']
 """
diff --git a/conformance/results/results.html b/conformance/results/results.html
index b94b97b2..a7aee5b0 100644
--- a/conformance/results/results.html
+++ b/conformance/results/results.html
@@ -936,11 +936,11 @@ <h3>Python Type System Conformance Test Results</h3>
 <th class="column col2 conformant">Pass</th>
 </tr>
 <tr><th class="column col1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;typeddicts_class_syntax</th>
+<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not support version-conditional items in TypedDict definitions.</p></span></div></th>
+<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not support version-conditional items in TypedDict definitions.</p></span></div></th>
+<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not support version-conditional items in TypedDict definitions.</p></span></div></th>
 <th class="column col2 conformant">Pass</th>
-<th class="column col2 conformant">Pass</th>
-<th class="column col2 conformant">Pass</th>
-<th class="column col2 conformant">Pass</th>
-<th class="column col2 conformant">Pass</th>
+<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Errors on version-conditional items in TypedDict definitions.</p></span></div></th>
 </tr>
 <tr><th class="column col1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;typeddicts_extra_items</th>
 <th class="column col2 not-conformant"><div class="hover-text">Unsupported<span class="tooltip-text" id="bottom"><p>Not supported.</p></span></div></th>
@@ -1054,9 +1054,9 @@ <h3>Python Type System Conformance Test Results</h3>
 <a class="test_group" href="https://typing.readthedocs.io/en/latest/spec/namedtuples.html">Named tuples</a>
 </th></tr>
 <tr><th class="column col1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;namedtuples_define_class</th>
-<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not reject override of named tuple attribute in child class.</p></span></div></th>
-<th class="column col2 conformant">Pass</th>
+<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not reject override of named tuple attribute in child class.</p><p>Does not support version-conditional fields.</p></span></div></th>
 <th class="column col2 conformant">Pass</th>
+<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not support version-conditional fields in NamedTuple definitions.</p></span></div></th>
 <th class="column col2 conformant">Pass</th>
 <th class="column col2 conformant">Pass</th>
 </tr>
diff --git a/conformance/results/ty/namedtuples_define_class.toml b/conformance/results/ty/namedtuples_define_class.toml
index fdf613b7..d4222170 100644
--- a/conformance/results/ty/namedtuples_define_class.toml
+++ b/conformance/results/ty/namedtuples_define_class.toml
@@ -2,18 +2,18 @@ conformance_automated = "Pass"
 errors_diff = """
 """
 output = """
-namedtuples_define_class.py:32:7: error[index-out-of-bounds] Index 3 is out of bounds for tuple `Point` with length 3
-namedtuples_define_class.py:33:7: error[index-out-of-bounds] Index -4 is out of bounds for tuple `Point` with length 3
-namedtuples_define_class.py:44:6: error[missing-argument] No argument provided for required parameter `y`
+namedtuples_define_class.py:33:7: error[index-out-of-bounds] Index 3 is out of bounds for tuple `Point` with length 3
+namedtuples_define_class.py:34:7: error[index-out-of-bounds] Index -4 is out of bounds for tuple `Point` with length 3
 namedtuples_define_class.py:45:6: error[missing-argument] No argument provided for required parameter `y`
-namedtuples_define_class.py:46:15: error[invalid-argument-type] Argument is incorrect: Expected `int`, found `Literal[""]`
-namedtuples_define_class.py:47:18: error[invalid-argument-type] Argument is incorrect: Expected `str`, found `Literal[3]`
-namedtuples_define_class.py:48:22: error[too-many-positional-arguments] Too many positional arguments: expected 4, got 5
-namedtuples_define_class.py:49:23: error[unknown-argument] Argument `other` does not match any known parameter
-namedtuples_define_class.py:69:20: error[too-many-positional-arguments] Too many positional arguments: expected 3, got 4
-namedtuples_define_class.py:76:5: error[invalid-named-tuple] NamedTuple field `_y` cannot start with an underscore
-namedtuples_define_class.py:86:5: error[invalid-named-tuple] NamedTuple field without default value cannot follow field(s) with default value(s): Field `latitude` defined here without a default value
-namedtuples_define_class.py:106:5: error[invalid-named-tuple-override] Cannot override NamedTuple field `x` inherited from `Point`
-namedtuples_define_class.py:125:19: error[invalid-argument-type] Argument is incorrect: Expected `str`, found `float`
-namedtuples_define_class.py:132:24: error[invalid-named-tuple] NamedTuple class `Unit` cannot use multiple inheritance except with `Generic[]`
+namedtuples_define_class.py:46:6: error[missing-argument] No argument provided for required parameter `y`
+namedtuples_define_class.py:47:15: error[invalid-argument-type] Argument is incorrect: Expected `int`, found `Literal[""]`
+namedtuples_define_class.py:48:18: error[invalid-argument-type] Argument is incorrect: Expected `str`, found `Literal[3]`
+namedtuples_define_class.py:49:22: error[too-many-positional-arguments] Too many positional arguments: expected 4, got 5
+namedtuples_define_class.py:50:23: error[unknown-argument] Argument `other` does not match any known parameter
+namedtuples_define_class.py:70:20: error[too-many-positional-arguments] Too many positional arguments: expected 3, got 4
+namedtuples_define_class.py:77:5: error[invalid-named-tuple] NamedTuple field `_y` cannot start with an underscore
+namedtuples_define_class.py:87:5: error[invalid-named-tuple] NamedTuple field without default value cannot follow field(s) with default value(s): Field `latitude` defined here without a default value
+namedtuples_define_class.py:107:5: error[invalid-named-tuple-override] Cannot override NamedTuple field `x` inherited from `Point`
+namedtuples_define_class.py:137:19: error[invalid-argument-type] Argument is incorrect: Expected `str`, found `float`
+namedtuples_define_class.py:144:24: error[invalid-named-tuple] NamedTuple class `Unit` cannot use multiple inheritance except with `Generic[]`
 """
diff --git a/conformance/results/ty/typeddicts_class_syntax.toml b/conformance/results/ty/typeddicts_class_syntax.toml
index 691787e7..f5f0a4af 100644
--- a/conformance/results/ty/typeddicts_class_syntax.toml
+++ b/conformance/results/ty/typeddicts_class_syntax.toml
@@ -1,10 +1,16 @@
-conformance_automated = "Pass"
+conformant = "Partial"
+notes = """
+Errors on version-conditional items in TypedDict definitions.
+"""
+conformance_automated = "Fail"
 errors_diff = """
+Line 58: Unexpected errors ['typeddicts_class_syntax.py:58:5: error[invalid-typed-dict-statement] invalid statement in TypedDict class body']
 """
 output = """
-typeddicts_class_syntax.py:29:5: error[invalid-typed-dict-statement] TypedDict class cannot have methods
-typeddicts_class_syntax.py:33:5: error[invalid-typed-dict-statement] TypedDict class cannot have methods
-typeddicts_class_syntax.py:38:5: error[invalid-typed-dict-statement] TypedDict class cannot have methods
-typeddicts_class_syntax.py:44:32: error[invalid-typed-dict-header] Custom metaclasses are not supported in `TypedDict` definitions
-typeddicts_class_syntax.py:49:32: error[unknown-argument] Unknown keyword argument `other` in `TypedDict` definition
+typeddicts_class_syntax.py:30:5: error[invalid-typed-dict-statement] TypedDict class cannot have methods
+typeddicts_class_syntax.py:34:5: error[invalid-typed-dict-statement] TypedDict class cannot have methods
+typeddicts_class_syntax.py:39:5: error[invalid-typed-dict-statement] TypedDict class cannot have methods
+typeddicts_class_syntax.py:45:32: error[invalid-typed-dict-header] Custom metaclasses are not supported in `TypedDict` definitions
+typeddicts_class_syntax.py:50:32: error[unknown-argument] Unknown keyword argument `other` in `TypedDict` definition
+typeddicts_class_syntax.py:58:5: error[invalid-typed-dict-statement] invalid statement in TypedDict class body
 """
diff --git a/conformance/results/zuban/namedtuples_define_class.toml b/conformance/results/zuban/namedtuples_define_class.toml
index e2e3edeb..b54a9d0f 100644
--- a/conformance/results/zuban/namedtuples_define_class.toml
+++ b/conformance/results/zuban/namedtuples_define_class.toml
@@ -1,21 +1,27 @@
+conformant = "Partial"
 notes = """
+Does not support version-conditional fields in NamedTuple definitions.
 """
-conformance_automated = "Pass"
+conformance_automated = "Fail"
 errors_diff = """
+Line 114: Unexpected errors ['namedtuples_define_class.py:114: error: Invalid statement in NamedTuple definition; expected "field_name: field_type [= default]"  [misc]']
+Line 118: Unexpected errors ['namedtuples_define_class.py:118: error: Too many arguments for "ConditionalField"  [call-arg]']
 """
 output = """
-namedtuples_define_class.py:32: error: Tuple index out of range  [misc]
 namedtuples_define_class.py:33: error: Tuple index out of range  [misc]
-namedtuples_define_class.py:44: error: Missing positional argument "y" in call to "Point"  [call-arg]
+namedtuples_define_class.py:34: error: Tuple index out of range  [misc]
 namedtuples_define_class.py:45: error: Missing positional argument "y" in call to "Point"  [call-arg]
-namedtuples_define_class.py:46: error: Argument 2 to "Point" has incompatible type "str"; expected "int"  [arg-type]
-namedtuples_define_class.py:47: error: Argument "units" to "Point" has incompatible type "int"; expected "str"  [arg-type]
-namedtuples_define_class.py:48: error: Too many arguments for "Point"  [call-arg]
-namedtuples_define_class.py:49: error: Unexpected keyword argument "other" for "Point"  [call-arg]
-namedtuples_define_class.py:69: error: Too many arguments for "Point2"  [call-arg]
-namedtuples_define_class.py:76: error: NamedTuple field name cannot start with an underscore: _y  [misc]
-namedtuples_define_class.py:86: error: Non-default NamedTuple fields cannot follow default fields  [misc]
-namedtuples_define_class.py:106: error: NamedTuple attributes cannot be overridden in subclasses  [misc]
-namedtuples_define_class.py:125: error: Argument 2 to "Property" has incompatible type "float"; expected "str"  [arg-type]
-namedtuples_define_class.py:132: error: NamedTuple should be a single base  [misc]
+namedtuples_define_class.py:46: error: Missing positional argument "y" in call to "Point"  [call-arg]
+namedtuples_define_class.py:47: error: Argument 2 to "Point" has incompatible type "str"; expected "int"  [arg-type]
+namedtuples_define_class.py:48: error: Argument "units" to "Point" has incompatible type "int"; expected "str"  [arg-type]
+namedtuples_define_class.py:49: error: Too many arguments for "Point"  [call-arg]
+namedtuples_define_class.py:50: error: Unexpected keyword argument "other" for "Point"  [call-arg]
+namedtuples_define_class.py:70: error: Too many arguments for "Point2"  [call-arg]
+namedtuples_define_class.py:77: error: NamedTuple field name cannot start with an underscore: _y  [misc]
+namedtuples_define_class.py:87: error: Non-default NamedTuple fields cannot follow default fields  [misc]
+namedtuples_define_class.py:107: error: NamedTuple attributes cannot be overridden in subclasses  [misc]
+namedtuples_define_class.py:114: error: Invalid statement in NamedTuple definition; expected "field_name: field_type [= default]"  [misc]
+namedtuples_define_class.py:118: error: Too many arguments for "ConditionalField"  [call-arg]
+namedtuples_define_class.py:137: error: Argument 2 to "Property" has incompatible type "float"; expected "str"  [arg-type]
+namedtuples_define_class.py:144: error: NamedTuple should be a single base  [misc]
 """
diff --git a/conformance/results/zuban/typeddicts_class_syntax.toml b/conformance/results/zuban/typeddicts_class_syntax.toml
index 68741c76..588fe869 100644
--- a/conformance/results/zuban/typeddicts_class_syntax.toml
+++ b/conformance/results/zuban/typeddicts_class_syntax.toml
@@ -1,10 +1,18 @@
-conformance_automated = "Pass"
+conformant = "Partial"
+notes = """
+Does not support version-conditional items in TypedDict definitions.
+"""
+conformance_automated = "Fail"
 errors_diff = """
+Line 58: Unexpected errors ['typeddicts_class_syntax.py:58: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]']
+Line 62: Unexpected errors ['typeddicts_class_syntax.py:62: error: Extra key "y" for TypedDict "ConditionalField"  [typeddict-unknown-key]']
 """
 output = """
-typeddicts_class_syntax.py:29: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]
-typeddicts_class_syntax.py:33: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]
-typeddicts_class_syntax.py:38: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]
-typeddicts_class_syntax.py:44: error: Unexpected keyword argument "metaclass" for "TypedDict"  [call-arg]
-typeddicts_class_syntax.py:49: error: Unexpected keyword argument "other" for "TypedDict"  [call-arg]
+typeddicts_class_syntax.py:30: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]
+typeddicts_class_syntax.py:34: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]
+typeddicts_class_syntax.py:39: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]
+typeddicts_class_syntax.py:45: error: Unexpected keyword argument "metaclass" for "TypedDict"  [call-arg]
+typeddicts_class_syntax.py:50: error: Unexpected keyword argument "other" for "TypedDict"  [call-arg]
+typeddicts_class_syntax.py:58: error: Invalid statement in TypedDict definition; expected "field_name: field_type"  [misc]
+typeddicts_class_syntax.py:62: error: Extra key "y" for TypedDict "ConditionalField"  [typeddict-unknown-key]
 """
diff --git a/conformance/tests/namedtuples_define_class.py b/conformance/tests/namedtuples_define_class.py
index 5e6e9c4c..bf6acc2c 100644
--- a/conformance/tests/namedtuples_define_class.py
+++ b/conformance/tests/namedtuples_define_class.py
@@ -7,6 +7,7 @@
 # > Type checkers should support the class syntax
 
 from typing import Generic, NamedTuple, TypeVar, assert_type
+import sys
 
 
 class Point(NamedTuple):
@@ -105,6 +106,17 @@ class BadPointWithName(Point):
     name: str = ""  # OK
     x: int = 0  # E
 
+# > Namedtuple fields may be conditional, via checks of the same statically-known
+# > conditions that a type-checker understands elsewhere, such as Python version::
+
+class ConditionalField(NamedTuple):
+    x: int
+    if sys.version_info >= (3, 12):
+        y: str
+
+# The conformance suite runs type checkers configured to Python 3.12 or later:
+ConditionalField(1, "hello")
+
 
 # > In Python 3.11 and newer, the class syntax supports generic named tuple classes.
 # > Type checkers should support this.
diff --git a/conformance/tests/typeddicts_class_syntax.py b/conformance/tests/typeddicts_class_syntax.py
index b83f50bf..f281fc84 100644
--- a/conformance/tests/typeddicts_class_syntax.py
+++ b/conformance/tests/typeddicts_class_syntax.py
@@ -5,6 +5,7 @@
 # Specification: https://typing.readthedocs.io/en/latest/spec/typeddict.html#typeddict
 
 from typing import Generic, TypeVar, TypedDict
+import sys
 
 
 class Movie(TypedDict):
@@ -49,6 +50,17 @@ class BadTypedDict2(TypedDict, metaclass=type):  # E
 class BadTypedDict3(TypedDict, other=True):  # E
     name: str
 
+# > `if` conditions that the type checker is able to
+# > statically evaluate are also permitted (e.g. `if sys.version_info > (3, 14)`),
+# > in order to specify items that exist only under the given conditions.
+class ConditionalField(TypedDict):
+    x: int
+    if sys.version_info >= (3, 12):
+        y: str
+
+# The conformance suite runs type checkers configured to Python 3.12 or later:
+ConditionalField(x=1, y="hello")
+
 
 # > TypedDicts may be made generic by adding Generic[T] among the bases.
 T = TypeVar("T")
diff --git a/docs/spec/namedtuples.rst b/docs/spec/namedtuples.rst
index 5ccf9d5b..87a6e433 100644
--- a/docs/spec/namedtuples.rst
+++ b/docs/spec/namedtuples.rst
@@ -54,6 +54,15 @@ in the base class::
         name: str  # OK
         x: int  # Type error (invalid override of named tuple field)
 
+Namedtuple fields may be conditional, via checks of the same
+:ref:`statically-known conditions<version-and-platform-checks>`
+that a type-checker understands elsewhere, such as Python version::
+
+    class ConditionalField(NamedTuple):
+        x: int
+        if sys.version_info >= (3, 14):
+            y: str
+
 In Python 3.11 and newer, the class syntax supports generic named tuple classes.
 Type checkers should support this::
 
diff --git a/docs/spec/typeddict.rst b/docs/spec/typeddict.rst
index 81b72ea9..cff7e849 100644
--- a/docs/spec/typeddict.rst
+++ b/docs/spec/typeddict.rst
@@ -122,10 +122,15 @@ in the class definition:
   :term:`read-only`. Other type qualifiers are not allowed. If the extra items type
   is ``Never``, no extra items are allowed, so this is equivalent to ``closed=True``.
 
-The body of the class definition defines the :term:`items <item>` of the TypedDict type.
-It may also contain a docstring or ``pass`` statements (primarily to allow the creation of
-an empty TypedDict). No other statements are allowed, and type checkers should report an
-error if any are present. Type comments are not supported for creating TypedDict items.
+The body of the class definition defines the :term:`items <item>` of the
+TypedDict type. It may also contain a docstring or ``pass`` statements
+(primarily to allow the creation of an empty TypedDict). `if` conditions that
+the type checker is able to
+:ref:`statically evaluate<version-and-platform-checks>` are also permitted (e.g.
+`if sys.version_info > (3, 14)`), in order to specify items that exist only under
+the given conditions. No other statements are allowed, and type checkers should
+report an error if any are present. Type comments are not supported for
+creating TypedDict items.
 
 .. _`required-notrequired`:
 .. _`required`: