diff --git a/conformance/results/mypy/specialtypes_promotions.toml b/conformance/results/mypy/specialtypes_promotions.toml
index 864bc73e..04499e86 100644
--- a/conformance/results/mypy/specialtypes_promotions.toml
+++ b/conformance/results/mypy/specialtypes_promotions.toml
@@ -1,7 +1,12 @@
-conformant = "Pass"
+conformant = "Partial"
+notes = """
+Does not narrow from float to int after isinstance() check
+"""
 output = """
-specialtypes_promotions.py:13: error: "float" has no attribute "numerator"  [attr-defined]
+specialtypes_promotions.py:17: error: "float" has no attribute "numerator"  [attr-defined]
+specialtypes_promotions.py:33: error: Incompatible return value type (got "complex", expected "float")  [return-value]
 """
-conformance_automated = "Pass"
+conformance_automated = "Fail"
 errors_diff = """
+Line 26: Expected 1 errors
 """
diff --git a/conformance/results/pyre/specialtypes_promotions.toml b/conformance/results/pyre/specialtypes_promotions.toml
index fb9055fb..f17ad77f 100644
--- a/conformance/results/pyre/specialtypes_promotions.toml
+++ b/conformance/results/pyre/specialtypes_promotions.toml
@@ -1,10 +1,13 @@
 conformant = "Partial"
 notes = """
 Does not reject use of attribute that is compatible only with float.
+Does not narrow from float to int after isinstance() check
 """
 output = """
+specialtypes_promotions.py:33:8 Incompatible return type [7]: Expected `float` but got `complex`.
 """
 conformance_automated = "Fail"
 errors_diff = """
-Line 13: Expected 1 errors
+Line 17: Expected 1 errors
+Line 26: Expected 1 errors
 """
diff --git a/conformance/results/pyre/version.toml b/conformance/results/pyre/version.toml
index c759e78d..6221116b 100644
--- a/conformance/results/pyre/version.toml
+++ b/conformance/results/pyre/version.toml
@@ -1,2 +1,2 @@
 version = "pyre 0.9.23"
-test_duration = 10.7
+test_duration = 10.4
diff --git a/conformance/results/pyright/specialtypes_promotions.toml b/conformance/results/pyright/specialtypes_promotions.toml
index 20daf3a3..dbe43b05 100644
--- a/conformance/results/pyright/specialtypes_promotions.toml
+++ b/conformance/results/pyright/specialtypes_promotions.toml
@@ -1,7 +1,11 @@
 conformant = "Pass"
 output = """
-specialtypes_promotions.py:13:7 - error: Cannot access attribute "numerator" for class "float"
+specialtypes_promotions.py:17:7 - error: Cannot access attribute "numerator" for class "float"
   Attribute "numerator" is unknown (reportAttributeAccessIssue)
+specialtypes_promotions.py:26:16 - error: Type "Literal['x']" is not assignable to return type "int"
+  "Literal['x']" is not assignable to "int" (reportReturnType)
+specialtypes_promotions.py:33:16 - error: Type "complex" is not assignable to return type "float"
+  "complex" is not assignable to "float" (reportReturnType)
 """
 conformance_automated = "Pass"
 errors_diff = """
diff --git a/conformance/results/pyright/version.toml b/conformance/results/pyright/version.toml
index ca4eb79c..6686c4e5 100644
--- a/conformance/results/pyright/version.toml
+++ b/conformance/results/pyright/version.toml
@@ -1,2 +1,2 @@
 version = "pyright 1.1.402"
-test_duration = 1.8
+test_duration = 1.5
diff --git a/conformance/results/results.html b/conformance/results/results.html
index 4cc4ea00..c60166c0 100644
--- a/conformance/results/results.html
+++ b/conformance/results/results.html
@@ -162,10 +162,10 @@ <h3>Python Type System Conformance Test Results</h3>
 <div class='tc-time'>2.2sec</div>
 </th>
 <th class='tc-header'><div class='tc-name'>pyright 1.1.402</div>
-<div class='tc-time'>1.8sec</div>
+<div class='tc-time'>1.5sec</div>
 </th>
 <th class='tc-header'><div class='tc-name'>pyre 0.9.23</div>
-<div class='tc-time'>10.7sec</div>
+<div class='tc-time'>10.4sec</div>
 </th>
 </tr>
 <tr><th class="column" colspan="4">
@@ -215,9 +215,9 @@ <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;specialtypes_promotions</th>
+<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not narrow from float to int after isinstance() check</p></span></div></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>Does not reject use of attribute that is compatible only with float.</p></span></div></th>
+<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not reject use of attribute that is compatible only with float.</p><p>Does not narrow from float to int after isinstance() check</p></span></div></th>
 </tr>
 <tr><th class="column col1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;specialtypes_type</th>
 <th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Does not treat `type` same as `type[Any]` for assert_type.</p><p>Does not allow access to unknown attributes from object of type `type[Any]`.</p></span></div></th>
@@ -324,7 +324,7 @@ <h3>Python Type System Conformance Test Results</h3>
 </tr>
 <tr><th class="column col1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;generics_type_erasure</th>
 <th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Infers Node[Never] instead of Node[Any] when argument is not provided.</p><p>False negative on instance attribute access on type(node).</p></span></div></th>
-<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>Missing error regarding `type(instance).generic_attribute`.</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 erase unspecified type variables to `Any` prior to `assert_type` handling.</p><p>False negatives on instance attribute access on the type.</p><p>Does not infer type of `DefaultDict` with explicit type parameters on constructor.</p><p>False negatives on assert_type uses.</p></span></div></th>
 </tr>
 <tr><th class="column col1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;generics_typevartuple_args</th>
@@ -423,7 +423,7 @@ <h3>Python Type System Conformance Test Results</h3>
 </tr>
 <tr><th class="column col1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;aliases_newtype</th>
 <th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>`NewType`s are considered classes, not functions.</p></span></div></th>
-<th class="column col2 partially-conformant"><div class="hover-text">Partial<span class="tooltip-text" id="bottom"><p>`NewType`s are considered classes, not functions.</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 use of NewType in `isinstance` call.</p><p>Does not reject use of NewType in class definition statement.</p><p>Does not report inconsistency between name of NewType and assigned identifier name.</p><p>Does not reject use of NewType with generic class with TypeVar.</p><p>Does not reject use of NewType with protocol class.</p><p>Does not reject use of NewType with TypedDict class.</p><p>Does not reject use of NewType with Any.</p></span></div></th>
 </tr>
 <tr><th class="column col1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;aliases_recursive</th>
diff --git a/conformance/tests/specialtypes_promotions.py b/conformance/tests/specialtypes_promotions.py
index fc51e133..0216337d 100644
--- a/conformance/tests/specialtypes_promotions.py
+++ b/conformance/tests/specialtypes_promotions.py
@@ -2,15 +2,36 @@
 Tests "type promotions" for float and complex when they appear in annotations.
 """
 
+from typing import assert_type
+
 # Specification: https://typing.readthedocs.io/en/latest/spec/special-types.html#special-cases-for-float-and-complex
 
-v1: float = 1
-v2: complex = 1.2
-v2 = 1
+v1: int = 1
+v2: float = 1
+v3: float = v1
+v4: complex = 1.2
+v4 = 1
+
+
+def func1(f: float) -> int:
+    f.numerator  # E: attribute exists on int but not float
 
+    if isinstance(f, float):
+        f.hex()  # OK (attribute exists on float but not int)
+        return 1
+    else:
+        assert_type(f, int)
+        # Make sure type checkers don't treat this branch as unreachable
+        # and skip checking it.
+        return "x"  # E
 
-def func1(f: float):
-    f.numerator  # E
 
-    if not isinstance(f, float):
-        f.numerator  # OK
+def func2(x: int) -> float:
+    if x == 0:
+        return 1
+    elif x == 1:
+        return 1j  # E
+    elif x > 10:
+        return x
+    else:
+        return 1.0
diff --git a/docs/spec/special-types.rst b/docs/spec/special-types.rst
index ce6f336b..5d1229e4 100644
--- a/docs/spec/special-types.rst
+++ b/docs/spec/special-types.rst
@@ -110,11 +110,25 @@ Special cases for ``float`` and ``complex``
 
 Python's numeric types ``complex``, ``float`` and ``int`` are not
 subtypes of each other, but to support common use cases, the type
-system contains a straightforward shortcut:
-when an argument is annotated as having
-type ``float``, an argument of type ``int`` is acceptable; similar,
-for an argument annotated as having type ``complex``, arguments of
-type ``float`` or ``int`` are acceptable.
+system contains a special case.
+
+When a reference to the built-in type ``float`` appears in a :term:`type expression`,
+it is interpreted as if it were a union of the built-in types ``float`` and ``int``.
+Similarly, when a reference to the type ``complex`` appears, it is interpreted as
+a union of the built-in types ``complex``, ``float`` and ``int``.
+These implicit unions behave exactly like the corresponding explicit union types,
+but type checkers may choose to display them differently in user-visible output
+for clarity.
+
+Type checkers should support narrowing the type of a variable to exactly ``float``
+or ``int``, without the implicit union, through a call to ``isinstance()``::
+
+  def f(x: float) -> None:
+      reveal_type(x)  # float | int, but type checkers may display just "float"
+      if isinstance(x, float):
+          reveal_type(x)  # float
+      else:
+          reveal_type(x)  # int
 
 .. _`type-brackets`: