diff --git a/src/Analyser/MutatingScope.php b/src/Analyser/MutatingScope.php
index 7a3ab4c970b..26280cdf852 100644
--- a/src/Analyser/MutatingScope.php
+++ b/src/Analyser/MutatingScope.php
@@ -1406,13 +1406,11 @@ private function resolveType(Expr $node): Type
 				return new ErrorType();
 			}
 
-			if (($leftType->isString()->yes() && !$leftType->isNumericString()->yes())
-				|| ($rightType->isString()->yes() && !$rightType->isNumericString()->yes())) {
-				return new ErrorType();
-			}
-
 			$leftNumberType = $leftType->toNumber();
 			$rightNumberType = $rightType->toNumber();
+			if ($leftNumberType instanceof ErrorType || $rightNumberType instanceof ErrorType) {
+				return new ErrorType();
+			}
 
 			if (
 				(new FloatType())->isSuperTypeOf($leftNumberType)->yes()
diff --git a/src/PhpDoc/PhpDocNodeResolver.php b/src/PhpDoc/PhpDocNodeResolver.php
index 845b9d31499..4aa27304236 100644
--- a/src/PhpDoc/PhpDocNodeResolver.php
+++ b/src/PhpDoc/PhpDocNodeResolver.php
@@ -279,7 +279,7 @@ public function resolveTemplateTags(PhpDocNode $phpDocNode, NameScope $nameScope
 
 			$resolved[$valueNode->name] = new TemplateTag(
 				$valueNode->name,
-				$valueNode->bound !== null ? $this->typeNodeResolver->resolve($valueNode->bound, $nameScope->unsetTemplateType($valueNode->name)) : new MixedType(),
+				$valueNode->bound !== null ? $this->typeNodeResolver->resolve($valueNode->bound, $nameScope->unsetTemplateType($valueNode->name)) : new MixedType(true),
 				$variance,
 			);
 			$resolvedPrefix[$valueNode->name] = $prefix;
diff --git a/src/Reflection/ClassReflection.php b/src/Reflection/ClassReflection.php
index 73f33b9a562..7be2d1651a8 100644
--- a/src/Reflection/ClassReflection.php
+++ b/src/Reflection/ClassReflection.php
@@ -82,6 +82,8 @@ class ClassReflection
 
 	private ?TemplateTypeMap $templateTypeMap = null;
 
+	private ?TemplateTypeMap $activeTemplateTypeMap = null;
+
 	/** @var array<string,ClassReflection>|null */
 	private ?array $ancestors = null;
 
@@ -181,7 +183,8 @@ public function getParentClass(): ?ClassReflection
 			if ($this->isGeneric()) {
 				$extendedType = TemplateTypeHelper::resolveTemplateTypes(
 					$extendedType,
-					$this->getActiveTemplateTypeMap(),
+					$this->getPossiblyIncompleteActiveTemplateTypeMap(),
+					true,
 				);
 			}
 
@@ -195,7 +198,7 @@ public function getParentClass(): ?ClassReflection
 		$parentReflection = $this->reflectionProvider->getClass($parentClass->getName());
 		if ($parentReflection->isGeneric()) {
 			return $parentReflection->withTypes(
-				array_values($parentReflection->getTemplateTypeMap()->resolveToBounds()->getTypes()),
+				array_values($parentReflection->getTemplateTypeMap()->map(static fn (): Type => new ErrorType())->getTypes()),
 			);
 		}
 
@@ -224,7 +227,7 @@ public function getDisplayName(bool $withTemplateTypes = true): string
 			return $name;
 		}
 
-		return $name . '<' . implode(',', array_map(static fn (Type $type): string => $type->describe(VerbosityLevel::typeOnly()), $this->resolvedTemplateTypeMap->getTypes())) . '>';
+		return $name . '<' . implode(',', array_map(static fn (Type $type): string => $type->describe(VerbosityLevel::typeOnly()), $this->getActiveTemplateTypeMap()->getTypes())) . '>';
 	}
 
 	public function getCacheKey(): string
@@ -728,7 +731,8 @@ public function getImmediateInterfaces(): array
 				if ($this->isGeneric()) {
 					$implementedType = TemplateTypeHelper::resolveTemplateTypes(
 						$implementedType,
-						$this->getActiveTemplateTypeMap(),
+						$this->getPossiblyIncompleteActiveTemplateTypeMap(),
+						true,
 					);
 				}
 
@@ -743,7 +747,7 @@ public function getImmediateInterfaces(): array
 
 			if ($immediateInterface->isGeneric()) {
 				$immediateInterfaces[$immediateInterface->getName()] = $immediateInterface->withTypes(
-					array_values($immediateInterface->getTemplateTypeMap()->resolveToBounds()->getTypes()),
+					array_values($immediateInterface->getTemplateTypeMap()->map(static fn (): Type => new ErrorType())->getTypes()),
 				);
 				continue;
 			}
@@ -1057,6 +1061,29 @@ public function getTemplateTypeMap(): TemplateTypeMap
 	}
 
 	public function getActiveTemplateTypeMap(): TemplateTypeMap
+	{
+		if ($this->activeTemplateTypeMap !== null) {
+			return $this->activeTemplateTypeMap;
+		}
+		$resolved = $this->resolvedTemplateTypeMap;
+		if ($resolved !== null) {
+			$templateTypeMap = $this->getTemplateTypeMap();
+			return $this->activeTemplateTypeMap = $resolved->map(static function (string $name, Type $type) use ($templateTypeMap): Type {
+				if ($type instanceof ErrorType) {
+					$templateType = $templateTypeMap->getType($name);
+					if ($templateType !== null) {
+						return TemplateTypeHelper::resolveToBounds($templateType);
+					}
+				}
+
+				return $type;
+			});
+		}
+
+		return $this->activeTemplateTypeMap = $this->getTemplateTypeMap();
+	}
+
+	public function getPossiblyIncompleteActiveTemplateTypeMap(): TemplateTypeMap
 	{
 		return $this->resolvedTemplateTypeMap ?? $this->getTemplateTypeMap();
 	}
diff --git a/src/Type/Accessory/AccessoryLiteralStringType.php b/src/Type/Accessory/AccessoryLiteralStringType.php
index 9eb9e3d6cd7..1c8a9bc81d7 100644
--- a/src/Type/Accessory/AccessoryLiteralStringType.php
+++ b/src/Type/Accessory/AccessoryLiteralStringType.php
@@ -130,10 +130,7 @@ public function isArray(): TrinaryLogic
 
 	public function toNumber(): Type
 	{
-		return new UnionType([
-			$this->toInteger(),
-			$this->toFloat(),
-		]);
+		return new ErrorType();
 	}
 
 	public function toInteger(): Type
diff --git a/src/Type/Accessory/AccessoryNonEmptyStringType.php b/src/Type/Accessory/AccessoryNonEmptyStringType.php
index 0219866213b..7e17a4f5248 100644
--- a/src/Type/Accessory/AccessoryNonEmptyStringType.php
+++ b/src/Type/Accessory/AccessoryNonEmptyStringType.php
@@ -131,10 +131,7 @@ public function isArray(): TrinaryLogic
 
 	public function toNumber(): Type
 	{
-		return new UnionType([
-			$this->toInteger(),
-			$this->toFloat(),
-		]);
+		return new ErrorType();
 	}
 
 	public function toInteger(): Type
diff --git a/src/Type/FileTypeMapper.php b/src/Type/FileTypeMapper.php
index a72aa670ee4..228adf69e55 100644
--- a/src/Type/FileTypeMapper.php
+++ b/src/Type/FileTypeMapper.php
@@ -180,7 +180,7 @@ private function resolvePhpDocStringToDocNode(string $phpDocString): PhpDocNode
 	private function getNameScopeMap(string $fileName): array
 	{
 		if (!isset($this->memoryCache[$fileName])) {
-			$cacheKey = sprintf('%s-phpdocstring-v20-template-tags', $fileName);
+			$cacheKey = sprintf('%s-phpdocstring-v21-explicit-mixed', $fileName);
 			$variableCacheKey = sprintf('%s-%s', implode(',', array_map(static fn (array $file): string => sprintf('%s-%d', $file['filename'], $file['modifiedTime']), $this->getCachedDependentFilesWithTimestamps($fileName))), $this->phpVersion->getVersionString());
 			$map = $this->cache->load($cacheKey, $variableCacheKey);
 
diff --git a/src/Type/Generic/TemplateTypeHelper.php b/src/Type/Generic/TemplateTypeHelper.php
index 6d5d6335745..f8e72514cf6 100644
--- a/src/Type/Generic/TemplateTypeHelper.php
+++ b/src/Type/Generic/TemplateTypeHelper.php
@@ -12,16 +12,16 @@ class TemplateTypeHelper
 	/**
 	 * Replaces template types with standin types
 	 */
-	public static function resolveTemplateTypes(Type $type, TemplateTypeMap $standins): Type
+	public static function resolveTemplateTypes(Type $type, TemplateTypeMap $standins, bool $keepErrorTypes = false): Type
 	{
-		return TypeTraverser::map($type, static function (Type $type, callable $traverse) use ($standins): Type {
+		return TypeTraverser::map($type, static function (Type $type, callable $traverse) use ($standins, $keepErrorTypes): Type {
 			if ($type instanceof TemplateType && !$type->isArgument()) {
 				$newType = $standins->getType($type->getName());
 				if ($newType === null) {
 					return $traverse($type);
 				}
 
-				if ($newType instanceof ErrorType) {
+				if ($newType instanceof ErrorType && !$keepErrorTypes) {
 					return $traverse($type->getBound());
 				}
 
diff --git a/src/Type/Generic/TemplateTypeMap.php b/src/Type/Generic/TemplateTypeMap.php
index b298c9c8c2d..f807e3d65e2 100644
--- a/src/Type/Generic/TemplateTypeMap.php
+++ b/src/Type/Generic/TemplateTypeMap.php
@@ -2,7 +2,6 @@
 
 namespace PHPStan\Type\Generic;
 
-use PHPStan\Type\MixedType;
 use PHPStan\Type\NeverType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
@@ -16,6 +15,8 @@ class TemplateTypeMap
 
 	private static ?TemplateTypeMap $empty = null;
 
+	private ?TemplateTypeMap $resolvedToBounds = null;
+
 	/**
 	 * @api
 	 * @param array<string, Type> $types
@@ -204,14 +205,10 @@ public function map(callable $cb): self
 
 	public function resolveToBounds(): self
 	{
-		return $this->map(static function (string $name, Type $type): Type {
-			$type = TemplateTypeHelper::resolveToBounds($type);
-			if ($type instanceof MixedType && $type->isExplicitMixed()) {
-				return new MixedType(false);
-			}
-
-			return $type;
-		});
+		if ($this->resolvedToBounds !== null) {
+			return $this->resolvedToBounds;
+		}
+		return $this->resolvedToBounds = $this->map(static fn (string $name, Type $type): Type => TemplateTypeHelper::resolveToBounds($type));
 	}
 
 	/**
diff --git a/src/Type/GenericTypeVariableResolver.php b/src/Type/GenericTypeVariableResolver.php
index 76551343e0c..17cabf4bd77 100644
--- a/src/Type/GenericTypeVariableResolver.php
+++ b/src/Type/GenericTypeVariableResolver.php
@@ -2,6 +2,8 @@
 
 namespace PHPStan\Type;
 
+use PHPStan\Type\Generic\TemplateTypeHelper;
+
 /** @api */
 class GenericTypeVariableResolver
 {
@@ -12,19 +14,37 @@ public static function getType(
 		string $typeVariableName,
 	): ?Type
 	{
-		$ancestor = $type->getAncestorWithClassName($genericClassName);
-		if ($ancestor === null) {
+		$classReflection = $type->getClassReflection();
+		if ($classReflection === null) {
 			return null;
 		}
-
-		$classReflection = $ancestor->getClassReflection();
-		if ($classReflection === null) {
+		$ancestorClassReflection = $classReflection->getAncestorWithClassName($genericClassName);
+		if ($ancestorClassReflection === null) {
 			return null;
 		}
 
-		$templateTypeMap = $classReflection->getActiveTemplateTypeMap();
+		$activeTemplateTypeMap = $ancestorClassReflection->getPossiblyIncompleteActiveTemplateTypeMap();
+
+		// todo if type is not defined, return the bound
+		// in case of mixed bound, return implicit mixed
+
+		$type = $activeTemplateTypeMap->getType($typeVariableName);
+		if ($type instanceof ErrorType) {
+			$templateTypeMap = $ancestorClassReflection->getTemplateTypeMap();
+			$templateType = $templateTypeMap->getType($typeVariableName);
+			if ($templateType === null) {
+				return $type;
+			}
+
+			$bound = TemplateTypeHelper::resolveToBounds($templateType);
+			if ($bound instanceof MixedType && $bound->isExplicitMixed()) {
+				return new MixedType(false);
+			}
+
+			return $bound;
+		}
 
-		return $templateTypeMap->getType($typeVariableName);
+		return $type;
 	}
 
 }
diff --git a/src/Type/ObjectType.php b/src/Type/ObjectType.php
index 920631de840..eb0f9265989 100644
--- a/src/Type/ObjectType.php
+++ b/src/Type/ObjectType.php
@@ -1110,7 +1110,7 @@ public function getClassReflection(): ?ClassReflection
 
 		$classReflection = $reflectionProvider->getClass($this->className);
 		if ($classReflection->isGeneric()) {
-			return $classReflection->withTypes(array_values($classReflection->getTemplateTypeMap()->resolveToBounds()->getTypes()));
+			return $classReflection->withTypes(array_values($classReflection->getTemplateTypeMap()->map(static fn (): Type => new ErrorType())->getTypes()));
 		}
 
 		return $classReflection;
diff --git a/src/Type/UnionType.php b/src/Type/UnionType.php
index fb76f4d1128..95c12bb7562 100644
--- a/src/Type/UnionType.php
+++ b/src/Type/UnionType.php
@@ -481,12 +481,12 @@ public function isCloneable(): TrinaryLogic
 
 	public function isSmallerThan(Type $otherType): TrinaryLogic
 	{
-		return $this->unionResults(static fn (Type $type): TrinaryLogic => $type->isSmallerThan($otherType));
+		return $this->notBenevolentUnionResults(static fn (Type $type): TrinaryLogic => $type->isSmallerThan($otherType));
 	}
 
 	public function isSmallerThanOrEqual(Type $otherType): TrinaryLogic
 	{
-		return $this->unionResults(static fn (Type $type): TrinaryLogic => $type->isSmallerThanOrEqual($otherType));
+		return $this->notBenevolentUnionResults(static fn (Type $type): TrinaryLogic => $type->isSmallerThanOrEqual($otherType));
 	}
 
 	public function getSmallerType(): Type
@@ -511,12 +511,12 @@ public function getGreaterOrEqualType(): Type
 
 	public function isGreaterThan(Type $otherType): TrinaryLogic
 	{
-		return $this->unionResults(static fn (Type $type): TrinaryLogic => $otherType->isSmallerThan($type));
+		return $this->notBenevolentUnionResults(static fn (Type $type): TrinaryLogic => $otherType->isSmallerThan($type));
 	}
 
 	public function isGreaterThanOrEqual(Type $otherType): TrinaryLogic
 	{
-		return $this->unionResults(static fn (Type $type): TrinaryLogic => $otherType->isSmallerThanOrEqual($type));
+		return $this->notBenevolentUnionResults(static fn (Type $type): TrinaryLogic => $otherType->isSmallerThanOrEqual($type));
 	}
 
 	public function toBoolean(): BooleanType
@@ -671,6 +671,14 @@ protected function unionResults(callable $getResult): TrinaryLogic
 		return TrinaryLogic::extremeIdentity(...array_map($getResult, $this->types));
 	}
 
+	/**
+	 * @param callable(Type $type): TrinaryLogic $getResult
+	 */
+	private function notBenevolentUnionResults(callable $getResult): TrinaryLogic
+	{
+		return TrinaryLogic::extremeIdentity(...array_map($getResult, $this->types));
+	}
+
 	/**
 	 * @param callable(Type $type): Type $getType
 	 */
diff --git a/tests/PHPStan/Analyser/NodeScopeResolverTest.php b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
index f27e9107b67..6e411d150c9 100644
--- a/tests/PHPStan/Analyser/NodeScopeResolverTest.php
+++ b/tests/PHPStan/Analyser/NodeScopeResolverTest.php
@@ -726,6 +726,8 @@ public function dataFileAsserts(): iterable
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/countable.php');
 
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6696.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/../Rules/Methods/data/filter-iterator-child-class.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/smaller-than-benevolent.php');
 	}
 
 	/**
diff --git a/tests/PHPStan/Analyser/data/bug-2676.php b/tests/PHPStan/Analyser/data/bug-2676.php
index 4daa2b55525..30723db8a9d 100644
--- a/tests/PHPStan/Analyser/data/bug-2676.php
+++ b/tests/PHPStan/Analyser/data/bug-2676.php
@@ -39,7 +39,7 @@ function (Wallet $wallet): void
 	assertType('DoctrineIntersectionTypeIsSupertypeOf\Collection&iterable<Bug2676\BankAccount>', $bankAccounts);
 
 	foreach ($bankAccounts as $key => $bankAccount) {
-		assertType('(int|string)', $key);
+		assertType('mixed', $key);
 		assertType('Bug2676\BankAccount', $bankAccount);
 	}
 };
diff --git a/tests/PHPStan/Analyser/data/smaller-than-benevolent.php b/tests/PHPStan/Analyser/data/smaller-than-benevolent.php
new file mode 100644
index 00000000000..6a43d008b9c
--- /dev/null
+++ b/tests/PHPStan/Analyser/data/smaller-than-benevolent.php
@@ -0,0 +1,35 @@
+<?php
+
+namespace SmallerThanBenevolent;
+
+use function PHPStan\Testing\assertType;
+
+class Foo
+{
+
+	/**
+	 * @param int[] $a
+	 * @return void
+	 */
+	public function doFoo(array $a)
+	{
+		uksort($a, function ($x, $y): int {
+			assertType('(int|string)', $x);
+			assertType('(int|string)', $y);
+			if ($x === 31 || $y === 31) {
+				return 1;
+			}
+
+			assertType('(int<min, 30>|int<32, max>|string)', $x);
+			assertType('(int<min, 30>|int<32, max>|string)', $y);
+
+			assertType('bool', $x < $y);
+			assertType('bool', $x <= $y);
+			assertType('bool', $x > $y);
+			assertType('bool', $x >= $y);
+
+			return $x < $y ? 1 : -1;
+		});
+	}
+
+}
diff --git a/tests/PHPStan/Rules/Generics/ClassAncestorsRuleTest.php b/tests/PHPStan/Rules/Generics/ClassAncestorsRuleTest.php
index 3f9ed11fec0..fda1c25d6f7 100644
--- a/tests/PHPStan/Rules/Generics/ClassAncestorsRuleTest.php
+++ b/tests/PHPStan/Rules/Generics/ClassAncestorsRuleTest.php
@@ -95,6 +95,11 @@ public function testRuleExtends(): void
 				'Template type T is declared as covariant, but occurs in invariant position in extended type ClassAncestorsExtends\FooGeneric8<T, T> of class ClassAncestorsExtends\FooGeneric9.',
 				192,
 			],
+			[
+				'Class ClassAncestorsExtends\FilterIteratorChild extends generic class FilterIterator but does not specify its types: TKey, TValue, TIterator',
+				197,
+				'You can turn this off by setting <fg=cyan>checkGenericClassInNonGenericObjectType: false</> in your <fg=cyan>%configurationFile%</>.',
+			],
 		]);
 	}
 
diff --git a/tests/PHPStan/Rules/Generics/data/class-ancestors-extends.php b/tests/PHPStan/Rules/Generics/data/class-ancestors-extends.php
index 62a1cd93034..caa906001a5 100644
--- a/tests/PHPStan/Rules/Generics/data/class-ancestors-extends.php
+++ b/tests/PHPStan/Rules/Generics/data/class-ancestors-extends.php
@@ -193,3 +193,13 @@ class FooGeneric9 extends FooGeneric8
 {
 
 }
+
+class FilterIteratorChild extends \FilterIterator
+{
+
+	public function accept()
+	{
+		return true;
+	}
+
+}
diff --git a/tests/PHPStan/Rules/Methods/MissingMethodParameterTypehintRuleTest.php b/tests/PHPStan/Rules/Methods/MissingMethodParameterTypehintRuleTest.php
index 45729c7ba72..28be69c2fa3 100644
--- a/tests/PHPStan/Rules/Methods/MissingMethodParameterTypehintRuleTest.php
+++ b/tests/PHPStan/Rules/Methods/MissingMethodParameterTypehintRuleTest.php
@@ -121,4 +121,9 @@ public function testBug6472(): void
 		$this->analyse([__DIR__ . '/data/bug-6472.php'], []);
 	}
 
+	public function testFilterIteratorChildClass(): void
+	{
+		$this->analyse([__DIR__ . '/data/filter-iterator-child-class.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Methods/data/filter-iterator-child-class.php b/tests/PHPStan/Rules/Methods/data/filter-iterator-child-class.php
new file mode 100644
index 00000000000..ee92479f4df
--- /dev/null
+++ b/tests/PHPStan/Rules/Methods/data/filter-iterator-child-class.php
@@ -0,0 +1,94 @@
+<?php declare(strict_types=1);
+
+namespace FilterIteratorChild;
+
+use function PHPStan\Testing\assertType;
+
+class ArchivableFilesFinder extends \FilterIterator
+{
+
+	public function __construct()
+	{
+		parent::__construct(new \ArrayIterator([]));
+	}
+
+	public function accept(): bool
+	{
+		return true;
+	}
+}
+
+class ArchivableFilesFinderTest
+{
+
+	public function doFoo(ArchivableFilesFinder $finder): void
+	{
+		foreach ($finder as $f) {
+			assertType('mixed', $f);
+		}
+	}
+
+}
+
+interface IteratorChild extends \Iterator
+{
+
+	/** @return int */
+	#[\ReturnTypeWillChange]
+	public function key();
+
+	/** @return int */
+	#[\ReturnTypeWillChange]
+	public function current();
+
+}
+
+/** @extends \Iterator<mixed, mixed> */
+interface IteratorChild2 extends \Iterator
+{
+
+	/** @return int */
+	#[\ReturnTypeWillChange]
+	public function key();
+
+	/** @return int */
+	#[\ReturnTypeWillChange]
+	public function current();
+
+}
+
+class Foo
+{
+
+	public function doFoo(IteratorChild $c)
+	{
+		foreach ($c as $k => $v) {
+			assertType('int', $k);
+			assertType('int', $v);
+		}
+	}
+
+	public function doFoo2(IteratorChild2 $c)
+	{
+		foreach ($c as $k => $v) {
+			assertType('mixed', $k);
+			assertType('mixed', $v);
+		}
+	}
+
+}
+
+interface IteratorChild3 extends \Iterator
+{
+
+}
+
+class IteratorChildTest
+{
+
+	public function doFoo(IteratorChild3 $c)
+	{
+
+	}
+
+}
diff --git a/tests/PHPStan/Rules/Operators/data/invalid-binary.php b/tests/PHPStan/Rules/Operators/data/invalid-binary.php
index c144298b6d0..3069c82ce8d 100644
--- a/tests/PHPStan/Rules/Operators/data/invalid-binary.php
+++ b/tests/PHPStan/Rules/Operators/data/invalid-binary.php
@@ -248,3 +248,9 @@ function bug6624_no_error($numericString) {
 	echo (10 * $numericLiteral);
 	echo (10 / $numericLiteral);
 }
+
+function benevolentPlus(array $a, int $i): void {
+	foreach ($a as $k => $v) {
+		echo $k + $i;
+	}
+};