diff --git a/CHANGELOG.md b/CHANGELOG.md
index 44792720..8f26716b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,8 @@
 ## Unreleased
 * support `components.pathItems` so `$ref`s into it resolve, unblocking OpenAPI 3.1 documents that use reusable path items
+* support array-form `type` (3.1) in value validation
 * add `SpecValidator` with `strict_specification_version` config (`:silent` / `:warn` / `:raise`) to detect version mismatches between declared OpenAPI version and actual field usage
+  * `TypeArrayIn30`: detect array-form `type` usage in 3.0 documents (3.1 form)
   * `NullableDeprecation`: detect `nullable` usage in 3.1 documents (removed in 3.1)
   * `ExampleSingularDeprecation`: detect singular `example` on schemas in 3.1 documents (deprecated in 3.1)
   * `PathItemsIn30`: detect `components.pathItems` usage in 3.0 documents (3.1 addition)
diff --git a/lib/openapi_parser/schema_validator.rb b/lib/openapi_parser/schema_validator.rb
index 1b653300..5ac92db3 100644
--- a/lib/openapi_parser/schema_validator.rb
+++ b/lib/openapi_parser/schema_validator.rb
@@ -13,7 +13,7 @@
 require_relative 'schema_validator/all_of_validator'
 require_relative 'schema_validator/one_of_validator'
 require_relative 'schema_validator/nil_validator'
-require_relative 'schema_validator/null_type_validator'
+require_relative 'schema_validator/type_mismatch_validator'
 require_relative 'schema_validator/unspecified_type_validator'
 
 class OpenAPIParser::SchemaValidator
@@ -104,7 +104,20 @@ def validator(value, schema)
       return one_of_validator if schema.one_of
       return nil_validator if value.nil?
 
-      case schema.type
+      # 3.1: pick the type from an Array whose primitive class matches the
+      # value, then dispatch as if it were a single-type schema. If nothing
+      # matches we still pick a candidate so the relevant validator emits
+      # a sensible error rather than silently accepting via the unspecified
+      # fallback.
+      effective_type = schema.type
+      if effective_type.is_a?(Array)
+        matched = pick_array_type(value, effective_type)
+        return type_mismatch_validator if matched.nil?
+
+        effective_type = matched
+      end
+
+      case effective_type
       when 'string'
         string_validator
       when 'integer'
@@ -121,14 +134,28 @@ def validator(value, schema)
         # 3.1: only nil values are valid here. nil is handled earlier in
         # this method, so a non-nil value reaching this branch is a type
         # mismatch that should fail validation.
-        null_type_validator
+        type_mismatch_validator
       else
         unspecified_type_validator
       end
     end
 
-    def null_type_validator
-      @null_type_validator ||= OpenAPIParser::SchemaValidator::NullTypeValidator.new(self, @coerce_value)
+    def type_mismatch_validator
+      @type_mismatch_validator ||= OpenAPIParser::SchemaValidator::TypeMismatchValidator.new(self, @coerce_value)
+    end
+
+    def pick_array_type(value, types)
+      types.find do |t|
+        case t
+        when 'string'  then value.is_a?(String)
+        when 'integer' then value.is_a?(Integer)
+        when 'number'  then value.is_a?(Numeric)
+        when 'boolean' then value == true || value == false
+        when 'array'   then value.is_a?(Array)
+        when 'object'  then value.is_a?(Hash)
+        when 'null'    then value.nil?
+        end
+      end
     end
 
     def string_validator
diff --git a/lib/openapi_parser/schema_validator/nil_validator.rb b/lib/openapi_parser/schema_validator/nil_validator.rb
index 1537e15a..ab3ca691 100644
--- a/lib/openapi_parser/schema_validator/nil_validator.rb
+++ b/lib/openapi_parser/schema_validator/nil_validator.rb
@@ -6,6 +6,8 @@ def coerce_and_validate(value, schema, **_keyword_args)
       return [value, nil] if schema.nullable
       # 3.1: `type: "null"` makes nil the only valid value for the schema.
       return [value, nil] if schema.type == 'null'
+      # 3.1: `type: [..., "null"]` lets nil coexist with another primitive.
+      return [value, nil] if schema.type.is_a?(Array) && schema.type.include?('null')
 
       [nil, OpenAPIParser::NotNullError.new(schema.object_reference)]
     end
diff --git a/lib/openapi_parser/schema_validator/null_type_validator.rb b/lib/openapi_parser/schema_validator/null_type_validator.rb
deleted file mode 100644
index 9aeb103a..00000000
--- a/lib/openapi_parser/schema_validator/null_type_validator.rb
+++ /dev/null
@@ -1,10 +0,0 @@
-class OpenAPIParser::SchemaValidator
-  # Validates schemas declared as `type: "null"` (3.1) against non-nil
-  # values. The nil case is short-circuited by NilValidator before this
-  # validator is even picked up.
-  class NullTypeValidator < Base
-    def coerce_and_validate(value, schema, **_keyword_args)
-      OpenAPIParser::ValidateError.build_error_result(value, schema)
-    end
-  end
-end
diff --git a/lib/openapi_parser/schema_validator/type_mismatch_validator.rb b/lib/openapi_parser/schema_validator/type_mismatch_validator.rb
new file mode 100644
index 00000000..23707cfb
--- /dev/null
+++ b/lib/openapi_parser/schema_validator/type_mismatch_validator.rb
@@ -0,0 +1,11 @@
+class OpenAPIParser::SchemaValidator
+  # Emits a ValidateError unconditionally. Used when the dispatcher has
+  # already decided that no primitive applies to the value, e.g.:
+  # - schema declares `type: "null"` and the value is non-nil (3.1)
+  # - schema declares `type: [t1, t2, ...]` and the value matches none
+  class TypeMismatchValidator < Base
+    def coerce_and_validate(value, schema, **_keyword_args)
+      OpenAPIParser::ValidateError.build_error_result(value, schema)
+    end
+  end
+end
diff --git a/lib/openapi_parser/spec_validator.rb b/lib/openapi_parser/spec_validator.rb
index 26068569..66820407 100644
--- a/lib/openapi_parser/spec_validator.rb
+++ b/lib/openapi_parser/spec_validator.rb
@@ -2,6 +2,7 @@
 require_relative 'spec_validator/rule'
 require_relative 'spec_validator/rules/exclusive_minimum'
 require_relative 'spec_validator/rules/exclusive_maximum'
+require_relative 'spec_validator/rules/type_array_in_30'
 require_relative 'spec_validator/rules/path_items_in_30'
 require_relative 'spec_validator/rules/nullable_deprecation'
 require_relative 'spec_validator/rules/example_singular_deprecation'
@@ -55,6 +56,7 @@ def rules
         [
           Rules::ExclusiveMinimum,
           Rules::ExclusiveMaximum,
+          Rules::TypeArrayIn30,
           Rules::PathItemsIn30,
           Rules::NullableDeprecation,
           Rules::ExampleSingularDeprecation,
diff --git a/lib/openapi_parser/spec_validator/rules/type_array_in_30.rb b/lib/openapi_parser/spec_validator/rules/type_array_in_30.rb
new file mode 100644
index 00000000..23dab065
--- /dev/null
+++ b/lib/openapi_parser/spec_validator/rules/type_array_in_30.rb
@@ -0,0 +1,25 @@
+module OpenAPIParser
+  class SpecValidator
+    module Rules
+      # 3.1 lets `type` be an Array of primitive type names (e.g.
+      # `["string", "null"]`). 3.0 only allowed a single String, so the
+      # array form on a 3.0 document is a spec violation.
+      class TypeArrayIn30 < Rule
+        def check(root)
+          return [] unless version == :v3_0
+
+          violations = []
+          each_schema(root) do |schema|
+            next unless schema.type.is_a?(Array)
+
+            violations << violation(
+              path: schema.object_reference,
+              message: '`type` as an Array of primitive names is a 3.1 addition; 3.0 expects a single type String',
+            )
+          end
+          violations
+        end
+      end
+    end
+  end
+end
diff --git a/sig/openapi_parser/spec_validator.rbs b/sig/openapi_parser/spec_validator.rbs
index 7ecc4546..776bb27f 100644
--- a/sig/openapi_parser/spec_validator.rbs
+++ b/sig/openapi_parser/spec_validator.rbs
@@ -45,6 +45,10 @@ module OpenAPIParser
         def check: (OpenAPIParser::Schemas::OpenAPI root) -> Array[SpecValidator::SpecViolation]
       end
 
+      class TypeArrayIn30 < Rule
+        def check: (OpenAPIParser::Schemas::OpenAPI root) -> Array[SpecValidator::SpecViolation]
+      end
+
       class PathItemsIn30 < Rule
         def check: (OpenAPIParser::Schemas::OpenAPI root) -> Array[SpecValidator::SpecViolation]
       end
diff --git a/spec/data/openapi_3_1/type_array_30.yaml b/spec/data/openapi_3_1/type_array_30.yaml
new file mode 100644
index 00000000..97ad7b14
--- /dev/null
+++ b/spec/data/openapi_3_1/type_array_30.yaml
@@ -0,0 +1,24 @@
+openapi: 3.0.3
+info:
+  title: Telemetry API
+  version: '1.0'
+paths:
+  /readings:
+    get:
+      summary: List sensor readings
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Reading'
+components:
+  schemas:
+    Reading:
+      type: object
+      properties:
+        # 3.1 form: `type` as an Array of primitive names. 3.0 only allows a
+        # single type String, so the array form is a spec violation here.
+        label:
+          type: [string, "null"]
diff --git a/spec/data/openapi_3_1/type_array_31.yaml b/spec/data/openapi_3_1/type_array_31.yaml
new file mode 100644
index 00000000..9f11fb92
--- /dev/null
+++ b/spec/data/openapi_3_1/type_array_31.yaml
@@ -0,0 +1,24 @@
+openapi: 3.1.0
+info:
+  title: Telemetry API
+  version: '1.0'
+paths:
+  /readings:
+    get:
+      summary: List sensor readings
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Reading'
+components:
+  schemas:
+    Reading:
+      type: object
+      properties:
+        # 3.1 allows `type` to be an Array of primitive names, so this is
+        # legitimate on a 3.1 document and no violation is expected.
+        label:
+          type: [string, "null"]
diff --git a/spec/openapi_parser/spec_validator/integration_3_1_spec.rb b/spec/openapi_parser/spec_validator/integration_3_1_spec.rb
index fd386bd2..5de0cb2f 100644
--- a/spec/openapi_parser/spec_validator/integration_3_1_spec.rb
+++ b/spec/openapi_parser/spec_validator/integration_3_1_spec.rb
@@ -74,6 +74,20 @@ def expect_clean(file)
     end
   end
 
+  describe 'type as an Array of names (3.1 form rejected by 3.0)' do
+    it 'warns on the version-mismatched document under :warn' do
+      expect_mismatch_warns('type_array_30.yaml', [:type_array_in30])
+    end
+
+    it 'raises SpecViolationError on the version-mismatched document under :raise' do
+      expect_mismatch_raises('type_array_30.yaml', [:type_array_in30])
+    end
+
+    it 'stays clean on the correctly-versioned document' do
+      expect_clean('type_array_31.yaml')
+    end
+  end
+
   describe 'components.pathItems (3.1 addition)' do
     it 'warns on the version-mismatched document under :warn' do
       expect_mismatch_warns('path_items_30.yaml', [:path_items_in30])
diff --git a/spec/openapi_parser/spec_validator/rules/type_array_in_30_spec.rb b/spec/openapi_parser/spec_validator/rules/type_array_in_30_spec.rb
new file mode 100644
index 00000000..76c420cf
--- /dev/null
+++ b/spec/openapi_parser/spec_validator/rules/type_array_in_30_spec.rb
@@ -0,0 +1,81 @@
+require_relative '../../../spec_helper'
+
+RSpec.describe 'OpenAPIParser::SpecValidator::Rules::TypeArrayIn30' do
+  def schema_with_type_array(openapi_version_string, types)
+    raw = {
+      'openapi' => openapi_version_string,
+      'info' => { 'title' => 'test', 'version' => '1.0' },
+      'paths' => {},
+      'components' => { 'schemas' => { 'Sample' => { 'type' => types } } },
+    }
+    OpenAPIParser.parse(raw, strict_reference_validation: false)
+  end
+
+  def run_rule_for(root)
+    OpenAPIParser::SpecValidator::Rules::TypeArrayIn30.new(root.openapi_version).check(root)
+  end
+
+  context 'with a 3.1 document using type as Array' do
+    it 'reports no violation' do
+      root = schema_with_type_array('3.1.0', ['string', 'null'])
+      expect(run_rule_for(root)).to eq []
+    end
+  end
+
+  context 'with a 3.0 document using type as Array' do
+    it 'reports one violation pointing at the offending schema' do
+      root = schema_with_type_array('3.0.0', ['string', 'null'])
+      violations = run_rule_for(root)
+      expect(violations.size).to eq 1
+      expect(violations.first.path).to eq '#/components/schemas/Sample'
+      expect(violations.first.rule_name).to eq :type_array_in30
+    end
+  end
+
+  context 'with a 3.0 document using type as plain string' do
+    it 'reports no violation' do
+      root = schema_with_type_array('3.0.0', 'string')
+      expect(run_rule_for(root)).to eq []
+    end
+  end
+
+  context 'with an :unknown version document using type as Array' do
+    it 'reports no violation (rule skipped)' do
+      root = schema_with_type_array('4.0.0', ['string', 'null'])
+      expect(run_rule_for(root)).to eq []
+    end
+  end
+end
+
+RSpec.describe 'runtime: type as Array semantic in 3.1' do
+  let(:options) { ::OpenAPIParser::SchemaValidator::Options.new }
+  let(:schema) do
+    raw = {
+      'openapi' => '3.1.0',
+      'info' => { 'title' => 'test', 'version' => '1.0' },
+      'paths' => {},
+      'components' => { 'schemas' => { 'NullableString' => { 'type' => ['string', 'null'] } } },
+    }
+    OpenAPIParser.parse(raw, strict_reference_validation: false).components.schemas['NullableString']
+  end
+
+  context 'when value is nil and array contains "null"' do
+    it 'passes validation' do
+      expect(OpenAPIParser::SchemaValidator.validate(nil, schema, options)).to eq nil
+    end
+  end
+
+  context 'when value matches one of the listed types' do
+    it 'passes validation' do
+      expect(OpenAPIParser::SchemaValidator.validate('hello', schema, options)).to eq 'hello'
+    end
+  end
+
+  context 'when value matches no listed type' do
+    it 'raises a type-mismatch error' do
+      expect do
+        OpenAPIParser::SchemaValidator.validate(42, schema, options)
+      end.to raise_error(OpenAPIParser::ValidateError)
+    end
+  end
+end