diff --git a/Package.swift b/Package.swift
index 0d6222aa..6f791d20 100644
--- a/Package.swift
+++ b/Package.swift
@@ -15,11 +15,17 @@
 import PackageDescription
 
 // General Swift-settings for all targets.
-let swiftSettings: [SwiftSetting] = [
-    // https://github.com/apple/swift-evolution/blob/main/proposals/0335-existential-any.md
-    // Require `any` for existential types.
+var swiftSettings: [SwiftSetting] = [
+    // https://github.com/swiftlang/swift-evolution/blob/main/proposals/0335-existential-any.md
     .enableUpcomingFeature("ExistentialAny")
 ]
+#if compiler(>=6.0)
+swiftSettings.append(contentsOf: [
+    // https://github.com/swiftlang/swift-evolution/blob/main/proposals/0409-access-level-on-imports.md
+    .enableUpcomingFeature("InternalImportsByDefault"),
+    .enableExperimentalFeature("AccessLevelOnImport"),
+])
+#endif
 
 let package = Package(
     name: "swift-openapi-runtime",
diff --git a/Sources/OpenAPIRuntime/Base/UndocumentedPayload.swift b/Sources/OpenAPIRuntime/Base/UndocumentedPayload.swift
index 399256de..9b16bc03 100644
--- a/Sources/OpenAPIRuntime/Base/UndocumentedPayload.swift
+++ b/Sources/OpenAPIRuntime/Base/UndocumentedPayload.swift
@@ -12,7 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import HTTPTypes
+public import HTTPTypes
 
 /// A payload value used by undocumented operation responses.
 ///
diff --git a/Sources/OpenAPIRuntime/Conversion/Configuration.swift b/Sources/OpenAPIRuntime/Conversion/Configuration.swift
index 2ee7ab00..279d1d46 100644
--- a/Sources/OpenAPIRuntime/Conversion/Configuration.swift
+++ b/Sources/OpenAPIRuntime/Conversion/Configuration.swift
@@ -11,7 +11,7 @@
 // SPDX-License-Identifier: Apache-2.0
 //
 //===----------------------------------------------------------------------===//
-import Foundation
+public import Foundation
 
 /// A type that allows customization of Date encoding and decoding.
 ///
diff --git a/Sources/OpenAPIRuntime/Conversion/Converter+Client.swift b/Sources/OpenAPIRuntime/Conversion/Converter+Client.swift
index 28abbdb2..dcaa27b2 100644
--- a/Sources/OpenAPIRuntime/Conversion/Converter+Client.swift
+++ b/Sources/OpenAPIRuntime/Conversion/Converter+Client.swift
@@ -12,7 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 import Foundation
-import HTTPTypes
+public import HTTPTypes
 
 extension Converter {
 
diff --git a/Sources/OpenAPIRuntime/Conversion/Converter+Common.swift b/Sources/OpenAPIRuntime/Conversion/Converter+Common.swift
index 73f8fecb..f4ff8852 100644
--- a/Sources/OpenAPIRuntime/Conversion/Converter+Common.swift
+++ b/Sources/OpenAPIRuntime/Conversion/Converter+Common.swift
@@ -12,7 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 import Foundation
-import HTTPTypes
+public import HTTPTypes
 
 extension Converter {
 
diff --git a/Sources/OpenAPIRuntime/Conversion/Converter+Server.swift b/Sources/OpenAPIRuntime/Conversion/Converter+Server.swift
index a3088bd3..f108c7f6 100644
--- a/Sources/OpenAPIRuntime/Conversion/Converter+Server.swift
+++ b/Sources/OpenAPIRuntime/Conversion/Converter+Server.swift
@@ -12,7 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 import Foundation
-import HTTPTypes
+public import HTTPTypes
 
 extension Converter {
 
diff --git a/Sources/OpenAPIRuntime/Conversion/ServerVariable.swift b/Sources/OpenAPIRuntime/Conversion/ServerVariable.swift
index a9658afa..69bf219d 100644
--- a/Sources/OpenAPIRuntime/Conversion/ServerVariable.swift
+++ b/Sources/OpenAPIRuntime/Conversion/ServerVariable.swift
@@ -12,7 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import Foundation
+public import Foundation
 
 extension URL {
     /// Returns a validated server URL created from the URL template, or
diff --git a/Sources/OpenAPIRuntime/Conversion/URLExtensions.swift b/Sources/OpenAPIRuntime/Conversion/URLExtensions.swift
index 432d78ae..b4eb5898 100644
--- a/Sources/OpenAPIRuntime/Conversion/URLExtensions.swift
+++ b/Sources/OpenAPIRuntime/Conversion/URLExtensions.swift
@@ -11,7 +11,7 @@
 // SPDX-License-Identifier: Apache-2.0
 //
 //===----------------------------------------------------------------------===//
-import Foundation
+public import Foundation
 
 extension URL {
     /// Returns the default server URL of "/".
diff --git a/Sources/OpenAPIRuntime/Deprecated/Deprecated.swift b/Sources/OpenAPIRuntime/Deprecated/Deprecated.swift
index 2ce41750..188a599d 100644
--- a/Sources/OpenAPIRuntime/Deprecated/Deprecated.swift
+++ b/Sources/OpenAPIRuntime/Deprecated/Deprecated.swift
@@ -11,7 +11,7 @@
 // SPDX-License-Identifier: Apache-2.0
 //
 //===----------------------------------------------------------------------===//
-import Foundation
+public import Foundation
 import HTTPTypes
 
 // MARK: - Functionality to be removed in the future
diff --git a/Sources/OpenAPIRuntime/Errors/ClientError.swift b/Sources/OpenAPIRuntime/Errors/ClientError.swift
index 90481bff..c7263e5a 100644
--- a/Sources/OpenAPIRuntime/Errors/ClientError.swift
+++ b/Sources/OpenAPIRuntime/Errors/ClientError.swift
@@ -12,13 +12,13 @@
 //
 //===----------------------------------------------------------------------===//
 
-import HTTPTypes
+public import HTTPTypes
 #if canImport(Darwin)
-import struct Foundation.URL
+public import struct Foundation.URL
 #else
-@preconcurrency import struct Foundation.URL
+@preconcurrency public import struct Foundation.URL
 #endif
-import protocol Foundation.LocalizedError
+public import protocol Foundation.LocalizedError
 
 /// An error thrown by a client performing an OpenAPI operation.
 ///
diff --git a/Sources/OpenAPIRuntime/Errors/ServerError.swift b/Sources/OpenAPIRuntime/Errors/ServerError.swift
index 92d0552e..af6eea59 100644
--- a/Sources/OpenAPIRuntime/Errors/ServerError.swift
+++ b/Sources/OpenAPIRuntime/Errors/ServerError.swift
@@ -12,8 +12,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-import HTTPTypes
-import protocol Foundation.LocalizedError
+public import HTTPTypes
+public import protocol Foundation.LocalizedError
 
 /// An error thrown by a server handling an OpenAPI operation.
 public struct ServerError: Error {
diff --git a/Sources/OpenAPIRuntime/EventStreams/JSONLinesDecoding.swift b/Sources/OpenAPIRuntime/EventStreams/JSONLinesDecoding.swift
index eed9acdc..69c26723 100644
--- a/Sources/OpenAPIRuntime/EventStreams/JSONLinesDecoding.swift
+++ b/Sources/OpenAPIRuntime/EventStreams/JSONLinesDecoding.swift
@@ -13,11 +13,11 @@
 //===----------------------------------------------------------------------===//
 
 #if canImport(Darwin)
-import class Foundation.JSONDecoder
+public import class Foundation.JSONDecoder
 #else
-@preconcurrency import class Foundation.JSONDecoder
+@preconcurrency public import class Foundation.JSONDecoder
 #endif
-import struct Foundation.Data
+public import struct Foundation.Data
 
 /// A sequence that parses arbitrary byte chunks into lines using the JSON Lines format.
 public struct JSONLinesDeserializationSequence<Upstream: AsyncSequence & Sendable>: Sendable
diff --git a/Sources/OpenAPIRuntime/EventStreams/JSONLinesEncoding.swift b/Sources/OpenAPIRuntime/EventStreams/JSONLinesEncoding.swift
index f1d9b9b8..6c200d80 100644
--- a/Sources/OpenAPIRuntime/EventStreams/JSONLinesEncoding.swift
+++ b/Sources/OpenAPIRuntime/EventStreams/JSONLinesEncoding.swift
@@ -13,9 +13,9 @@
 //===----------------------------------------------------------------------===//
 
 #if canImport(Darwin)
-import class Foundation.JSONEncoder
+public import class Foundation.JSONEncoder
 #else
-@preconcurrency import class Foundation.JSONEncoder
+@preconcurrency public import class Foundation.JSONEncoder
 #endif
 
 /// A sequence that serializes lines by concatenating them using the JSON Lines format.
diff --git a/Sources/OpenAPIRuntime/EventStreams/JSONSequenceDecoding.swift b/Sources/OpenAPIRuntime/EventStreams/JSONSequenceDecoding.swift
index 4b34658c..1e281666 100644
--- a/Sources/OpenAPIRuntime/EventStreams/JSONSequenceDecoding.swift
+++ b/Sources/OpenAPIRuntime/EventStreams/JSONSequenceDecoding.swift
@@ -13,12 +13,12 @@
 //===----------------------------------------------------------------------===//
 
 #if canImport(Darwin)
-import class Foundation.JSONDecoder
+public import class Foundation.JSONDecoder
 #else
-@preconcurrency import class Foundation.JSONDecoder
+@preconcurrency public import class Foundation.JSONDecoder
 #endif
-import protocol Foundation.LocalizedError
-import struct Foundation.Data
+public import protocol Foundation.LocalizedError
+public import struct Foundation.Data
 
 /// A sequence that parses arbitrary byte chunks into lines using the JSON Sequence format.
 public struct JSONSequenceDeserializationSequence<Upstream: AsyncSequence & Sendable>: Sendable
diff --git a/Sources/OpenAPIRuntime/EventStreams/JSONSequenceEncoding.swift b/Sources/OpenAPIRuntime/EventStreams/JSONSequenceEncoding.swift
index a6ffe940..343233e1 100644
--- a/Sources/OpenAPIRuntime/EventStreams/JSONSequenceEncoding.swift
+++ b/Sources/OpenAPIRuntime/EventStreams/JSONSequenceEncoding.swift
@@ -13,9 +13,9 @@
 //===----------------------------------------------------------------------===//
 
 #if canImport(Darwin)
-import class Foundation.JSONEncoder
+public import class Foundation.JSONEncoder
 #else
-@preconcurrency import class Foundation.JSONEncoder
+@preconcurrency public import class Foundation.JSONEncoder
 #endif
 
 /// A sequence that serializes lines by concatenating them using the JSON Sequence format.
diff --git a/Sources/OpenAPIRuntime/EventStreams/ServerSentEventsDecoding.swift b/Sources/OpenAPIRuntime/EventStreams/ServerSentEventsDecoding.swift
index 34f51b21..2ee107c7 100644
--- a/Sources/OpenAPIRuntime/EventStreams/ServerSentEventsDecoding.swift
+++ b/Sources/OpenAPIRuntime/EventStreams/ServerSentEventsDecoding.swift
@@ -13,11 +13,11 @@
 //===----------------------------------------------------------------------===//
 
 #if canImport(Darwin)
-import class Foundation.JSONDecoder
+public import class Foundation.JSONDecoder
 #else
-@preconcurrency import class Foundation.JSONDecoder
+@preconcurrency public import class Foundation.JSONDecoder
 #endif
-import struct Foundation.Data
+public import struct Foundation.Data
 
 /// A sequence that parses arbitrary byte chunks into events using the Server-sent Events format.
 ///
diff --git a/Sources/OpenAPIRuntime/EventStreams/ServerSentEventsEncoding.swift b/Sources/OpenAPIRuntime/EventStreams/ServerSentEventsEncoding.swift
index 853d76d2..aa0c6b28 100644
--- a/Sources/OpenAPIRuntime/EventStreams/ServerSentEventsEncoding.swift
+++ b/Sources/OpenAPIRuntime/EventStreams/ServerSentEventsEncoding.swift
@@ -13,9 +13,9 @@
 //===----------------------------------------------------------------------===//
 
 #if canImport(Darwin)
-import class Foundation.JSONEncoder
+public import class Foundation.JSONEncoder
 #else
-@preconcurrency import class Foundation.JSONEncoder
+@preconcurrency public import class Foundation.JSONEncoder
 #endif
 
 /// A sequence that serializes Server-sent Events.
diff --git a/Sources/OpenAPIRuntime/Interface/ClientTransport.swift b/Sources/OpenAPIRuntime/Interface/ClientTransport.swift
index cb20c651..29cdeff7 100644
--- a/Sources/OpenAPIRuntime/Interface/ClientTransport.swift
+++ b/Sources/OpenAPIRuntime/Interface/ClientTransport.swift
@@ -12,8 +12,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-import HTTPTypes
-import struct Foundation.URL
+public import HTTPTypes
+public import struct Foundation.URL
 
 /// A type that performs HTTP operations.
 ///
diff --git a/Sources/OpenAPIRuntime/Interface/CurrencyTypes.swift b/Sources/OpenAPIRuntime/Interface/CurrencyTypes.swift
index 7093bd75..df706419 100644
--- a/Sources/OpenAPIRuntime/Interface/CurrencyTypes.swift
+++ b/Sources/OpenAPIRuntime/Interface/CurrencyTypes.swift
@@ -12,7 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import HTTPTypes
+public import HTTPTypes
 
 /// A container for request metadata already parsed and validated
 /// by the server transport.
diff --git a/Sources/OpenAPIRuntime/Interface/ErrorHandlingMiddleware.swift b/Sources/OpenAPIRuntime/Interface/ErrorHandlingMiddleware.swift
index 55113ce5..1edd1dd4 100644
--- a/Sources/OpenAPIRuntime/Interface/ErrorHandlingMiddleware.swift
+++ b/Sources/OpenAPIRuntime/Interface/ErrorHandlingMiddleware.swift
@@ -12,7 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import HTTPTypes
+public import HTTPTypes
 
 /// An opt-in error handling middleware that converts an error to an HTTP response.
 ///
diff --git a/Sources/OpenAPIRuntime/Interface/HTTPBody.swift b/Sources/OpenAPIRuntime/Interface/HTTPBody.swift
index 59292ec9..f15ea3ee 100644
--- a/Sources/OpenAPIRuntime/Interface/HTTPBody.swift
+++ b/Sources/OpenAPIRuntime/Interface/HTTPBody.swift
@@ -12,9 +12,9 @@
 //
 //===----------------------------------------------------------------------===//
 
-import class Foundation.NSLock
-import protocol Foundation.LocalizedError
-import struct Foundation.Data  // only for convenience initializers
+public import class Foundation.NSLock
+public import protocol Foundation.LocalizedError
+public import struct Foundation.Data  // only for convenience initializers
 
 /// A body of an HTTP request or HTTP response.
 ///
diff --git a/Sources/OpenAPIRuntime/Interface/ServerTransport.swift b/Sources/OpenAPIRuntime/Interface/ServerTransport.swift
index 40e16e8f..29e0ed5a 100644
--- a/Sources/OpenAPIRuntime/Interface/ServerTransport.swift
+++ b/Sources/OpenAPIRuntime/Interface/ServerTransport.swift
@@ -12,7 +12,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-import HTTPTypes
+public import HTTPTypes
 
 /// A type that registers and handles HTTP operations.
 ///
diff --git a/Sources/OpenAPIRuntime/Interface/UniversalClient.swift b/Sources/OpenAPIRuntime/Interface/UniversalClient.swift
index 5afff2b1..04d221b3 100644
--- a/Sources/OpenAPIRuntime/Interface/UniversalClient.swift
+++ b/Sources/OpenAPIRuntime/Interface/UniversalClient.swift
@@ -11,11 +11,11 @@
 // SPDX-License-Identifier: Apache-2.0
 //
 //===----------------------------------------------------------------------===//
-import HTTPTypes
+public import HTTPTypes
 #if canImport(Darwin)
-import struct Foundation.URL
+public import struct Foundation.URL
 #else
-@preconcurrency import struct Foundation.URL
+@preconcurrency public import struct Foundation.URL
 #endif
 
 /// OpenAPI document-agnostic HTTP client used by OpenAPI document-specific,
diff --git a/Sources/OpenAPIRuntime/Interface/UniversalServer.swift b/Sources/OpenAPIRuntime/Interface/UniversalServer.swift
index 4608dafe..b3e09206 100644
--- a/Sources/OpenAPIRuntime/Interface/UniversalServer.swift
+++ b/Sources/OpenAPIRuntime/Interface/UniversalServer.swift
@@ -12,13 +12,13 @@
 //
 //===----------------------------------------------------------------------===//
 
-import HTTPTypes
+public import HTTPTypes
 #if canImport(Darwin)
-import struct Foundation.URL
+public import struct Foundation.URL
 #else
-@preconcurrency import struct Foundation.URL
+@preconcurrency public import struct Foundation.URL
 #endif
-import struct Foundation.URLComponents
+public import struct Foundation.URLComponents
 
 /// OpenAPI document-agnostic HTTP server used by OpenAPI document-specific,
 /// generated servers to perform request deserialization, middleware and handler
diff --git a/Sources/OpenAPIRuntime/Multipart/MultipartPublicTypes.swift b/Sources/OpenAPIRuntime/Multipart/MultipartPublicTypes.swift
index 6db356c3..8b46224a 100644
--- a/Sources/OpenAPIRuntime/Multipart/MultipartPublicTypes.swift
+++ b/Sources/OpenAPIRuntime/Multipart/MultipartPublicTypes.swift
@@ -13,7 +13,7 @@
 //===----------------------------------------------------------------------===//
 
 import Foundation
-import HTTPTypes
+public import HTTPTypes
 
 /// A raw multipart part containing the header fields and the body stream.
 public struct MultipartRawPart: Sendable, Hashable {
diff --git a/Sources/OpenAPIRuntime/Multipart/MultipartPublicTypesExtensions.swift b/Sources/OpenAPIRuntime/Multipart/MultipartPublicTypesExtensions.swift
index ac9d9d5f..4f24530a 100644
--- a/Sources/OpenAPIRuntime/Multipart/MultipartPublicTypesExtensions.swift
+++ b/Sources/OpenAPIRuntime/Multipart/MultipartPublicTypesExtensions.swift
@@ -13,7 +13,7 @@
 //===----------------------------------------------------------------------===//
 
 import Foundation
-import HTTPTypes
+public import HTTPTypes
 
 // MARK: - Extensions
 
diff --git a/Tests/OpenAPIRuntimeTests/Conversion/Test_Converter+Client.swift b/Tests/OpenAPIRuntimeTests/Conversion/Test_Converter+Client.swift
index 0f3bf066..dfdec68f 100644
--- a/Tests/OpenAPIRuntimeTests/Conversion/Test_Converter+Client.swift
+++ b/Tests/OpenAPIRuntimeTests/Conversion/Test_Converter+Client.swift
@@ -275,7 +275,7 @@ final class Test_ClientConverterExtensions: Test_Runtime {
 ///   - message: An optional custom message to display upon test failure.
 ///   - file: The file name to include in the failure message (default is the source file where this function is called).
 ///   - line: The line number to include in the failure message (default is the line where this function is called).
-public func XCTAssertEqualStringifiedData(
+func XCTAssertEqualStringifiedData(
     _ expression1: @autoclosure () throws -> Data,
     _ expression2: @autoclosure () throws -> String,
     _ message: @autoclosure () -> String = "",
diff --git a/Tests/OpenAPIRuntimeTests/Test_Runtime.swift b/Tests/OpenAPIRuntimeTests/Test_Runtime.swift
index 942c9df2..610a0381 100644
--- a/Tests/OpenAPIRuntimeTests/Test_Runtime.swift
+++ b/Tests/OpenAPIRuntimeTests/Test_Runtime.swift
@@ -259,7 +259,7 @@ struct MockCustomCoder: CustomCoder {
 ///   - rhs: The expected absolute string representation.
 ///   - file: The file name to include in the failure message (default is the source file where this function is called).
 ///   - line: The line number to include in the failure message (default is the line where this function is called).
-public func XCTAssertEqualURLString(_ lhs: URL?, _ rhs: String, file: StaticString = #filePath, line: UInt = #line) {
+func XCTAssertEqualURLString(_ lhs: URL?, _ rhs: String, file: StaticString = #filePath, line: UInt = #line) {
     guard let lhs else {
         XCTFail("URL is nil")
         return
@@ -384,7 +384,7 @@ public func XCTAssertEqualStringifiedData<S: Sequence>(
 ///   - file: The file name to include in the failure message (default is the source file where this function is called).
 ///   - line: The line number to include in the failure message (default is the line where this function is called).
 /// - Throws: If either of the autoclosures throws an error, the function will rethrow that error.
-public func XCTAssertEqualStringifiedData(
+func XCTAssertEqualStringifiedData(
     _ expression1: @autoclosure () throws -> HTTPBody?,
     _ expression2: @autoclosure () throws -> String,
     _ message: @autoclosure () -> String = "",
@@ -474,7 +474,7 @@ public func XCTAssertEqualAsyncData<C: Collection, AS: AsyncSequence>(
 }
 
 /// Asserts that the data matches the expected value.
-public func XCTAssertEqualData<C: Collection>(
+func XCTAssertEqualData<C: Collection>(
     _ expression1: @autoclosure () throws -> HTTPBody?,
     _ expression2: @autoclosure () throws -> C,
     _ message: @autoclosure () -> String = "Data doesn't match.",