diff --git a/Sources/NIOHTTP2/HTTP2ChannelHandler+InlineStreamMultiplexer.swift b/Sources/NIOHTTP2/HTTP2ChannelHandler+InlineStreamMultiplexer.swift
index bebe7b16..644ea1fc 100644
--- a/Sources/NIOHTTP2/HTTP2ChannelHandler+InlineStreamMultiplexer.swift
+++ b/Sources/NIOHTTP2/HTTP2ChannelHandler+InlineStreamMultiplexer.swift
@@ -148,7 +148,7 @@ extension InlineStreamMultiplexer {
         self.commonStreamMultiplexer.createStreamChannel(multiplexer: .inline(self), streamStateInitializer)
     }
 
-    internal func createStreamChannel<Output>(_ initializer: @escaping NIOChannelInitializerWithOutput<Output>) -> EventLoopFuture<Output> {
+    internal func createStreamChannel<Output: Sendable>(_ initializer: @escaping NIOChannelInitializerWithOutput<Output>) -> EventLoopFuture<Output> {
         self.commonStreamMultiplexer.createStreamChannel(multiplexer: .inline(self), initializer)
     }
 }
@@ -239,7 +239,7 @@ extension NIOHTTP2Handler {
         }
 
         /// Create a stream channel initialized with the provided closure
-        public func createStreamChannel<OutboundStreamOutput>(_ initializer: @escaping NIOChannelInitializerWithOutput<OutboundStreamOutput>) async throws -> OutboundStreamOutput {
+        public func createStreamChannel<OutboundStreamOutput: Sendable>(_ initializer: @escaping NIOChannelInitializerWithOutput<OutboundStreamOutput>) async throws -> OutboundStreamOutput {
             return try await self.inlineStreamMultiplexer.createStreamChannel(initializer).get()
         }
     }
diff --git a/Sources/NIOHTTP2/HTTP2ChannelHandler.swift b/Sources/NIOHTTP2/HTTP2ChannelHandler.swift
index 0bdc4d33..aa543973 100644
--- a/Sources/NIOHTTP2/HTTP2ChannelHandler.swift
+++ b/Sources/NIOHTTP2/HTTP2ChannelHandler.swift
@@ -1010,7 +1010,7 @@ extension NIOHTTP2Handler {
     /// The type of all `inboundStreamInitializer` callbacks which need to return data.
     public typealias StreamInitializer = NIOChannelInitializer
     /// The type of NIO Channel initializer callbacks which need to return untyped data.
-    internal typealias StreamInitializerWithAnyOutput = (Channel) -> EventLoopFuture<Any>
+    internal typealias StreamInitializerWithAnyOutput = (Channel) -> EventLoopFuture<any Sendable>
 #endif
 
     /// Creates a new ``NIOHTTP2Handler`` with a local multiplexer. (i.e. using
diff --git a/Sources/NIOHTTP2/HTTP2CommonInboundStreamMultiplexer.swift b/Sources/NIOHTTP2/HTTP2CommonInboundStreamMultiplexer.swift
index f0a82c70..e89c45e7 100644
--- a/Sources/NIOHTTP2/HTTP2CommonInboundStreamMultiplexer.swift
+++ b/Sources/NIOHTTP2/HTTP2CommonInboundStreamMultiplexer.swift
@@ -293,7 +293,7 @@ extension HTTP2CommonInboundStreamMultiplexer {
 }
 
 extension HTTP2CommonInboundStreamMultiplexer {
-    internal func _createStreamChannel<Output>(
+    internal func _createStreamChannel<Output: Sendable>(
         _ multiplexer: HTTP2StreamChannel.OutboundStreamMultiplexer,
         _ promise: EventLoopPromise<Output>?,
         _ streamStateInitializer: @escaping NIOChannelInitializerWithOutput<Output>
@@ -313,11 +313,10 @@ extension HTTP2CommonInboundStreamMultiplexer {
         self.pendingStreams[channel.channelID] = channel
 
         let anyInitializer: NIOChannelInitializerWithOutput<any Sendable> = { channel in
-            streamStateInitializer(channel).map { $0 }
+            streamStateInitializer(channel).map { return $0 }
         }
 
         let anyPromise: EventLoopPromise<Any>?
-
         if let promise = promise {
             anyPromise = channel.baseChannel.eventLoop.makePromise(of: Any.self)
             anyPromise?.futureResult.whenComplete { result in
@@ -335,7 +334,7 @@ extension HTTP2CommonInboundStreamMultiplexer {
         channel.configure(initializer: anyInitializer, userPromise: anyPromise)
     }
 
-    internal func createStreamChannel<Output>(
+    internal func createStreamChannel<Output: Sendable>(
         multiplexer: HTTP2StreamChannel.OutboundStreamMultiplexer,
         promise: EventLoopPromise<Output>?,
         _ streamStateInitializer: @escaping NIOChannelInitializerWithOutput<Output>
@@ -348,7 +347,7 @@ extension HTTP2CommonInboundStreamMultiplexer {
         }
     }
 
-    internal func createStreamChannel<Output>(
+    internal func createStreamChannel<Output: Sendable>(
         multiplexer: HTTP2StreamChannel.OutboundStreamMultiplexer,
         _ streamStateInitializer: @escaping NIOChannelInitializerWithOutput<Output>
     ) -> EventLoopFuture<Output> {
diff --git a/Sources/NIOHTTP2/HTTP2PipelineHelpers.swift b/Sources/NIOHTTP2/HTTP2PipelineHelpers.swift
index c8540c2a..65ff6340 100644
--- a/Sources/NIOHTTP2/HTTP2PipelineHelpers.swift
+++ b/Sources/NIOHTTP2/HTTP2PipelineHelpers.swift
@@ -596,7 +596,7 @@ extension ChannelPipeline.SynchronousOperations {
     /// be used to initiate new streams and iterate over inbound HTTP/2 stream channels.
     @available(macOS 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *)
     @_spi(AsyncChannel)
-    public func configureAsyncHTTP2Pipeline<Output>(
+    public func configureAsyncHTTP2Pipeline<Output: Sendable>(
         mode: NIOHTTP2Handler.ParserMode,
         configuration: NIOHTTP2Handler.Configuration = .init(),
         position: ChannelPipeline.Position = .last,
@@ -608,7 +608,7 @@ extension ChannelPipeline.SynchronousOperations {
             connectionConfiguration: configuration.connection,
             streamConfiguration: configuration.stream,
             inboundStreamInitializerWithAnyOutput: { channel in
-                inboundStreamInitializer(channel).map { $0 }
+                inboundStreamInitializer(channel).map { return $0 }
             }
         )
 
diff --git a/Sources/NIOHTTP2/HTTP2StreamMultiplexer.swift b/Sources/NIOHTTP2/HTTP2StreamMultiplexer.swift
index a723f511..e22b0a8b 100644
--- a/Sources/NIOHTTP2/HTTP2StreamMultiplexer.swift
+++ b/Sources/NIOHTTP2/HTTP2StreamMultiplexer.swift
@@ -141,7 +141,7 @@ public final class HTTP2StreamMultiplexer: ChannelInboundHandler, ChannelOutboun
     ///         channel that is created by the remote peer. For servers, these are channels created by
     ///         receiving a `HEADERS` frame from a client. For clients, these are channels created by
     ///         receiving a `PUSH_PROMISE` frame from a server. To initiate a new outbound channel, use
-    ///         ``createStreamChannel(promise:_:)-18bxc``.
+    ///         ``createStreamChannel(promise:_:)-1jk0q``.
     @available(*, deprecated, renamed: "init(mode:channel:targetWindowSize:outboundBufferSizeHighWatermark:outboundBufferSizeLowWatermark:inboundStreamInitializer:)")
     public convenience init(mode: NIOHTTP2Handler.ParserMode, channel: Channel, targetWindowSize: Int = 65535, inboundStreamStateInitializer: ((Channel, HTTP2StreamID) -> EventLoopFuture<Void>)? = nil) {
         // We default to an 8kB outbound buffer size: this is a good trade off for avoiding excessive buffering while ensuring that decent
@@ -170,7 +170,7 @@ public final class HTTP2StreamMultiplexer: ChannelInboundHandler, ChannelOutboun
     ///         channel that is created by the remote peer. For servers, these are channels created by
     ///         receiving a `HEADERS` frame from a client. For clients, these are channels created by
     ///         receiving a `PUSH_PROMISE` frame from a server. To initiate a new outbound channel, use
-    ///         ``createStreamChannel(promise:_:)-18bxc``.
+    ///         ``createStreamChannel(promise:_:)-1jk0q``.
     public convenience init(mode: NIOHTTP2Handler.ParserMode,
                             channel: Channel,
                             targetWindowSize: Int = 65535,
@@ -199,7 +199,7 @@ public final class HTTP2StreamMultiplexer: ChannelInboundHandler, ChannelOutboun
     ///         channel that is created by the remote peer. For servers, these are channels created by
     ///         receiving a `HEADERS` frame from a client. For clients, these are channels created by
     ///         receiving a `PUSH_PROMISE` frame from a server. To initiate a new outbound channel, use
-    ///         ``createStreamChannel(promise:_:)-18bxc``.
+    ///         ``createStreamChannel(promise:_:)-1jk0q``.
     @available(*, deprecated, renamed: "init(mode:channel:targetWindowSize:outboundBufferSizeHighWatermark:outboundBufferSizeLowWatermark:inboundStreamInitializer:)")
     public convenience init(mode: NIOHTTP2Handler.ParserMode,
                             channel: Channel,