• Core changes
• New Buffer API replaces ByteBuf
• ChannelHandler
• Simplified handler type hierarchy
• SimpleChannelInboundHandler.channelRead0() → messageReceived()
• ChannelHandler method signature changes.
• User events
• ChannelHandler.pendingOutboundBytes(...) method added
• Transport
• Half-closure
• ChannelHandlerContext doesn't extend AttributeMap anymore
• ChannelPipeline.add*(EventExecutorGroup...) removed
• Channel.eventLoop() renamed to Channel.executor()
• EventLoopGroup.isCompatible(...) method added
• EventLoop.registerForIo(...) and EventLoop.deregisterForIo added
• Channel.Unsafe removal
• ChannelOutboundBuffer not part of the Channel API anymore
• Channel.beforeBeforeWritable() removed and Channel.bytesBeforeUnwritable() renamed to writableBytes().
• Future / Promise
• ProgressiveFuture / ProgressivePromise and ChannelProgressiveFuture / ChannelProgressivePromise removal
• VoidChannelPromise removal
• API changes to Promise and Future
• Codec changes
• Compression support
• HTTP Codec
• Rarely used codecs moved to Netty Contrib
• GraalVM and Native Image