diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,11 @@
 # ChangeLog for http2
 
+## 5.4.2
+
+* Support informational (1xx) responses, e.g. 103 Early Hints. Servers can send
+  them via `auxSendInformational`; clients can observe them via the new
+  `confOnInformational` callback in `Config`.
+
 ## 5.4.1
 
 * Ensure sender notices when receiver has terminated.
diff --git a/Network/HTTP2/Client.hs b/Network/HTTP2/Client.hs
--- a/Network/HTTP2/Client.hs
+++ b/Network/HTTP2/Client.hs
@@ -82,6 +82,7 @@
     confMySockAddr,
     confPeerSockAddr,
     confReadNTimeout,
+    confOnInformational,
     allocSimpleConfig,
     allocSimpleConfig',
     freeSimpleConfig,
diff --git a/Network/HTTP2/H2/Config.hs b/Network/HTTP2/H2/Config.hs
--- a/Network/HTTP2/H2/Config.hs
+++ b/Network/HTTP2/H2/Config.hs
@@ -33,6 +33,7 @@
     confMySockAddr <- getSocketName s
     confPeerSockAddr <- getPeerName s
     let confReadNTimeout = False
+    let confOnInformational = \_ _ -> return ()
     return Config{..}
 
 -- | Deallocating the resource of the simple configuration.
diff --git a/Network/HTTP2/H2/Context.hs b/Network/HTTP2/H2/Context.hs
--- a/Network/HTTP2/H2/Context.hs
+++ b/Network/HTTP2/H2/Context.hs
@@ -92,6 +92,10 @@
     , threadManager      :: T.ThreadManager
     , receiverDone       :: TVar (Maybe SomeException)
     , workersDone        :: STM Bool
+    , informationalCallback :: StreamId -> TokenHeaderTable -> IO ()
+    -- ^ Client only: called when a 1xx informational response (e.g. 103 Early
+    --   Hints) is received, ahead of the final response. Copied from
+    --   'confOnInformational'; no-op by default.
     }
 {- FOURMOLU_ENABLE -}
 
@@ -139,6 +143,7 @@
     let peerSockAddr = confPeerSockAddr
     threadManager   <- T.newThreadManager timmgr
     receiverDone    <- newTVarIO Nothing
+    let informationalCallback = confOnInformational
     let workersDone = fromMaybe (T.isAllGone threadManager) mdone
     return Context{..}
   where
diff --git a/Network/HTTP2/H2/Receiver.hs b/Network/HTTP2/H2/Receiver.hs
--- a/Network/HTTP2/H2/Receiver.hs
+++ b/Network/HTTP2/H2/Receiver.hs
@@ -387,6 +387,27 @@
   where
     dep = streamDependency p
 
+-- | Handle a decoded response HEADERS section. On the client, a 1xx
+--   informational response (e.g. 103 Early Hints) is delivered to the
+--   informational callback and the stream keeps waiting for the final response;
+--   otherwise the headers become the (final) response.
+onResponseHeaders
+    :: Context
+    -> StreamId
+    -> Maybe ClosedCode
+    -> Bool
+    -> TokenHeaderTable
+    -> IO StreamState
+onResponseHeaders ctx streamId hcl endOfStream tbl
+    | endOfStream = return $ Open hcl (NoBody tbl)
+    | role ctx == Client && isInformational = do
+        informationalCallback ctx streamId tbl
+        return $ Open hcl JustOpened
+    | otherwise = return $ Open hcl (HasBody tbl)
+  where
+    isInformational =
+        maybe False ("1" `BS.isPrefixOf`) $ getFieldValue tokenStatus (snd tbl)
+
 stream
     :: FrameType
     -> FrameHeader
@@ -416,11 +437,7 @@
             if endOfHeader
                 then do
                     tbl <- hpackDecodeHeader frag streamId ctx
-                    return $
-                        if endOfStream
-                            then -- turned into HalfClosedRemote in processState
-                                Open hcl (NoBody tbl)
-                            else Open hcl (HasBody tbl)
+                    onResponseHeaders ctx streamId hcl endOfStream tbl
                 else do
                     let siz = BS.length frag
                     return $ Open hcl $ Continued [frag] siz 1 endOfStream
@@ -522,11 +539,7 @@
                 then do
                     let hdrblk = BS.concat $ reverse rfrags'
                     tbl <- hpackDecodeHeader hdrblk streamId ctx
-                    return $
-                        if endOfStream
-                            then -- turned into HalfClosedRemote in processState
-                                Open hcl (NoBody tbl)
-                            else Open hcl (HasBody tbl)
+                    onResponseHeaders ctx streamId hcl endOfStream tbl
                 else return $ Open hcl $ Continued rfrags' siz' n' endOfStream
 
 -- (No state transition)
diff --git a/Network/HTTP2/H2/Sender.hs b/Network/HTTP2/H2/Sender.hs
--- a/Network/HTTP2/H2/Sender.hs
+++ b/Network/HTTP2/H2/Sender.hs
@@ -167,6 +167,10 @@
                         (off', mout') <- outputHeader strm hdr mnext tlrmkr sync off
                         sync mout'
                         return off'
+                    OInformational hdr -> do
+                        off' <- outputInformational strm hdr off
+                        sync Nothing
+                        return off'
                     _ -> do
                         sws <- getStreamWindowSize strm
                         cws <- getConnectionWindowSize ctx -- not 0
@@ -209,6 +213,21 @@
                 Just next -> do
                     let out' = Output strm (ONext next tlrmkr) sync
                     return (off, Just out')
+
+        ----------------------------------------------------------------
+        -- Emit an informational (1xx) HEADERS section. Unlike 'outputHeader',
+        -- this never sets END_STREAM and never half-closes the stream, so the
+        -- final response can still be sent afterwards.
+        outputInformational
+            :: Stream
+            -> [Header]
+            -> Offset
+            -> IO Offset
+        outputInformational strm hdr off0 = do
+            let sid = streamNumber strm
+            (ths, _) <- toTokenHeaderTable $ fixHeaders hdr
+            off' <- headerContinue sid ths False {- not endOfStream -} off0
+            flushIfNecessary off'
 
         ----------------------------------------------------------------
         output :: Output -> Offset -> WindowSize -> IO (Offset, Maybe Output)
diff --git a/Network/HTTP2/H2/Types.hs b/Network/HTTP2/H2/Types.hs
--- a/Network/HTTP2/H2/Types.hs
+++ b/Network/HTTP2/H2/Types.hs
@@ -190,6 +190,7 @@
     = OHeader [Header] (Maybe DynaNext) TrailersMaker
     | OPush TokenHeaderList StreamId -- associated stream id from client
     | ONext DynaNext TrailersMaker
+    | OInformational [Header]
 
 data Sync = Done | Cont Output
 
@@ -271,6 +272,12 @@
     , confPeerSockAddr :: SockAddr
     -- ^ This is copied into 'Aux', if exist, on server.
     , confReadNTimeout :: Bool
+    , confOnInformational :: StreamId -> TokenHeaderTable -> IO ()
+    -- ^ Client only: called when a 1xx informational response (e.g. 103 Early
+    --   Hints) is received on the given stream, ahead of the final response.
+    --   No-op by default.
+    --
+    --   @since 5.4.2
     }
 
 -- | Default config. This is just a template to modify via
@@ -287,6 +294,7 @@
         , confMySockAddr = SockAddrInet 0 0
         , confPeerSockAddr = SockAddrInet 0 0
         , confReadNTimeout = False
+        , confOnInformational = \_ _ -> return ()
         }
 
 isAsyncException :: Exception e => e -> Bool
diff --git a/Network/HTTP2/Server.hs b/Network/HTTP2/Server.hs
--- a/Network/HTTP2/Server.hs
+++ b/Network/HTTP2/Server.hs
@@ -62,6 +62,7 @@
     confMySockAddr,
     confPeerSockAddr,
     confReadNTimeout,
+    confOnInformational,
     allocSimpleConfig,
     allocSimpleConfig',
     freeSimpleConfig,
diff --git a/Network/HTTP2/Server/Worker.hs b/Network/HTTP2/Server/Worker.hs
--- a/Network/HTTP2/Server/Worker.hs
+++ b/Network/HTTP2/Server/Worker.hs
@@ -6,6 +6,7 @@
 ) where
 
 import Control.Concurrent.STM
+import qualified Data.ByteString.Char8 as C8
 import Data.IORef
 import Network.HTTP.Semantics
 import Network.HTTP.Semantics.IO
@@ -29,6 +30,7 @@
                     { auxTimeHandle = th
                     , auxMySockAddr = mySockAddr
                     , auxPeerSockAddr = peerSockAddr
+                    , auxSendInformational = sendInformational ctx strm
                     }
             request = Request req'
         lc <- newLoopCheck strm Nothing
@@ -45,6 +47,19 @@
             bs <- readBody
             T.resume th -- this is the same as 'tickle'
             return bs
+
+----------------------------------------------------------------
+
+-- | Send an informational (1xx) response, e.g. 103 Early Hints, on the given
+--   stream ahead of the final response. This is wired into 'auxSendInformational'
+--   so that a server (or WAI handler via Warp) can emit early hints. It blocks
+--   until the informational HEADERS have been handed to the sender, preserving
+--   ordering with respect to the final response.
+sendInformational :: Context -> Stream -> Status -> ResponseHeaders -> IO ()
+sendInformational ctx strm st hdrs = do
+    lc <- newLoopCheck strm Nothing
+    let hdr = (":status", C8.pack (show (statusCode st))) : hdrs
+    syncWithSender ctx strm (OInformational hdr) lc
 
 ----------------------------------------------------------------
 
diff --git a/http2.cabal b/http2.cabal
--- a/http2.cabal
+++ b/http2.cabal
@@ -1,6 +1,6 @@
 cabal-version:      >=1.10
 name:               http2
-version:            5.4.1
+version:            5.4.2
 license:            BSD3
 license-file:       LICENSE
 maintainer:         Kazu Yamamoto <kazu@iij.ad.jp>
@@ -121,7 +121,7 @@
         network-byte-order >=0.1.7 && <0.2,
         network-control >=0.1 && <0.2,
         stm >=2.5 && <2.6,
-        time-manager >=0.2.3 && <0.4,
+        time-manager >=0.3.0 && <0.4,
         unix-time >=0.4.11 && <0.6,
         utf8-string >=1.0 && <1.1
 
diff --git a/test/HTTP2/ServerSpec.hs b/test/HTTP2/ServerSpec.hs
--- a/test/HTTP2/ServerSpec.hs
+++ b/test/HTTP2/ServerSpec.hs
@@ -49,6 +49,17 @@
                 threadDelay 10000
                 runClient allocSimpleConfig
 
+        it "delivers 103 Early Hints to the client's informational handler" $
+            E.bracket (forkIO runServer) killThread $ \_ -> do
+                threadDelay 10000
+                hintsRef <- newIORef []
+                runClientEarly hintsRef >>= (`shouldBe` Just ok200)
+                hints <- readIORef hintsRef
+                map (getFieldValue (toToken "link") . snd) hints
+                    `shouldBe` [ Just "</style.css>; rel=preload; as=style"
+                               , Just "</app.js>; rel=preload; as=script"
+                               ]
+
         it "should always send the connection preface first" $ do
             prefaceVar <- newEmptyMVar
             E.bracket (forkIO (runFakeServer prefaceVar)) killThread $ \_ -> do
@@ -103,9 +114,13 @@
         threadDelay 10000
 
 server :: Server
-server req _aux sendResponse = case requestMethod req of
+server req aux sendResponse = case requestMethod req of
     Just "GET" -> case requestPath req of
         Just "/" -> sendResponse responseHello []
+        Just "/early" -> do
+            auxSendInformational aux earlyHints103 [("link", "</style.css>; rel=preload; as=style")]
+            auxSendInformational aux earlyHints103 [("link", "</app.js>; rel=preload; as=script")]
+            sendResponse responseHello []
         Just "/stream" -> sendResponse responseInfinite []
         Just "/push" -> do
             let pp = pushPromise "/push-pp" responsePP 0
@@ -122,6 +137,9 @@
     header = [("Content-Type", "text/plain")]
     body = byteString "Hello, world!\n"
 
+earlyHints103 :: Status
+earlyHints103 = mkStatus 103 "Early Hints"
+
 responsePP :: Response
 responsePP = responseBuilder ok200 header body
   where
@@ -172,6 +190,17 @@
 trailersMaker ctx (Just bs) = return $ NextTrailersMaker $ trailersMaker ctx'
   where
     !ctx' = CH.hashUpdate ctx bs
+
+-- | Request @/early@ with an informational handler installed, recording each
+-- 103 Early Hints section and returning the final response status.
+runClientEarly :: IORef [TokenHeaderTable] -> IO (Maybe Status)
+runClientEarly hintsRef = runTCPClient host port $ \s ->
+    E.bracket (allocSimpleConfig s 4096) freeSimpleConfig $ \conf0 ->
+        C.run cliconf (conf0{confOnInformational = onInformational }) $ \sendRequest _aux ->
+            sendRequest (C.requestNoBody methodGet "/early" []) (return . C.responseStatus)
+  where
+    cliconf = C.defaultClientConfig{C.authority = host}
+    onInformational _sid tbl = modifyIORef' hintsRef (++ [tbl])
 
 runClient :: (Socket -> BufferSize -> IO Config) -> IO ()
 runClient allocConfig =