diff --git a/mercurial/wireprotoframing.py b/mercurial/wireprotoframing.py
--- a/mercurial/wireprotoframing.py
+++ b/mercurial/wireprotoframing.py
@@ -21,6 +21,7 @@
 from . import (
     encoding,
     error,
+    pycompat,
     util,
     wireprototypes,
 )
@@ -429,6 +430,26 @@
                             flags=FLAG_COMMAND_RESPONSE_EOS,
                             payload=b'')
 
+def createalternatelocationresponseframe(stream, requestid, location):
+    data = {
+        b'status': b'redirect',
+        b'location': {
+            b'url': location.url,
+            b'mediatype': location.mediatype,
+        }
+    }
+
+    for a in (r'size', r'fullhashes', r'fullhashseed', r'serverdercerts',
+              r'servercadercerts'):
+        value = getattr(location, a)
+        if value is not None:
+            data[b'location'][pycompat.bytestr(a)] = value
+
+    return stream.makeframe(requestid=requestid,
+                            typeid=FRAME_TYPE_COMMAND_RESPONSE,
+                            flags=FLAG_COMMAND_RESPONSE_CONTINUATION,
+                            payload=b''.join(cborutil.streamencode(data)))
+
 def createcommanderrorresponse(stream, requestid, message, args=None):
     # TODO should this be using a list of {'msg': ..., 'args': {}} so atom
     # formatting works consistently?
@@ -813,6 +834,7 @@
 
         def sendframes():
             emitted = False
+            alternatelocationsent = False
             emitter = bufferingcommandresponseemitter(stream, requestid)
             while True:
                 try:
@@ -841,6 +863,25 @@
                     break
 
                 try:
+                    # Alternate location responses can only be the first and
+                    # only object in the output stream.
+                    if isinstance(o, wireprototypes.alternatelocationresponse):
+                        if emitted:
+                            raise error.ProgrammingError(
+                                'alternatelocationresponse seen after initial '
+                                'output object')
+
+                        yield createalternatelocationresponseframe(
+                            stream, requestid, o)
+
+                        alternatelocationsent = True
+                        emitted = True
+                        continue
+
+                    if alternatelocationsent:
+                        raise error.ProgrammingError(
+                            'object follows alternatelocationresponse')
+
                     if not emitted:
                         yield createcommandresponseokframe(stream, requestid)
                         emitted = True
@@ -977,6 +1018,7 @@
             'requestid': requestid,
             'command': request[b'name'],
             'args': request[b'args'],
+            'redirect': request.get(b'redirect'),
             'data': entry['data'].getvalue() if entry['data'] else None,
         }
 
diff --git a/mercurial/wireprototypes.py b/mercurial/wireprototypes.py
--- a/mercurial/wireprototypes.py
+++ b/mercurial/wireprototypes.py
@@ -368,3 +368,20 @@
     and the content from this object is used instead.
     """
     data = attr.ib()
+
+@attr.s
+class alternatelocationresponse(object):
+    """Represents a response available at an alternate location.
+
+    Instances are sent in place of actual response objects when the server
+    is sending a "content redirect" response.
+
+    Only compatible with wire protocol version 2.
+    """
+    url = attr.ib()
+    mediatype = attr.ib()
+    size = attr.ib(default=None)
+    fullhashes = attr.ib(default=None)
+    fullhashseed = attr.ib(default=None)
+    serverdercerts = attr.ib(default=None)
+    servercadercerts = attr.ib(default=None)
diff --git a/mercurial/wireprotov2server.py b/mercurial/wireprotov2server.py
--- a/mercurial/wireprotov2server.py
+++ b/mercurial/wireprotov2server.py
@@ -312,7 +312,7 @@
     res.headers[b'Content-Type'] = FRAMINGTYPE
 
     try:
-        objs = dispatch(repo, proto, command['command'])
+        objs = dispatch(repo, proto, command['command'], command['redirect'])
 
         action, meta = reactor.oncommandresponsereadyobjects(
             outstream, command['requestid'], objs)
@@ -339,7 +339,7 @@
 def getdispatchrepo(repo, proto, command):
     return repo.filtered('served')
 
-def dispatch(repo, proto, command):
+def dispatch(repo, proto, command, redirect):
     """Run a wire protocol command.
 
     Returns an iterable of objects that will be sent to the client.
@@ -364,8 +364,17 @@
             yield o
         return
 
+    if redirect:
+        redirecttargets = redirect[b'targets']
+        redirecthashes = redirect[b'hashes']
+    else:
+        redirecttargets = []
+        redirecthashes = []
+
     cacher = makeresponsecacher(repo, proto, command, args,
-                                cborutil.streamencode)
+                                cborutil.streamencode,
+                                redirecttargets=redirecttargets,
+                                redirecthashes=redirecthashes)
 
     # But we have no cacher. Do default handling.
     if not cacher:
@@ -751,7 +760,8 @@
 
     return cachekeyfn
 
-def makeresponsecacher(repo, proto, command, args, objencoderfn):
+def makeresponsecacher(repo, proto, command, args, objencoderfn,
+                       redirecttargets, redirecthashes):
     """Construct a cacher for a cacheable command.
 
     Returns an ``iwireprotocolcommandcacher`` instance.
diff --git a/tests/test-http-api-httpv2.t b/tests/test-http-api-httpv2.t
--- a/tests/test-http-api-httpv2.t
+++ b/tests/test-http-api-httpv2.t
@@ -430,10 +430,10 @@
   s>     Server: testing stub value\r\n
   s>     Date: $HTTP_DATE$\r\n
   s>     Content-Type: text/plain\r\n
-  s>     Content-Length: 205\r\n
+  s>     Content-Length: 223\r\n
   s>     \r\n
   s>     received: 1 1 1 \xa2Dargs\xa2Dbar1CvalCfooDval1DnameHcommand1\n
-  s>     ["runcommand", {"args": {"bar1": "val", "foo": "val1"}, "command": "command1", "data": null, "requestid": 1}]\n
+  s>     ["runcommand", {"args": {"bar1": "val", "foo": "val1"}, "command": "command1", "data": null, "redirect": null, "requestid": 1}]\n
   s>     received: <no frame>\n
   s>     {"action": "noop"}
 
diff --git a/tests/test-wireproto-content-redirects.t b/tests/test-wireproto-content-redirects.t
--- a/tests/test-wireproto-content-redirects.t
+++ b/tests/test-wireproto-content-redirects.t
@@ -1,11 +1,20 @@
   $ . $TESTDIR/wireprotohelpers.sh
 
+  $ cat >> $HGRCPATH << EOF
+  > [extensions]
+  > blackbox =
+  > [blackbox]
+  > track = simplecache
+  > EOF
+
   $ hg init server
   $ enablehttpv2 server
   $ cd server
   $ cat >> .hg/hgrc << EOF
   > [extensions]
   > simplecache = $TESTDIR/wireprotosimplecache.py
+  > [simplecache]
+  > cacheapi = true
   > EOF
 
   $ echo a0 > a
@@ -1183,5 +1192,178 @@
     }
   ]
 
+Set up the server to issue content redirects to its built-in API server.
+
+  $ cat > redirects.py << EOF
+  > [
+  >   {
+  >     b'name': b'local',
+  >     b'protocol': b'http',
+  >     b'uris': [b'http://example.com/'],
+  >   },
+  > ]
+  > EOF
+
+Request to eventual cache URL should return 404 (validating the cache server works)
+
+  $ sendhttpraw << EOF
+  > httprequest GET api/simplecache/missingkey
+  >     user-agent: test
+  > EOF
+  using raw connection to peer
+  s>     GET /api/simplecache/missingkey HTTP/1.1\r\n
+  s>     Accept-Encoding: identity\r\n
+  s>     user-agent: test\r\n
+  s>     host: $LOCALIP:$HGPORT\r\n (glob)
+  s>     \r\n
+  s> makefile('rb', None)
+  s>     HTTP/1.1 404 Not Found\r\n
+  s>     Server: testing stub value\r\n
+  s>     Date: $HTTP_DATE$\r\n
+  s>     Content-Type: text/plain\r\n
+  s>     Content-Length: 22\r\n
+  s>     \r\n
+  s>     key not found in cache
+
+Send a cacheable request
+
+  $ sendhttpv2peer << EOF
+  > command manifestdata
+  >     nodes eval:[b'\x99\x2f\x47\x79\x02\x9a\x3d\xf8\xd0\x66\x6d\x00\xbb\x92\x4f\x69\x63\x4e\x26\x41']
+  >     tree eval:b''
+  >     fields eval:[b'parents']
+  > EOF
+  creating http peer for wire protocol version 2
+  sending manifestdata command
+  s>     POST /api/exp-http-v2-0002/ro/manifestdata HTTP/1.1\r\n
+  s>     Accept-Encoding: identity\r\n
+  s>     accept: application/mercurial-exp-framing-0005\r\n
+  s>     content-type: application/mercurial-exp-framing-0005\r\n
+  s>     content-length: 128\r\n
+  s>     host: $LOCALIP:$HGPORT\r\n (glob)
+  s>     user-agent: Mercurial debugwireproto\r\n
+  s>     \r\n
+  s>     x\x00\x00\x01\x00\x01\x01\x11\xa3Dargs\xa3Ffields\x81GparentsEnodes\x81T\x99/Gy\x02\x9a=\xf8\xd0fm\x00\xbb\x92OicN&ADtree@DnameLmanifestdataHredirect\xa2Fhashes\x82Fsha256Dsha1Gtargets\x81Elocal
+  s> makefile('rb', None)
+  s>     HTTP/1.1 200 OK\r\n
+  s>     Server: testing stub value\r\n
+  s>     Date: $HTTP_DATE$\r\n
+  s>     Content-Type: application/mercurial-exp-framing-0005\r\n
+  s>     Transfer-Encoding: chunked\r\n
+  s>     \r\n
+  s>     13\r\n
+  s>     \x0b\x00\x00\x01\x00\x02\x011
+  s>     \xa1FstatusBok
+  s>     \r\n
+  received frame(size=11; request=1; stream=2; streamflags=stream-begin; type=command-response; flags=continuation)
+  s>     63\r\n
+  s>     [\x00\x00\x01\x00\x02\x001
+  s>     \xa1Jtotalitems\x01\xa2DnodeT\x99/Gy\x02\x9a=\xf8\xd0fm\x00\xbb\x92OicN&AGparents\x82T\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00T\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00
+  s>     \r\n
+  received frame(size=91; request=1; stream=2; streamflags=; type=command-response; flags=continuation)
+  s>     8\r\n
+  s>     \x00\x00\x00\x01\x00\x02\x002
+  s>     \r\n
+  s>     0\r\n
+  s>     \r\n
+  received frame(size=0; request=1; stream=2; streamflags=; type=command-response; flags=eos)
+  response: gen[
+    {
+      b'totalitems': 1
+    },
+    {
+      b'node': b'\x99/Gy\x02\x9a=\xf8\xd0fm\x00\xbb\x92OicN&A',
+      b'parents': [
+        b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00',
+        b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
+      ]
+    }
+  ]
+
+Cached entry should be available on server
+
+  $ sendhttpraw << EOF
+  > httprequest GET api/simplecache/c045a581599d58608efd3d93d8129841f2af04a0
+  >     user-agent: test
+  > EOF
+  using raw connection to peer
+  s>     GET /api/simplecache/c045a581599d58608efd3d93d8129841f2af04a0 HTTP/1.1\r\n
+  s>     Accept-Encoding: identity\r\n
+  s>     user-agent: test\r\n
+  s>     host: $LOCALIP:$HGPORT\r\n (glob)
+  s>     \r\n
+  s> makefile('rb', None)
+  s>     HTTP/1.1 200 OK\r\n
+  s>     Server: testing stub value\r\n
+  s>     Date: $HTTP_DATE$\r\n
+  s>     Content-Type: application/mercurial-cbor\r\n
+  s>     Content-Length: 91\r\n
+  s>     \r\n
+  s>     \xa1Jtotalitems\x01\xa2DnodeT\x99/Gy\x02\x9a=\xf8\xd0fm\x00\xbb\x92OicN&AGparents\x82T\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00T\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00
+  cbor> [
+    {
+      b'totalitems': 1
+    },
+    {
+      b'node': b'\x99/Gy\x02\x9a=\xf8\xd0fm\x00\xbb\x92OicN&A',
+      b'parents': [
+        b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00',
+        b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
+      ]
+    }
+  ]
+
+2nd request should result in content redirect response
+
+  $ sendhttpv2peer << EOF
+  > command manifestdata
+  >     nodes eval:[b'\x99\x2f\x47\x79\x02\x9a\x3d\xf8\xd0\x66\x6d\x00\xbb\x92\x4f\x69\x63\x4e\x26\x41']
+  >     tree eval:b''
+  >     fields eval:[b'parents']
+  > EOF
+  creating http peer for wire protocol version 2
+  sending manifestdata command
+  s>     POST /api/exp-http-v2-0002/ro/manifestdata HTTP/1.1\r\n
+  s>     Accept-Encoding: identity\r\n
+  s>     accept: application/mercurial-exp-framing-0005\r\n
+  s>     content-type: application/mercurial-exp-framing-0005\r\n
+  s>     content-length: 128\r\n
+  s>     host: $LOCALIP:$HGPORT\r\n (glob)
+  s>     user-agent: Mercurial debugwireproto\r\n
+  s>     \r\n
+  s>     x\x00\x00\x01\x00\x01\x01\x11\xa3Dargs\xa3Ffields\x81GparentsEnodes\x81T\x99/Gy\x02\x9a=\xf8\xd0fm\x00\xbb\x92OicN&ADtree@DnameLmanifestdataHredirect\xa2Fhashes\x82Fsha256Dsha1Gtargets\x81Elocal
+  s> makefile('rb', None)
+  s>     HTTP/1.1 200 OK\r\n
+  s>     Server: testing stub value\r\n
+  s>     Date: $HTTP_DATE$\r\n
+  s>     Content-Type: application/mercurial-exp-framing-0005\r\n
+  s>     Transfer-Encoding: chunked\r\n
+  s>     \r\n
+  s>     *\r\n (glob)
+  s>     \x*\x00\x00\x01\x00\x02\x011 (glob)
+  s>     \xa2Hlocation\xa2ImediatypeX\x1aapplication/mercurial-cborCurl*http://*:$HGPORT/api/simplecache/c045a581599d58608efd3d93d8129841f2af04a0FstatusHredirect (glob)
+  s>     \r\n
+  received frame(size=*; request=1; stream=2; streamflags=stream-begin; type=command-response; flags=continuation) (glob)
+  s>     8\r\n
+  s>     \x00\x00\x00\x01\x00\x02\x001
+  s>     \r\n
+  s>     8\r\n
+  received frame(size=0; request=1; stream=2; streamflags=; type=command-response; flags=continuation)
+  s>     \x00\x00\x00\x01\x00\x02\x002
+  s>     \r\n
+  s>     0\r\n
+  s>     \r\n
+  received frame(size=0; request=1; stream=2; streamflags=; type=command-response; flags=eos)
+  abort: redirect responses not yet supported
+  [255]
+
   $ cat error.log
   $ killdaemons.py
+
+  $ cat .hg/blackbox.log
+  *> cacher constructed for manifestdata (glob)
+  *> cache miss for c045a581599d58608efd3d93d8129841f2af04a0 (glob)
+  *> storing cache entry for c045a581599d58608efd3d93d8129841f2af04a0 (glob)
+  *> cacher constructed for manifestdata (glob)
+  *> cache hit for c045a581599d58608efd3d93d8129841f2af04a0 (glob)
+  *> sending content redirect for c045a581599d58608efd3d93d8129841f2af04a0 to http://*:$HGPORT/api/simplecache/c045a581599d58608efd3d93d8129841f2af04a0 (glob)
diff --git a/tests/test-wireproto-serverreactor.py b/tests/test-wireproto-serverreactor.py
--- a/tests/test-wireproto-serverreactor.py
+++ b/tests/test-wireproto-serverreactor.py
@@ -69,6 +69,7 @@
             b'requestid': 1,
             b'command': b'mycommand',
             b'args': {},
+            b'redirect': None,
             b'data': None,
         })
 
@@ -86,6 +87,7 @@
             b'requestid': 41,
             b'command': b'mycommand',
             b'args': {b'foo': b'bar'},
+            b'redirect': None,
             b'data': None,
         })
 
@@ -100,6 +102,7 @@
             b'requestid': 1,
             b'command': b'mycommand',
             b'args': {b'foo': b'bar', b'biz': b'baz'},
+            b'redirect': None,
             b'data': None,
         })
 
@@ -115,6 +118,7 @@
             b'requestid': 1,
             b'command': b'mycommand',
             b'args': {},
+            b'redirect': None,
             b'data': b'data!',
         })
 
@@ -137,6 +141,7 @@
             b'requestid': 1,
             b'command': b'mycommand',
             b'args': {},
+            b'redirect': None,
             b'data': b'data1data2data3',
         })
 
@@ -160,6 +165,7 @@
                 b'key': b'val',
                 b'foo': b'bar',
             },
+            b'redirect': None,
             b'data': b'value1value2',
         })
 
@@ -235,6 +241,7 @@
                 b'requestid': 1,
                 b'command': b'command',
                 b'args': {},
+                b'redirect': None,
                 b'data': None,
             })
 
@@ -291,12 +298,14 @@
             b'requestid': 3,
             b'command': b'command3',
             b'args': {b'biz': b'baz', b'key': b'val'},
+            b'redirect': None,
             b'data': None,
         })
         self.assertEqual(results[5][1], {
             b'requestid': 1,
             b'command': b'command1',
             b'args': {b'foo': b'bar', b'key1': b'val'},
+            b'redirect': None,
             b'data': None,
         })
 
diff --git a/tests/wireprotosimplecache.py b/tests/wireprotosimplecache.py
--- a/tests/wireprotosimplecache.py
+++ b/tests/wireprotosimplecache.py
@@ -12,6 +12,7 @@
     registrar,
     repository,
     util,
+    wireprotoserver,
     wireprototypes,
     wireprotov2server,
 )
@@ -25,18 +26,59 @@
 configtable = {}
 configitem = registrar.configitem(configtable)
 
+configitem('simplecache', 'cacheapi',
+           default=False)
 configitem('simplecache', 'cacheobjects',
            default=False)
 configitem('simplecache', 'redirectsfile',
            default=None)
 
+# API handler that makes cached keys available.
+def handlecacherequest(rctx, req, res, checkperm, urlparts):
+    if rctx.repo.ui.configbool('simplecache', 'cacheobjects'):
+        res.status = b'500 Internal Server Error'
+        res.setbodybytes(b'cacheobjects not supported for api server')
+        return
+
+    if not urlparts:
+        res.status = b'200 OK'
+        res.headers[b'Content-Type'] = b'text/plain'
+        res.setbodybytes(b'simple cache server')
+        return
+
+    key = b'/'.join(urlparts)
+
+    if key not in CACHE:
+        res.status = b'404 Not Found'
+        res.headers[b'Content-Type'] = b'text/plain'
+        res.setbodybytes(b'key not found in cache')
+        return
+
+    res.status = b'200 OK'
+    res.headers[b'Content-Type'] = b'application/mercurial-cbor'
+    res.setbodybytes(CACHE[key])
+
+def cachedescriptor(req, repo):
+    return {}
+
+wireprotoserver.API_HANDLERS[b'simplecache'] = {
+    'config': (b'simplecache', b'cacheapi'),
+    'handler': handlecacherequest,
+    'apidescriptor': cachedescriptor,
+}
+
 @interfaceutil.implementer(repository.iwireprotocolcommandcacher)
 class memorycacher(object):
-    def __init__(self, ui, command, encodefn):
+    def __init__(self, ui, command, encodefn, redirecttargets, redirecthashes,
+                 req):
         self.ui = ui
         self.encodefn = encodefn
+        self.redirecttargets = redirecttargets
+        self.redirecthashes = redirecthashes
+        self.req = req
         self.key = None
         self.cacheobjects = ui.configbool('simplecache', 'cacheobjects')
+        self.cacheapi = ui.configbool('simplecache', 'cacheapi')
         self.buffered = []
 
         ui.log('simplecache', 'cacher constructed for %s\n', command)
@@ -65,6 +107,37 @@
         entry = CACHE[self.key]
         self.ui.log('simplecache', 'cache hit for %s\n', self.key)
 
+        redirectable = True
+
+        if not self.cacheapi:
+            redirectable = False
+        elif not self.redirecttargets:
+            redirectable = False
+        else:
+            clienttargets = set(self.redirecttargets)
+            ourtargets = set(t[b'name'] for t in loadredirecttargets(self.ui))
+
+            # We only ever redirect to a single target (for now). So we don't
+            # need to store which target matched.
+            if not clienttargets & ourtargets:
+                redirectable = False
+
+        if redirectable:
+            paths = self.req.dispatchparts[:-3]
+            paths.append(b'simplecache')
+            paths.append(self.key)
+
+            url = b'%s/%s' % (self.req.advertisedbaseurl, b'/'.join(paths))
+
+            #url = b'http://example.com/%s' % self.key
+            self.ui.log('simplecache', 'sending content redirect for %s to '
+                                       '%s\n', self.key, url)
+            response = wireprototypes.alternatelocationresponse(
+                url=url,
+                mediatype=b'application/mercurial-cbor')
+
+            return {'objs': [response]}
+
         if self.cacheobjects:
             return {
                 'objs': entry,
@@ -91,8 +164,10 @@
 
         return []
 
-def makeresponsecacher(orig, repo, proto, command, args, objencoderfn):
-    return memorycacher(repo.ui, command, objencoderfn)
+def makeresponsecacher(orig, repo, proto, command, args, objencoderfn,
+                       redirecttargets, redirecthashes):
+    return memorycacher(repo.ui, command, objencoderfn, redirecttargets,
+                        redirecthashes, proto._req)
 
 def loadredirecttargets(ui):
     path = ui.config('simplecache', 'redirectsfile')