diff --git a/mercurial/bundle2.py b/mercurial/bundle2.py
--- a/mercurial/bundle2.py
+++ b/mercurial/bundle2.py
@@ -1715,8 +1715,6 @@
             part.addparam(
                 b'targetphase', b'%d' % phases.secret, mandatory=False
             )
-        if b'exp-sidedata-flag' in repo.requirements:
-            part.addparam(b'exp-sidedata', b'1')
 
     if opts.get(b'streamv2', False):
         addpartbundlestream2(bundler, repo, stream=True)
@@ -1937,13 +1935,7 @@
 
 @parthandler(
     b'changegroup',
-    (
-        b'version',
-        b'nbchanges',
-        b'exp-sidedata',
-        b'treemanifest',
-        b'targetphase',
-    ),
+    (b'version', b'nbchanges', b'treemanifest', b'targetphase',),
 )
 def handlechangegroup(op, inpart):
     """apply a changegroup part on the repo
@@ -1979,13 +1971,6 @@
         )
         op.repo._writerequirements()
 
-    bundlesidedata = bool(b'exp-sidedata' in inpart.params)
-    reposidedata = bool(b'exp-sidedata-flag' in op.repo.requirements)
-    if reposidedata and not bundlesidedata:
-        msg = b"repository is using sidedata but the bundle source do not"
-        hint = b'this is currently unsupported'
-        raise error.Abort(msg, hint=hint)
-
     extrakwargs = {}
     targetphase = inpart.params.get(b'targetphase')
     if targetphase is not None:
@@ -2577,7 +2562,5 @@
         part.addparam(b'version', cgversion)
         if b'treemanifest' in repo.requirements:
             part.addparam(b'treemanifest', b'1')
-        if b'exp-sidedata-flag' in repo.requirements:
-            part.addparam(b'exp-sidedata', b'1')
 
     return bundler
diff --git a/mercurial/changelog.py b/mercurial/changelog.py
--- a/mercurial/changelog.py
+++ b/mercurial/changelog.py
@@ -362,6 +362,87 @@
 
 
 class changelog(revlog.revlog):
+    def _addrevision(
+        self,
+        node,
+        rawtext,
+        transaction,
+        link,
+        p1,
+        p2,
+        flags,
+        cachedelta,
+        ifh,
+        dfh,
+        alwayscache=False,
+        deltacomputer=None,
+    ):
+        assert flags & revlog.REVIDX_SIDEDATA
+        return revlog.revlog._addrevision(
+            self,
+            node,
+            rawtext,
+            transaction,
+            link,
+            p1,
+            p2,
+            flags,
+            cachedelta,
+            ifh,
+            dfh,
+            alwayscache=alwayscache,
+            deltacomputer=deltacomputer,
+        )
+
+    def addgroup(self, deltas, linkmapper, transaction, addrevisioncb=None):
+        from .revlogutils import sidedata as _sidedata, flagutil
+        from . import mdiff
+
+        def deltascb():
+            for data in deltas:
+                node, p1, p2, linknode, deltabase, delta, flags = data
+                if deltabase == nullid:
+                    delta = mdiff.patch(b'', delta)
+                else:
+                    delta = mdiff.patch(self._revisiondata(deltabase)[0], delta)
+                if flags & revlog.REVIDX_SIDEDATA:
+                    delta, validatehash, sidedata = flagutil.processflagsread(
+                        self, delta, flags
+                    )
+                    if validatehash:
+                        self.checkhash(delta, node, p1=p1, p2=p2)
+                else:
+                    sidedata = {}
+                sidedata.update(
+                    {
+                        _sidedata.SD_TEST1: b'test-key',
+                        _sidedata.SD_TEST2: b'test-node',
+                    }
+                )
+                flags |= revlog.REVIDX_SIDEDATA
+                data, validatehash = flagutil.processflagswrite(
+                    self, delta, flags, sidedata=sidedata
+                )
+                if validatehash:
+                    self.checkhash(data, node, p1=p1, p2=p2)
+                yield (
+                    node,
+                    p1,
+                    p2,
+                    linknode,
+                    nullid,
+                    mdiff.trivialdiffheader(len(data)) + data,
+                    flags,
+                )
+
+        return revlog.revlog.addgroup(
+            self,
+            deltascb(),
+            linkmapper,
+            transaction,
+            addrevisioncb=addrevisioncb,
+        )
+
     def __init__(self, opener, trypending=False):
         """Load a changelog revlog using an opener.
 
@@ -601,6 +682,13 @@
                 sidedata[sidedatamod.SD_FILESREMOVED] = filesremoved
             if not sidedata:
                 sidedata = None
+        if sidedata is None:
+            sidedata = {}
+        from .revlogutils import sidedata as _sidedata
+
+        sidedata.update(
+            {_sidedata.SD_TEST1: b'test-key', _sidedata.SD_TEST2: b'test-node',}
+        )
 
         if extra:
             extra = encodeextra(extra)
diff --git a/mercurial/configitems.py b/mercurial/configitems.py
--- a/mercurial/configitems.py
+++ b/mercurial/configitems.py
@@ -778,7 +778,7 @@
     experimental=True,
 )
 coreconfigitem(
-    b'format', b'exp-use-side-data', default=False, experimental=True,
+    b'format', b'exp-use-side-data', default=True, experimental=True,
 )
 coreconfigitem(
     b'format', b'internal-phase', default=False, experimental=True,
diff --git a/mercurial/exchange.py b/mercurial/exchange.py
--- a/mercurial/exchange.py
+++ b/mercurial/exchange.py
@@ -1070,8 +1070,6 @@
         cgpart.addparam(b'version', version)
     if b'treemanifest' in pushop.repo.requirements:
         cgpart.addparam(b'treemanifest', b'1')
-    if b'exp-sidedata-flag' in pushop.repo.requirements:
-        cgpart.addparam(b'exp-sidedata', b'1')
 
     def handlereply(op):
         """extract addchangegroup returns from server reply"""
@@ -2560,9 +2558,6 @@
     if b'treemanifest' in repo.requirements:
         part.addparam(b'treemanifest', b'1')
 
-    if b'exp-sidedata-flag' in repo.requirements:
-        part.addparam(b'exp-sidedata', b'1')
-
     if (
         kwargs.get('narrow', False)
         and kwargs.get('narrow_acl', False)
diff --git a/mercurial/wireprotov2server.py b/mercurial/wireprotov2server.py
--- a/mercurial/wireprotov2server.py
+++ b/mercurial/wireprotov2server.py
@@ -1046,7 +1046,7 @@
         followingdata = []
 
         if b'revision' in fields:
-            revisiondata = cl.rawdata(node)
+            revisiondata = cl._revisiondata(node)[0]
             followingmeta.append((b'revision', len(revisiondata)))
             followingdata.append(revisiondata)