diff --git a/mercurial/configitems.py b/mercurial/configitems.py
--- a/mercurial/configitems.py
+++ b/mercurial/configitems.py
@@ -754,7 +754,7 @@
     experimental=True,
 )
 coreconfigitem(
-    b'format', b'use-side-data', default=False, experimental=True,
+    b'format', b'exp-use-side-data', default=False, experimental=True,
 )
 coreconfigitem(
     b'format', b'internal-phase', default=False, experimental=True,
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -3526,8 +3526,8 @@
         if ui.configbool(b'format', b'sparse-revlog'):
             requirements.add(SPARSEREVLOG_REQUIREMENT)
 
-    # experimental config: format.use-side-data
-    if ui.configbool(b'format', b'use-side-data'):
+    # experimental config: format.exp-use-side-data
+    if ui.configbool(b'format', b'exp-use-side-data'):
         requirements.add(SIDEDATA_REQUIREMENT)
     # experimental config: format.exp-use-copies-side-data-changeset
     if ui.configbool(b'format', b'exp-use-copies-side-data-changeset'):
diff --git a/tests/test-copies-in-changeset.t b/tests/test-copies-in-changeset.t
--- a/tests/test-copies-in-changeset.t
+++ b/tests/test-copies-in-changeset.t
@@ -484,7 +484,7 @@
   $ hg debugsidedata -m -- 0
   $ cat << EOF > .hg/hgrc
   > [format]
-  > use-side-data = yes
+  > exp-use-side-data = yes
   > exp-use-copies-side-data-changeset = no
   > EOF
   $ hg debugupgraderepo --run --quiet --no-backup > /dev/null
diff --git a/tests/test-sidedata.t b/tests/test-sidedata.t
--- a/tests/test-sidedata.t
+++ b/tests/test-sidedata.t
@@ -10,7 +10,7 @@
   > testsidedata=$TESTDIR/testlib/ext-sidedata.py
   > EOF
 
-  $ hg init test-sidedata --config format.use-side-data=yes
+  $ hg init test-sidedata --config format.exp-use-side-data=yes
   $ cd test-sidedata
   $ echo aaa > a
   $ hg add a
@@ -48,7 +48,7 @@
 Check that we can upgrade to sidedata
 -------------------------------------
 
-  $ hg init up-no-side-data --config format.use-side-data=no
+  $ hg init up-no-side-data --config format.exp-use-side-data=no
   $ hg debugformat -v -R up-no-side-data
   format-variant    repo config default
   fncache:           yes    yes     yes
@@ -60,7 +60,7 @@
   plain-cl-delta:    yes    yes     yes
   compression:       zlib   zlib    zlib
   compression-level: default default default
-  $ hg debugformat -v -R up-no-side-data --config format.use-side-data=yes
+  $ hg debugformat -v -R up-no-side-data --config format.exp-use-side-data=yes
   format-variant    repo config default
   fncache:           yes    yes     yes
   dotencode:         yes    yes     yes
@@ -71,12 +71,12 @@
   plain-cl-delta:    yes    yes     yes
   compression:       zlib   zlib    zlib
   compression-level: default default default
-  $ hg debugupgraderepo -R up-no-side-data --config format.use-side-data=yes > /dev/null
+  $ hg debugupgraderepo -R up-no-side-data --config format.exp-use-side-data=yes > /dev/null
 
 Check that we can downgrade from sidedata
 -----------------------------------------
 
-  $ hg init up-side-data --config format.use-side-data=yes
+  $ hg init up-side-data --config format.exp-use-side-data=yes
   $ hg debugformat -v -R up-side-data
   format-variant    repo config default
   fncache:           yes    yes     yes
@@ -88,7 +88,7 @@
   plain-cl-delta:    yes    yes     yes
   compression:       zlib   zlib    zlib
   compression-level: default default default
-  $ hg debugformat -v -R up-side-data --config format.use-side-data=no
+  $ hg debugformat -v -R up-side-data --config format.exp-use-side-data=no
   format-variant    repo config default
   fncache:           yes    yes     yes
   dotencode:         yes    yes     yes
@@ -99,4 +99,4 @@
   plain-cl-delta:    yes    yes     yes
   compression:       zlib   zlib    zlib
   compression-level: default default default
-  $ hg debugupgraderepo -R up-side-data --config format.use-side-data=no > /dev/null
+  $ hg debugupgraderepo -R up-side-data --config format.exp-use-side-data=no > /dev/null
diff --git a/tests/test-upgrade-repo.t b/tests/test-upgrade-repo.t
--- a/tests/test-upgrade-repo.t
+++ b/tests/test-upgrade-repo.t
@@ -1410,7 +1410,7 @@
 
 upgrade
 
-  $ hg --config format.use-side-data=yes debugupgraderepo --run  --no-backup --config "extensions.sidedata=$TESTDIR/testlib/ext-sidedata.py" >/dev/null
+  $ hg --config format.exp-use-side-data=yes debugupgraderepo --run  --no-backup --config "extensions.sidedata=$TESTDIR/testlib/ext-sidedata.py" >/dev/null
   $ hg debugformat -v
   format-variant    repo config default
   fncache:           yes    yes     yes
@@ -1439,7 +1439,7 @@
 
 downgrade
 
-  $ hg debugupgraderepo --config format.use-side-data=no --run --no-backup > /dev/null
+  $ hg debugupgraderepo --config format.exp-use-side-data=no --run --no-backup > /dev/null
   $ hg debugformat -v
   format-variant    repo config default
   fncache:           yes    yes     yes
@@ -1466,7 +1466,7 @@
 
   $ cat >> .hg/hgrc << EOF
   > [format]
-  > use-side-data=yes
+  > exp-use-side-data=yes
   > EOF
   $ hg debugupgraderepo --run --no-backup > /dev/null
   $ hg debugformat -v