diff --git a/Makefile.inc1 b/Makefile.inc1
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -1071,10 +1071,12 @@
 # tree changes, particularly with respect to removing source files and
 # replacing generated files.  Handle these cases here in an ad-hoc fashion.
 _cleanobj_fast_depend_hack: .PHONY
+.if ${MK_DEPEND_CLEANUP} != "no"
 	@echo ">>> Deleting stale dependencies...";
 	MACHINE=${MACHINE} MACHINE_ARCH=${MACHINE_ARCH} \
-	    ALL_libcompats=${_ALL_libcompats:Q} \
+	    ALL_libcompats=${_ALL_libcompats:Q} MAKE=${MAKE} \
 	    sh ${.CURDIR}/tools/build/depend-cleanup.sh ${OBJTOP} ${SRCTOP}
+.endif
 
 _cleanworldtmp: .PHONY
 .if ${MK_CLEAN} == "yes"
@@ -1168,7 +1170,7 @@
 .endfor
 .else
 	${_+_}cd ${.CURDIR}; env CLEANMK="_NO_INCLUDE_COMPILERMK=t ${CLEANDIR}" \
-	    MAKE=${MAKE} ${WMAKE} _cleanobj_fast_depend_hack
+	    ${WMAKE} _cleanobj_fast_depend_hack
 .endif	# ${MK_CLEAN} == "yes"
 _obj:
 	@echo
diff --git a/share/man/man5/src.conf.5 b/share/man/man5/src.conf.5
--- a/share/man/man5/src.conf.5
+++ b/share/man/man5/src.conf.5
@@ -1,5 +1,5 @@
 .\" DO NOT EDIT-- this file is @generated by tools/build/options/makeman.
-.Dd October 22, 2025
+.Dd December 7, 2025
 .Dt SRC.CONF 5
 .Os
 .Sh NAME
@@ -449,6 +449,14 @@
 Note that recording a new epoch in
 .Pa .clean_build_epoch
 in the root of the source tree will also force a clean world build.
+When set, these options are also in effect:
+.Pp
+.Bl -inset -compact
+.It Va WITHOUT_DEPEND_CLEANUP
+(unless
+.Va WITH_DEPEND_CLEANUP
+is set explicitly)
+.El
 .It Va WITHOUT_CPP
 Do not build
 .Xr cpp 1 .
@@ -537,6 +545,12 @@
 .It Va WITHOUT_DEBUG_FILES
 Avoid building or installing standalone debug files for each
 executable binary and shared library.
+.It Va WITHOUT_DEPEND_CLEANUP
+Do not attempt to detect if the object tree needs cleaning in part or in
+whole before building.
+This speeds up incremental builds, especially when experimenting with
+build options, but may cause the build to inexplicably fail or produce
+non-functioning binaries.
 .It Va WITH_DETECT_TZ_CHANGES
 Make the time handling code detect changes to the timezone files.
 .It Va WITH_DIALOG
diff --git a/share/mk/src.opts.mk b/share/mk/src.opts.mk
--- a/share/mk/src.opts.mk
+++ b/share/mk/src.opts.mk
@@ -86,6 +86,7 @@
     CRYPT \
     CUSE \
     CXGBETOOL \
+    DEPEND_CLEANUP \
     DICT \
     DMAGENT \
     DTRACE \
@@ -513,6 +514,10 @@
 MK_LOADER_VERIEXEC_PASS_MANIFEST := no
 .endif
 
+.if ${MK_CLEAN} == "yes"
+MK_DEPEND_CLEANUP:=	no
+.endif
+
 #
 # MK_* options whose default value depends on another option.
 #
diff --git a/tools/build/depend-cleanup.sh b/tools/build/depend-cleanup.sh
--- a/tools/build/depend-cleanup.sh
+++ b/tools/build/depend-cleanup.sh
@@ -124,10 +124,8 @@
 fi
 
 : ${CLEANMK=""}
-if [ -n "$CLEANMK" ]; then
-	if [ -z "${MAKE+set}" ]; then
-		err "MAKE not set"
-	fi
+if [ -z "${MAKE+set}" ]; then
+	err "MAKE not set"
 fi
 
 if [ -z "${MACHINE+set}" ]; then
@@ -202,9 +200,41 @@
 	awk 'int($1) > 0 { epoch = $1 } END { print epoch }' "$1"
 }
 
+# Regular expression matching the names of src.conf(5) options which
+# don't affect the build.
+#
+# This filter is applied to both the current options and the cached
+# options so we don't force a rebuild just because the filter itself
+# changed.
+IGNORED_OPTS="CLEAN|DEPEND_CLEANUP|EXAMPLES|MAN|TESTS|WARNS|WERROR"
+IGNORED_OPTS="${IGNORED_OPTS}|INSTALL.*|STAGING.*"
+# Also ignore TOOLCHAIN and the options it forces if set.  It is
+# commonly used to speed up a build and is safe to toggle.
+IGNORED_OPTS="${IGNORED_OPTS}|TOOLCHAIN|CLANG.*|LLDB?|LLVM_(BIN|COV).*"
+
+extract_src_opts()
+{
+	$MAKE -C "$SRCTOP" -f "$SRCTOP"/Makefile.inc1 \
+	    -V $'SRC_OPT_LIST:O:ts\n' |
+	egrep -v "^WITH(OUT)?_(${IGNORED_OPTS})="
+}
+
+extract_obj_opts()
+{
+	for fn; do
+		if [ -f "${fn}" ]; then
+			cat "${fn}"
+		else
+			echo "# ${fn}"
+		fi
+	done |
+	egrep -v "^WITH(OUT)?_(${IGNORED_OPTS})="
+}
+
 clean_world()
 {
 	local buildepoch="$1"
+	local srcopts="$2"
 
 	# The caller may set CLEANMK in the environment to make target(s) that
 	# should be invoked instead of just destroying everything.  This is
@@ -227,34 +257,45 @@
 
 	mkdir -p "$OBJTOP"
 	echo "$buildepoch" > "$OBJTOP"/.clean_build_epoch
+	echo "$srcopts" > "$OBJTOP"/.src_opts
 
 	exit 0
 }
 
-check_epoch()
+check_epoch_and_opts()
 {
 	local srcepoch objepoch
+	local srcopts objopts
 
 	srcepoch=$(extract_epoch "$SRCTOP"/.clean_build_epoch)
 	if [ -z "$srcepoch" ]; then
 		err "Malformed .clean_build_epoch; please validate the last line"
 	fi
 
+	srcopts=$(extract_src_opts)
+	if [ -z "$srcopts" ]; then
+		err "Unable to extract source options"
+	fi
+
 	# We don't discriminate between the varying degrees of difference
 	# between epochs.  If it went backwards we could be bisecting across
 	# epochs, in which case the original need to clean likely still stands.
 	objepoch=$(extract_epoch "$OBJTOP"/.clean_build_epoch)
 	if [ -z "$objepoch" ] || [ "$srcepoch" -ne "$objepoch" ]; then
-		if [ "$VERBOSE" ]; then
-			echo "Cleaning - src epoch: $srcepoch, objdir epoch: ${objepoch:-unknown}"
-		fi
+		echo "Cleaning - src epoch: $srcepoch, objdir epoch: ${objepoch:-unknown}"
+		clean_world "$srcepoch" "$srcopts"
+		# NORETURN
+	fi
 
-		clean_world "$srcepoch"
+	objopts=$(extract_obj_opts "$OBJTOP"/.src_opts)
+	if [ "$srcopts" != "$objopts" ]; then
+		echo "Cleaning - build options have changed"
+		clean_world "$srcepoch" "$srcopts"
 		# NORETURN
 	fi
 }
 
-check_epoch
+check_epoch_and_opts
 
 #### Typical dependency cleanup begins here.
 
diff --git a/tools/build/options/WITHOUT_DEPEND_CLEANUP b/tools/build/options/WITHOUT_DEPEND_CLEANUP
new file mode 100644
--- /dev/null
+++ b/tools/build/options/WITHOUT_DEPEND_CLEANUP
@@ -0,0 +1,5 @@
+Do not attempt to detect if the object tree needs cleaning in part or in
+whole before building.
+This speeds up incremental builds, especially when experimenting with
+build options, but may cause the build to inexplicably fail or produce
+non-functioning binaries.