diff --git a/launcher-package/citest/build.sbt b/launcher-package/citest/build.sbt
index 9afef5b42..12f5f108b 100644
--- a/launcher-package/citest/build.sbt
+++ b/launcher-package/citest/build.sbt
@@ -1,5 +1,8 @@
 lazy val check = taskKey[Unit]("")
 lazy val check2 = taskKey[Unit]("")
+lazy val checkEvalArgHandling = taskKey[Unit]("")
+lazy val checkDArgHandling = taskKey[Unit]("")
+lazy val checkXXArgHandling = taskKey[Unit]("")
 
 lazy val root = (project in file("."))
   .settings(
@@ -18,5 +21,47 @@ lazy val root = (project in file("."))
       val ys = IO.readLines(file("err.txt")).toVector.distinct
 
       assert(ys.isEmpty, s"there's an stderr: $ys")
+    },
+    // Regression check for https://github.com/sbt/sbt/issues/9660, run as a
+    // real .bat command by test.bat rather than via a JVM-constructed command
+    // line, so cmd.exe parses the argument the same way it would if a person
+    // had typed it at a prompt.
+    checkEvalArgHandling := {
+      val evalOut = IO.readLines(file("evalOutput.txt")).toVector
+      println(evalOut)
+      assert(
+        evalOut.exists(_.contains("barqux")),
+        s"""eval ("bar") ++ ("qux") should print barqux, but got: $evalOut"""
+      )
+      assert(
+        !evalOut.exists(l =>
+          l.contains("was unexpected at this time") || l.contains("is not recognized")
+        ),
+        s"eval with quoted parens should not trigger a cmd.exe parse error: $evalOut"
+      )
+
+      assert(
+        !file("injected.txt").exists,
+        "the & in the eval argument must not escape sbt.bat's quoting and run as a separate command"
+      )
+    },
+    // Regression check for https://github.com/sbt/sbt/issues/9660, matching a
+    // reporter-confirmed case: "sbt" "-Dfoo=()&calc" pops calc when typed at a
+    // real cmd.exe prompt, even though the whole value sits inside one clean,
+    // matched pair of quotes (no embedded quote characters to lose parity).
+    checkDArgHandling := {
+      assert(
+        !file("injected2.txt").exists,
+        "the & in a -D argument value must not escape sbt.bat's quoting and run as a separate command"
+      )
+    },
+    // Regression check for https://github.com/sbt/sbt/issues/9660: the -XX
+    // handling in args_loop has the same shape as -D, so the same reporter-
+    // confirmed bypass applies to it.
+    checkXXArgHandling := {
+      assert(
+        !file("injected3.txt").exists,
+        "the & in a -XX argument value must not escape sbt.bat's quoting and run as a separate command"
+      )
     }
   )
diff --git a/launcher-package/citest/test.bat b/launcher-package/citest/test.bat
index c35ddae49..608abff66 100755
--- a/launcher-package/citest/test.bat
+++ b/launcher-package/citest/test.bat
@@ -28,4 +28,24 @@ SET SBT_OPTS=-Xmx4g -Dfile.encoding=UTF8
 "freshly-baked\sbt\bin\sbt" -Dsbt.no.format=true --version > version.txt
 "freshly-baked\sbt\bin\sbt" -Dsbt.no.format=true checkVersion
 
+rem Regression test for https://github.com/sbt/sbt/issues/9660, run as a real
+rem .bat command (parsed by cmd.exe the same way as if typed at a prompt),
+rem rather than via a JVM-constructed command line.
+"freshly-baked\sbt\bin\sbt" -Dsbt.no.format=true "eval (\"bar\") ++ (\"qux\")" 1> evalOutput.txt 2> evalErr.txt
+
+"freshly-baked\sbt\bin\sbt" -Dsbt.no.format=true "eval (\"foo\") & echo INJECTED>injected.txt & rem (" 1> evalInjOutput.txt 2> evalInjErr.txt
+
+"freshly-baked\sbt\bin\sbt" -Dsbt.no.format=true checkEvalArgHandling
+
+rem "about" comes before the risky argument so sbt.bat always receives a real
+rem command and cannot fall into an interactive shell (which would hang this
+rem script) even if the & below does escape its quoting.
+"freshly-baked\sbt\bin\sbt" -Dsbt.no.format=true about "-Dfoo=()&copy nul injected2.txt"
+
+"freshly-baked\sbt\bin\sbt" -Dsbt.no.format=true checkDArgHandling
+
+"freshly-baked\sbt\bin\sbt" -Dsbt.no.format=true about "-XXbar=()&copy nul injected3.txt"
+
+"freshly-baked\sbt\bin\sbt" -Dsbt.no.format=true checkXXArgHandling
+
 ENDLOCAL
diff --git a/launcher-package/integration-test/src/test/scala/RunnerMemoryScriptTest.scala b/launcher-package/integration-test/src/test/scala/RunnerMemoryScriptTest.scala
index 7f2c3ffd0..1a68cae65 100644
--- a/launcher-package/integration-test/src/test/scala/RunnerMemoryScriptTest.scala
+++ b/launcher-package/integration-test/src/test/scala/RunnerMemoryScriptTest.scala
@@ -75,12 +75,14 @@ object RunnerMemoryScriptTest extends verify.BasicTestSuite with ShellScriptUtil
     assert(out.contains[String]("-Xss12m"))
 
   // Test for issue #5742: -X options passed directly on command line
+  // Note: the -v preview quotes these (see #9660), so match by substring rather
+  // than exact line equality.
   testOutput("sbt -Xmx1G directly on command line")("-Xmx1G", "-v"): (out: List[String]) =>
-    assert(out.contains[String]("-Xmx1G"))
+    assert(out.exists(_.contains("-Xmx1G")))
 
   testOutput("sbt -Xms512M -Xmx1G directly on command line")("-Xms512M", "-Xmx1G", "-v"):
     (out: List[String]) =>
-      assert(out.contains[String]("-Xms512M"))
-      assert(out.contains[String]("-Xmx1G"))
+      assert(out.exists(_.contains("-Xms512M")))
+      assert(out.exists(_.contains("-Xmx1G")))
 
 end RunnerMemoryScriptTest
diff --git a/launcher-package/integration-test/src/test/scala/RunnerScriptTest.scala b/launcher-package/integration-test/src/test/scala/RunnerScriptTest.scala
index ad5774e77..ebf8af331 100644
--- a/launcher-package/integration-test/src/test/scala/RunnerScriptTest.scala
+++ b/launcher-package/integration-test/src/test/scala/RunnerScriptTest.scala
@@ -24,7 +24,8 @@ object RunnerScriptTest extends verify.BasicTestSuite with ShellScriptUtil:
     assert(out.contains[String]("-Dsbt.log.noformat=true"))
 
   testOutput("sbt --color=false")("compile", "--color=false", "-v"): (out: List[String]) =>
-    assert(out.contains[String]("-Dsbt.color=false"))
+    // Note: the -v preview quotes this (see #9660), so match by substring.
+    assert(out.exists(_.contains("-Dsbt.color=false")))
 
   testOutput("sbt --no-colors in SBT_OPTS", sbtOpts = "--no-colors")("compile", "-v"):
     (out: List[String]) =>
@@ -38,16 +39,21 @@ object RunnerScriptTest extends verify.BasicTestSuite with ShellScriptUtil:
     assert(out.contains[String]("-Dxsbt.inc.debug=true"))
 
   testOutput("sbt --supershell=never")("compile", "--supershell=never", "-v"):
-    (out: List[String]) => assert(out.contains[String]("-Dsbt.supershell=never"))
+    (out: List[String]) =>
+      // Note: the -v preview quotes this (see #9660), so match by substring.
+      assert(out.exists(_.contains("-Dsbt.supershell=never")))
 
   testOutput("sbt --timings")("compile", "--timings", "-v"): (out: List[String]) =>
     assert(out.contains[String]("-Dsbt.task.timings=true"))
 
   testOutput("sbt -D arguments")("-Dsbt.supershell=false", "compile", "-v"): (out: List[String]) =>
-    assert(out.contains[String]("-Dsbt.supershell=false"))
+    // Note: the -v preview quotes CLI -D arguments (see #9660), so match by
+    // substring rather than exact line equality.
+    assert(out.exists(_.contains("-Dsbt.supershell=false")))
 
   testOutput("sbt --sbt-version")("--sbt-version", "1.3.13", "-v"): (out: List[String]) =>
-    assert(out.contains[String]("-Dsbt.version=1.3.13"))
+    // Note: the -v preview quotes this (see #9660), so match by substring.
+    assert(out.exists(_.contains("-Dsbt.version=1.3.13")))
 
   testOutput(
     name = "sbt with -Dhttp.proxyHost=proxy -Dhttp.proxyPort=8080 in SBT_OPTS",
@@ -365,6 +371,12 @@ object RunnerScriptTest extends verify.BasicTestSuite with ShellScriptUtil:
       s"Should not have shell expansion errors, but found: ${errorMessages.mkString(", ")}"
     )
 
+  // NOTE on https://github.com/sbt/sbt/issues/9660: an argument with an
+  // unquoted &, (, or ) can be split apart by cmd.exe's parse of the command
+  // line used to *invoke* sbt.bat, before any line of sbt.bat runs -- no code
+  // inside the script can intervene there. Closing that would require a real
+  // executable entry point instead of a .bat file (see the sbtw project).
+
   // Test for issue #8755: Inline comments should be supported in .jvmopts
   testOutput(
     "sbt with inline comments in .jvmopts",
@@ -411,6 +423,8 @@ object RunnerScriptTest extends verify.BasicTestSuite with ShellScriptUtil:
     )
 
   testOutput("sbt --experimental_execution_log=true")("--experimental_execution_log=true", "-v"):
-    (out: List[String]) => assert(out.contains[String]("-Dsbt.experimental_execution_log=true"))
+    (out: List[String]) =>
+      // Note: the -v preview quotes this (see #9660), so match by substring.
+      assert(out.exists(_.contains("-Dsbt.experimental_execution_log=true")))
 
 end RunnerScriptTest
diff --git a/launcher-package/src/universal/bin/sbt.bat b/launcher-package/src/universal/bin/sbt.bat
index 9c5fe2252..68f8d26cb 100755
--- a/launcher-package/src/universal/bin/sbt.bat
+++ b/launcher-package/src/universal/bin/sbt.bat
@@ -537,71 +537,75 @@ if "%~0" == "init" (
   )
 )
 
-if "%g:~0,2%" == "-D" (
-  rem special handling for -D since '=' gets parsed away
-  for /F "tokens=1 delims==" %%a in ("%g%") do (
-    rem make sure it doesn't have the '=' already
-    if "%g%" == "%%a" (
-      if not "%~1" == "" (
-        call :dlog [args_loop] -D argument %~0=%~1
-        set "SBT_ARGS=!SBT_ARGS! %~0=%~1"
-        shift
-        goto args_loop
-      ) else (
-        echo %g% is missing a value
-        goto error
-      )
-    ) else (
-      call :dlog [args_loop] -D argument %~0
-      set "SBT_ARGS=!SBT_ARGS! %~0"
-      goto args_loop
-    )
-  )
-)
+rem NOTE: -D handling below is intentionally flat (goto-based, single-line
+rem `for` bodies) rather than nested if/for blocks. cmd.exe finds a multi-line
+rem block's closing paren by counting every literal ( and ) across the lines
+rem it spans, including ones arriving via variable substitution -- splicing an
+rem argument value (which may itself contain unbalanced-looking parens, see
+rem #9660) into a deeply nested multi-line construct risks miscounting that.
+rem A flat, single-line-per-command shape does not put cmd.exe in a position
+rem where it needs to hunt across multiple lines for a matching paren.
+if not "%g:~0,2%" == "-D" goto args_loop_after_D
+rem special handling for -D since '=' gets parsed away
+set "g_key="
+for /F "tokens=1 delims==" %%a in ("%g%") do set "g_key=%%a"
+if not "%g%" == "%g_key%" goto args_loop_D_has_value
+if "%~1" == "" goto args_loop_D_missing_value
+call :dlog [args_loop] -D argument %~0=%~1
+set SBT_ARGS=!SBT_ARGS! "%~0=%~1"
+shift
+goto args_loop
+:args_loop_D_missing_value
+echo %g% is missing a value
+goto error
+:args_loop_D_has_value
+call :dlog [args_loop] -D argument %~0
+set SBT_ARGS=!SBT_ARGS! "%~0"
+goto args_loop
+:args_loop_after_D
 
-if not "%g:~0,5%" == "-XX:+" if not "%g:~0,5%" == "-XX:-" if "%g:~0,3%" == "-XX" (
-  rem special handling for -XX since '=' gets parsed away
-  for /F "tokens=1 delims==" %%a in ("%g%") do (
-    rem make sure it doesn't have the '=' already
-    if "%g%" == "%%a" (
-      if not "%~1" == "" (
-        call :dlog [args_loop] -XX argument %~0=%~1
-        set "SBT_ARGS=!SBT_ARGS! %~0=%~1"
-        shift
-        goto args_loop
-      ) else (
-        echo %g% is missing a value
-        goto error
-      )
-    ) else (
-      call :dlog [args_loop] -XX argument %~0
-      set "SBT_ARGS=!SBT_ARGS! %~0"
-      goto args_loop
-    )
-  )
-)
+rem See the -D handling above for why this is flat rather than nested blocks.
+if "%g:~0,5%" == "-XX:+" goto args_loop_after_XX
+if "%g:~0,5%" == "-XX:-" goto args_loop_after_XX
+if not "%g:~0,3%" == "-XX" goto args_loop_after_XX
+rem special handling for -XX since '=' gets parsed away
+set "g_key="
+for /F "tokens=1 delims==" %%a in ("%g%") do set "g_key=%%a"
+if not "%g%" == "%g_key%" goto args_loop_XX_has_value
+if "%~1" == "" goto args_loop_XX_missing_value
+call :dlog [args_loop] -XX argument %~0=%~1
+set SBT_ARGS=!SBT_ARGS! "%~0=%~1"
+shift
+goto args_loop
+:args_loop_XX_missing_value
+echo %g% is missing a value
+goto error
+:args_loop_XX_has_value
+call :dlog [args_loop] -XX argument %~0
+set SBT_ARGS=!SBT_ARGS! "%~0"
+goto args_loop
+:args_loop_after_XX
 
 rem handle -X JVM options (e.g., -Xmx1G, -Xms512M, -Xss4M) - fixes #5742
 if "%g:~0,2%" == "-X" (
   call :dlog [args_loop] -X JVM argument %~0
-  call :addJava %~0
+  call :addJava "%~0"
   goto args_loop
 )
 
-if defined sbt_new if "%g:~0,2%" == "--" (
-  rem special handling for -- template arguments since '=' gets parsed away on Windows
-  for /F "tokens=1 delims==" %%a in ("%g%") do (
-    rem make sure it doesn't have the '=' already
-    if "%g%" == "%%a" (
-      if not "%~1" == "" (
-        call :dlog [args_loop] -- argument %~0=%~1
-        set "SBT_ARGS=!SBT_ARGS! %~0=%~1"
-        shift
-        goto args_loop
-      )
-    )
-  )
-)
+rem See the -D handling above for why this is flat rather than nested blocks.
+if not defined sbt_new goto args_loop_after_dashdash
+if not "%g:~0,2%" == "--" goto args_loop_after_dashdash
+rem special handling for -- template arguments since '=' gets parsed away on Windows
+set "g_key="
+for /F "tokens=1 delims==" %%a in ("%g%") do set "g_key=%%a"
+if not "%g%" == "%g_key%" goto args_loop_after_dashdash
+if "%~1" == "" goto args_loop_after_dashdash
+call :dlog [args_loop] -- argument %~0=%~1
+set SBT_ARGS=!SBT_ARGS! "%~0=%~1"
+shift
+goto args_loop
+:args_loop_after_dashdash
 
 rem the %0 (instead of %~0) preserves original argument quoting
 set sbt_args_seen_command=1
@@ -655,7 +659,11 @@ if !sbt_args_print_sbt_script_version! equ 1 (
 call :checkjava
 
 if !run_native_client! equ 1 if not defined sbt_args_print_version (
-  goto :runnative !SBT_ARGS!
+  rem Do not append !SBT_ARGS! here: `goto` ignores it, it is not a real
+  rem argument-passing mechanism, but the text is still spliced into this
+  rem line and re-scanned by cmd.exe, so it is live to shell operators ^(#9660^).
+  rem :runnative reads SBT_ARGS via delayed expansion instead.
+  goto :runnative
   goto :eof
 )
 
@@ -675,7 +683,11 @@ if defined JVM_DEBUG_PORT (
 
 call :sync_preloaded
 
-call :run !SBT_ARGS!
+rem Do not append !SBT_ARGS! to this call: splicing it onto a `call` command
+rem line makes cmd.exe re-tokenize it, letting shell operators inside a
+rem quoted user argument escape their quoting and run ^(#9660^).
+rem :run reads SBT_ARGS via delayed expansion instead.
+call :run
 
 if ERRORLEVEL 1 goto error
 goto end
@@ -700,34 +712,38 @@ if defined sbt_args_no_share (
   set _SBT_OPTS=-Dsbt.global.base=project/.sbtboot -Dsbt.boot.directory=project/.boot -Dsbt.ivy.home=project/.ivy !_SBT_OPTS!
 )
 
+rem NOTE: each user-supplied value below is wrapped in its own quotes before
+rem being appended to _SBT_OPTS. _SBT_OPTS is later spliced unquoted into
+rem exec lines ^(:copyrt, the final java invocation^), so an unquoted shell
+rem operator here would be live to cmd.exe at that point ^(#9660^).
 if defined sbt_args_supershell (
-  set _SBT_OPTS=-Dsbt.supershell=!sbt_args_supershell! !_SBT_OPTS!
+  set _SBT_OPTS="-Dsbt.supershell=!sbt_args_supershell!" !_SBT_OPTS!
 )
 
 if defined sbt_args_sbt_version (
-  set _SBT_OPTS=-Dsbt.version=!sbt_args_sbt_version! !_SBT_OPTS!
+  set _SBT_OPTS="-Dsbt.version=!sbt_args_sbt_version!" !_SBT_OPTS!
 )
 
 if defined sbt_args_sbt_dir (
-  set _SBT_OPTS=-Dsbt.global.base=!sbt_args_sbt_dir! !_SBT_OPTS!
+  set _SBT_OPTS="-Dsbt.global.base=!sbt_args_sbt_dir!" !_SBT_OPTS!
 ) else if defined LOCALAPPDATA (
-  set _SBT_OPTS=-Dsbt.global.base=!LOCALAPPDATA!\sbt !_SBT_OPTS!
+  set _SBT_OPTS="-Dsbt.global.base=!LOCALAPPDATA!\sbt" !_SBT_OPTS!
 )
 
 if defined sbt_args_sbt_boot (
-  set _SBT_OPTS=-Dsbt.boot.directory=!sbt_args_sbt_boot! !_SBT_OPTS!
+  set _SBT_OPTS="-Dsbt.boot.directory=!sbt_args_sbt_boot!" !_SBT_OPTS!
 )
 
 if defined sbt_args_sbt_cache (
-  set _SBT_OPTS=-Dsbt.global.localcache=!sbt_args_sbt_cache! !_SBT_OPTS!
+  set _SBT_OPTS="-Dsbt.global.localcache=!sbt_args_sbt_cache!" !_SBT_OPTS!
 )
 
 if defined sbt_args_ivy (
-  set _SBT_OPTS=-Dsbt.ivy.home=!sbt_args_ivy! !_SBT_OPTS!
+  set _SBT_OPTS="-Dsbt.ivy.home=!sbt_args_ivy!" !_SBT_OPTS!
 )
 
 if defined sbt_args_color (
-  set _SBT_OPTS=-Dsbt.color=!sbt_args_color! !_SBT_OPTS!
+  set _SBT_OPTS="-Dsbt.color=!sbt_args_color!" !_SBT_OPTS!
 )
 
 if defined sbt_args_mem (
@@ -755,7 +771,7 @@ if not defined sbt_args_no_hide_jdk_warnings (
 )
 
 if defined sbt_args_experimental_execution_log (
-  set _SBT_OPTS=-Dsbt.experimental_execution_log=!sbt_args_experimental_execution_log! !_SBT_OPTS!
+  set _SBT_OPTS="-Dsbt.experimental_execution_log=!sbt_args_experimental_execution_log!" !_SBT_OPTS!
 )
 
 rem TODO: _SBT_OPTS needs to be processed as args and diffed against SBT_ARGS
@@ -792,11 +808,14 @@ if defined sbt_args_verbose (
   echo -cp
   echo "!sbt_jar!"
   echo xsbt.boot.Boot
-  if not "%~1" == "" ( call :echolist %* )
+  if defined SBT_ARGS ( call :echolist !SBT_ARGS! )
   echo.
 )
 
-"!_JAVACMD!" !_JAVA_OPTS! !_SBT_OPTS! %JAVA_TOOL_OPTIONS% %JDK_JAVA_OPTIONS% -cp "!sbt_jar!" xsbt.boot.Boot %*
+rem one-hop marker: drop it before the server JVM
+set "SBT_EXPLICIT_JAVA_HOME="
+
+"!_JAVACMD!" !_JAVA_OPTS! !_SBT_OPTS! %JAVA_TOOL_OPTIONS% %JDK_JAVA_OPTIONS% -cp "!sbt_jar!" xsbt.boot.Boot !SBT_ARGS!
 
 goto :eof
 
@@ -804,14 +823,19 @@ goto :eof
 
 set "_SBTNCMD=!SBT_BIN_DIR!sbtn-x86_64-pc-win32.exe"
 
+rem NOTE: SBT_ARGS entries may carry their own embedded quotes, see the
+rem args_loop -D/-XX/catch-all handling above, to keep shell operators safe
+rem across the re-scan below. Do not wrap these set lines in an outer pair
+rem of quotes: that would pair up with an embedded quote instead of its
+rem match, breaking the quoting it is meant to preserve ^(#9660^).
 if defined sbt_args_verbose (
   echo # running native client
   if not "%~1" == "" ( call :echolist %* )
-  set "SBT_ARGS=-v !SBT_ARGS!"
+  set SBT_ARGS=-v !SBT_ARGS!
 )
 
 for %%I in ("!SBT_BIN_DIR!sbt.bat") do set "SBT_SCRIPT=%%~sI"
-set "SBT_ARGS=--sbt-script=!SBT_SCRIPT! %SBT_ARGS%"
+set SBT_ARGS=--sbt-script=!SBT_SCRIPT! %SBT_ARGS%
 
 rem Microsoft Visual C++ 2010 SP1 Redistributable Package (x64) is required
 rem https://www.microsoft.com/en-us/download/details.aspx?id=13523
@@ -885,7 +909,7 @@ exit /B 0
 
 :addJava
   call :dlog [addJava] arg = '%*'
-  set "_JAVA_OPTS=!_JAVA_OPTS! %*"
+  set _JAVA_OPTS=!_JAVA_OPTS! %*
 exit /B 0
 
 :addMemory