diff --git a/runtime/doc/editing.txt b/runtime/doc/editing.txt
index dbff1fc2d2..b3a1e759ad 100644
--- a/runtime/doc/editing.txt
+++ b/runtime/doc/editing.txt
@@ -1209,8 +1209,8 @@ ZZ			Write current file, if modified, and close the current
 ZQ			Quit without checking for changes (same as ":q!").
 
 							*ZR*
-[count]ZR		Performs |:restart|. If a [count] is given, restarts
-			without checking for changes (":restart +qall!").
+[count]ZR		Performs |:restart!|. If a [count] is given, restarts
+			without checking for changes (":restart! +qall!").
 
 MULTIPLE WINDOWS AND BUFFERS				*window-exit*
 
diff --git a/runtime/doc/gui.txt b/runtime/doc/gui.txt
index b21f072e33..0af0a07495 100644
--- a/runtime/doc/gui.txt
+++ b/runtime/doc/gui.txt
@@ -75,20 +75,23 @@ Stop or detach the current UI
 ------------------------------------------------------------------------------
 Restart Nvim
 
-                                                *:restart*
-:restart [+cmd] [command]
+                                                *:restart* *:restart!*
+:restart[!] [+cmd] [command]
                 Restarts Nvim. Sets |v:exitreason|. See also |ZR|.
+                When [!] is included, the session is not restored.
 
-                1. Stops Nvim using `:qall` (or |+cmd|, if given).
-                2. Starts a new Nvim server using the same |v:argv| (except
-                   `-- [file…]` files).
-                3. Attaches all UIs to the new Nvim server and runs `[command]`
+                1. Saves the current session (unless [!] was given).
+                2. Stops Nvim using `:qall` (or |+cmd|, if given).
+                3. Starts a new Nvim server using the same |v:argv| (except
+                   `-- [file…]` files and `-S [file]`), and sets |v:startreason|.
+                4. Restores the saved session (unless [!] was given).
+                5. Attaches all UIs to the new Nvim server and runs `[command]`
                    on it.
 
                 Example: discard changes and stop with `:qall!`, then restart: >
                     :restart +qall!
 <                Example: restart and restore the current session: >
-                    :mksession! Session.vim | restart source Session.vim
+                    :mksession! Session.vim | restart! source Session.vim
 <                Example: restart and update plugins: >
                     :restart lua vim.pack.update()
 <
@@ -96,8 +99,9 @@ Restart Nvim
                 • Only works if the UI and server are on the same system.
                 • Windows limitation: when +cmd is executed, |v:servername|
                   refers to a temporary address.
-                • If no UI handles the "restart" event, this command will lead
-                  to a dangling server process.
+                • If no UI handles the "restart" event, this leaves a dangling
+                  process.
+                • To adjust what `:restart` restores, set 'sessionoptions'.
 
 ------------------------------------------------------------------------------
 Connect UI to a different server
diff --git a/runtime/doc/news.txt b/runtime/doc/news.txt
index 1ab7346ff0..456b2798cc 100644
--- a/runtime/doc/news.txt
+++ b/runtime/doc/news.txt
@@ -191,7 +191,8 @@ EDITOR
   codeblocks via treesitter and executes them as Lua instead of Vimscript.
   (Or use `:{range}lua` to skip the detection.)
 • |:wall| with |++p| auto-creates missing parent directories.
-• |ZR| restarts Nvim (|:restart|).
+• |:restart| now restores the current session while |:restart!| does not.
+• |ZR| restarts Nvim (|:restart!|).
 
 EVENTS
 
@@ -453,6 +454,7 @@ VIMSCRIPT
 • |v:vim_did_init| is set after sourcing |init.vim| but before |load-plugins|.
 • |prompt_appendbuf()| appends text to prompt-buffer.
 • |v:exitreason| is set before |QuitPre|.
+• |v:startreason| differentiates between restart and normal start.
 • |v:starttime| is the process start time (nanoseconds since UNIX epoch).
 
 ==============================================================================
diff --git a/runtime/doc/starting.txt b/runtime/doc/starting.txt
index ce79b9416d..85a4de3eae 100644
--- a/runtime/doc/starting.txt
+++ b/runtime/doc/starting.txt
@@ -434,7 +434,7 @@ Initialization                                  *initialization* *startup*
 At startup, Nvim checks environment variables and files and sets values
 accordingly, proceeding as follows:
 
-1. Set |v:starttime|.
+1. Set |v:starttime| and |v:startreason|.
 
 2. Set the 'shell' option.                      *SHELL* *COMSPEC*
    The environment variable SHELL, if it exists, is used to set the 'shell'
diff --git a/runtime/doc/vvars.txt b/runtime/doc/vvars.txt
index e61bc78624..16a5cd55f0 100644
--- a/runtime/doc/vvars.txt
+++ b/runtime/doc/vvars.txt
@@ -633,6 +633,15 @@ v:stacktrace
 		stack trace.  See also |v:exception|, |v:throwpoint|, and
 		|throw-variables|.
 
+				*v:startreason* *startreason-variable*
+v:startreason
+		The reason Nvim started. Possible values:
+		  - "normal"    normal startup.
+		  - "restart"   started by |:restart|.
+		  - "restart!"  started by |:restart!| or |ZR|.
+
+		Read-only.
+
 				*v:starttime* *starttime-variable*
 v:starttime
 		Timestamp (nanoseconds since UNIX epoch) when the Nvim process
diff --git a/runtime/lua/vim/_core/server.lua b/runtime/lua/vim/_core/server.lua
index 3b05142a33..4d9640ebd6 100644
--- a/runtime/lua/vim/_core/server.lua
+++ b/runtime/lua/vim/_core/server.lua
@@ -1,3 +1,5 @@
+local fs = vim.fs
+local uv = vim.uv
 -- For "--listen" and related functionality.
 
 local M = {}
@@ -97,4 +99,59 @@ function M.rebind_after_restart(canonical_addr, expected_uis)
   end)
 end
 
+-- Called by ex_restart(). Saves the current session and calls back to
+-- ex_restart() with the necessary arguments to restore the session.
+-- TODO: https://github.com/neovim/neovim/issues/34204
+function M.ex_session_restart(after_cmd, quit_cmd)
+  -- Commands to run after restart
+  assert(not after_cmd:find(']==]'))
+
+  -- Use custom quit command if provided
+  if quit_cmd == '' then
+    quit_cmd = 'qall'
+  end
+
+  -- Preserve the value of v:this_session
+  local this_session = vim.v.this_session
+  assert(not this_session:find(']==]'))
+
+  -- Get temp file to write session to
+  local temp_dir = fs.abspath(fs.dirname(fs.dirname(vim.fn.tempname())))
+  assert(not temp_dir:find(']==]'))
+  local fd, session = uv.fs_mkstemp(fs.joinpath(temp_dir, 'restart_session_XXXXXX'))
+  if not fd then
+    error('Failed to get temporary filename for restart session')
+  end
+  uv.fs_close(fd)
+
+  -- Write session
+  local session_arg = vim.fn.fnameescape(session)
+  vim.cmd('%argdelete')
+  vim.cmd.mksession { session_arg, bang = true }
+
+  -- Lua commands to restore the session and remove the session file
+  local after_list = {}
+  table.insert(after_list, ('vim.cmd("source %s")'):format(session_arg))
+  table.insert(after_list, ('pcall(vim.fs.rm, [==[%s]==])'):format(session))
+  table.insert(after_list, ('vim.v.this_session = [==[%s]==]'):format(this_session))
+  -- User provided command
+  if after_cmd ~= '' then
+    table.insert(after_list, ('vim.cmd([==[%s]==])'):format(after_cmd))
+  end
+  -- Concatenate everything together
+  local after = 'lua ' .. table.concat(after_list, ';')
+
+  -- Restart Neovim and run our Lua commands
+  local success, msg = pcall(function()
+    -- "+:::" special argument tells the C handler that this is actually a non-bang restart
+    -- That way, v:startreason can be set correctly
+    vim.cmd.restart { '+:::', quit_cmd, after, bang = true }
+  end)
+
+  if not success then
+    fs.rm(session, { force = true })
+    error(msg)
+  end
+end
+
 return M
diff --git a/runtime/lua/vim/_meta/vvars.gen.lua b/runtime/lua/vim/_meta/vvars.gen.lua
index 543d4169c1..f31865f19c 100644
--- a/runtime/lua/vim/_meta/vvars.gen.lua
+++ b/runtime/lua/vim/_meta/vvars.gen.lua
@@ -667,6 +667,15 @@ vim.v.shell_error = ...
 --- @type table[]
 vim.v.stacktrace = ...
 
+--- The reason Nvim started. Possible values:
+---   - "normal"    normal startup.
+---   - "restart"   started by `:restart`.
+---   - "restart!"  started by `:restart!` or `ZR`.
+---
+--- Read-only.
+--- @type string
+vim.v.startreason = ...
+
 --- Timestamp (nanoseconds since UNIX epoch) when the Nvim process
 --- started.
 ---
diff --git a/src/nvim/channel.c b/src/nvim/channel.c
index 31f6c80bd6..08cd76c398 100644
--- a/src/nvim/channel.c
+++ b/src/nvim/channel.c
@@ -562,9 +562,9 @@ uint64_t channel_from_stdio(bool rpc, CallbackReader on_output, const char **err
     os_set_cloexec(stdout_dup_fd);
     // :restart spawns a replacement server that must not borrow the parent
     // Nvim process console, because that parent process will soon exit.
-    const bool restart_alloc_console = os_env_exists("__NVIM_RESTART_ALLOC_CONSOLE", true);
+    const bool restart_alloc_console = os_env_exists(ENV_RESTART_ALLOC_CONSOLE, true);
     if (restart_alloc_console) {
-      os_unsetenv("__NVIM_RESTART_ALLOC_CONSOLE");
+      os_unsetenv(ENV_RESTART_ALLOC_CONSOLE);
     }
     if (!GetConsoleWindow()) {
       // Borrow the parent's console so CONOUT$ resolves to the real terminal,
diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index d2c339f008..afe356a72c 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -3385,8 +3385,11 @@ static const char *required_env_vars[] = {
   NULL
 };
 
+/// Builds an environment dict for a child process (job).
+///
+/// @param set_nvim_addr  Set the $NVIM env var.
 dict_T *create_environment(const dictitem_T *job_env, const bool clear_env, const bool pty,
-                           const char * const pty_term_name)
+                           const bool set_nvim_addr, const char * const pty_term_name)
 {
   dict_T *env = tv_dict_alloc();
 
@@ -3427,13 +3430,15 @@ dict_T *create_environment(const dictitem_T *job_env, const bool clear_env, cons
   }
 
   // Set $NVIM (in the child process) to v:servername. #3118
-  char *nvim_addr = get_vim_var_str(VV_SEND_SERVER);
-  if (nvim_addr[0] != NUL) {
-    dictitem_T *dv = tv_dict_find(env, S_LEN("NVIM"));
-    if (dv) {
-      tv_dict_item_remove(env, dv);
+  if (set_nvim_addr) {
+    char *nvim_addr = get_vim_var_str(VV_SEND_SERVER);
+    if (nvim_addr[0] != NUL) {
+      dictitem_T *dv = tv_dict_find(env, S_LEN("NVIM"));
+      if (dv) {
+        tv_dict_item_remove(env, dv);
+      }
+      tv_dict_add_str(env, S_LEN("NVIM"), nvim_addr);
     }
-    tv_dict_add_str(env, S_LEN("NVIM"), nvim_addr);
   }
 
   if (job_env) {
@@ -3619,7 +3624,7 @@ void f_jobstart(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
     term_name = term_name ? term_name : "ansi";
   }
 
-  dict_T *env = create_environment(job_env, clear_env, pty, term_name);
+  dict_T *env = create_environment(job_env, clear_env, pty, true, term_name);
   Channel *chan = channel_job_start(argv, NULL, on_stdout, on_stderr, on_exit, pty,
                                     rpc, overlapped, detach, stdin_mode, cwd,
                                     width, height, env, &rettv->vval.v_number);
diff --git a/src/nvim/eval/vars.c b/src/nvim/eval/vars.c
index 803b121133..958af29d7e 100644
--- a/src/nvim/eval/vars.c
+++ b/src/nvim/eval/vars.c
@@ -217,6 +217,7 @@ static struct vimvar {
   VV(VV_VIRTNUM,          "virtnum",          VAR_NUMBER, VV_RO),
   VV(VV_STARTTIME,        "starttime",        VAR_NUMBER, VV_RO),
   VV(VV_EXITREASON,       "exitreason",       VAR_STRING, VV_RO),
+  VV(VV_STARTREASON,      "startreason",      VAR_STRING, VV_RO),
 };
 #undef VV
 
@@ -316,6 +317,7 @@ void evalvars_init(void)
   set_vim_var_nr(VV_SEARCHFORWARD, 1);
   set_vim_var_nr(VV_HLSEARCH, 1);
   set_vim_var_nr(VV_COUNT1, 1);
+  set_vim_var_string(VV_STARTREASON, S_LEN("normal"));
   set_vim_var_special(VV_EXITING, kSpecialVarNull);
 
   set_vim_var_nr(VV_TYPE_NUMBER, VAR_TYPE_NUMBER);
@@ -345,6 +347,15 @@ void evalvars_init(void)
   set_vim_var_partial(VV_LUA, vvlua_partial);
 
   set_reg_var(0);  // default for v:register is not 0 but '"'
+
+  // Set v:startreason via environment variable
+  const char *startreason = os_getenv_noalloc(ENV_STARTREASON);
+  if (strequal(startreason, "restart!") || strequal(startreason, "restart")) {
+    set_vim_var_string(VV_STARTREASON, startreason, -1);
+  }
+  if (os_env_exists(ENV_STARTREASON, false)) {
+    os_unsetenv(ENV_STARTREASON);
+  }
 }
 
 #if defined(EXITFREE)
diff --git a/src/nvim/eval_defs.h b/src/nvim/eval_defs.h
index 7cec3d6167..f45cb35213 100644
--- a/src/nvim/eval_defs.h
+++ b/src/nvim/eval_defs.h
@@ -137,4 +137,5 @@ typedef enum {
   VV_VIRTNUM,
   VV_STARTTIME,
   VV_EXITREASON,
+  VV_STARTREASON,
 } VimVarIndex;
diff --git a/src/nvim/ex_cmds.lua b/src/nvim/ex_cmds.lua
index 5ecb2b2be2..ceece89702 100644
--- a/src/nvim/ex_cmds.lua
+++ b/src/nvim/ex_cmds.lua
@@ -2260,7 +2260,7 @@ M.cmds = {
   },
   {
     command = 'restart',
-    flags = bit.bor(CMDARG, EXTRA, NOTRLCOM),
+    flags = bit.bor(BANG, CMDARG, EXTRA, NOTRLCOM),
     addr_type = 'ADDR_NONE',
     func = 'ex_restart',
   },
diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index 9531fc34c7..194d8af615 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -38,6 +38,7 @@
 #include "nvim/edit.h"
 #include "nvim/errors.h"
 #include "nvim/eval/fs.h"
+#include "nvim/eval/funcs.h"
 #include "nvim/eval/typval.h"
 #include "nvim/eval/typval_defs.h"
 #include "nvim/eval/userfunc.h"
@@ -4975,6 +4976,41 @@ static void ex_quitall(exarg_T *eap)
 /// ":restart +cmd <command>": restart the Nvim server using ":cmd" and runs <command> in the new server.
 static void ex_restart(exarg_T *eap)
 {
+  if (!eap->forceit) {
+    Error err = ERROR_INIT;
+    MAXSIZE_TEMP_ARRAY(args, 2);
+
+    ADD_C(args, CSTR_AS_OBJ(eap->arg));
+    ADD_C(args, CSTR_AS_OBJ(eap->do_ecmd_cmd ? eap->do_ecmd_cmd : ""));
+
+    NLUA_EXEC_STATIC("require'vim._core.server'.ex_session_restart(...)", args, kRetNilBool, NULL,
+                     &err);
+
+    if (ERROR_SET(&err)) {
+      emsg(err.msg);
+    }
+    api_clear_error(&err);
+    return;
+  }
+
+  const char *startreason = "restart!";
+  char *quit_cmd = (eap->do_ecmd_cmd) ? eap->do_ecmd_cmd : "qall";
+  char *after_cmd = eap->arg;
+
+  // "+:::" is how ex_session_restart() signals that it (recursively) called into :restart.
+  if (strequal(quit_cmd, ":::")) {
+    startreason = "restart";
+    // Set quit_cmd and after_cmd from args
+    if (eap->argc > 1) {
+      eap->args[1][eap->arglens[1]] = NUL;
+      quit_cmd = eap->args[1];
+      after_cmd = eap->argc > 2 ? eap->args[2] : "";
+    } else {
+      emsg("restart failed: +cmd did not quit the server");
+      return;
+    }
+  }
+
   Error err = ERROR_INIT;
   const bool no_ui = !ui_active();
   const char *exepath = get_vim_var_str(VV_PROGPATH);
@@ -4992,6 +5028,16 @@ static void ex_restart(exarg_T *eap)
     if (i > 0 && strequal(arg, "--")) {
       break;
     }
+    // Drop "-S [file]". It conflicts with :restart and usually isn't wanted for :restart!
+    if (i > 0 && strequal(arg, "-S")) {
+      if (li->li_next != NULL) {
+        const char *next_arg = tv_get_string(TV_LIST_ITEM_TV(li->li_next));
+        if (next_arg[0] != '-') {
+          li = li->li_next;
+        }
+      }
+      continue;
+    }
     // Drop "-s <scriptfile>": skip the scriptfile arg too.
     if (i > 0 && strequal(arg, "-s")) {
       li = li->li_next;
@@ -5051,11 +5097,10 @@ static void ex_restart(exarg_T *eap)
   bool server_stopped = listen_arg ? server_stop(listen_arg, true) : false;
 #endif
 
+  dict_T *env = create_environment(NULL, false, false, false, NULL);
+  tv_dict_add_str(env, S_LEN(ENV_STARTREASON), startreason);
 #ifdef MSWIN
-  bool restart_alloc_console_env = false;
-  if (os_setenv("__NVIM_RESTART_ALLOC_CONSOLE", "1", 1) == 0) {
-    restart_alloc_console_env = true;
-  }
+  tv_dict_add_str(env, S_LEN(ENV_RESTART_ALLOC_CONSOLE), "1");
 #endif
 
   CallbackReader on_err = CALLBACK_READER_INIT;
@@ -5072,12 +5117,7 @@ static void ex_restart(exarg_T *eap)
   Channel *channel = channel_job_start(argv, exepath,
                                        CALLBACK_READER_INIT, on_err, CALLBACK_NONE,
                                        false, true, true, detach, kChannelStdinPipe,
-                                       NULL, 0, 0, NULL, &exit_status);
-#ifdef MSWIN
-  if (restart_alloc_console_env) {
-    os_unsetenv("__NVIM_RESTART_ALLOC_CONSOLE");
-  }
-#endif
+                                       NULL, 0, 0, env, &exit_status);
   if (!channel) {
     emsg("cannot create a channel job");
     goto fail_1;
@@ -5094,12 +5134,12 @@ static void ex_restart(exarg_T *eap)
   arena_mem_free(result_mem);
   result_mem = NULL;
 
-  if (*eap->arg != NUL) {
+  if (*after_cmd != NUL) {
     // Execute [command] on new server on UIEnter.
     MAXSIZE_TEMP_DICT(autocmd_opts, 3);
     PUT_C(autocmd_opts, "once", BOOLEAN_OBJ(true));
     PUT_C(autocmd_opts, "nested", BOOLEAN_OBJ(true));
-    PUT_C(autocmd_opts, "command", CSTR_AS_OBJ(eap->arg));
+    PUT_C(autocmd_opts, "command", CSTR_AS_OBJ(after_cmd));
     MAXSIZE_TEMP_ARRAY(autocmd_args, 2);
     ADD_C(autocmd_args, CSTR_AS_OBJ("UIEnter"));
     ADD_C(autocmd_args, DICT_OBJ(autocmd_opts));
@@ -5154,7 +5194,6 @@ static void ex_restart(exarg_T *eap)
 
   set_vim_var_string(VV_EXITREASON, S_LEN("restart"));
 
-  char *quit_cmd = (eap->do_ecmd_cmd) ? eap->do_ecmd_cmd : "qall";
   char *quit_cmd_copy = NULL;
 
   // Prepend "confirm " to cmd if :confirm is used
diff --git a/src/nvim/log.c b/src/nvim/log.c
index 58eda798e5..c7c46ff11e 100644
--- a/src/nvim/log.c
+++ b/src/nvim/log.c
@@ -73,7 +73,7 @@ static void log_path_init(void)
       || !log_try_create(log_file_path)) {
     if (user_set) {  // User-provided $NVIM_LOG_FILE.
       // Used by _core/log.lua:check_log_file to validate logfile on startup.
-      os_setenv("__NVIM_LOG_FILE_WANT", log_file_path, true);
+      os_setenv(ENV_LOGFILE_WANT, log_file_path, true);
     }
     // Make $XDG_STATE_HOME if it does not exist.
     char *loghome = get_xdg_home(kXDGStateHome);
@@ -91,7 +91,7 @@ static void log_path_init(void)
     if (len >= size || !log_try_create(log_file_path)) {
       if (!user_set) {  // Default fallback path.
         // Used by _core/log.lua:check_log_file to validate logfile on startup.
-        os_setenv("__NVIM_LOG_FILE_WANT", log_file_path, true);
+        os_setenv(ENV_LOGFILE_WANT, log_file_path, true);
       }
       len = xstrlcpy(log_file_path, "nvim.log", size);
     }
diff --git a/src/nvim/msgpack_rpc/server.c b/src/nvim/msgpack_rpc/server.c
index 48f3e8ce04..2cd7207ff7 100644
--- a/src/nvim/msgpack_rpc/server.c
+++ b/src/nvim/msgpack_rpc/server.c
@@ -54,7 +54,7 @@ bool server_init(const char *listen_addr)
   int rv = server_start(listen_addr);
 
   // TODO(justinmk): this is for log_spec. Can remove this after nvim_log #7062 is merged.
-  if (os_env_exists("__NVIM_TEST_LOG", false)) {
+  if (os_env_exists(ENV_TEST_LOG, false)) {
     ELOG("test log message");
   }
 
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index ddb0966b7d..b2b64b1c5d 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -3302,9 +3302,9 @@ static void nv_Zet(cmdarg_T *cap)
   // "ZR": restart. With count, restart without checking for changes.
   case 'R':
     if (cap->count0 >= 1) {
-      do_cmdline_cmd("restart +qall!");
+      do_cmdline_cmd("restart! +qall!");
     } else {
-      do_cmdline_cmd("restart");
+      do_cmdline_cmd("restart!");
     }
     break;
 
diff --git a/src/nvim/os/os.h b/src/nvim/os/os.h
index cd7db3bf80..d9677cb58b 100644
--- a/src/nvim/os/os.h
+++ b/src/nvim/os/os.h
@@ -25,4 +25,8 @@ extern char *default_lib_dir;
 // IWYU pragma: end_exports
 
 #define ENV_LOGFILE "NVIM_LOG_FILE"
+#define ENV_LOGFILE_WANT "__NVIM_LOG_FILE_WANT"
 #define ENV_NVIM "NVIM"
+#define ENV_RESTART_ALLOC_CONSOLE "__NVIM_RESTART_ALLOC_CONSOLE"
+#define ENV_STARTREASON "__NVIM_STARTREASON"
+#define ENV_TEST_LOG "__NVIM_TEST_LOG"
diff --git a/src/nvim/ui_client.c b/src/nvim/ui_client.c
index e5ad4dcb7d..0a769cfcae 100644
--- a/src/nvim/ui_client.c
+++ b/src/nvim/ui_client.c
@@ -159,7 +159,7 @@ void ui_client_run(void)
   ui_client_attach(tui_width, tui_height, tui_term, tui_rgb);
 
   // TODO(justinmk): this is for log_spec. Can remove this after nvim_log #7062 is merged.
-  if (os_env_exists("__NVIM_TEST_LOG", true)) {
+  if (os_env_exists(ENV_TEST_LOG, true)) {
     ELOG("test log message");
   }
 
diff --git a/src/nvim/vvars.lua b/src/nvim/vvars.lua
index db87bcda28..e90695b40c 100644
--- a/src/nvim/vvars.lua
+++ b/src/nvim/vvars.lua
@@ -765,6 +765,17 @@ M.vars = {
       Read-only.
     ]=],
   },
+  startreason = {
+    type = 'string',
+    desc = [=[
+      The reason Nvim started. Possible values:
+        - "normal"    normal startup.
+        - "restart"   started by |:restart|.
+        - "restart!"  started by |:restart!| or |ZR|.
+
+      Read-only.
+    ]=],
+  },
   statusmsg = {
     type = 'string',
     desc = [=[
diff --git a/test/functional/core/main_spec.lua b/test/functional/core/main_spec.lua
index 904beb1444..2d8eecce99 100644
--- a/test/functional/core/main_spec.lua
+++ b/test/functional/core/main_spec.lua
@@ -217,7 +217,7 @@ describe('vim._core', function()
 
     -- All `vim._core.*` modules are builtin.
     t.eq(
-      { 'rebind_after_restart', 'serverlist' },
+      { 'ex_session_restart', 'rebind_after_restart', 'serverlist' },
       n.exec_lua([[local k = vim.tbl_keys(require('vim._core.server')); table.sort(k); return k]])
     )
     local expected = {
diff --git a/test/functional/core/server_spec.lua b/test/functional/core/server_spec.lua
index cf79fe817f..05d1b546e3 100644
--- a/test/functional/core/server_spec.lua
+++ b/test/functional/core/server_spec.lua
@@ -352,8 +352,8 @@ describe('startup --listen', function()
   end)
 end)
 
-it(':restart works in headless server (no UI)', function()
-  t.skip(is_os('win'), 'FIXME: --listen not preserved by :restart on Windows')
+it(':restart! works in headless server (no UI)', function()
+  t.skip(is_os('win'), 'FIXME: --listen not preserved by :restart! on Windows')
 
   local nvim0 = clear()
   local server_pipe = n.new_pipename()
@@ -364,18 +364,28 @@ it(':restart works in headless server (no UI)', function()
     n.set_session(nil)
   end)
 
-  fn.jobstart({ n.nvim_prog, '--clean', '--headless', '--listen', server_pipe })
+  fn.jobstart({
+    n.nvim_prog,
+    '--clean',
+    '--headless',
+    '--listen',
+    server_pipe,
+    '--cmd',
+    'let g:early_startreason = v:startreason',
+  })
   t.retry(nil, nil, function()
     neq(nil, vim.uv.fs_stat(server_pipe))
   end)
   n.set_session(n.connect(server_pipe))
 
-  n.expect_exit(n.command, 'restart')
+  n.expect_exit(n.command, 'restart!')
   n.set_session(n.connect(server_pipe))
   eq(1, api.nvim_get_vvar('vim_did_enter'))
+  eq('restart!', api.nvim_get_vvar('startreason'))
+  eq('restart!', n.eval('g:early_startreason'))
 
   -- TODO: [command] is currently not executed without UI
-  -- n.expect_exit(n.command, 'restart lua _G.new_server = 1')
+  -- n.expect_exit(n.command, 'restart! lua _G.new_server = 1')
   -- n.set_session(n.connect(server_pipe))
   -- eq(1, n.exec_lua('return _G.new_server'))
 end)
diff --git a/test/functional/terminal/tui_spec.lua b/test/functional/terminal/tui_spec.lua
index 27d6374626..01e5a99b53 100644
--- a/test/functional/terminal/tui_spec.lua
+++ b/test/functional/terminal/tui_spec.lua
@@ -261,11 +261,86 @@ describe('TUI :restart', function()
   end
 
   it('validation', function()
-    eq('Vim(restart):E481: No range allowed: :1restart', t.pcall_err(n.command, ':1restart'))
+    eq('Vim(restart):E481: No range allowed: :1restart!', t.pcall_err(n.command, ':1restart!'))
+  end)
+
+  it(':restart (no bang) restores session, window layout', function()
+    local file = 'Xtest-restart-file'
+    write_file(file, 'foobar')
+    finally(function()
+      os.remove(file)
+    end)
+
+    local server_pipe = new_pipename()
+    local server_session
+    finally(function()
+      if server_session then
+        server_session:close()
+      end
+    end)
+    local screen = tt.setup_child_nvim({
+      '--clean',
+      '--listen',
+      server_pipe,
+      '--cmd',
+      'set notermguicolors laststatus=0 noruler noshowcmd',
+    }, {
+      env = vim.tbl_extend('force', env_notermguicolors, {
+        -- Ignore logs, because assert_restarted may log "connection refused" while it retries.
+        NVIM_LOG_FILE = testlog,
+      }),
+    })
+    finally(function()
+      os.remove(testlog)
+    end)
+
+    feed_data(':edit ' .. file .. '\r')
+    feed_data(':wincmd v\r')
+    screen:expect([[
+      ^foobar                   │foobar                  |
+      ~                        │~                       |
+      ~                        │~                       |
+      ~                        │~                       |
+      ~                        │~                       |
+      :wincmd v                                         |
+      {5:-- TERMINAL --}                                    |
+    ]])
+    server_session = n.connect(server_pipe)
+    local _, starttime = server_session:request('nvim_eval', 'v:starttime')
+    eq({ true, '' }, { server_session:request('nvim_get_vvar', 'this_session') })
+
+    -- :restart
+    feed_data(':restart\r')
+    screen:expect([[
+      ^foobar                   │foobar                  |
+      ~                        │~                       |
+      ~                        │~                       |
+      ~                        │~                       |
+      ~                        │~                       |
+                                                        |
+      {5:-- TERMINAL --}                                    |
+    ]])
+    starttime, server_session = assert_restarted(starttime, server_session, server_pipe)
+    eq({ true, 'restart' }, { server_session:request('nvim_get_vvar', 'startreason') })
+    eq({ true, '' }, { server_session:request('nvim_get_vvar', 'this_session') })
+
+    -- :restart!
+    feed_data(':restart!\r')
+    screen:expect([[
+      ^                                                  |
+      ~                                                 |*4
+                                                        |
+      {5:-- TERMINAL --}                                    |
+    ]])
+    starttime, server_session = assert_restarted(starttime, server_session, server_pipe)
+    eq({ true, 'restart!' }, { server_session:request('nvim_get_vvar', 'startreason') })
+
+    feed_data(':qall!\r')
+    screen:expect({ any = vim.pesc('[Process exited 0]') })
   end)
 
   it('ZR', function()
-    -- Just exercise ZR, don't need to test all :restart functionality here.
+    -- Just exercise ZR, don't need to test all :restart! functionality here.
     local server_pipe = new_pipename()
     local server_session
     finally(function()
@@ -345,8 +420,8 @@ describe('TUI :restart', function()
     }, { env = { COLORTERM = 'truecolor' } })
     screen:set_option('rgb', true)
 
-    -- 'termguicolors' support should be detected properly after :restart.
-    -- The value of has("gui_running") should be 0 before and after :restart.
+    -- 'termguicolors' support should be detected properly after :restart!
+    -- The value of has("gui_running") should be 0 before and after :restart!
     local function assert_termguicolors_and_no_gui_running()
       tt.feed_data(':echo "&termguicolors: " .. &termguicolors\013')
       screen:expect({ any = '&termguicolors: 1' })
@@ -392,14 +467,14 @@ describe('TUI :restart', function()
 
     tt.feed_data(':set nomodified\013')
     -- Command is run on new server.
-    tt.feed_data(":restart put ='Hello1'\013")
+    tt.feed_data(":restart! put ='Hello1'\013")
     screen:expect(s1)
     assert_new_pid()
     assert_exitreason()
     assert_termguicolors_and_no_gui_running()
 
     -- Complex command following +cmd.
-    tt.feed_data(":restart +qall! put ='Hello2' | put ='World2'\013")
+    tt.feed_data(":restart! +qall! put ='Hello2' | put ='World2'\013")
     screen:expect([[
                                                         |
       Hello2                                            |
@@ -413,24 +488,24 @@ describe('TUI :restart', function()
     assert_exitreason()
     assert_termguicolors_and_no_gui_running()
 
-    -- Check ":restart" on an unmodified buffer.
+    -- Check ":restart!" on an unmodified buffer.
     tt.feed_data(':set nomodified\013')
-    tt.feed_data(':restart\013')
+    tt.feed_data(':restart!\013')
     screen:expect(s0)
     assert_new_pid()
     assert_exitreason()
     assert_termguicolors_and_no_gui_running()
 
-    -- Check ":restart +qall!" on an unmodified buffer.
-    tt.feed_data(':restart +qall!\013')
+    -- Check ":restart! +qall!" on an unmodified buffer.
+    tt.feed_data(':restart! +qall!\013')
     screen:expect(s0)
     assert_new_pid()
     assert_exitreason()
     assert_termguicolors_and_no_gui_running()
 
-    -- Check ":restart +echo" cannot restart server.
+    -- Check ":restart! +echo" cannot restart server.
     -- Check the full screen state to ensure this doesn't pollute the current UI.
-    tt.feed_data(':restart +echo\013')
+    tt.feed_data(':restart! +echo\013')
     screen:expect([[
       ^                                                  |
       {1:~}{18:                                                 }|*3
@@ -442,8 +517,8 @@ describe('TUI :restart', function()
     tt.feed_data('ithis will be removed\027')
     screen:expect({ any = vim.pesc('this will be remove^d') })
 
-    -- Check ":confirm restart" on a modified buffer.
-    tt.feed_data(':confirm restart\013')
+    -- Check ":confirm restart!" on a modified buffer.
+    tt.feed_data(':confirm restart!\013')
     screen:expect({ any = vim.pesc('Save changes to "Untitled"?') })
 
     -- Cancel the operation (abandons restart).
@@ -452,9 +527,9 @@ describe('TUI :restart', function()
     -- Failed/cancelled restarts still fire QuitPre/ExitPre (but not VimLeave[Pre]).
     assert_exitreason('QuitPre:restart\nExitPre:restart\n')
 
-    -- Check :restart respects 'confirm' option.
+    -- Check :restart! respects 'confirm' option.
     tt.feed_data(':set confirm\013')
-    tt.feed_data(':restart\013')
+    tt.feed_data(':restart!\013')
     screen:expect({ any = vim.pesc('Save changes to "Untitled"?') })
     tt.feed_data('C\013')
     screen:expect({ any = vim.pesc('[No Name]') })
@@ -462,8 +537,8 @@ describe('TUI :restart', function()
     -- Failed/cancelled restarts still fire QuitPre/ExitPre (but not VimLeave[Pre]).
     assert_exitreason('QuitPre:restart\nExitPre:restart\n')
 
-    -- Check ":confirm restart <cmd>" on a modified buffer.
-    tt.feed_data(":confirm restart put ='Hello3'\013")
+    -- Check ":confirm restart! <cmd>" on a modified buffer.
+    tt.feed_data(":confirm restart! put ='Hello3'\013")
     screen:expect({ any = vim.pesc('Save changes to "Untitled"?') })
     tt.feed_data('N\013')
     screen:expect({ any = '%^Hello3' })
@@ -471,19 +546,19 @@ describe('TUI :restart', function()
     assert_exitreason()
     assert_termguicolors_and_no_gui_running()
 
-    -- Check ":confirm restart +echo" correctly ignores ":confirm"
-    tt.feed_data(':confirm restart +echo\013')
+    -- Check ":confirm restart! +echo" correctly ignores ":confirm"
+    tt.feed_data(':confirm restart! +echo\013')
     screen:expect({ any = vim.pesc('+cmd did not quit the server') })
 
-    -- Check ":restart" on a modified buffer.
+    -- Check ":restart!" on a modified buffer.
     tt.feed_data('ithis will be removed\027')
-    tt.feed_data(':restart\013')
+    tt.feed_data(':restart!\013')
     screen:expect({ any = vim.pesc('Vim(qall):E37: No write since last change') })
     assert_exitreason('QuitPre:restart\nExitPre:restart\n')
 
-    -- Check ":restart +qall!" on a modified buffer.
+    -- Check ":restart! +qall!" on a modified buffer.
     tt.feed_data('ithis will be removed\027')
-    tt.feed_data(':restart +qall!\013')
+    tt.feed_data(':restart! +qall!\013')
     screen:expect(s0)
     assert_new_pid()
     assert_exitreason()
@@ -491,7 +566,7 @@ describe('TUI :restart', function()
 
     if not is_os('win') then
       -- No --listen conflict when server exit is delayed.
-      feed_data(':lua vim.schedule(function() vim.wait(100) end); vim.cmd.restart()\n')
+      feed_data(':lua vim.schedule(function() vim.wait(100) end); vim.cmd("restart!")\n')
       screen:expect(s0)
       assert_new_pid()
       assert_exitreason()
@@ -507,8 +582,8 @@ describe('TUI :restart', function()
       {5:-- TERMINAL --}                                              |
     ]])
 
-    --- Check that ":restart" uses the updated size after terminal resize.
-    tt.feed_data(':restart echo "restarted"\013')
+    --- Check that ":restart!" uses the updated size after terminal resize.
+    tt.feed_data(':restart! echo "restarted"\013')
     screen:expect([[
       ^                                                            |
       {1:~}{18:                                                           }|*2
@@ -527,6 +602,11 @@ describe('TUI :restart', function()
 
   it('drops "-" and "-- [files…]" from v:argv #34417', function()
     t.skip(is_os('win'), 'stdin behavior differs on Windows')
+    local file = 'file.lua'
+    write_file(file, "print('-S works')\n")
+    finally(function()
+      os.remove(file)
+    end)
     local server_session
     finally(function()
       if server_session then
@@ -543,6 +623,8 @@ describe('TUI :restart', function()
       server_pipe,
       '--cmd',
       'set notermguicolors',
+      '-S',
+      file,
       '-s',
       '-',
       '-',
@@ -554,16 +636,18 @@ describe('TUI :restart', function()
       ^                                                  |
       ~                                                 |*3
       {2:Xtest-file1                     0,0-1          All}|
-                                                        |
+      -S works                                          |
       {5:-- TERMINAL --}                                    |
     ]])
     server_session = n.connect(server_pipe)
     local expr = 'index(v:argv, "-") >= 0 || index(v:argv, "--") >= 0 ? v:true : v:false'
     local has_s = 'index(v:argv, "-s") >= 0 ? v:true : v:false'
+    local has_S = 'index(v:argv, "-S") >= 0 ? v:true : v:false'
     eq({ true, true }, { server_session:request('nvim_eval', expr) })
     eq({ true, true }, { server_session:request('nvim_eval', has_s) })
+    eq({ true, true }, { server_session:request('nvim_eval', has_S) })
 
-    tt.feed_data(":restart put='foo'\013")
+    tt.feed_data(":restart! put='foo'\013")
     screen:expect([[
                                                         |
       ^foo                                               |
@@ -577,6 +661,7 @@ describe('TUI :restart', function()
 
     eq({ true, false }, { server_session:request('nvim_eval', expr) })
     eq({ true, false }, { server_session:request('nvim_eval', has_s) })
+    eq({ true, false }, { server_session:request('nvim_eval', has_S) })
 
     -- local argv = ({ server_session:request('nvim_eval', 'v:argv') })[2] --[[@type table]]
     -- eq(13, #argv)
@@ -603,7 +688,7 @@ describe('TUI :restart', function()
     ]])
 
     -- 'laststatus' should be 0 in the new Nvim and FileType event should be triggered.
-    feed_data(':restart set nowrap | edit test/functional/fixtures/bigfile.txt\r')
+    feed_data(':restart! set nowrap | edit test/functional/fixtures/bigfile.txt\r')
     screen:expect([[
       ^0000;<control>;Cc;0;BN;;;;;N;NULL;;;;             |
       0001;<control>;Cc;0;BN;;;;;N;START OF HEADING;;;; |
@@ -666,7 +751,7 @@ describe('TUI :restart', function()
       {5:-- TERMINAL --}                                    |
     ]])
 
-    feed_data(':restart echo "restarted"\r')
+    feed_data(':restart! echo "restarted"\r')
     screen:expect([[
       ^                     │0000;<control>;Cc;0;BN;;;;;N|
       ~                    │0001;<control>;Cc;0;BN;;;;;N|
@@ -677,7 +762,7 @@ describe('TUI :restart', function()
       {5:-- TERMINAL --}                                    |
     ]])
 
-    feed_data(':set sessionoptions-=winsize | restart\r')
+    feed_data(':set sessionoptions-=winsize | restart!\r')
     screen:expect([[
       ^                         │0000;<control>;Cc;0;BN;;|
       ~                        │0001;<control>;Cc;0;BN;;|
@@ -3034,8 +3119,8 @@ describe('TUI', function()
       { 'tty', 'tty' },
       child_exec_lua('return { vim.uv.guess_handle(0), vim.uv.guess_handle(1) }')
     )
-    -- Also works after :restart #38745
-    feed_data(':restart lua ={ vim.uv.guess_handle(0), vim.uv.guess_handle(1) }\r')
+    -- Also works after :restart! #38745
+    feed_data(':restart! lua ={ vim.uv.guess_handle(0), vim.uv.guess_handle(1) }\r')
     screen:expect([[
       ^                                                  |
       {100:~                                                 }|*3
@@ -4441,11 +4526,11 @@ describe('TUI client', function()
     screen_server:expect(s1)
   end)
 
-  it(':restart works when connecting to remote instance (with its own TUI)', function()
+  it(':restart! works when connecting to remote instance (with its own TUI)', function()
     local _, screen_server, screen_client = start_tui_and_remote_client()
 
     -- Both clients should attach to the new server.
-    feed_data(':restart +qall!\n')
+    feed_data(':restart! +qall!\n')
     local screen_restarted = [[
       ^                                                  |
       {100:~                                                 }|*3
@@ -4460,7 +4545,7 @@ describe('TUI client', function()
     screen_client:expect({ any = 'GUI Running: 0' })
 
     -- The :vsplit command should only be executed once.
-    feed_data(':restart vsplit\r')
+    feed_data(':restart! vsplit\r')
     screen_restarted = [[
       ^                         │                        |
       {100:~                        }│{100:~                       }|*3
@@ -4552,11 +4637,11 @@ describe('TUI client', function()
     screen_client:expect({ any = 'GUI Running: 0' })
   end)
 
-  it(':restart works when connecting to remote instance (--headless)', function()
+  it(':restart! works when connecting to remote instance (--headless)', function()
     local _, server_pipe, screen_client = start_headless_server_and_client(false)
 
     -- The client should attach to the new server and the original server should exit.
-    feed_data(':restart +qall!\n')
+    feed_data(':restart! +qall!\n')
     screen_client:expect([[
       ^                                                  |
       {100:~                                                 }|*4
diff --git a/test/functional/vimscript/vvars_spec.lua b/test/functional/vimscript/vvars_spec.lua
index 377d6296fa..8afe719299 100644
--- a/test/functional/vimscript/vvars_spec.lua
+++ b/test/functional/vimscript/vvars_spec.lua
@@ -48,3 +48,11 @@ describe('v:argf', function()
     eq({ abs1, abs2, abs3 }, n.eval('v:argf'))
   end)
 end)
+
+describe('v:startreason', function()
+  it('is read-only and starts as "normal"', function()
+    n.clear { args = { '--cmd', 'let g:early_startreason = v:startreason' } }
+    eq('normal', eval('g:early_startreason'))
+    t.matches('E46', t.pcall_err(command, "let v:startreason = 'restart'"))
+  end)
+end)