diff --git a/clients/elixir/sync/src/un.ex b/clients/elixir/sync/src/un.ex
index a3ef621..187faa5 100755
--- a/clients/elixir/sync/src/un.ex
+++ b/clients/elixir/sync/src/un.ex
@@ -51,8 +51,10 @@ defmodule Un do
 
   Credentials are loaded in priority order:
   1. Function arguments (public_key, secret_key)
-  2. Environment variables (UNSANDBOX_PUBLIC_KEY, UNSANDBOX_SECRET_KEY)
-  3. Config file (~/.unsandbox/accounts.csv)
+  2. --account N -> accounts.csv row N (bypasses env vars)
+  3. Environment variables (UNSANDBOX_PUBLIC_KEY, UNSANDBOX_SECRET_KEY)
+  4. ~/.unsandbox/accounts.csv row 0 (or UNSANDBOX_ACCOUNT env)
+  5. ./accounts.csv row 0
   """
 
   @blue "\e[34m"
@@ -1112,25 +1114,50 @@ defmodule Un do
   # CLI Entry Point
   # ============================================================================
 
-  def main([]), do: print_usage()
-  def main(["session" | rest]), do: session_command(rest)
-  def main(["service" | rest]), do: service_command(rest)
-  def main(["snapshot" | rest]), do: snapshot_command(rest)
-  def main(["image" | rest]), do: image_command(rest)
-  def main(["key" | rest]), do: key_command(rest)
-  def main(["languages" | rest]), do: languages_command(rest)
-  def main(args), do: execute_command(args)
+  def main(raw_args) do
+    {account_index, args} = extract_account_arg(raw_args, nil, [])
+    if account_index != nil do
+      Process.put(:account_index, account_index)
+    end
+    dispatch(args)
+  end
+
+  defp dispatch([]), do: print_usage()
+  defp dispatch(["session" | rest]), do: session_command(rest)
+  defp dispatch(["service" | rest]), do: service_command(rest)
+  defp dispatch(["snapshot" | rest]), do: snapshot_command(rest)
+  defp dispatch(["image" | rest]), do: image_command(rest)
+  defp dispatch(["key" | rest]), do: key_command(rest)
+  defp dispatch(["languages" | rest]), do: languages_command(rest)
+  defp dispatch(args), do: execute_command(args)
+
+  defp extract_account_arg([], acc, rest_acc), do: {acc, Enum.reverse(rest_acc)}
+  defp extract_account_arg(["--account", n_str | rest], _acc, rest_acc) do
+    n = case Integer.parse(n_str) do
+      {n, ""} -> n
+      _ ->
+        IO.puts(:stderr, "Error: --account requires an integer argument")
+        System.halt(1)
+    end
+    extract_account_arg(rest, n, rest_acc)
+  end
+  defp extract_account_arg([arg | rest], acc, rest_acc) do
+    extract_account_arg(rest, acc, [arg | rest_acc])
+  end
 
   defp print_usage do
-    IO.puts("Usage: un.ex [options] <source_file>")
-    IO.puts("       un.ex session [options]")
-    IO.puts("       un.ex service [options]")
-    IO.puts("       un.ex service env <action> <service_id>")
-    IO.puts("       un.ex snapshot [options]")
-    IO.puts("       un.ex image [options]")
-    IO.puts("       un.ex key [--extend]")
+    IO.puts("Usage: un.ex [--account N] [options] <source_file>")
+    IO.puts("       un.ex [--account N] session [options]")
+    IO.puts("       un.ex [--account N] service [options]")
+    IO.puts("       un.ex [--account N] service env <action> <service_id>")
+    IO.puts("       un.ex [--account N] snapshot [options]")
+    IO.puts("       un.ex [--account N] image [options]")
+    IO.puts("       un.ex [--account N] key [--extend]")
     IO.puts("       un.ex languages [--json]")
     IO.puts("")
+    IO.puts("Global options:")
+    IO.puts("  --account N    Use accounts.csv row N (bypasses env vars)")
+    IO.puts("")
     IO.puts("Service options: --name, --ports, --bootstrap, -e KEY=VALUE, --env-file FILE")
     IO.puts("                --set-unfreeze-on-demand ID true|false")
     IO.puts("Service env commands: status, set, export, delete")
@@ -1913,21 +1940,85 @@ defmodule Un do
   end
 
   # Helpers
+
+  defp load_credentials_from_csv(csv_path, account_index) do
+    case File.read(csv_path) do
+      {:ok, content} ->
+        accounts =
+          content
+          |> String.split("\n")
+          |> Enum.map(&String.trim/1)
+          |> Enum.filter(fn line -> line != "" and not String.starts_with?(line, "#") end)
+          |> Enum.flat_map(fn line ->
+            case String.split(line, ",") do
+              [pk, sk | _] ->
+                pk = String.trim(pk)
+                sk = String.trim(sk)
+                if String.length(pk) > 8 and String.length(sk) > 8 do
+                  [{pk, sk}]
+                else
+                  []
+                end
+              _ -> []
+            end
+          end)
+        case Enum.at(accounts, account_index) do
+          nil -> :error
+          creds -> {:ok, creds}
+        end
+      _ -> :error
+    end
+  end
+
   defp get_api_keys do
-    public_key = System.get_env("UNSANDBOX_PUBLIC_KEY")
-    secret_key = System.get_env("UNSANDBOX_SECRET_KEY")
+    home = System.get_env("HOME") || "."
+    home_csv = Path.join([home, ".unsandbox", "accounts.csv"])
 
-    # Fall back to UNSANDBOX_API_KEY for backwards compatibility
-    api_key = System.get_env("UNSANDBOX_API_KEY")
+    # Priority 1: --account N (stored in process dict by main/1)
+    case Process.get(:account_index) do
+      nil ->
+        # Priority 2: environment variables
+        public_key = System.get_env("UNSANDBOX_PUBLIC_KEY")
+        secret_key = System.get_env("UNSANDBOX_SECRET_KEY")
+        api_key = System.get_env("UNSANDBOX_API_KEY")
 
-    cond do
-      public_key && secret_key ->
-        {public_key, secret_key}
-      api_key ->
-        {api_key, nil}
-      true ->
-        IO.puts(:stderr, "Error: UNSANDBOX_PUBLIC_KEY and UNSANDBOX_SECRET_KEY not set (or UNSANDBOX_API_KEY for backwards compat)")
-        System.halt(1)
+        cond do
+          public_key && secret_key ->
+            {public_key, secret_key}
+          api_key ->
+            {api_key, nil}
+          true ->
+            # Priority 3: ~/.unsandbox/accounts.csv (or UNSANDBOX_ACCOUNT index)
+            default_index =
+              case System.get_env("UNSANDBOX_ACCOUNT") do
+                nil -> 0
+                s -> case Integer.parse(s) do {n, ""} -> n; _ -> 0 end
+              end
+            case load_credentials_from_csv(home_csv, default_index) do
+              {:ok, {pk, sk}} -> {pk, sk}
+              :error ->
+                # Priority 4: ./accounts.csv
+                case load_credentials_from_csv("accounts.csv", default_index) do
+                  {:ok, {pk, sk}} -> {pk, sk}
+                  :error ->
+                    IO.puts(:stderr, "Error: UNSANDBOX_PUBLIC_KEY and UNSANDBOX_SECRET_KEY not set (or UNSANDBOX_API_KEY for backwards compat)")
+                    System.halt(1)
+                end
+            end
+        end
+
+      account_index ->
+        # Priority 1: --account N -> accounts.csv
+        case load_credentials_from_csv(home_csv, account_index) do
+          {:ok, {pk, sk}} -> {pk, sk}
+          :error ->
+            case load_credentials_from_csv("accounts.csv", account_index) do
+              {:ok, {pk, sk}} -> {pk, sk}
+              :error ->
+                IO.puts(:stderr, "Error: No credentials found for account index #{account_index} in accounts.csv")
+                System.halt(1)
+            end
+        end
     end
   end
 
diff --git a/clients/erlang/sync/src/un.erl b/clients/erlang/sync/src/un.erl
index 17ec8df..3c34b65 100755
--- a/clients/erlang/sync/src/un.erl
+++ b/clients/erlang/sync/src/un.erl
@@ -56,8 +56,10 @@
 %%%
 %%% Authentication Priority:
 %%%   1. Function arguments (PublicKey, SecretKey)
-%%%   2. Environment variables (UNSANDBOX_PUBLIC_KEY, UNSANDBOX_SECRET_KEY)
-%%%   3. Config file (~/.unsandbox/accounts.csv)
+%%%   2. --account N -> accounts.csv row N (bypasses env vars)
+%%%   3. Environment variables (UNSANDBOX_PUBLIC_KEY, UNSANDBOX_SECRET_KEY)
+%%%   4. ~/.unsandbox/accounts.csv row 0 (or UNSANDBOX_ACCOUNT env)
+%%%   5. ./accounts.csv row 0
 
 -define(API_BASE, "https://api.unsandbox.com").
 -define(PORTAL_BASE, "https://unsandbox.com").
@@ -719,37 +721,60 @@ not_contains_error(Response) ->
 %% CLI Entry Point
 %% ============================================================================
 
-main([]) ->
-    io:format("Usage: un.erl [options] <source_file>~n"),
-    io:format("       un.erl session [options]~n"),
-    io:format("       un.erl service [options]~n"),
-    io:format("       un.erl snapshot [options]~n"),
-    io:format("       un.erl image [options]~n"),
-    io:format("       un.erl key [options]~n"),
+main(RawArgs) ->
+    %% Strip --account N from args and store index in process dict before dispatch
+    {AccountIndex, Args} = extract_account_arg(RawArgs, undefined, []),
+    case AccountIndex of
+        undefined -> ok;
+        N -> erlang:put(account_index, N)
+    end,
+    dispatch(Args).
+
+dispatch([]) ->
+    io:format("Usage: un.erl [--account N] [options] <source_file>~n"),
+    io:format("       un.erl [--account N] session [options]~n"),
+    io:format("       un.erl [--account N] service [options]~n"),
+    io:format("       un.erl [--account N] snapshot [options]~n"),
+    io:format("       un.erl [--account N] image [options]~n"),
+    io:format("       un.erl [--account N] key [options]~n"),
     io:format("       un.erl languages [--json]~n"),
+    io:format("~nGlobal options:~n"),
+    io:format("  --account N    Use accounts.csv row N (bypasses env vars)~n"),
     halt(1);
 
-main(["session" | Rest]) ->
+dispatch(["session" | Rest]) ->
     session_command(Rest);
 
-main(["service" | Rest]) ->
+dispatch(["service" | Rest]) ->
     service_command(Rest);
 
-main(["snapshot" | Rest]) ->
+dispatch(["snapshot" | Rest]) ->
     snapshot_command(Rest);
 
-main(["image" | Rest]) ->
+dispatch(["image" | Rest]) ->
     image_command(Rest);
 
-main(["key" | Rest]) ->
+dispatch(["key" | Rest]) ->
     key_command(Rest);
 
-main(["languages" | Rest]) ->
+dispatch(["languages" | Rest]) ->
     languages_command(Rest);
 
-main(Args) ->
+dispatch(Args) ->
     execute_command(Args).
 
+%% Strip --account N from argument list, return {Index | undefined, RestArgs}
+extract_account_arg([], Acc, RestAcc) ->
+    {Acc, lists:reverse(RestAcc)};
+extract_account_arg(["--account", NStr | Rest], _Acc, RestAcc) ->
+    N = try list_to_integer(NStr) catch _:_ ->
+        io:format("Error: --account requires an integer argument~n"),
+        halt(1)
+    end,
+    extract_account_arg(Rest, N, RestAcc);
+extract_account_arg([Arg | Rest], Acc, RestAcc) ->
+    extract_account_arg(Rest, Acc, [Arg | RestAcc]).
+
 %% Execute command
 execute_command(Args) ->
     {File, _Opts} = parse_exec_args(Args, #{file => undefined}),
@@ -1452,19 +1477,96 @@ open_extend_page(PublicKey) ->
     end.
 
 %% Helpers
-get_api_keys() ->
-    PublicKey = os:getenv("UNSANDBOX_PUBLIC_KEY"),
-    SecretKey = os:getenv("UNSANDBOX_SECRET_KEY"),
-    ApiKey = os:getenv("UNSANDBOX_API_KEY"),
 
-    if
-        PublicKey =/= false andalso SecretKey =/= false ->
-            {PublicKey, SecretKey};
-        ApiKey =/= false ->
-            {ApiKey, false};
-        true ->
-            io:format("Error: UNSANDBOX_PUBLIC_KEY and UNSANDBOX_SECRET_KEY not set (or UNSANDBOX_API_KEY for backwards compat)~n"),
-            halt(1)
+%% @doc Load credentials from a CSV file at the given path.
+%% Skips blank lines and comment lines (#). Returns {ok, {PK, SK}} or error.
+load_credentials_from_csv(CsvPath, AccountIndex) ->
+    case file:read_file(CsvPath) of
+        {ok, Bin} ->
+            Lines = string:split(binary_to_list(Bin), "\n", all),
+            ValidAccounts = lists:filtermap(fun(Line) ->
+                Trimmed = string:trim(Line),
+                case Trimmed of
+                    "" -> false;
+                    [$# | _] -> false;
+                    _ ->
+                        Parts = string:split(Trimmed, ",", all),
+                        case Parts of
+                            [PK, SK | _] ->
+                                PKt = string:trim(PK),
+                                SKt = string:trim(SK),
+                                if
+                                    length(PKt) > 8 andalso length(SKt) > 8 ->
+                                        {true, {PKt, SKt}};
+                                    true -> false
+                                end;
+                            _ -> false
+                        end
+                end
+            end, Lines),
+            if
+                AccountIndex < length(ValidAccounts) ->
+                    {ok, lists:nth(AccountIndex + 1, ValidAccounts)};
+                true ->
+                    error
+            end;
+        _ ->
+            error
+    end.
+
+%% @doc Resolve credentials with correct priority:
+%%   1. --account N process-dict override -> accounts.csv row N
+%%   2. UNSANDBOX_PUBLIC_KEY / UNSANDBOX_SECRET_KEY env vars
+%%   3. ~/.unsandbox/accounts.csv row 0 (or UNSANDBOX_ACCOUNT env)
+%%   4. ./accounts.csv row 0
+get_api_keys() ->
+    Home = case os:getenv("HOME") of false -> "."; H -> H end,
+    HomeCsv = filename:join([Home, ".unsandbox", "accounts.csv"]),
+    %% Priority 1: explicit --account N (stored in process dict by main/1)
+    case erlang:get(account_index) of
+        undefined ->
+            %% Priority 2: environment variables
+            PublicKey = os:getenv("UNSANDBOX_PUBLIC_KEY"),
+            SecretKey = os:getenv("UNSANDBOX_SECRET_KEY"),
+            ApiKey = os:getenv("UNSANDBOX_API_KEY"),
+            if
+                PublicKey =/= false andalso SecretKey =/= false ->
+                    {PublicKey, SecretKey};
+                ApiKey =/= false ->
+                    {ApiKey, false};
+                true ->
+                    %% Priority 3: ~/.unsandbox/accounts.csv (or UNSANDBOX_ACCOUNT index)
+                    DefaultIndex = case os:getenv("UNSANDBOX_ACCOUNT") of
+                        false -> 0;
+                        IdxStr -> try list_to_integer(string:trim(IdxStr)) catch _:_ -> 0 end
+                    end,
+                    case load_credentials_from_csv(HomeCsv, DefaultIndex) of
+                        {ok, {PK, SK}} ->
+                            {PK, SK};
+                        error ->
+                            %% Priority 4: ./accounts.csv
+                            case load_credentials_from_csv("accounts.csv", DefaultIndex) of
+                                {ok, {PK2, SK2}} ->
+                                    {PK2, SK2};
+                                error ->
+                                    io:format("Error: UNSANDBOX_PUBLIC_KEY and UNSANDBOX_SECRET_KEY not set (or UNSANDBOX_API_KEY for backwards compat)~n"),
+                                    halt(1)
+                            end
+                    end
+            end;
+        AccountIndex ->
+            case load_credentials_from_csv(HomeCsv, AccountIndex) of
+                {ok, {PK, SK}} ->
+                    {PK, SK};
+                error ->
+                    case load_credentials_from_csv("accounts.csv", AccountIndex) of
+                        {ok, {PK2, SK2}} ->
+                            {PK2, SK2};
+                        error ->
+                            io:format("Error: No credentials found for account index ~B in accounts.csv~n", [AccountIndex]),
+                            halt(1)
+                    end
+            end
     end.
 
 get_api_key() ->
diff --git a/clients/fsharp/sync/src/un.fs b/clients/fsharp/sync/src/un.fs
index 58dcbdb..5752bd1 100644
--- a/clients/fsharp/sync/src/un.fs
+++ b/clients/fsharp/sync/src/un.fs
@@ -77,6 +77,7 @@ type Args = {
     mutable Command: string option
     mutable SourceFile: string option
     mutable ApiKey: string option
+    mutable AccountIndex: int option
     mutable Network: string option
     mutable Vcpu: int
     Env: ResizeArray<string>
@@ -144,19 +145,70 @@ type Args = {
     mutable ImagePorts: string option
 }
 
-let getApiKeys (argsKey: string option) =
-    let publicKey = Environment.GetEnvironmentVariable("UNSANDBOX_PUBLIC_KEY")
-    let secretKey = Environment.GetEnvironmentVariable("UNSANDBOX_SECRET_KEY")
+let loadCredentialsFromCsv (csvPath: string) (accountIndex: int) =
+    if File.Exists(csvPath) then
+        try
+            let lines = File.ReadAllLines(csvPath)
+            let accounts =
+                lines
+                |> Array.map (fun l -> l.Trim())
+                |> Array.filter (fun l -> l.Length > 0 && not (l.StartsWith("#")))
+                |> Array.choose (fun line ->
+                    let parts = line.Split(',')
+                    if parts.Length >= 2 then
+                        let pk = parts.[0].Trim()
+                        let sk = parts.[1].Trim()
+                        if pk.Length > 8 && sk.Length > 8 then Some (pk, sk)
+                        else None
+                    else None)
+            if accountIndex < accounts.Length then Some accounts.[accountIndex]
+            else None
+        with _ -> None
+    else None
 
-    // Fall back to UNSANDBOX_API_KEY for backwards compatibility
-    if String.IsNullOrEmpty(publicKey) || String.IsNullOrEmpty(secretKey) then
-        let legacyKey = match argsKey with | Some k -> k | None -> Environment.GetEnvironmentVariable("UNSANDBOX_API_KEY")
-        if String.IsNullOrEmpty(legacyKey) then
-            eprintfn "%sError: UNSANDBOX_PUBLIC_KEY and UNSANDBOX_SECRET_KEY not set%s" red reset
+let getApiKeys (argsKey: string option) (accountIndex: int option) =
+    let home = Environment.GetFolderPath(Environment.SpecialFolder.UserProfile)
+    let homeCsv = Path.Combine(home, ".unsandbox", "accounts.csv")
+
+    // Priority 1: --account N -> accounts.csv row N (bypasses env vars)
+    match accountIndex with
+    | Some idx ->
+        let creds =
+            match loadCredentialsFromCsv homeCsv idx with
+            | Some c -> Some c
+            | None -> loadCredentialsFromCsv "accounts.csv" idx
+        match creds with
+        | Some (pk, sk) -> (pk, sk)
+        | None ->
+            eprintfn "%sError: No credentials found for account index %d in accounts.csv%s" red idx reset
             exit 1
-        (legacyKey, null)
-    else
-        (publicKey, secretKey)
+    | None ->
+        let publicKey = Environment.GetEnvironmentVariable("UNSANDBOX_PUBLIC_KEY")
+        let secretKey = Environment.GetEnvironmentVariable("UNSANDBOX_SECRET_KEY")
+
+        // Priority 2: environment variables
+        if not (String.IsNullOrEmpty(publicKey)) && not (String.IsNullOrEmpty(secretKey)) then
+            (publicKey, secretKey)
+        else
+            // Fall back to legacy UNSANDBOX_API_KEY
+            let legacyKey = match argsKey with | Some k -> k | None -> Environment.GetEnvironmentVariable("UNSANDBOX_API_KEY")
+            if not (String.IsNullOrEmpty(legacyKey)) then
+                (legacyKey, null)
+            else
+                // Priority 3: ~/.unsandbox/accounts.csv (or UNSANDBOX_ACCOUNT index)
+                let defaultIndex =
+                    let envIdx = Environment.GetEnvironmentVariable("UNSANDBOX_ACCOUNT")
+                    if String.IsNullOrEmpty(envIdx) then 0
+                    else match System.Int32.TryParse(envIdx) with | (true, n) -> n | _ -> 0
+                let creds =
+                    match loadCredentialsFromCsv homeCsv defaultIndex with
+                    | Some c -> Some c
+                    | None -> loadCredentialsFromCsv "accounts.csv" defaultIndex
+                match creds with
+                | Some (pk, sk) -> (pk, sk)
+                | None ->
+                    eprintfn "%sError: UNSANDBOX_PUBLIC_KEY and UNSANDBOX_SECRET_KEY not set%s" red reset
+                    exit 1
 
 let detectLanguage (filename: string) =
     let dotIndex = filename.LastIndexOf('.')
@@ -631,7 +683,7 @@ let cmdServiceEnv (args: Args) (publicKey: string) (secretKey: string) =
         exit 1
 
 let cmdExecute (args: Args) =
-    let (publicKey, secretKey) = getApiKeys args.ApiKey
+    let (publicKey, secretKey) = getApiKeys args.ApiKey args.AccountIndex
     let code = File.ReadAllText(args.SourceFile.Value)
     let language = detectLanguage args.SourceFile.Value
 
@@ -680,7 +732,7 @@ let cmdExecute (args: Args) =
     exit exitCode
 
 let cmdSession (args: Args) =
-    let (publicKey, secretKey) = getApiKeys args.ApiKey
+    let (publicKey, secretKey) = getApiKeys args.ApiKey args.AccountIndex
 
     if args.SessionSnapshot.IsSome then
         let mutable payload = []
@@ -740,7 +792,7 @@ let openBrowser (url: string) =
         eprintfn "%sError opening browser: %s%s" red ex.Message reset
 
 let cmdKey (args: Args) =
-    let (publicKey, secretKey) = getApiKeys args.ApiKey
+    let (publicKey, secretKey) = getApiKeys args.ApiKey args.AccountIndex
 
     ServicePointManager.SecurityProtocol <- SecurityProtocolType.Tls12 ||| SecurityProtocolType.Tls11 ||| SecurityProtocolType.Tls
 
@@ -817,7 +869,7 @@ let cmdKey (args: Args) =
         exit 1
 
 let cmdLanguages (args: Args) =
-    let (publicKey, secretKey) = getApiKeys args.ApiKey
+    let (publicKey, secretKey) = getApiKeys args.ApiKey args.AccountIndex
 
     // Try to load from cache first
     let cachedResponse = loadLanguagesCache ()
@@ -872,7 +924,7 @@ let cmdLanguages (args: Args) =
             printfn "%s" lang
 
 let cmdImage (args: Args) =
-    let (publicKey, secretKey) = getApiKeys args.ApiKey
+    let (publicKey, secretKey) = getApiKeys args.ApiKey args.AccountIndex
 
     if args.ImageList then
         let result = apiRequest "/images" "GET" None publicKey secretKey
@@ -928,7 +980,7 @@ let cmdImage (args: Args) =
         exit 1
 
 let cmdSnapshot (args: Args) =
-    let (publicKey, secretKey) = getApiKeys args.ApiKey
+    let (publicKey, secretKey) = getApiKeys args.ApiKey args.AccountIndex
 
     if args.SnapshotList then
         let result = apiRequest "/snapshots" "GET" None publicKey secretKey
@@ -959,7 +1011,7 @@ let cmdSnapshot (args: Args) =
         exit 1
 
 let cmdService (args: Args) =
-    let (publicKey, secretKey) = getApiKeys args.ApiKey
+    let (publicKey, secretKey) = getApiKeys args.ApiKey args.AccountIndex
 
     // Handle env subcommand
     if args.EnvAction.IsSome then
@@ -1107,6 +1159,7 @@ let parseArgs (argv: string[]) =
         Command = None
         SourceFile = None
         ApiKey = None
+        AccountIndex = None
         Network = None
         Vcpu = 0
         Env = ResizeArray<string>()
@@ -1192,6 +1245,13 @@ let parseArgs (argv: string[]) =
                     i <- i + 1
                     args.EnvTarget <- Some argv.[i]
         | "-k" | "--api-key" -> i <- i + 1; args.ApiKey <- Some argv.[i]
+        | "--account" ->
+            i <- i + 1
+            match System.Int32.TryParse(argv.[i]) with
+            | (true, n) -> args.AccountIndex <- Some n
+            | _ ->
+                eprintfn "Error: --account requires an integer argument"
+                Environment.Exit(1)
         | "-n" | "--network" -> i <- i + 1; args.Network <- Some argv.[i]
         | "-v" | "--vcpu" -> i <- i + 1; args.Vcpu <- int argv.[i]
         | "-e" | "--env" -> i <- i + 1; args.Env.Add(argv.[i])
@@ -1358,6 +1418,7 @@ let printHelp () =
     printfn "  -n MODE           Network mode (zerotrust/semitrusted)"
     printfn "  -v N              vCPU count (1-8)"
     printfn "  -k KEY            API key"
+    printfn "  --account N       Use accounts.csv row N (bypasses env vars)"
     printfn ""
     printfn "Session options:"
     printfn "  --list            List active sessions"
diff --git a/clients/haskell/sync/src/un.hs b/clients/haskell/sync/src/un.hs
index d17d0b5..91d7a34 100644
--- a/clients/haskell/sync/src/un.hs
+++ b/clients/haskell/sync/src/un.hs
@@ -66,6 +66,8 @@ import Data.Char (isDigit, ord)
 import Text.Printf (printf)
 import Control.Monad (when, unless, forM_)
 import Control.Exception (try, catch, IOError)
+import Data.IORef (IORef, newIORef, readIORef, writeIORef)
+import System.IO.Unsafe (unsafePerformIO)
 import qualified Data.ByteString as BS
 import qualified Data.ByteString.Char8 as BSC
 import qualified Data.ByteString.Base64 as B64
@@ -86,6 +88,11 @@ portalBase = "https://unsandbox.com"
 languagesCacheTtl :: Int
 languagesCacheTtl = 3600  -- 1 hour in seconds
 
+-- Global account index set by --account N flag (Nothing = not set)
+{-# NOINLINE cliAccountIndex #-}
+cliAccountIndex :: IORef (Maybe Int)
+cliAccountIndex = unsafePerformIO (newIORef Nothing)
+
 -- ANSI colors
 blue, red, green, yellow, reset :: String
 blue = "\x1b[34m"
@@ -838,10 +845,26 @@ threadDelay us = do
   _ <- readProcessWithExitCode "sleep" [show (fromIntegral ms / 1000.0 :: Double)] ""
   return ()
 
+-- Strip --account N from argument list, set cliAccountIndex IORef
+stripAccountArg :: [String] -> IO [String]
+stripAccountArg [] = return []
+stripAccountArg ("--account":n_str:rest) = do
+  case reads n_str of
+    [(n, "")] -> do
+      writeIORef cliAccountIndex (Just n)
+      stripAccountArg rest
+    _ -> do
+      hPutStrLn stderr "Error: --account requires an integer argument"
+      exitFailure
+stripAccountArg (arg:rest) = do
+  rest' <- stripAccountArg rest
+  return (arg : rest')
+
 -- Main
 main :: IO ()
 main = do
-  args <- getArgs
+  rawArgs <- getArgs
+  args <- stripAccountArg rawArgs
   cmd <- parseArgs args
   case cmd of
     Execute opts -> executeCommand opts
@@ -865,6 +888,9 @@ printHelp = do
   putStrLn "  un.hs languages [--json]               List available languages"
   putStrLn "  un.hs key [options]                    Validate/extend API key"
   putStrLn ""
+  putStrLn "Global options:"
+  putStrLn "  --account N     Use accounts.csv row N (bypasses env vars)"
+  putStrLn ""
   putStrLn "Execute options:"
   putStrLn "  -e KEY=VALUE    Environment variable"
   putStrLn "  -f FILE         Input file"
@@ -1433,18 +1459,77 @@ serviceEnvDelete serviceId = do
   (exitCode, _, _) <- curlDelete apiKey (apiBase ++ "/services/" ++ serviceId ++ "/env")
   return (exitCode == ExitSuccess)
 
--- Get API keys from environment
+-- Load credentials from a CSV file at a given account index
+loadCredentialsFromCsv :: FilePath -> Int -> IO (Maybe (String, String))
+loadCredentialsFromCsv csvPath accountIndex = do
+  result <- (try (readFile csvPath) :: IO (Either IOError String))
+  case result of
+    Left _ -> return Nothing
+    Right content -> do
+      let ls = filter (\l -> not (null l) && head l /= '#') $
+                 map trim $
+                 lines content
+          accounts = [ (pk', sk')
+                     | l <- ls
+                     , let (pk, rest) = break (== ',') l
+                     , not (null rest)
+                     , let pk' = trim pk
+                           sk' = trim (drop 1 rest)
+                     , length pk' > 8 && length sk' > 8
+                     ]
+      if accountIndex < length accounts then
+        return $ Just (accounts !! accountIndex)
+      else
+        return Nothing
+  where
+    trim = reverse . dropWhile (== ' ') . reverse . dropWhile (== ' ')
+
+-- Get API keys with correct priority:
+--   1. --account N (cliAccountIndex IORef) -> accounts.csv row N
+--   2. UNSANDBOX_PUBLIC_KEY / UNSANDBOX_SECRET_KEY env vars
+--   3. ~/.unsandbox/accounts.csv row 0 (or UNSANDBOX_ACCOUNT env)
+--   4. ./accounts.csv row 0
 getApiKeys :: IO (String, Maybe String)
 getApiKeys = do
-  publicKey <- lookupEnv "UNSANDBOX_PUBLIC_KEY"
-  secretKey <- lookupEnv "UNSANDBOX_SECRET_KEY"
-  apiKey <- lookupEnv "UNSANDBOX_API_KEY"
-  case (publicKey, secretKey, apiKey) of
-    (Just pk, Just sk, _) -> return (pk, Just sk)
-    (_, _, Just ak) -> return (ak, Nothing)
-    _ -> do
-      hPutStrLn stderr "Error: UNSANDBOX_PUBLIC_KEY and UNSANDBOX_SECRET_KEY not set (or UNSANDBOX_API_KEY for backwards compat)"
-      exitFailure
+  home <- maybe "." id <$> lookupEnv "HOME"
+  let homeCsv = home ++ "/.unsandbox/accounts.csv"
+  -- Priority 1: --account N
+  mIdx <- readIORef cliAccountIndex
+  case mIdx of
+    Just idx -> do
+      creds <- loadCredentialsFromCsv homeCsv idx
+      case creds of
+        Just (pk, sk) -> return (pk, Just sk)
+        Nothing -> do
+          creds2 <- loadCredentialsFromCsv "accounts.csv" idx
+          case creds2 of
+            Just (pk, sk) -> return (pk, Just sk)
+            Nothing -> do
+              hPutStrLn stderr $ "Error: No credentials found for account index " ++ show idx ++ " in accounts.csv"
+              exitFailure
+    Nothing -> do
+      -- Priority 2: environment variables
+      publicKey <- lookupEnv "UNSANDBOX_PUBLIC_KEY"
+      secretKey <- lookupEnv "UNSANDBOX_SECRET_KEY"
+      apiKey <- lookupEnv "UNSANDBOX_API_KEY"
+      case (publicKey, secretKey, apiKey) of
+        (Just pk, Just sk, _) -> return (pk, Just sk)
+        (_, _, Just ak) -> return (ak, Nothing)
+        _ -> do
+          -- Priority 3: ~/.unsandbox/accounts.csv (or UNSANDBOX_ACCOUNT index)
+          defaultIndexStr <- lookupEnv "UNSANDBOX_ACCOUNT"
+          let defaultIndex = maybe 0 (\s -> case reads s of [(n,"")] -> n; _ -> 0) defaultIndexStr
+          creds <- loadCredentialsFromCsv homeCsv defaultIndex
+          case creds of
+            Just (pk, sk) -> return (pk, Just sk)
+            Nothing -> do
+              -- Priority 4: ./accounts.csv
+              creds2 <- loadCredentialsFromCsv "accounts.csv" defaultIndex
+              case creds2 of
+                Just (pk, sk) -> return (pk, Just sk)
+                Nothing -> do
+                  hPutStrLn stderr "Error: UNSANDBOX_PUBLIC_KEY and UNSANDBOX_SECRET_KEY not set (or UNSANDBOX_API_KEY for backwards compat)"
+                  exitFailure
 
 getApiKey :: IO String
 getApiKey = do
diff --git a/clients/ocaml/sync/src/un.ml b/clients/ocaml/sync/src/un.ml
index 3baaf4a..b08d7d6 100755
--- a/clients/ocaml/sync/src/un.ml
+++ b/clients/ocaml/sync/src/un.ml
@@ -281,39 +281,53 @@ let extract_json_int json_str key =
    Credentials Management
    ============================================================================ *)
 
-(** Get credentials from config file ~/.unsandbox/accounts.csv *)
-let get_credentials_from_file ?(account_index=0) () =
-  let home = try Sys.getenv "HOME" with Not_found -> "." in
-  let accounts_path = Filename.concat home ".unsandbox/accounts.csv" in
-  if Sys.file_exists accounts_path then
+(** Global account index set by --account N CLI flag; -1 means not set *)
+let cli_account_index = ref (-1)
+
+(** Parse accounts from CSV content, return list of (pk, sk) pairs *)
+let parse_accounts_csv content =
+  let lines = String.split_on_char '\n' content in
+  List.filter_map (fun line ->
+    let line = String.trim line in
+    if String.length line = 0 || line.[0] = '#' then None
+    else
+      try
+        let comma_pos = String.index line ',' in
+        let pk = String.trim (String.sub line 0 comma_pos) in
+        let sk = String.trim (String.sub line (comma_pos + 1) (String.length line - comma_pos - 1)) in
+        if String.length pk > 8 && String.length sk > 8 then
+          Some (pk, sk)
+        else None
+      with Not_found -> None
+  ) lines
+
+(** Load credentials from a specific CSV path at the given account index *)
+let load_csv_at path account_index =
+  if Sys.file_exists path then
     try
-      let content = read_file accounts_path in
-      let lines = String.split_on_char '\n' content in
-      let valid_accounts = List.filter_map (fun line ->
-        let line = String.trim line in
-        if String.length line = 0 || line.[0] = '#' then None
-        else
-          try
-            let comma_pos = String.index line ',' in
-            let pk = String.sub line 0 comma_pos in
-            let sk = String.sub line (comma_pos + 1) (String.length line - comma_pos - 1) in
-            if String.length pk > 8 && String.sub pk 0 8 = "unsb-pk-" &&
-               String.length sk > 8 && String.sub sk 0 8 = "unsb-sk-" then
-              Some (pk, sk)
-            else None
-          with Not_found -> None
-      ) lines in
-      if account_index < List.length valid_accounts then
-        Some (List.nth valid_accounts account_index)
+      let content = read_file path in
+      let accounts = parse_accounts_csv content in
+      if account_index < List.length accounts then
+        Some (List.nth accounts account_index)
       else None
     with _ -> None
   else None
 
+(** Get credentials from config file ~/.unsandbox/accounts.csv *)
+let get_credentials_from_file ?(account_index=0) () =
+  let home = try Sys.getenv "HOME" with Not_found -> "." in
+  let home_csv = Filename.concat home ".unsandbox/accounts.csv" in
+  match load_csv_at home_csv account_index with
+  | Some _ as r -> r
+  | None -> load_csv_at "accounts.csv" account_index
+
 (**
    Get API credentials in priority order:
-   1. Function arguments
-   2. Environment variables
-   3. ~/.unsandbox/accounts.csv
+   1. Function arguments (public_key, secret_key)
+   2. --account N (cli_account_index ref) -> accounts.csv row N
+   3. Environment variables (UNSANDBOX_PUBLIC_KEY, UNSANDBOX_SECRET_KEY)
+   4. ~/.unsandbox/accounts.csv row 0 (or UNSANDBOX_ACCOUNT env)
+   5. ./accounts.csv row 0
 
    @param public_key Optional public key override
    @param secret_key Optional secret key override
@@ -326,18 +340,32 @@ let get_credentials ?public_key ?secret_key ?(account_index=0) () =
   match (public_key, secret_key) with
   | (Some pk, Some sk) -> (pk, sk)
   | _ ->
-    (* Priority 2: Environment variables *)
-    let env_pk = try Some (Sys.getenv "UNSANDBOX_PUBLIC_KEY") with Not_found -> None in
-    let env_sk = try Some (Sys.getenv "UNSANDBOX_SECRET_KEY") with Not_found -> None in
-    match (env_pk, env_sk) with
-    | (Some pk, Some sk) -> (pk, sk)
-    | _ ->
-      (* Priority 3: Config file *)
-      match get_credentials_from_file ~account_index () with
+    (* Priority 2: --account N CLI flag overrides env vars *)
+    let effective_index = if !cli_account_index >= 0 then !cli_account_index else account_index in
+    if !cli_account_index >= 0 then begin
+      match get_credentials_from_file ~account_index:effective_index () with
       | Some (pk, sk) -> (pk, sk)
       | None ->
-        failwith "No credentials found. Set UNSANDBOX_PUBLIC_KEY and UNSANDBOX_SECRET_KEY, \
-                  or create ~/.unsandbox/accounts.csv, or pass credentials to function."
+        Printf.fprintf stderr "Error: No credentials found for account index %d in accounts.csv\n" !cli_account_index;
+        exit 1
+    end else begin
+      (* Priority 3: Environment variables *)
+      let env_pk = try Some (Sys.getenv "UNSANDBOX_PUBLIC_KEY") with Not_found -> None in
+      let env_sk = try Some (Sys.getenv "UNSANDBOX_SECRET_KEY") with Not_found -> None in
+      match (env_pk, env_sk) with
+      | (Some pk, Some sk) -> (pk, sk)
+      | _ ->
+        (* Priority 4: ~/.unsandbox/accounts.csv (or UNSANDBOX_ACCOUNT index) *)
+        let default_index =
+          try int_of_string (String.trim (Sys.getenv "UNSANDBOX_ACCOUNT"))
+          with Not_found | Failure _ -> 0
+        in
+        match get_credentials_from_file ~account_index:default_index () with
+        | Some (pk, sk) -> (pk, sk)
+        | None ->
+          failwith "No credentials found. Set UNSANDBOX_PUBLIC_KEY and UNSANDBOX_SECRET_KEY, \
+                    or create ~/.unsandbox/accounts.csv, or pass credentials to function."
+    end
 
 (* Legacy function for backward compatibility *)
 let get_api_keys () =
@@ -2038,18 +2066,34 @@ let image_command args =
   in
   parse_args false "" "" "" "" "" "" "" "" "" "" "" "" args
 
+let strip_account_arg args =
+  let rec aux = function
+    | [] -> []
+    | "--account" :: n_str :: rest ->
+      (try cli_account_index := int_of_string (String.trim n_str)
+       with Failure _ ->
+         Printf.fprintf stderr "Error: --account requires an integer argument\n";
+         exit 1);
+      aux rest
+    | arg :: rest -> arg :: aux rest
+  in
+  aux args
+
 let () =
   Random.self_init ();
-  let args = Array.to_list Sys.argv in
-  match List.tl args with
+  let raw_args = Array.to_list Sys.argv in
+  let args = strip_account_arg (List.tl raw_args) in
+  match args with
   | [] ->
-    Printf.printf "Usage: un.ml [options] <source_file>\n";
-    Printf.printf "       un.ml session [options]\n";
-    Printf.printf "       un.ml service [options]\n";
-    Printf.printf "       un.ml image [options]\n";
-    Printf.printf "       un.ml service env <action> <service_id>\n";
+    Printf.printf "Usage: un.ml [--account N] [options] <source_file>\n";
+    Printf.printf "       un.ml [--account N] session [options]\n";
+    Printf.printf "       un.ml [--account N] service [options]\n";
+    Printf.printf "       un.ml [--account N] image [options]\n";
+    Printf.printf "       un.ml [--account N] service env <action> <service_id>\n";
     Printf.printf "       un.ml languages [--json]\n";
     Printf.printf "       un.ml key [--extend]\n\n";
+    Printf.printf "Global options:\n";
+    Printf.printf "  --account N    Use accounts.csv row N (bypasses env vars)\n\n";
     Printf.printf "Service options: --name, --ports, --bootstrap, --bootstrap-file, -e KEY=VALUE, --env-file FILE\n";
     Printf.printf "Service env commands: status, set, export, delete\n";
     Printf.printf "Image options: --list, --info ID, --delete ID, --lock ID, --unlock ID,\n";