diff --git a/src/tyro/_backends/_tyro_backend.py b/src/tyro/_backends/_tyro_backend.py
index 13407c5f..d8be7654 100644
--- a/src/tyro/_backends/_tyro_backend.py
+++ b/src/tyro/_backends/_tyro_backend.py
@@ -25,6 +25,10 @@
 from ._argparse_formatter import TyroArgumentParser
 from ._base import ParserBackend
 
+_FLAG_ACTIONS = frozenset(
+    {"store_true", "store_false", "boolean_optional_action", "count"}
+)
+
 
 class KwargMap:
     """Look-up table for tracking keyword arguments. Due to aliases, each
@@ -78,17 +82,33 @@ def contains_normalized(self, token_key: str) -> bool:
             return normalized in self._arg_from_kwarg
         return False
 
-    def is_counter_flag(self, token: str) -> bool:
-        """Check if a token like -vvv is a repeated counter short flag."""
-        if len(token) <= 2 or not token.startswith("-") or token.startswith("--"):
-            return False
-        short_key = token[:2]
-        arg = self._arg_from_kwarg.get(short_key)
-        return (
-            arg is not None
-            and arg.lowered.action == "count"
-            and all(token[i] == token[1] for i in range(2, len(token)))
-        )
+    def expand_short_cluster(self, token: str) -> list[str] | None:
+        """POSIX-style expansion of clustered short flags.
+
+        ``-abc`` -> ``[-a, -b, -c]``; ``-nfoo`` -> ``[-n, foo]`` when ``-n``
+        takes a value; ``-vvv`` -> ``[-v, -v, -v]`` (the count-action handler
+        increments once per character). Returns ``None`` if the token isn't
+        a short cluster or contains an unknown character.
+
+        The caller must strip any trailing ``=value`` before calling, and
+        must already have ruled out an exact alias match (so explicit
+        multi-char shorts like ``-cail`` are preferred).
+        """
+        if not (token.startswith("-") and len(token) > 2 and token[1] != "-"):
+            return None
+        expanded: list[str] = []
+        for i, ch in enumerate(token[1:], start=1):
+            arg = self._arg_from_kwarg.get("-" + ch)
+            if arg is None:
+                return None
+            expanded.append("-" + ch)
+            if arg.lowered.action not in _FLAG_ACTIONS:
+                # Value-taking short: the rest of the token is its value.
+                rest = token[i + 1 :]
+                if rest:
+                    expanded.append(rest)
+                break
+        return expanded
 
     def get_boolean_value(self, kwarg: str) -> bool | None:
         return self._value_from_boolean_flag.get(kwarg, None)
@@ -449,16 +469,8 @@ def _recurse(
                     maybe_flag_delimiter_swapped
                 )
                 full_arg = kwarg_map.get_kwarg(maybe_flag_delimiter_swapped)
-                short_counter_arg = kwarg_map.get_kwarg(arg_value[:2])
-                enforce_mutex_group(short_counter_arg, maybe_flag_delimiter_swapped)
                 enforce_mutex_group(full_arg, maybe_flag_delimiter_swapped)
-                if kwarg_map.is_counter_flag(arg_value):
-                    assert short_counter_arg is not None
-                    dest = short_counter_arg.lowered.dest
-                    output[dest] = cast(int, output[dest]) + len(arg_value) - 1
-                    args_to_pop.append(short_counter_arg)
-                    continue
-                elif boolean_value is not None:
+                if boolean_value is not None:
                     assert full_arg is not None
                     output[full_arg.lowered.dest] = boolean_value
                     args_to_pop.append(full_arg)
@@ -530,6 +542,19 @@ def _recurse(
                             )
                     continue
 
+                # POSIX-style short flag clustering (-abc -> -a -b -c).
+                # Tried only after exact-match lookups, so registered
+                # multi-char shorts like -cail still win.
+                flag_token = (
+                    arg_value if equals_value is None else arg_value.partition("=")[0]
+                )
+                expanded = kwarg_map.expand_short_cluster(flag_token)
+                if expanded is not None:
+                    if equals_value is not None:
+                        expanded.append(equals_value)
+                    args_deque.extendleft(reversed(expanded))
+                    continue
+
                 # Implicitly select default subcommands.
                 if CascadeSubcommandArgs in parser_spec.markers:
                     # Note: maybe_flag_delimiter_swapped already has the "=value"
@@ -870,8 +895,6 @@ def _consume_argument(
                     token_key = args_deque[0].partition("=")[0]
                     if kwarg_map.contains_normalized(token_key):
                         break
-                    if kwarg_map.is_counter_flag(token_key):
-                        break
 
                     # To match argparse behavior, any flag-like string
                     # terminates positional nargs consumption. We check for
diff --git a/tests/test_py311_generated/test_short_flag_clustering_generated.py b/tests/test_py311_generated/test_short_flag_clustering_generated.py
new file mode 100644
index 00000000..dbe1679c
--- /dev/null
+++ b/tests/test_py311_generated/test_short_flag_clustering_generated.py
@@ -0,0 +1,249 @@
+"""Tests for POSIX-style short flag clustering (issue #465).
+
+POSIX commands let you combine single-letter options: ``-abc`` is equivalent
+to ``-a -b -c``. If a flag in the cluster takes a value, the rest of the
+token (after an optional ``=``) becomes that value: ``-nfoo`` -> ``-n foo``.
+"""
+
+from __future__ import annotations
+
+import dataclasses
+from typing import Annotated, Optional, Tuple
+
+import pytest
+
+import tyro
+from tyro.conf import UseCounterAction, arg
+
+
+@dataclasses.dataclass
+class Flags:
+    a: Annotated[bool, arg(aliases=["-a"])] = False
+    b: Annotated[bool, arg(aliases=["-b"])] = False
+    c: Annotated[bool, arg(aliases=["-c"])] = False
+
+
+def test_cluster_all_bool() -> None:
+    out = tyro.cli(Flags, args=["-abc"])
+    assert out == Flags(a=True, b=True, c=True)
+
+
+def test_cluster_partial_bool() -> None:
+    assert tyro.cli(Flags, args=["-ab"]) == Flags(a=True, b=True, c=False)
+    assert tyro.cli(Flags, args=["-ac"]) == Flags(a=True, b=False, c=True)
+    assert tyro.cli(Flags, args=["-bc"]) == Flags(a=False, b=True, c=True)
+
+
+def test_cluster_with_separate_short() -> None:
+    assert tyro.cli(Flags, args=["-ab", "-c"]) == Flags(a=True, b=True, c=True)
+    assert tyro.cli(Flags, args=["-a", "-bc"]) == Flags(a=True, b=True, c=True)
+
+
+def test_cluster_unknown_char_raises() -> None:
+    with pytest.raises(SystemExit):
+        tyro.cli(Flags, args=["-abz"])
+
+
+def test_cluster_repeated_char_is_idempotent_for_bool() -> None:
+    # -aa -> -a -a (both store_true, second overwrites; net effect a=True)
+    assert tyro.cli(Flags, args=["-aa"]) == Flags(a=True)
+
+
+def test_value_taking_short_glued() -> None:
+    @dataclasses.dataclass
+    class C:
+        n: Annotated[str, arg(aliases=["-n"])] = "default"
+
+    assert tyro.cli(C, args=["-nfoo"]).n == "foo"
+    # -n=foo also works.
+    assert tyro.cli(C, args=["-n=foo"]).n == "foo"
+    # Spaced form still works.
+    assert tyro.cli(C, args=["-n", "foo"]).n == "foo"
+
+
+def test_value_taking_short_at_end_of_cluster() -> None:
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        b: Annotated[bool, arg(aliases=["-b"])] = False
+        n: Annotated[str, arg(aliases=["-n"])] = "default"
+
+    # -abn foo -> -a -b -n foo
+    out = tyro.cli(C, args=["-abn", "foo"])
+    assert out == C(a=True, b=True, n="foo")
+    # Glued: -abnfoo -> -a -b -n foo
+    out = tyro.cli(C, args=["-abnfoo"])
+    assert out == C(a=True, b=True, n="foo")
+    # Equals: -abn=foo
+    out = tyro.cli(C, args=["-abn=foo"])
+    assert out == C(a=True, b=True, n="foo")
+
+
+def test_value_taking_short_in_middle_consumes_rest() -> None:
+    """If a value-taking short appears mid-cluster, the rest is its value
+    (POSIX semantics), even if subsequent characters look like other flags."""
+
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        b: Annotated[bool, arg(aliases=["-b"])] = False
+        n: Annotated[str, arg(aliases=["-n"])] = "default"
+
+    # -anb -> -a -n b (b becomes the value of -n, not a flag).
+    out = tyro.cli(C, args=["-anb"])
+    assert out == C(a=True, b=False, n="b")
+
+
+def test_counter_short_cluster() -> None:
+    @dataclasses.dataclass
+    class C:
+        verbose: Annotated[int, arg(aliases=["-v"]), UseCounterAction] = 0
+
+    assert tyro.cli(C, args=["-vvv"]).verbose == 3
+    assert tyro.cli(C, args=["-v", "-v"]).verbose == 2
+    assert tyro.cli(C, args=[]).verbose == 0
+
+
+def test_counter_mixed_with_bool_cluster() -> None:
+    @dataclasses.dataclass
+    class C:
+        verbose: Annotated[int, arg(aliases=["-v"]), UseCounterAction] = 0
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+
+    assert tyro.cli(C, args=["-va"]) == C(verbose=1, a=True)
+    assert tyro.cli(C, args=["-vva"]) == C(verbose=2, a=True)
+    assert tyro.cli(C, args=["-avv"]) == C(verbose=2, a=True)
+    assert tyro.cli(C, args=["-vav"]) == C(verbose=2, a=True)
+
+
+def test_registered_multichar_short_takes_precedence() -> None:
+    """If ``-cail`` is explicitly registered as an alias, it must win over
+    cluster expansion of ``-c -a -i -l``."""
+
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        c: Annotated[bool, arg(aliases=["-c"])] = False
+        i: Annotated[bool, arg(aliases=["-i"])] = False
+        l: Annotated[bool, arg(aliases=["-l"])] = False
+        cail: Annotated[bool, arg(aliases=["-cail"])] = False
+
+    out = tyro.cli(C, args=["-cail"])
+    # The exact alias wins.
+    assert out.cail is True
+    assert out.a is False
+    assert out.c is False
+
+
+def test_double_dash_long_flag_not_clustered() -> None:
+    """``--abc`` is a long flag; never expanded as a cluster."""
+
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        b: Annotated[bool, arg(aliases=["-b"])] = False
+        c: Annotated[bool, arg(aliases=["-c"])] = False
+
+    with pytest.raises(SystemExit):
+        tyro.cli(C, args=["--abc"])
+
+
+def test_cluster_after_double_dash_marker_treated_as_positional() -> None:
+    """Tokens after the ``--`` end-of-options marker are not flags."""
+
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        rest: tyro.conf.Positional[Tuple[str, ...]] = ()
+
+    out = tyro.cli(C, args=["-a", "--", "-bc"])
+    assert out.a is True
+    assert out.rest == ("-bc",)
+
+
+def test_negative_number_not_cluster() -> None:
+    """Negative numbers must still be parseable as positional/value args."""
+
+    @dataclasses.dataclass
+    class C:
+        n: int = 0
+
+    assert tyro.cli(C, args=["--n", "-3"]).n == -3
+
+
+def test_cluster_with_value_taking_first() -> None:
+    """If the first short in a cluster takes a value, the entire rest is
+    its value (no further flag interpretation)."""
+
+    @dataclasses.dataclass
+    class C:
+        n: Annotated[str, arg(aliases=["-n"])] = "x"
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+
+    # -nabc -> -n abc, NOT -n -a -b -c.
+    assert tyro.cli(C, args=["-nabc"]).n == "abc"
+
+
+def test_cluster_int_value() -> None:
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        n: Annotated[int, arg(aliases=["-n"])] = 0
+
+    out = tyro.cli(C, args=["-an42"])
+    assert out == C(a=True, n=42)
+
+
+def test_cluster_optional_value_taking() -> None:
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        n: Annotated[Optional[str], arg(aliases=["-n"])] = None
+
+    out = tyro.cli(C, args=["-an", "hi"])
+    assert out == C(a=True, n="hi")
+
+
+def test_lone_short_not_affected() -> None:
+    """Sanity check: lone ``-a`` still works."""
+
+    out = tyro.cli(Flags, args=["-a"])
+    assert out == Flags(a=True)
+
+
+def test_cluster_does_not_match_long_flag_chars() -> None:
+    """Cluster expansion must use only registered single-letter shorts, not
+    arbitrary characters from long flag names."""
+
+    @dataclasses.dataclass
+    class C:
+        apple: bool = False
+        banana: bool = False
+
+    with pytest.raises(SystemExit):
+        tyro.cli(C, args=["-ab"])
+
+
+def test_cluster_with_unrelated_short() -> None:
+    """If only some chars are registered shorts, the cluster as a whole
+    fails (we don't partial-expand)."""
+
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        # -b NOT registered.
+
+    with pytest.raises(SystemExit):
+        tyro.cli(C, args=["-ab"])
+
+
+def test_help_short_unaffected() -> None:
+    """``-h`` still triggers help and is not interpreted as a cluster."""
+
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+
+    with pytest.raises(SystemExit) as exc_info:
+        tyro.cli(C, args=["-h"])
+    assert exc_info.value.code == 0
diff --git a/tests/test_short_flag_clustering.py b/tests/test_short_flag_clustering.py
new file mode 100644
index 00000000..6c114fba
--- /dev/null
+++ b/tests/test_short_flag_clustering.py
@@ -0,0 +1,250 @@
+"""Tests for POSIX-style short flag clustering (issue #465).
+
+POSIX commands let you combine single-letter options: ``-abc`` is equivalent
+to ``-a -b -c``. If a flag in the cluster takes a value, the rest of the
+token (after an optional ``=``) becomes that value: ``-nfoo`` -> ``-n foo``.
+"""
+
+from __future__ import annotations
+
+import dataclasses
+from typing import Optional, Tuple
+
+import pytest
+from typing_extensions import Annotated
+
+import tyro
+from tyro.conf import UseCounterAction, arg
+
+
+@dataclasses.dataclass
+class Flags:
+    a: Annotated[bool, arg(aliases=["-a"])] = False
+    b: Annotated[bool, arg(aliases=["-b"])] = False
+    c: Annotated[bool, arg(aliases=["-c"])] = False
+
+
+def test_cluster_all_bool() -> None:
+    out = tyro.cli(Flags, args=["-abc"])
+    assert out == Flags(a=True, b=True, c=True)
+
+
+def test_cluster_partial_bool() -> None:
+    assert tyro.cli(Flags, args=["-ab"]) == Flags(a=True, b=True, c=False)
+    assert tyro.cli(Flags, args=["-ac"]) == Flags(a=True, b=False, c=True)
+    assert tyro.cli(Flags, args=["-bc"]) == Flags(a=False, b=True, c=True)
+
+
+def test_cluster_with_separate_short() -> None:
+    assert tyro.cli(Flags, args=["-ab", "-c"]) == Flags(a=True, b=True, c=True)
+    assert tyro.cli(Flags, args=["-a", "-bc"]) == Flags(a=True, b=True, c=True)
+
+
+def test_cluster_unknown_char_raises() -> None:
+    with pytest.raises(SystemExit):
+        tyro.cli(Flags, args=["-abz"])
+
+
+def test_cluster_repeated_char_is_idempotent_for_bool() -> None:
+    # -aa -> -a -a (both store_true, second overwrites; net effect a=True)
+    assert tyro.cli(Flags, args=["-aa"]) == Flags(a=True)
+
+
+def test_value_taking_short_glued() -> None:
+    @dataclasses.dataclass
+    class C:
+        n: Annotated[str, arg(aliases=["-n"])] = "default"
+
+    assert tyro.cli(C, args=["-nfoo"]).n == "foo"
+    # -n=foo also works.
+    assert tyro.cli(C, args=["-n=foo"]).n == "foo"
+    # Spaced form still works.
+    assert tyro.cli(C, args=["-n", "foo"]).n == "foo"
+
+
+def test_value_taking_short_at_end_of_cluster() -> None:
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        b: Annotated[bool, arg(aliases=["-b"])] = False
+        n: Annotated[str, arg(aliases=["-n"])] = "default"
+
+    # -abn foo -> -a -b -n foo
+    out = tyro.cli(C, args=["-abn", "foo"])
+    assert out == C(a=True, b=True, n="foo")
+    # Glued: -abnfoo -> -a -b -n foo
+    out = tyro.cli(C, args=["-abnfoo"])
+    assert out == C(a=True, b=True, n="foo")
+    # Equals: -abn=foo
+    out = tyro.cli(C, args=["-abn=foo"])
+    assert out == C(a=True, b=True, n="foo")
+
+
+def test_value_taking_short_in_middle_consumes_rest() -> None:
+    """If a value-taking short appears mid-cluster, the rest is its value
+    (POSIX semantics), even if subsequent characters look like other flags."""
+
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        b: Annotated[bool, arg(aliases=["-b"])] = False
+        n: Annotated[str, arg(aliases=["-n"])] = "default"
+
+    # -anb -> -a -n b (b becomes the value of -n, not a flag).
+    out = tyro.cli(C, args=["-anb"])
+    assert out == C(a=True, b=False, n="b")
+
+
+def test_counter_short_cluster() -> None:
+    @dataclasses.dataclass
+    class C:
+        verbose: Annotated[int, arg(aliases=["-v"]), UseCounterAction] = 0
+
+    assert tyro.cli(C, args=["-vvv"]).verbose == 3
+    assert tyro.cli(C, args=["-v", "-v"]).verbose == 2
+    assert tyro.cli(C, args=[]).verbose == 0
+
+
+def test_counter_mixed_with_bool_cluster() -> None:
+    @dataclasses.dataclass
+    class C:
+        verbose: Annotated[int, arg(aliases=["-v"]), UseCounterAction] = 0
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+
+    assert tyro.cli(C, args=["-va"]) == C(verbose=1, a=True)
+    assert tyro.cli(C, args=["-vva"]) == C(verbose=2, a=True)
+    assert tyro.cli(C, args=["-avv"]) == C(verbose=2, a=True)
+    assert tyro.cli(C, args=["-vav"]) == C(verbose=2, a=True)
+
+
+def test_registered_multichar_short_takes_precedence() -> None:
+    """If ``-cail`` is explicitly registered as an alias, it must win over
+    cluster expansion of ``-c -a -i -l``."""
+
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        c: Annotated[bool, arg(aliases=["-c"])] = False
+        i: Annotated[bool, arg(aliases=["-i"])] = False
+        l: Annotated[bool, arg(aliases=["-l"])] = False
+        cail: Annotated[bool, arg(aliases=["-cail"])] = False
+
+    out = tyro.cli(C, args=["-cail"])
+    # The exact alias wins.
+    assert out.cail is True
+    assert out.a is False
+    assert out.c is False
+
+
+def test_double_dash_long_flag_not_clustered() -> None:
+    """``--abc`` is a long flag; never expanded as a cluster."""
+
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        b: Annotated[bool, arg(aliases=["-b"])] = False
+        c: Annotated[bool, arg(aliases=["-c"])] = False
+
+    with pytest.raises(SystemExit):
+        tyro.cli(C, args=["--abc"])
+
+
+def test_cluster_after_double_dash_marker_treated_as_positional() -> None:
+    """Tokens after the ``--`` end-of-options marker are not flags."""
+
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        rest: tyro.conf.Positional[Tuple[str, ...]] = ()
+
+    out = tyro.cli(C, args=["-a", "--", "-bc"])
+    assert out.a is True
+    assert out.rest == ("-bc",)
+
+
+def test_negative_number_not_cluster() -> None:
+    """Negative numbers must still be parseable as positional/value args."""
+
+    @dataclasses.dataclass
+    class C:
+        n: int = 0
+
+    assert tyro.cli(C, args=["--n", "-3"]).n == -3
+
+
+def test_cluster_with_value_taking_first() -> None:
+    """If the first short in a cluster takes a value, the entire rest is
+    its value (no further flag interpretation)."""
+
+    @dataclasses.dataclass
+    class C:
+        n: Annotated[str, arg(aliases=["-n"])] = "x"
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+
+    # -nabc -> -n abc, NOT -n -a -b -c.
+    assert tyro.cli(C, args=["-nabc"]).n == "abc"
+
+
+def test_cluster_int_value() -> None:
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        n: Annotated[int, arg(aliases=["-n"])] = 0
+
+    out = tyro.cli(C, args=["-an42"])
+    assert out == C(a=True, n=42)
+
+
+def test_cluster_optional_value_taking() -> None:
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        n: Annotated[Optional[str], arg(aliases=["-n"])] = None
+
+    out = tyro.cli(C, args=["-an", "hi"])
+    assert out == C(a=True, n="hi")
+
+
+def test_lone_short_not_affected() -> None:
+    """Sanity check: lone ``-a`` still works."""
+
+    out = tyro.cli(Flags, args=["-a"])
+    assert out == Flags(a=True)
+
+
+def test_cluster_does_not_match_long_flag_chars() -> None:
+    """Cluster expansion must use only registered single-letter shorts, not
+    arbitrary characters from long flag names."""
+
+    @dataclasses.dataclass
+    class C:
+        apple: bool = False
+        banana: bool = False
+
+    with pytest.raises(SystemExit):
+        tyro.cli(C, args=["-ab"])
+
+
+def test_cluster_with_unrelated_short() -> None:
+    """If only some chars are registered shorts, the cluster as a whole
+    fails (we don't partial-expand)."""
+
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+        # -b NOT registered.
+
+    with pytest.raises(SystemExit):
+        tyro.cli(C, args=["-ab"])
+
+
+def test_help_short_unaffected() -> None:
+    """``-h`` still triggers help and is not interpreted as a cluster."""
+
+    @dataclasses.dataclass
+    class C:
+        a: Annotated[bool, arg(aliases=["-a"])] = False
+
+    with pytest.raises(SystemExit) as exc_info:
+        tyro.cli(C, args=["-h"])
+    assert exc_info.value.code == 0