diff --git a/cmd/openai/completion_test.go b/cmd/openai/completion_test.go
new file mode 100644
index 00000000..421cc2cc
--- /dev/null
+++ b/cmd/openai/completion_test.go
@@ -0,0 +1,67 @@
+package main
+
+import (
+	"bytes"
+	"os"
+	"os/exec"
+	"slices"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestInheritedCompletionMainHelper(t *testing.T) {
+	if os.Getenv("OPENAI_CLI_INHERITANCE_HELPER") != "1" {
+		return
+	}
+	os.Args = os.Args[slices.Index(os.Args, "--")+1:]
+	main()
+	os.Exit(0)
+}
+
+func TestInheritedCompletionMain(t *testing.T) {
+	binary, err := os.Executable()
+	require.NoError(t, err)
+	// Keep real credentials and environment-selected client configuration out of
+	// subprocesses; completion never needs an API request or credential values.
+	var env []string
+	for _, e := range os.Environ() {
+		if !strings.HasPrefix(e, "OPENAI_") && !strings.HasPrefix(e, "COMPLETION_STYLE=") {
+			env = append(env, e)
+		}
+	}
+	env = append(env, "OPENAI_CLI_INHERITANCE_HELPER=1", "COMPLETION_STYLE=bash")
+	for _, tc := range []struct {
+		args   []string
+		output string
+		code   int
+	}{
+		{[]string{"--fo"}, "--format\n--format-error\n", 0},
+		{[]string{"models", "list", "--fo"}, "--format\n--format-error\n", 0},
+		{[]string{"models", "list", "--format", ""}, "", 11},
+		// requestflag.Flag declares IsLocal=true, including root credential flags.
+		{[]string{"models", "list", "--api-"}, "", 0},
+		{[]string{"models", "--format", "list", "li"}, "list\n", 0},
+		{[]string{"models", "list", "-r", "--fo"}, "--format\n--format-error\n", 0},
+	} {
+		t.Run(strings.Join(tc.args, " "), func(t *testing.T) {
+			args := append([]string{"-test.run=^TestInheritedCompletionMainHelper$", "--", "openai", "__complete", "--"}, tc.args...)
+			child := exec.Command(binary, args...)
+			child.Env = env
+			var out, errs bytes.Buffer
+			child.Stdout = &out
+			child.Stderr = &errs
+			err := child.Run()
+			code := 0
+			if exit, ok := err.(*exec.ExitError); ok {
+				code = exit.ExitCode()
+			} else {
+				require.NoError(t, err)
+			}
+			require.Equal(t, tc.code, code)
+			require.Equal(t, tc.output, out.String())
+			require.Empty(t, errs.String())
+		})
+	}
+}
diff --git a/internal/autocomplete/autocomplete.go b/internal/autocomplete/autocomplete.go
index 056bfbc6..a61b5b9e 100644
--- a/internal/autocomplete/autocomplete.go
+++ b/internal/autocomplete/autocomplete.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"embed"
 	"fmt"
+	"iter"
 	"os"
 	"slices"
 	"strings"
@@ -101,7 +102,7 @@ func isFlag(arg string) bool {
 	return strings.HasPrefix(arg, "-")
 }
 
-func findFlag(cmd *cli.Command, arg string) *cli.Flag {
+func findFlag(cmd *cli.Command, arg string, ancestors []*cli.Command) *cli.Flag {
 	name := strings.TrimLeft(arg, "-")
 	for _, flag := range cmd.Flags {
 		if vf, ok := flag.(cli.VisibleFlag); ok && !vf.IsVisible() {
@@ -112,9 +113,44 @@ func findFlag(cmd *cli.Command, arg string) *cli.Flag {
 			return &flag
 		}
 	}
+	for flag := range inheritedFlags(cmd, ancestors) {
+		if slices.Contains(flag.Names(), name) {
+			return &flag
+		}
+	}
 	return nil
 }
 
+// Match urfave's applied flags: nearest ancestors first, and any collision
+// with a command's own names or aliases excludes the entire ancestor flag.
+// Keep ancestry explicitly while walking raw trees, whose parent links are unset.
+func inheritedFlags(cmd *cli.Command, ancestors []*cli.Command) iter.Seq[cli.Flag] {
+	return func(yield func(cli.Flag) bool) {
+		localNames := map[string]bool{}
+		for _, flag := range cmd.Flags {
+			for _, name := range flag.Names() {
+				localNames[name] = true
+			}
+		}
+		for _, ancestor := range ancestors {
+		flags:
+			for _, flag := range ancestor.Flags {
+				if local, ok := flag.(cli.LocalFlag); !ok || local.IsLocal() {
+					continue
+				}
+				for _, name := range flag.Names() {
+					if localNames[name] {
+						continue flags
+					}
+				}
+				if !yield(flag) {
+					return
+				}
+			}
+		}
+	}
+}
+
 func findChild(cmd *cli.Command, name string) *cli.Command {
 	for _, c := range cmd.Commands {
 		if !c.Hidden && c.Name == name {
@@ -224,12 +260,13 @@ func getAllPossibleCompletions(completionStyle CompletionStyle, root *cli.Comman
 	current := args[len(args)-1]
 	preceding := args[0 : len(args)-1]
 	cmd := root
+	ancestors := root.Lineage()[1:]
 	i := 0
 	for i < len(preceding) {
 		arg := preceding[i]
 
 		if isFlag(arg) {
-			flag := findFlag(cmd, arg)
+			flag := findFlag(cmd, arg, ancestors)
 			if flag == nil {
 				i++
 			} else if docFlag, ok := (*flag).(cli.DocGenerationFlag); ok && docFlag.TakesValue() {
@@ -241,6 +278,7 @@ func getAllPossibleCompletions(completionStyle CompletionStyle, root *cli.Comman
 		} else {
 			child := findChild(cmd, arg)
 			if child != nil {
+				ancestors = append([]*cli.Command{cmd}, ancestors...)
 				cmd = child
 			}
 			i++
@@ -248,10 +286,10 @@ func getAllPossibleCompletions(completionStyle CompletionStyle, root *cli.Comman
 	}
 
 	// Check if the previous arg was a flag expecting a value
-	if len(preceding) > 0 {
+	if len(preceding) > 0 && i > len(preceding) {
 		prev := preceding[len(preceding)-1]
 		if isFlag(prev) {
-			flag := findFlag(cmd, prev)
+			flag := findFlag(cmd, prev, ancestors)
 			if flag != nil {
 				if fb, ok := (*flag).(*cli.StringFlag); ok && fb.TakesFile {
 					return CompletionResult{Completions: completions, Behavior: ShellCompletionBehaviorFile}
@@ -267,6 +305,17 @@ func getAllPossibleCompletions(completionStyle CompletionStyle, root *cli.Comman
 		for _, flag := range cmd.Flags {
 			completions = builder.createFromFlag(current, &flag, completions)
 		}
+		seen := map[string]bool{}
+		for flag := range inheritedFlags(cmd, ancestors) {
+			for _, candidate := range builder.createFromFlag(current, &flag, nil) {
+				if !seen[candidate.Name] {
+					seen[candidate.Name] = true
+					if visible, ok := flag.(cli.VisibleFlag); !ok || visible.IsVisible() {
+						completions = append(completions, candidate)
+					}
+				}
+			}
+		}
 	}
 
 	for _, child := range cmd.Commands {
diff --git a/internal/autocomplete/inheritance_test.go b/internal/autocomplete/inheritance_test.go
new file mode 100644
index 00000000..ef48587d
--- /dev/null
+++ b/internal/autocomplete/inheritance_test.go
@@ -0,0 +1,120 @@
+package autocomplete
+
+import (
+	"context"
+	"io"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"github.com/urfave/cli/v3"
+)
+
+func inheritedTree() (*cli.Command, *cli.Command) {
+	leaf := &cli.Command{Name: "leaf", HideHelp: true, Flags: []cli.Flag{&cli.BoolFlag{Name: "override", Aliases: []string{"o"}}}}
+	middle := &cli.Command{Name: "middle", HideHelp: true, Flags: []cli.Flag{
+		&cli.StringFlag{Name: "near", Aliases: []string{"shared"}, Usage: "near"},
+	}, Commands: []*cli.Command{leaf, {Name: "value", HideHelp: true}}}
+	root := &cli.Command{Name: "test", HideHelp: true, Writer: io.Discard, ErrWriter: io.Discard,
+		ExitErrHandler: func(context.Context, *cli.Command, error) {},
+		Flags: []cli.Flag{
+			&cli.StringFlag{Name: "format", Aliases: []string{"f"}},
+			&cli.StringFlag{Name: "file", TakesFile: true},
+			&cli.StringFlag{Name: "private", Hidden: true},
+			&cli.StringFlag{Name: "root-only", Local: true},
+			&cli.StringFlag{Name: "replaced", Aliases: []string{"o"}},
+			&cli.StringFlag{Name: "far", Aliases: []string{"shared"}, Usage: "far"},
+		}, Commands: []*cli.Command{middle}}
+	return root, leaf
+}
+
+func TestInheritedCompletion(t *testing.T) {
+	for _, initialized := range []bool{false, true} {
+		t.Run(map[bool]string{false: "raw", true: "initialized"}[initialized], func(t *testing.T) {
+			root, leaf := inheritedTree()
+			if initialized {
+				leaf.Action = func(context.Context, *cli.Command) error { return nil }
+				require.NoError(t, root.Run(context.Background(), []string{"test", "middle", "leaf"}))
+			}
+			for _, tc := range []struct {
+				args     []string
+				names    []string
+				behavior ShellCompletionBehavior
+			}{
+				{[]string{"middle", "leaf", "--fo"}, []string{"--format"}, 0},
+				{[]string{"middle", "leaf", "-f"}, []string{"-f"}, 0},
+				{[]string{"middle", "leaf", "--format", ""}, nil, 11},
+				{[]string{"middle", "leaf", "--format", "--file", "--fo"}, []string{"--format"}, 0},
+				{[]string{"middle", "leaf", "--format=synthetic", "--fo"}, []string{"--format"}, 0},
+				{[]string{"middle", "leaf", "-f", "--fo"}, nil, 11},
+				{[]string{"middle", "leaf", "--file", ""}, nil, 10},
+				{[]string{"middle", "leaf", "--private", "--fo"}, nil, 11},
+				{[]string{"middle", "leaf", "--pr"}, nil, 0},
+				{[]string{"middle", "leaf", "--root-"}, nil, 0},
+				{[]string{"middle", "leaf", "--repl"}, nil, 0},
+				{[]string{"middle", "leaf", "-o", "--fo"}, []string{"--format"}, 0},
+				{[]string{"middle", "--format", "value", "le"}, []string{"leaf"}, 0},
+				{[]string{"middle", "leaf", "--"}, []string{"--override", "--near", "--shared", "--format", "--file", "--far"}, 0},
+			} {
+				t.Run(strings.Join(tc.args, " "), func(t *testing.T) {
+					beforeRoot, beforeLeaf := root.Root(), leaf.Root()
+					rootFlags, leafFlags := append([]cli.Flag(nil), root.Flags...), append([]cli.Flag(nil), leaf.Flags...)
+					got := GetCompletions(CompletionStyleBash, root, tc.args)
+					var names []string
+					for _, c := range got.Completions {
+						names = append(names, c.Name)
+					}
+					require.Equal(t, tc.names, names)
+					require.Equal(t, tc.behavior, got.Behavior)
+					require.Same(t, beforeRoot, root.Root())
+					require.Same(t, beforeLeaf, leaf.Root())
+					require.Equal(t, rootFlags, root.Flags)
+					require.Equal(t, leafFlags, leaf.Flags)
+				})
+			}
+		})
+	}
+}
+
+func TestInheritedFlagShadowing(t *testing.T) {
+	for _, hidden := range []bool{false, true} {
+		for _, parentName := range []string{"override", "global"} {
+			root, leaf := inheritedTree()
+			leaf.Flags = []cli.Flag{&cli.BoolFlag{Name: "override", Aliases: []string{"o"}, Hidden: hidden}}
+			root.Flags = []cli.Flag{&cli.StringFlag{Name: parentName, Aliases: []string{"o", "other"}}}
+			// Even a hidden child declaration suppresses every parent alias.
+			got := GetCompletions(CompletionStyleBash, root, []string{"middle", "leaf", "--other"})
+			require.Empty(t, got.Completions)
+		}
+	}
+}
+
+// Pin the parser's contract: a child alias suppresses the entire parent flag,
+// while overlapping inherited aliases resolve to the nearest ancestor.
+func TestInheritedParserContract(t *testing.T) {
+	for _, tc := range []struct {
+		flag     string
+		accepted bool
+	}{
+		{"--format", true}, {"-f", true}, {"--private", true}, {"--file", true},
+		{"--root-only", false}, {"--replaced", false}, {"--near", true}, {"--far", true}, {"--shared", true},
+	} {
+		t.Run(tc.flag, func(t *testing.T) {
+			root, leaf := inheritedTree()
+			called := false
+			leaf.Action = func(context.Context, *cli.Command) error { called = true; return nil }
+			err := root.Run(context.Background(), []string{"test", "middle", "leaf", tc.flag, "synthetic"})
+			if tc.accepted {
+				require.NoError(t, err)
+				require.True(t, called)
+			} else {
+				require.Error(t, err)
+				require.False(t, called)
+			}
+			if tc.flag == "--shared" {
+				require.Equal(t, "synthetic", root.Commands[0].Flags[0].(*cli.StringFlag).Get())
+				require.Equal(t, "", root.Flags[5].(*cli.StringFlag).Get())
+			}
+		})
+	}
+}
diff --git a/internal/autocomplete/protocol_test.go b/internal/autocomplete/protocol_test.go
index 907f9351..c720c47d 100644
--- a/internal/autocomplete/protocol_test.go
+++ b/internal/autocomplete/protocol_test.go
@@ -63,6 +63,10 @@ func TestShellCompletionProtocol(t *testing.T) {
 	}{
 		{"root value", []string{"--format", "candidate-"}, 11, "", ""},
 		{"nested local value", []string{"models", "list", "--max-items", "candidate-"}, 11, "", ""},
+		{"nested inherited name", []string{"models", "list", "--fo"}, 0, "--format\n", "--format\n"},
+		{"nested inherited value", []string{"models", "list", "--format", "candidate-"}, 11, "", ""},
+		{"nested inherited file", []string{"models", "list", "--file", "candidate-"}, 10, "", "candidate-fixture.txt\n"},
+		{"nested explicit file prefix", []string{"models", "list", "--format", "@candidate-"}, 11, "", "@candidate-fixture.txt\n"},
 		{"file value", []string{"--file", "candidate-"}, 10, "", "candidate-fixture.txt\n"},
 		{"spaced preceding value", []string{"--format", "two words", "--file", "candidate-"}, 10, "", "candidate-fixture.txt\n"},
 		{"empty preceding value", []string{"--format", "", "--file", "candidate-"}, 10, "", "candidate-fixture.txt\n"},