diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index ceaab866d5..186f342d9d 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -31,3 +31,36 @@ jobs:
 
       - name: Test
         run: go run ./cmd/task test
+
+  completion:
+    name: Completion
+    strategy:
+      fail-fast: false
+      matrix:
+        platform: [ubuntu-latest, macos-latest]
+    runs-on: ${{matrix.platform}}
+    steps:
+      - name: Check out code
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+
+      - name: Set up Go
+        uses: actions/setup-go@4a3601121dd01d1626a1e23e37211e3254c1c06c # v6.4.0
+        with:
+          go-version: 1.26.x
+
+      # zsh and pwsh are preinstalled on the runners; only fish is missing
+      # (plus zsh on the Linux image).
+      - name: Install shells (Linux)
+        if: runner.os == 'Linux'
+        run: sudo apt-get update && sudo apt-get install -y zsh fish
+
+      - name: Install shells (macOS)
+        if: runner.os == 'macOS'
+        run: brew install fish
+
+      - name: Test completion
+        # Strict mode fails the run if any shell is missing, so we never get a
+        # false pass when a runner image stops shipping one (e.g. pwsh).
+        env:
+          TASK_COMPLETION_STRICT: "1"
+        run: go run ./cmd/task test:completion
diff --git a/CHANGELOG.md b/CHANGELOG.md
index bc921400c5..f9c1b5002e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,14 @@
   (#2184 by @jubr).
 - Fixed `joinUrl` collapsing the `//` in a URL scheme (e.g. producing
   `http:/localhost` instead of `http://localhost`) (#2915 by @vsaraikin).
+- Added a new completion engine that unifies Bash, Fish, Zsh and PowerShell
+  behind a single `task __complete` command, so every shell offers the same
+  suggestions: task names, aliases, flags, flag values and per-task CLI
+  variables. The Zsh `show-aliases` and `verbose` zstyles keep working, now
+  backed by the `--no-aliases` and `--no-descriptions` completion flags. It is
+  opt-in for now via `task --new-completion <shell>`, leaving `--completion`
+  unchanged, and will become the default in a future release (#2897 by
+  @vmaerten).
 
 ## v3.52.0 - 2026-07-02
 
diff --git a/Taskfile.yml b/Taskfile.yml
index 6b9b69a772..93976d5626 100644
--- a/Taskfile.yml
+++ b/Taskfile.yml
@@ -158,6 +158,15 @@ tasks:
     cmds:
       - go test -bench=. -benchmem -tags=fsbench -run=^$ ./...
 
+  test:completion:
+    desc: Tests the shell completion engine and wrappers (bash, zsh, fish, powershell)
+    sources:
+      - internal/complete/**/*.go
+      - cmd/task/**/*.go
+      - completion/**/*
+    cmds:
+      - bash completion/tests/run.sh
+
   goreleaser:test:
     desc: Tests release process without publishing
     cmds:
diff --git a/cmd/task/complete_cmd.go b/cmd/task/complete_cmd.go
new file mode 100644
index 0000000000..f0fa13ff4f
--- /dev/null
+++ b/cmd/task/complete_cmd.go
@@ -0,0 +1,55 @@
+package main
+
+import (
+	"io"
+	"os"
+
+	"github.com/spf13/pflag"
+
+	"github.com/go-task/task/v3"
+	"github.com/go-task/task/v3/internal/complete"
+)
+
+func runComplete(args []string) error {
+	// Strip the completion-control flags the wrapper prepends; the rest is the
+	// user's command line to complete.
+	opts, args := complete.ParseOptions(args)
+
+	dir, entrypoint, global := extractTaskfileFlags(args)
+
+	e := task.NewExecutor(
+		task.WithDir(dir),
+		task.WithEntrypoint(entrypoint),
+		task.WithStdout(io.Discard),
+		task.WithStderr(io.Discard),
+		task.WithVersionCheck(false),
+	)
+	if global {
+		if home, err := os.UserHomeDir(); err == nil {
+			e.Options(task.WithDir(home))
+		}
+	}
+
+	// Loading the Taskfile parses YAML (and may hit the network for remote
+	// Taskfiles), so skip it entirely when completing flags or their values.
+	// Best-effort: a missing or broken Taskfile must not break completion.
+	if complete.NeedsTaskfile(args, pflag.CommandLine) {
+		_ = e.Setup()
+	}
+
+	suggs, dirv := complete.Complete(e, pflag.CommandLine, args, opts)
+	complete.Write(os.Stdout, suggs, dirv)
+	return nil
+}
+
+func extractTaskfileFlags(args []string) (dir, entrypoint string, global bool) {
+	fs := pflag.NewFlagSet("complete", pflag.ContinueOnError)
+	fs.SetOutput(io.Discard)
+	fs.ParseErrorsAllowlist.UnknownFlags = true
+	fs.Usage = func() {}
+	fs.StringVarP(&dir, "dir", "d", "", "")
+	fs.StringVarP(&entrypoint, "taskfile", "t", "", "")
+	fs.BoolVarP(&global, "global", "g", false, "")
+	_ = fs.Parse(args)
+	return
+}
diff --git a/cmd/task/task.go b/cmd/task/task.go
index b81e23dd5f..2332845199 100644
--- a/cmd/task/task.go
+++ b/cmd/task/task.go
@@ -13,6 +13,7 @@ import (
 	"github.com/go-task/task/v3/args"
 	"github.com/go-task/task/v3/errors"
 	"github.com/go-task/task/v3/experiments"
+	"github.com/go-task/task/v3/internal/complete"
 	"github.com/go-task/task/v3/internal/filepathext"
 	"github.com/go-task/task/v3/internal/flags"
 	"github.com/go-task/task/v3/internal/logger"
@@ -58,6 +59,12 @@ func emitCIErrorAnnotation(err error) {
 }
 
 func run() error {
+	// Dispatched before flag validation: the args after __complete are the
+	// user's command line, not Task's own flags.
+	if complete.IsActive() {
+		return runComplete(os.Args[2:])
+	}
+
 	log := &logger.Logger{
 		Stdout:  os.Stdout,
 		Stderr:  os.Stderr,
@@ -126,6 +133,15 @@ func run() error {
 		return nil
 	}
 
+	if flags.NewCompletion != "" {
+		script, err := task.CompletionNext(flags.NewCompletion)
+		if err != nil {
+			return err
+		}
+		fmt.Println(script)
+		return nil
+	}
+
 	e := task.NewExecutor(
 		flags.WithFlags(),
 		task.WithVersionCheck(true),
diff --git a/completion.go b/completion.go
index 1ab08e76f6..685c08b9c0 100644
--- a/completion.go
+++ b/completion.go
@@ -17,9 +17,25 @@ var completionPowershell string
 //go:embed completion/zsh/_task
 var completionZsh string
 
-func Completion(completion string) (string, error) {
-	// Get the file extension for the selected shell
-	switch completion {
+// The completion/next/* scripts are thin wrappers around the `task __complete`
+// engine. They are served only via `--new-completion` for now (opt-in) and will
+// replace the scripts above once the engine becomes the default.
+
+//go:embed completion/next/bash/task.bash
+var completionBashNext string
+
+//go:embed completion/next/fish/task.fish
+var completionFishNext string
+
+//go:embed completion/next/ps/task.ps1
+var completionPowershellNext string
+
+//go:embed completion/next/zsh/_task
+var completionZshNext string
+
+// Completion returns the default (stable) completion script for the given shell.
+func Completion(shell string) (string, error) {
+	switch shell {
 	case "bash":
 		return completionBash, nil
 	case "fish":
@@ -29,6 +45,23 @@ func Completion(completion string) (string, error) {
 	case "zsh":
 		return completionZsh, nil
 	default:
-		return "", fmt.Errorf("unknown shell: %s", completion)
+		return "", fmt.Errorf("unknown shell: %s", shell)
+	}
+}
+
+// CompletionNext returns the new `task __complete` engine wrapper for the given
+// shell, exposed via `--new-completion` while the engine is opt-in.
+func CompletionNext(shell string) (string, error) {
+	switch shell {
+	case "bash":
+		return completionBashNext, nil
+	case "fish":
+		return completionFishNext, nil
+	case "powershell":
+		return completionPowershellNext, nil
+	case "zsh":
+		return completionZshNext, nil
+	default:
+		return "", fmt.Errorf("unknown shell: %s", shell)
 	}
 }
diff --git a/completion/next/bash/task.bash b/completion/next/bash/task.bash
new file mode 100644
index 0000000000..44e8d37777
--- /dev/null
+++ b/completion/next/bash/task.bash
@@ -0,0 +1,98 @@
+# vim: set tabstop=2 shiftwidth=2 expandtab:
+#
+# Thin wrapper around `task __complete`. All suggestion logic lives in the
+# Go engine — do not add completion logic here.
+
+TASK_CMD="${TASK_EXE:-task}"
+
+# Wraps _filedir so an inline `--flag=` prefix is stripped before completion and
+# re-applied to the results. `=` is kept inside the current word (see the
+# `_init_completion -n =:` below), so the whole `--flag=value` token would
+# otherwise be treated as the path and never match.
+_task_filedir() {
+  local fpfx="" savecur="$cur"
+  if [[ "$cur" == -*=* ]]; then
+    fpfx="${cur%%=*}="
+    cur="${cur#*=}"
+  fi
+  _filedir ${1:+"$1"}
+  cur="$savecur"
+  if [[ -n "$fpfx" ]]; then
+    COMPREPLY=( ${COMPREPLY[@]+"${COMPREPLY[@]/#/$fpfx}"} )
+  fi
+}
+
+_task() {
+  local cur prev words cword
+
+  # Completion directives, mirroring internal/complete/complete.go.
+  local -ri NO_SPACE=2 NO_FILE_COMP=4 FILTER_FILE_EXT=8 FILTER_DIRS=16
+
+  # Exclude both `=` and `:` from the word breaks so `--output=` and
+  # `docs:serve` reach the engine as single tokens.
+  _init_completion -n =: || return
+
+  local -a args=()
+  if (( cword > 0 )); then
+    args=( "${words[@]:1:cword}" )
+  fi
+  if (( ${#args[@]} == 0 )); then
+    args=( "" )
+  fi
+
+  local output
+  output=$("$TASK_CMD" __complete "${args[@]}" 2>/dev/null)
+  if [[ -z "$output" ]]; then
+    _task_filedir
+    return
+  fi
+
+  local -a lines=()
+  local line
+  while IFS= read -r line; do
+    lines+=( "$line" )
+  done <<< "$output"
+
+  local last_idx=$(( ${#lines[@]} - 1 ))
+  local directive="${lines[$last_idx]#:}"
+  unset 'lines[$last_idx]'
+
+  if (( directive & FILTER_FILE_EXT )); then
+    local exts=""
+    # ${arr[@]+…} guards against "unbound variable" on an empty array under
+    # `set -u` in bash 3.2 (macOS).
+    for line in ${lines[@]+"${lines[@]}"}; do
+      exts+="${exts:+|}$line"
+    done
+    _task_filedir "@($exts)"
+    return
+  fi
+
+  if (( directive & FILTER_DIRS )); then
+    _task_filedir -d
+    return
+  fi
+
+  # Prefix-filter by hand instead of `compgen -W`: the latter joins/splits the
+  # word list on IFS, which mangles any suggestion value containing a space.
+  local value
+  COMPREPLY=()
+  for line in ${lines[@]+"${lines[@]}"}; do
+    value="${line%%$'\t'*}"
+    if [[ -z "$cur" || "$value" == "$cur"* ]]; then
+      COMPREPLY+=( "$value" )
+    fi
+  done
+
+  if (( directive & NO_SPACE )); then
+    compopt -o nospace 2>/dev/null
+  fi
+
+  __ltrim_colon_completions "$cur"
+
+  if (( ${#COMPREPLY[@]} == 0 )) && ! (( directive & NO_FILE_COMP )); then
+    _task_filedir
+  fi
+}
+
+complete -F _task "$TASK_CMD"
diff --git a/completion/next/fish/task.fish b/completion/next/fish/task.fish
new file mode 100644
index 0000000000..d323b4ad98
--- /dev/null
+++ b/completion/next/fish/task.fish
@@ -0,0 +1,110 @@
+# Thin wrapper around `task __complete`. All suggestion logic lives in the
+# Go engine — do not add completion logic here.
+
+set -l GO_TASK_PROGNAME (if set -q GO_TASK_PROGNAME; echo $GO_TASK_PROGNAME; else if set -q TASK_EXE; echo $TASK_EXE; else; echo task; end)
+
+# Completion directives, mirroring internal/complete/complete.go. fish's `math`
+# has no bitwise operators, so bits are stored as their power-of-two value and
+# tested with integer division + modulo via __task_test_bit.
+set -g __task_directive_no_space 2
+set -g __task_directive_no_file_comp 4
+set -g __task_directive_filter_file_ext 8
+set -g __task_directive_filter_dirs 16
+set -g __task_directive_keep_order 32
+
+function __task_test_bit --argument-names value bit
+  test (math "floor($value / $bit) % 2") -eq 1
+end
+
+function __task_complete --inherit-variable GO_TASK_PROGNAME
+  set -l tokens (commandline -opc)
+  set -l current (commandline -ct)
+  set -l args
+  if test (count $tokens) -gt 1
+    set args $tokens[2..-1]
+  end
+  set args $args $current
+
+  set -l output ($GO_TASK_PROGNAME __complete $args 2>/dev/null)
+  set -l count (count $output)
+  if test $count -eq 0
+    return
+  end
+
+  set -l last $output[$count]
+  if not string match -q ':*' -- $last
+    # Protocol violation: emit raw lines as a fallback.
+    printf '%s\n' $output
+    return
+  end
+
+  set -l directive (string replace -r '^:' '' -- $last)
+  set -l data
+  if test $count -gt 1
+    set data $output[1..(math $count - 1)]
+  end
+
+  # The main completion is registered with `--no-files`, which disables fish's
+  # native file fallback. Every file-completion directive must therefore be
+  # served here, otherwise nothing is offered (e.g. `--cacert`, after `--`).
+
+  # For an inline `--flag=path`, complete against the path part but keep the
+  # `--flag=` prefix on every candidate (fish replaces the whole token). flagpfx
+  # is empty for the normal case, so the prefixing below is a no-op then.
+  set -l flagpfx ""
+  set -l pathcur $current
+  if string match -qr '^--?[^=]+=' -- $current
+    set flagpfx (string replace -r '=.*$' '=' -- $current)
+    set pathcur (string replace -r '^--?[^=]+=' '' -- $current)
+  end
+
+  # __fish_complete_suffix only *prioritizes* the extension rather than
+  # filtering, so filter the file list ourselves (keeping dirs to descend into).
+  if __task_test_bit $directive $__task_directive_filter_file_ext
+    for entry in (__fish_complete_path $pathcur)
+      set -l name (string split -f1 \t -- $entry)
+      if string match -qr '/$' -- $name
+        printf '%s%s\n' $flagpfx $entry
+        continue
+      end
+      for ext in $data
+        if string match -qr "\.$ext\$" -- $name
+          printf '%s%s\n' $flagpfx $entry
+          break
+        end
+      end
+    end
+    return
+  end
+
+  if __task_test_bit $directive $__task_directive_filter_dirs
+    for entry in (__fish_complete_directories $pathcur)
+      printf '%s%s\n' $flagpfx $entry
+    end
+    return
+  end
+
+  # Emit the candidates verbatim; fish reads the tab as the value/description
+  # separator.
+  for line in $data
+    printf '%s\n' $line
+  end
+
+  # NoFileComp unset → also offer files, since `--no-files` suppressed the
+  # native fallback. Covers DirectiveDefault (e.g. `--cacert`, after `--`).
+  if not __task_test_bit $directive $__task_directive_no_file_comp
+    for entry in (__fish_complete_path $pathcur)
+      printf '%s%s\n' $flagpfx $entry
+    end
+  end
+end
+
+# Erase any inherited rules first: fish accumulates `complete` entries (unlike
+# bash/zsh/PowerShell which replace), so a previously loaded completion would
+# otherwise keep contributing alongside the engine.
+complete -c $GO_TASK_PROGNAME -e
+
+# Single registration: all task names, flags, flag values and file completion
+# flow through the engine. `--no-files` prevents fish from mixing in files when
+# the engine says not to (NoFileComp); `__task_complete` re-adds them otherwise.
+complete -c $GO_TASK_PROGNAME --no-files -a "(__task_complete)"
diff --git a/completion/next/ps/task.ps1 b/completion/next/ps/task.ps1
new file mode 100644
index 0000000000..ca30d30dd0
--- /dev/null
+++ b/completion/next/ps/task.ps1
@@ -0,0 +1,102 @@
+using namespace System.Management.Automation
+
+# Thin wrapper around `task __complete`. All suggestion logic lives in the
+# Go engine — do not add completion logic here.
+
+$cmdNames = @('task') + (Get-Alias -Definition task,task.exe,*\task,*\task.exe -ErrorAction SilentlyContinue).Name | Select-Object -Unique
+
+Register-ArgumentCompleter -Native -CommandName $cmdNames -ScriptBlock {
+	param($wordToComplete, $commandAst, $cursorPosition)
+
+	$TaskExe = if ($env:TASK_EXE) { $env:TASK_EXE } else { 'task' }
+
+	# Words after the program name, truncated to the cursor.
+	$argsToPass = @()
+	$elements = $commandAst.CommandElements
+	if ($elements.Count -gt 1) {
+		for ($i = 1; $i -lt $elements.Count; $i++) {
+			$el = $elements[$i]
+			if ($el.Extent.StartOffset -ge $cursorPosition) { break }
+			$argsToPass += $el.ToString()
+		}
+	}
+	# The trailing word (possibly empty) must reach the engine so it knows
+	# the cursor sits on a fresh word. It is already present when it coincides
+	# with the last command element captured above.
+	if ($argsToPass.Count -eq 0 -or $argsToPass[-1] -ne $wordToComplete) {
+		$argsToPass += $wordToComplete
+	}
+
+	$output = & $TaskExe __complete @argsToPass 2>$null
+	if (-not $output) { return }
+
+	$lines = @($output)
+	if ($lines.Count -eq 0) { return }
+	$last = $lines[-1]
+	if (-not $last.StartsWith(':')) { return }
+
+	$directive = [int]($last.Substring(1))
+	$data = if ($lines.Count -gt 1) { $lines[0..($lines.Count - 2)] } else { @() }
+
+	# Completion directives, mirroring internal/complete/complete.go.
+	$NoFileComp    = 4
+	$FilterFileExt = 8
+	$FilterDirs    = 16
+
+	# PowerShell replaces the whole token with the completion text, so both an
+	# inline `--flag=` and any directory the user already typed (e.g. `sub/`)
+	# must be preserved. Query the filesystem with the path portion only
+	# ($pathArg), but prepend the flag + directory prefix to every candidate.
+	$flagPrefix = ''
+	$pathArg = $wordToComplete
+	if ($wordToComplete -match '^(--?[^=]+=)(.*)$') {
+		$flagPrefix = $Matches[1]
+		$pathArg = $Matches[2]
+	}
+	$pathPrefix = $flagPrefix + ($pathArg -replace '[^\\/]*$', '')
+
+	# Note: DirectiveNoSpace (bit 2) cannot be honored here — PowerShell's
+	# CompletionResult API has no per-item "no trailing space" option, so a
+	# suggestion like `VAR=` gets a trailing space. This is a PowerShell limit.
+
+	# FilterFileExt: keep files whose extension matches, plus directories so the
+	# user can still descend into them. `-Include` is unreliable without
+	# `-Recurse`, so filter with Where-Object instead.
+	if ($directive -band $FilterFileExt) {
+		$exts = $data | ForEach-Object { ".$_" }
+		return Get-ChildItem -Path "$pathArg*" -ErrorAction SilentlyContinue |
+			Where-Object { $_.PSIsContainer -or $exts -contains $_.Extension } |
+			ForEach-Object {
+				$type = if ($_.PSIsContainer) { [CompletionResultType]::ProviderContainer } else { [CompletionResultType]::ProviderItem }
+				[CompletionResult]::new("$pathPrefix$($_.Name)", $_.Name, $type, $_.Name)
+			}
+	}
+
+	if ($directive -band $FilterDirs) {
+		return Get-ChildItem -Path "$pathArg*" -Directory -ErrorAction SilentlyContinue |
+			ForEach-Object { [CompletionResult]::new("$pathPrefix$($_.Name)", $_.Name, [CompletionResultType]::ProviderContainer, $_.Name) }
+	}
+
+	# Build candidates, filtering by the current word. PowerShell does not filter
+	# native argument-completer results itself, so without this every suggestion
+	# would be offered regardless of what the user typed.
+	$results = @($data | ForEach-Object {
+		$parts = $_ -split "`t", 2
+		$value = $parts[0]
+		if ($wordToComplete -and -not $value.StartsWith($wordToComplete, [System.StringComparison]::OrdinalIgnoreCase)) { return }
+		$desc = if ($parts.Count -gt 1 -and $parts[1]) { $parts[1] } else { $value }
+		[CompletionResult]::new($value, $value, [CompletionResultType]::ParameterValue, $desc)
+	})
+
+	# NoFileComp (bit 4) unset and nothing matched → fall back to file completion,
+	# since the engine returned DirectiveDefault (e.g. --cacert, after `--`).
+	if ($results.Count -eq 0 -and -not ($directive -band $NoFileComp)) {
+		return Get-ChildItem -Path "$pathArg*" -ErrorAction SilentlyContinue |
+			ForEach-Object {
+				$type = if ($_.PSIsContainer) { [CompletionResultType]::ProviderContainer } else { [CompletionResultType]::ProviderItem }
+				[CompletionResult]::new("$pathPrefix$($_.Name)", $_.Name, $type, $_.Name)
+			}
+	}
+
+	return $results
+}
diff --git a/completion/next/zsh/_task b/completion/next/zsh/_task
new file mode 100755
index 0000000000..a4d5d92e99
--- /dev/null
+++ b/completion/next/zsh/_task
@@ -0,0 +1,80 @@
+#compdef task
+#
+# Thin wrapper around `task __complete`. All suggestion logic lives in the
+# Go engine — do not add completion logic here.
+
+TASK_CMD="${TASK_EXE:-task}"
+
+_task() {
+	local -a args lines completions opts ctl
+	local output directive line
+
+	# Completion directives, mirroring internal/complete/complete.go.
+	local -ri NO_SPACE=2 NO_FILE_COMP=4 FILTER_FILE_EXT=8 FILTER_DIRS=16 KEEP_ORDER=32
+
+	# Map the zsh completion zstyles to engine flags. `-T` is true when the
+	# style is unset (its default) or explicitly true, so a flag is only passed
+	# when the user turned the style off.
+	zstyle -T ":completion:${curcontext}:" show-aliases || ctl+=(--no-aliases)
+	zstyle -T ":completion:${curcontext}:" verbose      || ctl+=(--no-descriptions)
+
+	# (@) preserves a trailing empty string, which the engine relies on to
+	# know the cursor is on a fresh word.
+	args=("${(@)words[2,CURRENT]}")
+	(( ${#args} == 0 )) && args=("")
+
+	output=$("$TASK_CMD" __complete "${ctl[@]}" "${args[@]}" 2>/dev/null)
+	if [[ -z "$output" ]]; then
+		_files
+		return
+	fi
+
+	lines=("${(f)output}")
+	directive="${lines[-1]#:}"
+	lines=("${(@)lines[1,-2]}")
+
+	if (( directive & FILTER_FILE_EXT )); then
+		local -a globs
+		for line in "${lines[@]}"; do
+			globs+=("*.${line}")
+		done
+		# Strip an inline `--flag=` into IPREFIX so file completion runs on the
+		# value; zsh re-inserts the prefix. Only in the file branches — doing it
+		# globally would break `_describe` matching for inline enums.
+		compset -P '*='
+		_files -g "(${(j:|:)globs})"
+		return
+	fi
+
+	if (( directive & FILTER_DIRS )); then
+		compset -P '*='
+		_path_files -/
+		return
+	fi
+
+	# `:` inside the value must be escaped: _describe splits on the first
+	# unescaped colon (e.g. "docs:serve" would otherwise become value "docs").
+	local value desc
+	for line in "${lines[@]}"; do
+		if [[ "$line" == *$'\t'* ]]; then
+			value="${line%%$'\t'*}"
+			desc="${line#*$'\t'}"
+			completions+=("${value//:/\\:}:$desc")
+		else
+			completions+=("${line//:/\\:}")
+		fi
+	done
+
+	(( directive & NO_SPACE ))  && opts+=(-S '')
+	(( directive & KEEP_ORDER )) && opts+=(-V)
+
+	if (( ${#completions} > 0 )); then
+		_describe -t tasks 'task' completions "${opts[@]}"
+	fi
+
+	(( directive & NO_FILE_COMP )) && return
+	compset -P '*='
+	_files
+}
+
+compdef _task "$TASK_CMD"
diff --git a/completion/protocol_test.go b/completion/protocol_test.go
new file mode 100644
index 0000000000..54a35f6459
--- /dev/null
+++ b/completion/protocol_test.go
@@ -0,0 +1,173 @@
+// Package completion_test black-box tests the `task __complete` wire protocol:
+// the candidates and directive the real binary emits for a command line. The
+// shell wrappers only need to be smoke-tested for how they interpret the
+// directive (see completion/tests/wrapper.*).
+package completion_test
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/go-task/task/v3/internal/complete"
+)
+
+var taskBin string
+
+func TestMain(m *testing.M) {
+	dir, err := os.MkdirTemp("", "task-completion-test")
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	taskBin = filepath.Join(dir, "task")
+	if runtime.GOOS == "windows" {
+		taskBin += ".exe"
+	}
+	if out, err := exec.CommandContext(context.Background(), "go", "build", "-o", taskBin, "github.com/go-task/task/v3/cmd/task").CombinedOutput(); err != nil {
+		fmt.Fprintf(os.Stderr, "failed to build task binary: %v\n%s", err, out)
+		os.RemoveAll(dir)
+		os.Exit(1)
+	}
+	code := m.Run()
+	os.RemoveAll(dir)
+	os.Exit(code)
+}
+
+const fixtureTaskfile = `version: '3'
+
+tasks:
+  build:
+    desc: Build it
+  deploy:
+    desc: Deploy the application
+    aliases: [dep, ship]
+    requires:
+      vars:
+        - name: ENV
+          enum: [dev, staging, prod]
+        - REGION
+  docs:serve:
+    desc: Serve docs locally
+`
+
+// completeArgs runs `task __complete <args>` in a fresh fixture directory and
+// returns the offered candidate values plus the emitted directive.
+func completeArgs(t *testing.T, args ...string) ([]string, complete.Directive) {
+	t.Helper()
+
+	dir := t.TempDir()
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "Taskfile.yml"), []byte(fixtureTaskfile), 0o644))
+
+	// taskBin is the test-built binary and args are test-controlled literals.
+	cmd := exec.CommandContext(t.Context(), taskBin, append([]string{complete.CommandName}, args...)...) //nolint:gosec
+	cmd.Dir = dir
+	out, err := cmd.Output()
+	require.NoError(t, err)
+
+	lines := strings.Split(strings.TrimRight(string(out), "\n"), "\n")
+	require.NotEmpty(t, lines, "protocol output must end with a directive line")
+
+	last := lines[len(lines)-1]
+	require.True(t, strings.HasPrefix(last, ":"), "last line must be the :<directive> line, got %q", last)
+	n, err := strconv.Atoi(strings.TrimPrefix(last, ":"))
+	require.NoError(t, err)
+
+	values := make([]string, 0, len(lines)-1)
+	for _, line := range lines[:len(lines)-1] {
+		values = append(values, strings.SplitN(line, "\t", 2)[0])
+	}
+	return values, complete.Directive(n)
+}
+
+func TestProtocol(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name      string
+		args      []string
+		want      []string // candidate values that must be offered
+		absent    []string // candidate values that must NOT be offered
+		directive complete.Directive
+	}{
+		{
+			name:      "task names and aliases",
+			args:      []string{""},
+			want:      []string{"build", "deploy", "dep", "ship", "docs:serve"},
+			directive: complete.DirectiveNoFileComp,
+		},
+		{
+			name:      "no-aliases drops aliases",
+			args:      []string{"--no-aliases", ""},
+			want:      []string{"build", "deploy"},
+			absent:    []string{"dep", "ship"},
+			directive: complete.DirectiveNoFileComp,
+		},
+		{
+			name:      "flag names",
+			args:      []string{"-"},
+			want:      []string{"--taskfile", "--dir", "--output"},
+			directive: complete.DirectiveNoFileComp,
+		},
+		{
+			name:      "separate flag value is bare",
+			args:      []string{"--output", ""},
+			want:      []string{"interleaved", "group", "prefixed"},
+			directive: complete.DirectiveNoFileComp,
+		},
+		{
+			name:      "inline flag value is full form",
+			args:      []string{"--output="},
+			want:      []string{"--output=interleaved", "--output=group", "--output=prefixed"},
+			directive: complete.DirectiveNoFileComp,
+		},
+		{
+			name:      "sort enum values",
+			args:      []string{"--sort", ""},
+			want:      []string{"default", "alphanumeric", "none"},
+			directive: complete.DirectiveNoFileComp,
+		},
+		{
+			name:      "taskfile filters by extension",
+			args:      []string{"--taskfile", ""},
+			want:      []string{"yml", "yaml"},
+			directive: complete.DirectiveFilterFileExt,
+		},
+		{
+			name:      "dir filters to directories",
+			args:      []string{"--dir", ""},
+			directive: complete.DirectiveFilterDirs,
+		},
+		{
+			name:      "task variables keep order and suppress the space",
+			args:      []string{"deploy", ""},
+			want:      []string{"ENV=dev", "ENV=staging", "ENV=prod", "REGION="},
+			directive: complete.DirectiveNoSpace | complete.DirectiveNoFileComp | complete.DirectiveKeepOrder,
+		},
+		{
+			name:      "after -- yields default file completion",
+			args:      []string{"deploy", "--", ""},
+			directive: complete.DirectiveDefault,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			values, directive := completeArgs(t, tt.args...)
+			require.Equal(t, tt.directive, directive)
+			require.Subset(t, values, tt.want)
+			for _, a := range tt.absent {
+				require.NotContains(t, values, a)
+			}
+		})
+	}
+}
diff --git a/completion/tests/run.sh b/completion/tests/run.sh
new file mode 100755
index 0000000000..4f9fe154f5
--- /dev/null
+++ b/completion/tests/run.sh
@@ -0,0 +1,99 @@
+#!/usr/bin/env bash
+# Runs the completion test suite: builds the task binary, creates a fixture
+# Taskfile with sample files and directories, then exercises the engine and
+# every installed shell wrapper. Skips shells that are not installed.
+set -u
+
+here=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+root=$(cd "$here/../.." && pwd)
+
+# Temp dirs for the binary and the fixture; removed on exit (including on early
+# failure via the trap).
+bindir=$(mktemp -d)
+fixture=$(mktemp -d)
+trap 'rm -rf "$bindir" "$fixture"' EXIT
+
+# Build the binary under test.
+if ! go build -o "$bindir/task" "$root/cmd/task"; then
+  echo "failed to build task binary" >&2
+  exit 1
+fi
+export TASK_BIN="$bindir/task"
+# fish and PowerShell register completion for the command name `task`, so make
+# `task` on PATH resolve to the binary under test.
+export PATH="$bindir:$PATH"
+
+# Fixture: a Taskfile plus files/dirs so file/dir completion has real entries.
+cat > "$fixture/Taskfile.yml" <<'YML'
+version: '3'
+
+tasks:
+  build:
+    desc: Build it
+  deploy:
+    desc: Deploy it
+    aliases: [dep]
+    requires:
+      vars:
+        - name: ENV
+          enum: [dev, prod]
+        - REGION
+  docs:serve:
+    desc: Serve docs
+YML
+touch "$fixture/extra.yaml" "$fixture/notes.txt"
+mkdir -p "$fixture/sub" "$fixture/other"
+# A file inside sub/ so nested-path completion (keeping the dir prefix) is tested.
+touch "$fixture/sub/nested.yml"
+export TASK_FIXTURE="$fixture"
+
+# In strict mode (set TASK_COMPLETION_STRICT=1, used in CI) a missing shell is
+# a failure instead of a skip, so we never get a false pass when a shell the
+# environment was expected to provide (e.g. pwsh on CI runners) is absent.
+strict=${TASK_COMPLETION_STRICT:-}
+
+fails=0
+run() { # LABEL COMMAND...
+  echo "== $1 =="
+  if "${@:2}"; then :; else fails=$((fails + 1)); fi
+  echo
+}
+skip() { # LABEL
+  if [[ -n "$strict" ]]; then
+    echo "== $1 == (MISSING — required under TASK_COMPLETION_STRICT)"
+    fails=$((fails + 1))
+  else
+    echo "== $1 == (skipped: not installed)"
+  fi
+  echo
+}
+
+# The engine/protocol itself is covered by the Go tests (completion/protocol_test.go
+# and internal/complete); these smokes only check how each shell wrapper
+# interprets the directive.
+run "bash wrapper"  bash "$here/wrapper.bash"
+
+if command -v zsh >/dev/null 2>&1; then
+  run "zsh wrapper" zsh "$here/wrapper.zsh"
+else
+  skip "zsh wrapper"
+fi
+
+if command -v fish >/dev/null 2>&1; then
+  run "fish wrapper" fish "$here/wrapper.fish"
+else
+  skip "fish wrapper"
+fi
+
+pwsh_bin=$(command -v pwsh || command -v pwsh-preview || true)
+if [[ -n "$pwsh_bin" ]]; then
+  run "powershell wrapper" "$pwsh_bin" -NoProfile -File "$here/wrapper.ps1"
+else
+  skip "powershell wrapper"
+fi
+
+if ((fails)); then
+  echo "completion tests: $fails suite(s) failed"
+  exit 1
+fi
+echo "completion tests: all suites passed"
diff --git a/completion/tests/wrapper.bash b/completion/tests/wrapper.bash
new file mode 100755
index 0000000000..1d6599a18e
--- /dev/null
+++ b/completion/tests/wrapper.bash
@@ -0,0 +1,83 @@
+#!/usr/bin/env bash
+# Smoke-tests how the bash wrapper routes each directive by stubbing the
+# bash-completion helpers (_filedir / compopt / …) and asserting what it calls.
+# Suggestion logic lives in the Go tests. Requires TASK_BIN and TASK_FIXTURE.
+set -u
+
+: "${TASK_BIN:?}"; : "${TASK_FIXTURE:?}"
+export TASK_EXE="$TASK_BIN"
+cd "$TASK_FIXTURE" || exit 1
+
+fails=0
+CAP=""
+
+# Stubs standing in for the bash-completion runtime.
+_init_completion() {
+  words=("${TEST_WORDS[@]}")
+  cword=$TEST_CWORD
+  cur="${TEST_WORDS[$TEST_CWORD]}"
+  prev="${TEST_WORDS[$((TEST_CWORD - 1))]}"
+  return 0
+}
+# Records the extension arg and the value of $cur it was called with, so tests
+# can assert the inline `--flag=` prefix was stripped before file completion.
+_filedir() { CAP+="filedir:$* cur=$cur"$'\n'; }
+compopt() { CAP+="compopt:$*"$'\n'; }
+__ltrim_colon_completions() { :; }
+
+source "$(dirname "${BASH_SOURCE[0]}")/../next/bash/task.bash"
+
+run() {
+  CAP=""
+  TEST_WORDS=("$@")
+  TEST_CWORD=$((${#TEST_WORDS[@]} - 1))
+  COMPREPLY=()
+  _task
+}
+
+reply_has() { # LABEL VALUE
+  local v
+  for v in "${COMPREPLY[@]}"; do [[ "$v" == "$2" ]] && { echo "  ok   $1"; return; }; done
+  echo "  FAIL $1 — '$2' missing from COMPREPLY: ${COMPREPLY[*]}"
+  fails=$((fails + 1))
+}
+cap_has() { # LABEL PATTERN
+  if [[ "$CAP" == *"$2"* ]]; then echo "  ok   $1"; else
+    echo "  FAIL $1 — expected '$2' in: $CAP"; fails=$((fails + 1)); fi
+}
+cap_hasnot() { # LABEL PATTERN
+  if [[ "$CAP" == *"$2"* ]]; then
+    echo "  FAIL $1 — '$2' should be absent in: $CAP"; fails=$((fails + 1)); else
+    echo "  ok   $1"; fi
+}
+
+echo "bash: :4 (NoFileComp) forwards candidates, no file fallback"
+run task ''
+reply_has  "candidate forwarded" build
+cap_hasnot "no file fallback"     "filedir:"
+
+echo "bash: :2 (NoSpace) disables the trailing space"
+run task deploy ''
+cap_has    "nospace applied"      "compopt:-o nospace"
+
+echo "bash: :8 (FilterFileExt) routes to extension-filtered files"
+run task --taskfile ''
+cap_has    "filedir ext glob"     "filedir:@(yml|yaml)"
+
+echo "bash: :16 (FilterDirs) routes to directory completion"
+run task --dir ''
+cap_has    "filedir -d"           "filedir:-d"
+
+echo "bash: :0 (Default) falls back to files"
+run task build -- ''
+cap_has    "filedir default"      "filedir:"
+
+echo "bash: inline --flag= strips the prefix before file completion"
+run task --taskfile=sub/x
+cap_has    "inline cur stripped"  "cur=sub/x"
+
+if ((fails)); then
+  echo "bash: $fails failure(s)"
+  exit 1
+fi
+echo "bash: all passed"
diff --git a/completion/tests/wrapper.fish b/completion/tests/wrapper.fish
new file mode 100755
index 0000000000..373406f81c
--- /dev/null
+++ b/completion/tests/wrapper.fish
@@ -0,0 +1,56 @@
+#!/usr/bin/env fish
+# Smoke-tests how the fish wrapper routes each directive, via `complete -C`
+# (real completions, no TTY). Suggestion logic lives in the Go tests.
+# Set up by run.sh: TASK_FIXTURE, and `task` on PATH = the binary under test.
+
+cd $TASK_FIXTURE
+source (dirname (status -f))/../next/fish/task.fish
+
+set -g fails 0
+
+function cands
+    complete -C $argv[1] | string split -f1 \t
+end
+
+function has # LABEL LINE VALUE
+    if contains -- $argv[3] (cands $argv[2])
+        echo "  ok   $argv[1]"
+    else
+        echo "  FAIL $argv[1] — '$argv[3]' missing from: "(cands $argv[2])
+        set fails (math $fails + 1)
+    end
+end
+
+function hasnot # LABEL LINE VALUE
+    if contains -- $argv[3] (cands $argv[2])
+        echo "  FAIL $argv[1] — '$argv[3]' should be absent"
+        set fails (math $fails + 1)
+    else
+        echo "  ok   $argv[1]"
+    end
+end
+
+echo "fish: :4 (NoFileComp) forwards candidates, offers no files"
+has    "candidate forwarded"  'task ' build
+hasnot "no file fallback"     'task ' notes.txt
+
+echo "fish: :16 (FilterDirs) offers directories only"
+has    "dir offered"          'task --dir ' sub/
+hasnot "no plain file"        'task --dir ' notes.txt
+
+echo "fish: :8 (FilterFileExt) filters by extension"
+has    "matching file"        'task --taskfile ' Taskfile.yml
+hasnot "non-matching file"    'task --taskfile ' notes.txt
+
+echo "fish: :0 (Default) falls back to files"
+has    "file offered"         'task build -- ' notes.txt
+
+echo "fish: inline --flag=path keeps the --flag= prefix"
+has    "inline nested"        'task --taskfile=sub/' --taskfile=sub/nested.yml
+hasnot "inline non-matching"  'task --taskfile=' --taskfile=notes.txt
+
+if test $fails -ne 0
+    echo "fish: $fails failure(s)"
+    exit 1
+end
+echo "fish: all passed"
diff --git a/completion/tests/wrapper.ps1 b/completion/tests/wrapper.ps1
new file mode 100644
index 0000000000..46b2d4b544
--- /dev/null
+++ b/completion/tests/wrapper.ps1
@@ -0,0 +1,61 @@
+# Smoke-tests how the PowerShell wrapper routes each directive (plus its own
+# prefix filtering), via the completion API (real completions, no TTY).
+# Suggestion logic lives in the Go tests. Set up by run.sh: $env:TASK_FIXTURE,
+# and `task` on PATH = the binary under test.
+
+Set-Location $env:TASK_FIXTURE
+. "$PSScriptRoot/../next/ps/task.ps1"
+
+$fails = 0
+
+function Cands($line) {
+	([System.Management.Automation.CommandCompletion]::CompleteInput($line, $line.Length, $null)).CompletionMatches |
+		ForEach-Object { $_.CompletionText }
+}
+
+function Has($label, $line, $value) {
+	if ((Cands $line) -contains $value) {
+		Write-Output "  ok   $label"
+	} else {
+		Write-Output "  FAIL $label — '$value' missing from: $((Cands $line) -join ' ')"
+		$script:fails++
+	}
+}
+
+function HasNot($label, $line, $value) {
+	if ((Cands $line) -contains $value) {
+		Write-Output "  FAIL $label — '$value' should be absent"
+		$script:fails++
+	} else {
+		Write-Output "  ok   $label"
+	}
+}
+
+Write-Output "powershell: :4 (NoFileComp) forwards candidates, offers no files"
+Has    "candidate forwarded" 'task ' 'build'
+HasNot "no file fallback"    'task ' 'notes.txt'
+
+Write-Output "powershell: filters candidates by the current word"
+Has    "prefix keeps match"  'task b' 'build'
+HasNot "prefix drops others" 'task b' 'deploy'
+
+Write-Output "powershell: :16 (FilterDirs) offers directories only"
+Has    "dir offered"         'task --dir ' 'sub'
+HasNot "no plain file"       'task --dir ' 'notes.txt'
+
+Write-Output "powershell: :8 (FilterFileExt) filters by extension"
+Has    "matching file"       'task --taskfile ' 'Taskfile.yml'
+HasNot "non-matching file"   'task --taskfile ' 'notes.txt'
+
+Write-Output "powershell: nested path completion keeps the directory prefix"
+Has    "prefix kept"         'task --taskfile sub/' 'sub/nested.yml'
+
+Write-Output "powershell: inline --flag=path keeps the --flag= prefix"
+Has    "inline nested"       'task --taskfile=sub/' '--taskfile=sub/nested.yml'
+HasNot "inline non-matching" 'task --taskfile=' '--taskfile=notes.txt'
+
+if ($fails -ne 0) {
+	Write-Output "powershell: $fails failure(s)"
+	exit 1
+}
+Write-Output "powershell: all passed"
diff --git a/completion/tests/wrapper.zsh b/completion/tests/wrapper.zsh
new file mode 100755
index 0000000000..ddbfa11ae3
--- /dev/null
+++ b/completion/tests/wrapper.zsh
@@ -0,0 +1,77 @@
+#!/usr/bin/env zsh
+# Smoke-tests how the zsh wrapper routes each directive by stubbing the
+# completion functions (_describe / _files / _path_files) and asserting what it
+# calls. Suggestion logic lives in the Go tests. Requires TASK_BIN, TASK_FIXTURE.
+
+export TASK_EXE=$TASK_BIN
+cd $TASK_FIXTURE
+
+integer fails=0
+local CAP
+compdef() { }   # no-op: we call _task directly, not through compinit
+
+_describe() {
+    local arr=$4
+    CAP+="describe_opts:${@[5,-1]}"$'\n'
+    local c; for c in ${(P)arr}; do CAP+="cand:$c"$'\n'; done
+}
+_files()      { CAP+="files:$*"$'\n' }
+_path_files() { CAP+="path_files:$*"$'\n' }
+
+# Sourcing (not autoloading) defines _task and avoids the autoload first-call
+# quirk; the trailing `compdef` call is stubbed above.
+source ${0:A:h}/../next/zsh/_task
+
+run() {
+    CAP=""
+    local -a words=("$@")
+    integer CURRENT=$#words
+    local curcontext=":completion:complete:task:"
+    _task
+}
+
+has() { # LABEL PATTERN
+    if [[ "$CAP" == *"$2"* ]]; then
+        echo "  ok   $1"
+    else
+        echo "  FAIL $1 — expected '$2' in:"$'\n'"$CAP"
+        (( fails++ ))
+    fi
+}
+hasnot() { # LABEL PATTERN
+    if [[ "$CAP" == *"$2"* ]]; then
+        echo "  FAIL $1 — '$2' should be absent in:"$'\n'"$CAP"
+        (( fails++ ))
+    else
+        echo "  ok   $1"
+    fi
+}
+
+echo "zsh: :4 (NoFileComp) forwards candidates, no file fallback"
+run task ''
+has    "candidate forwarded"  "cand:build"
+hasnot "no file fallback"     "files:"
+
+echo "zsh: :2|:32 (NoSpace|KeepOrder) map to -S and -V"
+run task deploy ''
+has    "NoSpace -> -S"         "describe_opts:-S"
+has    "KeepOrder -> -V"       "-V"
+
+echo "zsh: :8 (FilterFileExt) routes to extension-filtered files"
+run task --taskfile ''
+has    "files glob"            "files:"
+has    "yml in glob"           "yml"
+
+echo "zsh: :16 (FilterDirs) routes to directory completion"
+run task --dir ''
+has    "path_files -/"         "path_files:-/"
+
+echo "zsh: :0 (Default) falls back to files"
+run task build -- ''
+has    "files default"         "files:"
+
+if (( fails )); then
+    echo "zsh: $fails failure(s)"
+    exit 1
+fi
+echo "zsh: all passed"
diff --git a/internal/complete/complete.go b/internal/complete/complete.go
new file mode 100644
index 0000000000..2cbc9c99c9
--- /dev/null
+++ b/internal/complete/complete.go
@@ -0,0 +1,90 @@
+// Package complete implements the `task __complete` protocol consumed by the
+// shell completion wrappers. The protocol mirrors cobra v2 so a future
+// migration stays cheap.
+package complete
+
+import "os"
+
+// CommandName is the hidden subcommand the shell wrappers invoke to drive
+// completion: `task __complete <words...>`.
+const CommandName = "__complete"
+
+// IsActive reports whether the process was invoked in completion mode, i.e.
+// the first argument is the __complete subcommand.
+func IsActive() bool {
+	return len(os.Args) >= 2 && os.Args[1] == CommandName
+}
+
+// Directive mirrors cobra's ShellCompDirective bitfield. It is emitted on the
+// final output line as `:<directive>` and tells the shell wrapper how to treat
+// the suggestions (file fallback, trailing space, ordering, …).
+type Directive int
+
+const (
+	// DirectiveDefault leaves the shell to perform its default file completion.
+	DirectiveDefault Directive = 0
+	// DirectiveError signals an error; the shell should not offer completion.
+	DirectiveError Directive = 1 << 0
+	// DirectiveNoSpace prevents the shell from appending a space after the
+	// suggestion (e.g. so `VAR=` can be followed by a value).
+	DirectiveNoSpace Directive = 1 << 1
+	// DirectiveNoFileComp disables the shell's fallback file completion.
+	DirectiveNoFileComp Directive = 1 << 2
+	// DirectiveFilterFileExt restricts file completion to the emitted extensions.
+	DirectiveFilterFileExt Directive = 1 << 3
+	// DirectiveFilterDirs restricts completion to directories.
+	DirectiveFilterDirs Directive = 1 << 4
+	// DirectiveKeepOrder tells the shell to preserve the emitted order instead
+	// of sorting alphabetically.
+	DirectiveKeepOrder Directive = 1 << 5
+)
+
+// Suggestion is a single completion candidate: the Value inserted on the
+// command line and an optional human-readable Description.
+type Suggestion struct {
+	Value       string
+	Description string
+}
+
+// Options tunes what the engine emits. Its zero value shows neither aliases nor
+// descriptions; DefaultOptions returns the standard set (both shown), which
+// ParseOptions then flips off per the __complete control flags.
+type Options struct {
+	ShowAliases      bool
+	ShowDescriptions bool
+}
+
+// DefaultOptions returns the options used when no completion-control flag is
+// passed: aliases and descriptions are both shown.
+func DefaultOptions() Options {
+	return Options{ShowAliases: true, ShowDescriptions: true}
+}
+
+// Completion-control flags. Shell wrappers prepend these to the __complete
+// invocation to tune the output (e.g. zsh maps its show-aliases / verbose
+// zstyles to them). They are consumed by ParseOptions before the remaining
+// args are treated as the user's command line.
+const (
+	FlagNoAliases      = "--no-aliases"
+	FlagNoDescriptions = "--no-descriptions"
+)
+
+// ParseOptions peels the leading completion-control flags off args and returns
+// the resulting Options together with the remaining args (the user's command
+// line to complete). Only leading flags are consumed, so a `--no-aliases` typed
+// by the user further down the line is left untouched.
+func ParseOptions(args []string) (Options, []string) {
+	opts := DefaultOptions()
+	for len(args) > 0 {
+		switch args[0] {
+		case FlagNoAliases:
+			opts.ShowAliases = false
+		case FlagNoDescriptions:
+			opts.ShowDescriptions = false
+		default:
+			return opts, args
+		}
+		args = args[1:]
+	}
+	return opts, args
+}
diff --git a/internal/complete/complete_test.go b/internal/complete/complete_test.go
new file mode 100644
index 0000000000..746600f2d0
--- /dev/null
+++ b/internal/complete/complete_test.go
@@ -0,0 +1,367 @@
+package complete_test
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/spf13/pflag"
+	"github.com/stretchr/testify/require"
+
+	"github.com/go-task/task/v3"
+	"github.com/go-task/task/v3/internal/complete"
+)
+
+func newTestFlagSet() *pflag.FlagSet {
+	fs := pflag.NewFlagSet("test", pflag.ContinueOnError)
+	var b bool
+	var s string
+	fs.BoolVarP(&b, "list-all", "a", false, "Lists all tasks")
+	fs.BoolVarP(&b, "list", "l", false, "Lists tasks with descriptions")
+	fs.BoolVarP(&b, "verbose", "v", false, "Verbose mode")
+	fs.StringVarP(&s, "taskfile", "t", "", "Taskfile path")
+	fs.StringVarP(&s, "dir", "d", "", "Run dir")
+	fs.StringVarP(&s, "output", "o", "", "Output style")
+	fs.StringVar(&s, "sort", "", "Sort order")
+	fs.StringVar(&s, "cacert", "", "CA cert path")
+	return fs
+}
+
+const testTaskfile = `version: '3'
+
+vars:
+  ALLOWED_ENVS:
+    - dev
+    - staging
+    - prod
+
+tasks:
+  deploy:
+    desc: Deploy the application
+    aliases: [dep, ship]
+    requires:
+      vars:
+        - name: ENV
+          enum:
+            - dev
+            - staging
+            - prod
+        - REGION
+    cmds:
+      - 'echo {{.ENV}} {{.REGION}}'
+
+  build:
+    desc: Build it
+    cmds:
+      - 'echo build'
+
+  dynenum:
+    desc: Dynamic enum
+    requires:
+      vars:
+        - name: ENV
+          enum:
+            ref: .ALLOWED_ENVS
+    cmds:
+      - 'echo {{.ENV}}'
+
+  docs:serve:
+    desc: Serve docs locally
+    cmds:
+      - 'echo serving'
+`
+
+func setupExecutor(t *testing.T) *task.Executor {
+	t.Helper()
+	dir := t.TempDir()
+	require.NoError(t, os.WriteFile(filepath.Join(dir, "Taskfile.yml"), []byte(testTaskfile), 0o644))
+
+	e := task.NewExecutor(
+		task.WithDir(dir),
+		task.WithStdout(io.Discard),
+		task.WithStderr(io.Discard),
+		task.WithVersionCheck(false),
+	)
+	require.NoError(t, e.Setup())
+	return e
+}
+
+func TestComplete_TaskNames(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{""}, complete.DefaultOptions())
+
+	require.ElementsMatch(t,
+		[]string{"build", "deploy", "dep", "ship", "dynenum", "docs:serve"},
+		values(suggs),
+	)
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+	require.Contains(t, descriptions(suggs), "Deploy the application")
+}
+
+func TestComplete_AliasResolvesToTaskVars(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"dep", ""}, complete.DefaultOptions())
+	require.Equal(t, []string{"ENV=dev", "ENV=staging", "ENV=prod", "REGION="}, values(suggs))
+	require.Equal(t, complete.DirectiveNoSpace|complete.DirectiveNoFileComp|complete.DirectiveKeepOrder, dir)
+}
+
+func TestComplete_StaticEnum(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"deploy", ""}, complete.DefaultOptions())
+
+	require.Equal(t, []string{"ENV=dev", "ENV=staging", "ENV=prod", "REGION="}, values(suggs))
+	require.Equal(t, complete.DirectiveNoSpace|complete.DirectiveNoFileComp|complete.DirectiveKeepOrder, dir)
+}
+
+func TestComplete_EnumRef(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, _ := complete.Complete(e, newTestFlagSet(), []string{"dynenum", ""}, complete.DefaultOptions())
+	require.Equal(t, []string{"ENV=dev", "ENV=staging", "ENV=prod"}, values(suggs))
+}
+
+func TestComplete_NoRequires(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"build", ""}, complete.DefaultOptions())
+	require.Empty(t, suggs)
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+}
+
+func TestComplete_FlagValueNotConfusedWithTaskName(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"--dir", "deploy", ""}, complete.DefaultOptions())
+	require.ElementsMatch(t,
+		[]string{"build", "deploy", "dep", "ship", "dynenum", "docs:serve"},
+		values(suggs),
+	)
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+}
+
+func TestComplete_NamespacedTaskName(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"docs:serve", ""}, complete.DefaultOptions())
+	require.Empty(t, suggs)
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+}
+
+func TestComplete_FlagValueInlineEquals(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"--output="}, complete.DefaultOptions())
+	// Inline form returns full `--output=value` tokens so the shell can match
+	// against the whole current word.
+	require.Equal(t, []string{"--output=interleaved", "--output=group", "--output=prefixed"}, values(suggs))
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+}
+
+func TestComplete_AfterDash(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"deploy", "--", ""}, complete.DefaultOptions())
+	require.Empty(t, suggs)
+	require.Equal(t, complete.DirectiveDefault, dir)
+}
+
+func TestComplete_FlagNames(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"-"}, complete.DefaultOptions())
+	require.NotEmpty(t, suggs)
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+
+	vals := values(suggs)
+	require.Contains(t, vals, "--list-all")
+	require.Contains(t, vals, "--taskfile")
+	require.Contains(t, vals, "-a")
+}
+
+func TestComplete_EnumFlagValue_Output(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"--output", ""}, complete.DefaultOptions())
+	require.Equal(t, []string{"interleaved", "group", "prefixed"}, values(suggs))
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+}
+
+func TestComplete_EnumFlagValue_Sort(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, _ := complete.Complete(e, newTestFlagSet(), []string{"--sort", ""}, complete.DefaultOptions())
+	require.Equal(t, []string{"default", "alphanumeric", "none"}, values(suggs))
+}
+
+func TestComplete_PathFlag_Taskfile(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"--taskfile", ""}, complete.DefaultOptions())
+	require.Equal(t, []string{"yml", "yaml"}, values(suggs))
+	require.Equal(t, complete.DirectiveFilterFileExt, dir)
+}
+
+func TestComplete_PathFlag_Dir(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"--dir", ""}, complete.DefaultOptions())
+	require.Empty(t, suggs)
+	require.Equal(t, complete.DirectiveFilterDirs, dir)
+}
+
+func TestComplete_PathFlag_Cacert(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{"--cacert", ""}, complete.DefaultOptions())
+	require.Empty(t, suggs)
+	require.Equal(t, complete.DirectiveDefault, dir)
+}
+
+func TestComplete_NilExecutor(t *testing.T) {
+	t.Parallel()
+
+	suggs, dir := complete.Complete(nil, newTestFlagSet(), []string{"-"}, complete.DefaultOptions())
+	require.NotEmpty(t, suggs)
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+}
+
+func TestComplete_NoAliases(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	opts := complete.Options{ShowAliases: false, ShowDescriptions: true}
+	suggs, dir := complete.Complete(e, newTestFlagSet(), []string{""}, opts)
+
+	require.ElementsMatch(t,
+		[]string{"build", "deploy", "dynenum", "docs:serve"},
+		values(suggs),
+	)
+	require.NotContains(t, values(suggs), "dep")
+	require.NotContains(t, values(suggs), "ship")
+	require.Equal(t, complete.DirectiveNoFileComp, dir)
+}
+
+func TestComplete_NoDescriptions(t *testing.T) {
+	t.Parallel()
+
+	e := setupExecutor(t)
+	opts := complete.Options{ShowAliases: true, ShowDescriptions: false}
+	suggs, _ := complete.Complete(e, newTestFlagSet(), []string{""}, opts)
+
+	require.ElementsMatch(t,
+		[]string{"build", "deploy", "dep", "ship", "dynenum", "docs:serve"},
+		values(suggs),
+	)
+	for _, d := range descriptions(suggs) {
+		require.Empty(t, d)
+	}
+}
+
+func TestParseOptions(t *testing.T) {
+	t.Parallel()
+
+	t.Run("defaults", func(t *testing.T) {
+		t.Parallel()
+		opts, rest := complete.ParseOptions([]string{"deploy", ""})
+		require.Equal(t, complete.DefaultOptions(), opts)
+		require.Equal(t, []string{"deploy", ""}, rest)
+	})
+
+	t.Run("both flags", func(t *testing.T) {
+		t.Parallel()
+		opts, rest := complete.ParseOptions([]string{"--no-aliases", "--no-descriptions", "deploy", ""})
+		require.False(t, opts.ShowAliases)
+		require.False(t, opts.ShowDescriptions)
+		require.Equal(t, []string{"deploy", ""}, rest)
+	})
+
+	t.Run("only leading flags consumed", func(t *testing.T) {
+		t.Parallel()
+		// A flag appearing after the user's words is left in the command line.
+		opts, rest := complete.ParseOptions([]string{"deploy", "--no-aliases"})
+		require.True(t, opts.ShowAliases)
+		require.Equal(t, []string{"deploy", "--no-aliases"}, rest)
+	})
+}
+
+func TestNeedsTaskfile(t *testing.T) {
+	t.Parallel()
+
+	tests := map[string]struct {
+		args []string
+		want bool
+	}{
+		"task name":            {[]string{""}, true},
+		"partial task name":    {[]string{"bui"}, true},
+		"task var":             {[]string{"deploy", ""}, true},
+		"value flag then name": {[]string{"--dir", "/tmp", ""}, true},
+		"flag name":            {[]string{"-"}, false},
+		"long flag name":       {[]string{"--li"}, false},
+		"inline flag value":    {[]string{"--output="}, false},
+		"flag value":           {[]string{"--output", ""}, false},
+		"path flag value":      {[]string{"--taskfile", ""}, false},
+		"after dash":           {[]string{"deploy", "--", ""}, false},
+	}
+
+	for name, tt := range tests {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+			require.Equal(t, tt.want, complete.NeedsTaskfile(tt.args, newTestFlagSet()))
+		})
+	}
+}
+
+func TestWrite_Format(t *testing.T) {
+	t.Parallel()
+
+	var buf bytes.Buffer
+	complete.Write(&buf, []complete.Suggestion{
+		{Value: "deploy", Description: "Deploy the app"},
+		{Value: "build"},
+	}, complete.DirectiveNoSpace|complete.DirectiveNoFileComp)
+	require.Equal(t, "deploy\tDeploy the app\nbuild\n:6\n", buf.String())
+}
+
+func TestWrite_EmptyWithDirective(t *testing.T) {
+	t.Parallel()
+
+	var buf bytes.Buffer
+	complete.Write(&buf, nil, complete.DirectiveFilterDirs)
+	require.Equal(t, ":16\n", buf.String())
+}
+
+func values(suggs []complete.Suggestion) []string {
+	out := make([]string, 0, len(suggs))
+	for _, s := range suggs {
+		out = append(out, s.Value)
+	}
+	return out
+}
+
+func descriptions(suggs []complete.Suggestion) []string {
+	out := make([]string, 0, len(suggs))
+	for _, s := range suggs {
+		out = append(out, s.Description)
+	}
+	return out
+}
diff --git a/internal/complete/context.go b/internal/complete/context.go
new file mode 100644
index 0000000000..06c6ba7832
--- /dev/null
+++ b/internal/complete/context.go
@@ -0,0 +1,78 @@
+package complete
+
+import (
+	"slices"
+	"strings"
+
+	"github.com/spf13/pflag"
+)
+
+type completionContext struct {
+	toComplete string
+	prev       string
+	afterDash  bool
+}
+
+// parseContext infers the cursor position from args alone. It deliberately
+// avoids the task list so flag completion never pays to load it; the task word
+// is resolved separately by detectTaskName only once a task context is reached.
+func parseContext(args []string) completionContext {
+	ctx := completionContext{}
+	if len(args) == 0 {
+		return ctx
+	}
+
+	ctx.toComplete = args[len(args)-1]
+	if len(args) >= 2 {
+		ctx.prev = args[len(args)-2]
+	}
+
+	if slices.Contains(args[:len(args)-1], "--") {
+		ctx.afterDash = true
+	}
+
+	return ctx
+}
+
+// detectTaskName scans args for the task word the cursor is completing under
+// (e.g. "deploy" in `task deploy ENV=<tab>`). fs is needed to skip the word
+// following a value-taking flag, otherwise `task --dir deploy` would mistake
+// "deploy" (the directory) for a task name.
+func detectTaskName(args []string, knownTasks []string, fs *pflag.FlagSet) string {
+	if len(args) <= 1 {
+		return ""
+	}
+
+	known := make(map[string]struct{}, len(knownTasks))
+	for _, t := range knownTasks {
+		known[t] = struct{}{}
+	}
+
+	taskName := ""
+	skipNext := false
+	for _, w := range args[:len(args)-1] {
+		if skipNext {
+			skipNext = false
+			continue
+		}
+		if w == "--" {
+			return taskName
+		}
+		if strings.HasPrefix(w, "-") {
+			if !strings.Contains(w, "=") {
+				if f := matchFlagName(fs, w); f != nil && flagTakesValue(f) {
+					skipNext = true
+				}
+			}
+			continue
+		}
+		if strings.Contains(w, "=") {
+			continue
+		}
+		if _, ok := known[w]; ok {
+			taskName = w
+		}
+	}
+
+	return taskName
+}
diff --git a/internal/complete/engine.go b/internal/complete/engine.go
new file mode 100644
index 0000000000..a39674f0bc
--- /dev/null
+++ b/internal/complete/engine.go
@@ -0,0 +1,203 @@
+package complete
+
+import (
+	"strings"
+
+	"github.com/spf13/pflag"
+
+	"github.com/go-task/task/v3"
+	"github.com/go-task/task/v3/internal/templater"
+	"github.com/go-task/task/v3/taskfile/ast"
+)
+
+// Complete is the single entry point used by `task __complete`. e may be nil
+// when the Taskfile failed to load; flag completion still works in that case.
+func Complete(e *task.Executor, fs *pflag.FlagSet, args []string, opts Options) ([]Suggestion, Directive) {
+	ctx := parseContext(args)
+
+	if ctx.afterDash {
+		return nil, DirectiveDefault
+	}
+
+	if ctx.prev != "" {
+		if flag := matchFlagName(fs, ctx.prev); flag != nil && flagTakesValue(flag) {
+			return completeFlagValue(flag.Name, "")
+		}
+	}
+
+	if strings.HasPrefix(ctx.toComplete, "-") {
+		if eqIdx := strings.Index(ctx.toComplete, "="); eqIdx != -1 {
+			flagWord := ctx.toComplete[:eqIdx]
+			if f := matchFlagName(fs, flagWord); f != nil && flagTakesValue(f) {
+				// Return full `--flag=value` candidates: shells match/insert
+				// against the whole current token, so bare values never match.
+				return completeFlagValue(f.Name, flagWord+"=")
+			}
+		}
+		return listFlags(fs), DirectiveNoFileComp
+	}
+
+	// A task-var context needs the task list to spot the task word under the
+	// cursor, but that only exists once a prior word is present. Guard on
+	// len(args) > 1 so `task <tab>` / `task buil<tab>` never pay to build it.
+	if e != nil && e.Taskfile != nil && len(args) > 1 {
+		if taskName := detectTaskName(args, taskNames(e), fs); taskName != "" {
+			return completeTaskVars(e, taskName)
+		}
+	}
+
+	return completeTaskNames(e, opts), DirectiveNoFileComp
+}
+
+// NeedsTaskfile reports whether completing args requires a loaded Taskfile.
+// Flag-name and flag-value completion (and words after `--`) do not, so the
+// caller can skip the potentially expensive Taskfile parse for those keystrokes.
+func NeedsTaskfile(args []string, fs *pflag.FlagSet) bool {
+	ctx := parseContext(args)
+	if ctx.afterDash {
+		return false
+	}
+	if ctx.prev != "" {
+		if flag := matchFlagName(fs, ctx.prev); flag != nil && flagTakesValue(flag) {
+			return false
+		}
+	}
+	return !strings.HasPrefix(ctx.toComplete, "-")
+}
+
+func taskNames(e *task.Executor) []string {
+	if e == nil || e.Taskfile == nil {
+		return nil
+	}
+	var out []string
+	for t := range e.Taskfile.Tasks.Values(nil) {
+		if t.Internal {
+			continue
+		}
+		out = append(out, strings.TrimSuffix(t.Task, ":"))
+		for _, alias := range t.Aliases {
+			out = append(out, strings.TrimSuffix(alias, ":"))
+		}
+	}
+	return out
+}
+
+func completeTaskNames(e *task.Executor, opts Options) []Suggestion {
+	if e == nil || e.Taskfile == nil {
+		return nil
+	}
+	tasks, err := e.GetTaskList(task.FilterOutInternal)
+	if err != nil {
+		return nil
+	}
+	desc := func(t *ast.Task) string {
+		if !opts.ShowDescriptions {
+			return ""
+		}
+		return t.Desc
+	}
+	out := make([]Suggestion, 0, len(tasks))
+	for _, t := range tasks {
+		out = append(out, Suggestion{
+			Value:       strings.TrimSuffix(t.Task, ":"),
+			Description: desc(t),
+		})
+		if !opts.ShowAliases {
+			continue
+		}
+		for _, alias := range t.Aliases {
+			out = append(out, Suggestion{
+				Value:       strings.TrimSuffix(alias, ":"),
+				Description: desc(t),
+			})
+		}
+	}
+	return out
+}
+
+// completeFlagValue completes the value of a value-taking flag. prefix is empty
+// for the separate-argument form (`--output <TAB>`) and `<flag>=` for the inline
+// form (`--output=<TAB>`), so enum candidates come back as full `--output=value`
+// tokens the shell can match against the current word.
+func completeFlagValue(flagName, prefix string) ([]Suggestion, Directive) {
+	// Absent keys yield the zero value (DirectiveDefault), which falls through
+	// to the enum lookup below.
+	switch flagDirective[flagName] {
+	case DirectiveFilterFileExt:
+		suggs := make([]Suggestion, 0, len(taskfileExtensions))
+		for _, ext := range taskfileExtensions {
+			suggs = append(suggs, Suggestion{Value: ext})
+		}
+		return suggs, DirectiveFilterFileExt
+	case DirectiveFilterDirs:
+		return nil, DirectiveFilterDirs
+	}
+
+	if values, ok := flagEnums[flagName]; ok {
+		out := make([]Suggestion, 0, len(values))
+		for _, v := range values {
+			out = append(out, Suggestion{Value: prefix + v})
+		}
+		return out, DirectiveNoFileComp
+	}
+
+	return nil, DirectiveDefault
+}
+
+func completeTaskVars(e *task.Executor, taskName string) ([]Suggestion, Directive) {
+	compiled, err := e.FastCompiledTask(&task.Call{Task: taskName})
+	if err != nil || compiled == nil || compiled.Requires == nil {
+		return nil, DirectiveNoFileComp
+	}
+
+	cache := &templater.Cache{Vars: compiled.Vars}
+	out := make([]Suggestion, 0, 8)
+	for _, v := range compiled.Requires.Vars {
+		if v == nil || v.Name == "" {
+			continue
+		}
+		values := enumValues(v.Enum, cache)
+		if len(values) == 0 {
+			out = append(out, Suggestion{Value: v.Name + "="})
+			continue
+		}
+		for _, val := range values {
+			out = append(out, Suggestion{Value: v.Name + "=" + val})
+		}
+	}
+	if len(out) == 0 {
+		return nil, DirectiveNoFileComp
+	}
+	// KeepOrder preserves the declaration order of the `requires` block instead
+	// of letting the shell sort the variables alphabetically.
+	return out, DirectiveNoSpace | DirectiveNoFileComp | DirectiveKeepOrder
+}
+
+func enumValues(enum *ast.Enum, cache *templater.Cache) []string {
+	if enum == nil {
+		return nil
+	}
+	if len(enum.Value) > 0 {
+		return enum.Value
+	}
+	if enum.Ref == "" {
+		return nil
+	}
+	resolved := templater.ResolveRef(enum.Ref, cache)
+	if cache.Err() != nil {
+		return nil
+	}
+	arr, ok := resolved.([]any)
+	if !ok {
+		return nil
+	}
+	out := make([]string, 0, len(arr))
+	for _, item := range arr {
+		s, ok := item.(string)
+		if !ok {
+			return nil
+		}
+		out = append(out, s)
+	}
+	return out
+}
diff --git a/internal/complete/flags.go b/internal/complete/flags.go
new file mode 100644
index 0000000000..e8a895d9b3
--- /dev/null
+++ b/internal/complete/flags.go
@@ -0,0 +1,75 @@
+package complete
+
+import (
+	"sort"
+	"strings"
+
+	"github.com/spf13/pflag"
+)
+
+// flagEnums lists allowed values for enum-style flags. Keep in sync with the
+// help strings in internal/flags/flags.go.
+var flagEnums = map[string][]string{
+	"output":         {"interleaved", "group", "prefixed"},
+	"sort":           {"default", "alphanumeric", "none"},
+	"completion":     {"bash", "zsh", "fish", "powershell"},
+	"new-completion": {"bash", "zsh", "fish", "powershell"},
+}
+
+// flagDirective maps value-taking flags to a file-completion directive.
+// DirectiveDefault entries (and any flag absent here) fall back to the shell's
+// default file completion.
+var flagDirective = map[string]Directive{
+	"taskfile":         DirectiveFilterFileExt,
+	"dir":              DirectiveFilterDirs,
+	"remote-cache-dir": DirectiveFilterDirs,
+	"cacert":           DirectiveDefault,
+	"cert":             DirectiveDefault,
+	"cert-key":         DirectiveDefault,
+}
+
+var taskfileExtensions = []string{"yml", "yaml"}
+
+// flagTakesValue is false for boolean switches (NoOptDefVal == "true").
+func flagTakesValue(f *pflag.Flag) bool {
+	return f.NoOptDefVal == ""
+}
+
+// listFlags walks fs at call time so experiment-gated flags appear or
+// disappear based on the active experiments.
+func listFlags(fs *pflag.FlagSet) []Suggestion {
+	if fs == nil {
+		return nil
+	}
+	out := make([]Suggestion, 0, 64)
+	fs.VisitAll(func(f *pflag.Flag) {
+		if f.Hidden || f.Deprecated != "" {
+			return
+		}
+		out = append(out, Suggestion{
+			Value:       "--" + f.Name,
+			Description: f.Usage,
+		})
+		if f.Shorthand != "" {
+			out = append(out, Suggestion{
+				Value:       "-" + f.Shorthand,
+				Description: f.Usage,
+			})
+		}
+	})
+	sort.Slice(out, func(i, j int) bool { return out[i].Value < out[j].Value })
+	return out
+}
+
+func matchFlagName(fs *pflag.FlagSet, word string) *pflag.Flag {
+	if fs == nil {
+		return nil
+	}
+	switch {
+	case strings.HasPrefix(word, "--"):
+		return fs.Lookup(strings.TrimPrefix(word, "--"))
+	case strings.HasPrefix(word, "-") && len(word) == 2:
+		return fs.ShorthandLookup(word[1:])
+	}
+	return nil
+}
diff --git a/internal/complete/output.go b/internal/complete/output.go
new file mode 100644
index 0000000000..158a539c6b
--- /dev/null
+++ b/internal/complete/output.go
@@ -0,0 +1,31 @@
+package complete
+
+import (
+	"fmt"
+	"io"
+	"strings"
+)
+
+// Write emits the cobra-v2 completion protocol: one `value\tdescription` (or
+// bare `value`) per suggestion, followed by a trailing `:<directive>` line
+// that shell wrappers split off even when there are zero suggestions.
+func Write(w io.Writer, suggs []Suggestion, dir Directive) {
+	for _, s := range suggs {
+		value := sanitize(s.Value)
+		desc := sanitize(s.Description)
+		if desc == "" {
+			fmt.Fprintln(w, value)
+			continue
+		}
+		fmt.Fprintf(w, "%s\t%s\n", value, desc)
+	}
+	fmt.Fprintf(w, ":%d\n", dir)
+}
+
+// completionSanitizer collapses the bytes that would corrupt the line-based
+// protocol (a value's tab/newline would be read as a field/record separator).
+var completionSanitizer = strings.NewReplacer("\n", " ", "\r", " ", "\t", " ")
+
+func sanitize(s string) string {
+	return completionSanitizer.Replace(s)
+}
diff --git a/internal/flags/flags.go b/internal/flags/flags.go
index f1bf6c767f..41e57d7b97 100644
--- a/internal/flags/flags.go
+++ b/internal/flags/flags.go
@@ -14,6 +14,7 @@ import (
 	"github.com/go-task/task/v3"
 	"github.com/go-task/task/v3/errors"
 	"github.com/go-task/task/v3/experiments"
+	"github.com/go-task/task/v3/internal/complete"
 	"github.com/go-task/task/v3/internal/env"
 	"github.com/go-task/task/v3/internal/sort"
 	"github.com/go-task/task/v3/taskfile/ast"
@@ -48,6 +49,7 @@ var (
 	Help                bool
 	Init                bool
 	Completion          string
+	NewCompletion       string
 	List                bool
 	ListAll             bool
 	ListJson            bool
@@ -124,6 +126,7 @@ func init() {
 	pflag.BoolVarP(&Help, "help", "h", false, "Shows Task usage.")
 	pflag.BoolVarP(&Init, "init", "i", false, "Creates a new Taskfile.yml in the current folder.")
 	pflag.StringVar(&Completion, "completion", "", "Generates shell completion script.")
+	pflag.StringVar(&NewCompletion, "new-completion", "", "Generates the new (experimental) shell completion script, powered by the `task __complete` engine.")
 	pflag.BoolVarP(&List, "list", "l", false, "Lists tasks with description of current Taskfile.")
 	pflag.BoolVarP(&ListAll, "list-all", "a", false, "Lists tasks with or without a description.")
 	pflag.BoolVarP(&ListJson, "json", "j", false, "Formats task list as JSON.")
@@ -177,6 +180,13 @@ func init() {
 		pflag.StringVar(&Cert, "cert", getConfig(config, "REMOTE_CERT", func() *string { return config.Remote.Cert }, ""), "Path to a client certificate for HTTPS connections.")
 		pflag.StringVar(&CertKey, "cert-key", getConfig(config, "REMOTE_CERT_KEY", func() *string { return config.Remote.CertKey }, ""), "Path to a client certificate key for HTTPS connections.")
 	}
+	// In completion mode the user's `--flag` words must reach the engine
+	// untouched. The BoolVar/StringVar calls above already populated
+	// pflag.CommandLine, which is all the engine needs.
+	if complete.IsActive() {
+		return
+	}
+
 	pflag.Parse()
 
 	// Auto-detect color based on environment when not explicitly configured
diff --git a/website/src/docs/installation.md b/website/src/docs/installation.md
index a983dc0e0f..1e9d9dd318 100644
--- a/website/src/docs/installation.md
+++ b/website/src/docs/installation.md
@@ -446,3 +446,41 @@ canonical task names, add the `show-aliases` zstyle:
 ```shell
 zstyle ':completion:*:*:task:*' show-aliases false
 ```
+
+### Trying the new completion engine (experimental)
+
+Task is migrating to a new completion engine, where every shell shares a single
+source of truth: the `task __complete` command. This gives Bash, Zsh, Fish and
+PowerShell the exact same suggestions (task names, aliases, flags, flag values
+and `requires` vars, including their enums). It is currently **opt-in** and will
+become the default of `--completion` in a future release.
+
+To try it, swap `--completion` for `--new-completion` in any of the snippets
+above, for example:
+
+::: code-group
+
+```shell [bash]
+# ~/.bashrc
+eval "$(task --new-completion bash)"
+```
+
+```shell [zsh]
+# ~/.zshrc
+eval "$(task --new-completion zsh)"
+```
+
+```shell [fish]
+# ~/.config/fish/config.fish
+task --new-completion fish | source
+```
+
+```powershell [powershell]
+# $PROFILE\Microsoft.PowerShell_profile.ps1
+Invoke-Expression  (&task --new-completion powershell | Out-String)
+```
+
+:::
+
+The `verbose` and `show-aliases` zstyles documented above work with the new Zsh
+completion too.