diff --git a/internal/transcriber/adapter_whisper_cpp.go b/internal/transcriber/adapter_whisper_cpp.go
new file mode 100644
index 0000000..75e2754
--- /dev/null
+++ b/internal/transcriber/adapter_whisper_cpp.go
@@ -0,0 +1,107 @@
+package transcriber
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"log"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"github.com/leonardotrapani/hyprvoice/internal/language"
+)
+
+// WhisperCppAdapter implements BatchAdapter for local whisper-cpp transcription
+type WhisperCppAdapter struct {
+	modelPath string
+	language  string
+	threads   int
+}
+
+// NewWhisperCppAdapter creates a new whisper-cpp adapter
+// modelPath: full path to the model file (e.g., ~/.local/share/hyprvoice/models/whisper/ggml-base.en.bin)
+// lang: canonical language code (will be converted to whisper-cpp format)
+// threads: number of CPU threads (0 for auto)
+func NewWhisperCppAdapter(modelPath, lang string, threads int) *WhisperCppAdapter {
+	return &WhisperCppAdapter{
+		modelPath: modelPath,
+		language:  lang,
+		threads:   threads,
+	}
+}
+
+func (a *WhisperCppAdapter) Transcribe(ctx context.Context, audioData []byte) (string, error) {
+	if len(audioData) == 0 {
+		return "", nil
+	}
+
+	// check whisper-cli exists
+	whisperPath, err := exec.LookPath("whisper-cli")
+	if err != nil {
+		return "", fmt.Errorf("whisper-cli not found: install whisper.cpp first")
+	}
+
+	// check model file exists
+	if _, err := os.Stat(a.modelPath); os.IsNotExist(err) {
+		return "", fmt.Errorf("model file not found: %s", a.modelPath)
+	}
+
+	// convert raw PCM to WAV
+	wavData, err := convertToWAV(audioData)
+	if err != nil {
+		return "", fmt.Errorf("convert to WAV: %w", err)
+	}
+
+	// write to temp file
+	tmpDir := os.TempDir()
+	tmpFile := filepath.Join(tmpDir, fmt.Sprintf("hyprvoice-%d.wav", time.Now().UnixNano()))
+	if err := os.WriteFile(tmpFile, wavData, 0600); err != nil {
+		return "", fmt.Errorf("write temp file: %w", err)
+	}
+	defer os.Remove(tmpFile)
+
+	// convert language to whisper-cpp format
+	lang := language.ToProviderFormat(a.language, "whisper-cpp")
+
+	// build command args
+	args := []string{
+		"-m", a.modelPath,
+		"-l", lang,
+		"-nt", // no timestamps
+		"-np", // no progress
+		"-f", tmpFile,
+	}
+
+	// add threads if specified
+	if a.threads > 0 {
+		args = append(args, "-t", fmt.Sprintf("%d", a.threads))
+	}
+
+	// execute whisper-cli
+	cmd := exec.CommandContext(ctx, whisperPath, args...)
+	var stdout, stderr bytes.Buffer
+	cmd.Stdout = &stdout
+	cmd.Stderr = &stderr
+
+	start := time.Now()
+	err = cmd.Run()
+	duration := time.Since(start)
+
+	if err != nil {
+		// check if context was cancelled
+		if ctx.Err() != nil {
+			return "", ctx.Err()
+		}
+		log.Printf("whisper-cpp: command failed after %v: %v\nstderr: %s", duration, err, stderr.String())
+		return "", fmt.Errorf("whisper-cli failed: %w", err)
+	}
+
+	// parse output - whisper-cli outputs transcription text directly (with -nt flag)
+	text := strings.TrimSpace(stdout.String())
+
+	log.Printf("whisper-cpp: transcribed %d bytes in %v: %q", len(audioData), duration, text)
+	return text, nil
+}
diff --git a/internal/transcriber/adapter_whisper_cpp_test.go b/internal/transcriber/adapter_whisper_cpp_test.go
new file mode 100644
index 0000000..e870d69
--- /dev/null
+++ b/internal/transcriber/adapter_whisper_cpp_test.go
@@ -0,0 +1,125 @@
+package transcriber
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestWhisperCppAdapter_ImplementsBatchAdapter(t *testing.T) {
+	// compile-time check that WhisperCppAdapter implements BatchAdapter
+	var _ BatchAdapter = (*WhisperCppAdapter)(nil)
+}
+
+func TestWhisperCppAdapter_EmptyAudio(t *testing.T) {
+	adapter := NewWhisperCppAdapter("/nonexistent/model.bin", "en", 4)
+	text, err := adapter.Transcribe(context.Background(), []byte{})
+	if err != nil {
+		t.Errorf("expected no error for empty audio, got: %v", err)
+	}
+	if text != "" {
+		t.Errorf("expected empty text for empty audio, got: %q", text)
+	}
+}
+
+func TestWhisperCppAdapter_MissingModel(t *testing.T) {
+	adapter := NewWhisperCppAdapter("/nonexistent/path/model.bin", "en", 4)
+
+	// create minimal valid PCM data (just zeros)
+	audioData := make([]byte, 32000) // 1 second at 16kHz 16-bit
+
+	_, err := adapter.Transcribe(context.Background(), audioData)
+	if err == nil {
+		t.Error("expected error for missing model file")
+	}
+	if err != nil && !contains(err.Error(), "model file not found") {
+		t.Errorf("expected 'model file not found' error, got: %v", err)
+	}
+}
+
+func TestWhisperCppAdapter_LanguageConversion(t *testing.T) {
+	// verify adapter stores language for later conversion
+	adapter := NewWhisperCppAdapter("/fake/model.bin", "", 4)
+	if adapter.language != "" {
+		t.Errorf("expected empty language for auto, got: %q", adapter.language)
+	}
+
+	adapter = NewWhisperCppAdapter("/fake/model.bin", "en", 4)
+	if adapter.language != "en" {
+		t.Errorf("expected 'en' language, got: %q", adapter.language)
+	}
+}
+
+func TestWhisperCppAdapter_ThreadsConfig(t *testing.T) {
+	adapter := NewWhisperCppAdapter("/fake/model.bin", "en", 0)
+	if adapter.threads != 0 {
+		t.Errorf("expected threads=0 (auto), got: %d", adapter.threads)
+	}
+
+	adapter = NewWhisperCppAdapter("/fake/model.bin", "en", 8)
+	if adapter.threads != 8 {
+		t.Errorf("expected threads=8, got: %d", adapter.threads)
+	}
+}
+
+func TestWhisperCppAdapter_TempFileCleanup(t *testing.T) {
+	// this test requires whisper-cli and a model to be installed
+	// skip if not available
+	modelPath := os.Getenv("WHISPER_TEST_MODEL")
+	if modelPath == "" {
+		t.Skip("WHISPER_TEST_MODEL not set, skipping temp file cleanup test")
+	}
+
+	adapter := NewWhisperCppAdapter(modelPath, "en", 4)
+
+	// create minimal audio data
+	audioData := make([]byte, 32000)
+
+	// run transcription
+	_, _ = adapter.Transcribe(context.Background(), audioData)
+
+	// check that temp file was cleaned up
+	// (we can't easily verify this without modifying the adapter to expose temp path)
+	// this is more of a visual/log verification
+}
+
+func TestWhisperCppAdapter_ContextCancellation(t *testing.T) {
+	// skip if whisper-cli not installed
+	if _, err := os.Stat("/usr/local/bin/whisper-cli"); os.IsNotExist(err) {
+		t.Skip("whisper-cli not installed")
+	}
+
+	// create a fake model file for this test
+	tmpDir := t.TempDir()
+	fakeModel := filepath.Join(tmpDir, "fake.bin")
+	if err := os.WriteFile(fakeModel, []byte("fake"), 0600); err != nil {
+		t.Fatalf("failed to create fake model: %v", err)
+	}
+
+	adapter := NewWhisperCppAdapter(fakeModel, "en", 4)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // cancel immediately
+
+	// create minimal audio data
+	audioData := make([]byte, 32000)
+
+	_, err := adapter.Transcribe(ctx, audioData)
+	if err == nil {
+		t.Error("expected error for cancelled context")
+	}
+}
+
+func contains(s, substr string) bool {
+	return len(s) >= len(substr) && (s == substr || len(s) > 0 && containsHelper(s, substr))
+}
+
+func containsHelper(s, substr string) bool {
+	for i := 0; i <= len(s)-len(substr); i++ {
+		if s[i:i+len(substr)] == substr {
+			return true
+		}
+	}
+	return false
+}
diff --git a/progress.txt b/progress.txt
index 1fa9f73..be337ee 100644
--- a/progress.txt
+++ b/progress.txt
@@ -184,4 +184,24 @@ Started: Sun Feb  1 12:22:47 AM CET 2026
 - Remove(modelID) deletes model file
 - GetInstalledPath(modelID) returns path or error if not installed
 - Download uses temp file + rename for atomicity, respects context cancellation
+- All tests passing, typecheck passes
+
+### Task 20: Create WhisperCppAdapter implementing BatchAdapter
+- Created `internal/transcriber/adapter_whisper_cpp.go`
+- WhisperCppAdapter struct with modelPath, language, threads fields
+- Constructor: `NewWhisperCppAdapter(modelPath, lang string, threads int)`
+- Transcribe() implementation:
+  - Returns empty string for empty audio (no error)
+  - Checks whisper-cli exists via exec.LookPath
+  - Checks model file exists via os.Stat
+  - Converts raw PCM to WAV using existing convertToWAV helper
+  - Writes to temp file in os.TempDir() with unique timestamp
+  - Uses defer os.Remove(tmpFile) for cleanup
+  - Converts language via language.ToProviderFormat(lang, "whisper-cpp")
+  - Executes: whisper-cli -m {modelPath} -l {lang} -nt -np -f {tempfile}
+  - Adds -t {threads} flag if threads > 0
+  - Respects context cancellation
+  - Parses stdout for transcription text
+- Created comprehensive test file adapter_whisper_cpp_test.go
+- Tests: interface implementation, empty audio, missing model, language, threads, context cancellation
 - All tests passing, typecheck passes
\ No newline at end of file
diff --git a/tasks/prd.jsonc b/tasks/prd.jsonc
index b6b1065..f49804e 100644
--- a/tasks/prd.jsonc
+++ b/tasks/prd.jsonc
@@ -480,7 +480,7 @@
 				"Cleans up temp files",
 				"Typecheck passes"
 			],
-			"passes": false
+			"passes": true
 		},
 		{
 			"title": "Create whisper-cpp Provider",