diff --git a/agent/job_runner.go b/agent/job_runner.go
index c99aa02e15..06bbd52e78 100644
--- a/agent/job_runner.go
+++ b/agent/job_runner.go
@@ -732,7 +732,7 @@ func (w LogWriter) Write(bytes []byte) (int, error) {
 func (r *JobRunner) executePreBootstrapHook(ctx context.Context, hook string) (bool, error) {
 	r.logger.Info("Running pre-bootstrap hook %q", hook)
 
-	sh, err := shell.New()
+	sh, err := shell.New(ctx, shell.Config{})
 	if err != nil {
 		return false, err
 	}
diff --git a/bootstrap/bootstrap.go b/bootstrap/bootstrap.go
index 88932131e2..ddc9867988 100644
--- a/bootstrap/bootstrap.go
+++ b/bootstrap/bootstrap.go
@@ -70,16 +70,20 @@ func New(conf Config) *Bootstrap {
 func (b *Bootstrap) Run(ctx context.Context) (exitCode int) {
 	// Check if not nil to allow for tests to overwrite shell
 	if b.shell == nil {
-		var err error
-		b.shell, err = shell.New()
+		// The Agent API socket could be important for file locking.
+		cfg := shell.Config{
+			SocketsPath: b.Config.SocketsPath,
+		}
+		sh, err := shell.New(ctx, cfg)
 		if err != nil {
 			fmt.Printf("Error creating shell: %v", err)
 			return 1
 		}
 
-		b.shell.PTY = b.Config.RunInPty
-		b.shell.Debug = b.Config.Debug
-		b.shell.InterruptSignal = b.Config.CancelSignal
+		sh.PTY = b.Config.RunInPty
+		sh.Debug = b.Config.Debug
+		sh.InterruptSignal = b.Config.CancelSignal
+		b.shell = sh
 	}
 	if experiments.IsEnabled(experiments.KubernetesExec) {
 		kubernetesClient := &kubernetes.Client{}
diff --git a/bootstrap/bootstrap_test.go b/bootstrap/bootstrap_test.go
index 1dce8bdf9a..71234cc422 100644
--- a/bootstrap/bootstrap_test.go
+++ b/bootstrap/bootstrap_test.go
@@ -86,7 +86,7 @@ func TestStartTracing_NoTracingBackend(t *testing.T) {
 	b := New(Config{})
 
 	oriCtx := context.Background()
-	b.shell, err = shell.New()
+	b.shell, err = shell.New(oriCtx, shell.Config{})
 	assert.NoError(t, err)
 
 	span, _, stopper := b.startTracing(oriCtx)
@@ -107,7 +107,7 @@ func TestStartTracing_Datadog(t *testing.T) {
 	b := New(cfg)
 
 	oriCtx := context.Background()
-	b.shell, err = shell.New()
+	b.shell, err = shell.New(oriCtx, shell.Config{})
 	assert.NoError(t, err)
 
 	span, ctx, stopper := b.startTracing(oriCtx)
diff --git a/bootstrap/shell/shell.go b/bootstrap/shell/shell.go
index 6d9eb1e07d..c96227c695 100644
--- a/bootstrap/shell/shell.go
+++ b/bootstrap/shell/shell.go
@@ -23,7 +23,9 @@ import (
 	"github.com/opentracing/opentracing-go"
 
 	"github.com/buildkite/agent/v3/env"
+	"github.com/buildkite/agent/v3/experiments"
 	"github.com/buildkite/agent/v3/internal/shellscript"
+	"github.com/buildkite/agent/v3/lock"
 	"github.com/buildkite/agent/v3/logger"
 	"github.com/buildkite/agent/v3/process"
 	"github.com/buildkite/agent/v3/tracetools"
@@ -67,23 +69,45 @@ type Shell struct {
 	cmd     *command
 	cmdLock sync.Mutex
 
+	// Lock service client, if available
+	lockClient *lock.Client
+
 	// The signal to use to interrupt the command
 	InterruptSignal process.Signal
 }
 
-// New returns a new Shell
-func New() (*Shell, error) {
+// Config contains configuration options for creating a Shell.
+type Config struct {
+	SocketsPath string
+}
+
+// New returns a new Shell.
+func New(ctx context.Context, cfg Config) (*Shell, error) {
 	wd, err := os.Getwd()
 	if err != nil {
 		return nil, fmt.Errorf("Failed to find current working directory: %w", err)
 	}
 
-	return &Shell{
+	sh := &Shell{
 		Logger: StderrLogger,
 		Env:    env.FromSlice(os.Environ()),
 		Writer: os.Stdout,
 		wd:     wd,
-	}, nil
+	}
+
+	// Use the Agent API for locking?
+	if cfg.SocketsPath != "" && experiments.IsEnabled(experiments.AgentAPI) {
+		ctx, canc := context.WithTimeout(ctx, 10*time.Second)
+		defer canc()
+		lc, err := lock.NewClient(ctx, cfg.SocketsPath)
+		if err != nil {
+			sh.Logger.Errorf("Couldn't use Agent API for locking, so falling back to using flock-based locks: %v", err)
+			lc = nil
+		}
+		sh.lockClient = lc
+	}
+
+	return sh, nil
 }
 
 // WithStdin returns a copy of the Shell with the provided io.Reader set as the
@@ -181,8 +205,8 @@ func (s *Shell) WaitStatus() (process.WaitStatus, error) {
 	return s.cmd.proc.WaitStatus(), nil
 }
 
-// LockFile is a pid-based lock for cross-process locking
-type LockFile interface {
+// Unlocker types can unlock a cross-process lock (such as an flock).
+type Unlocker interface {
 	Unlock() error
 }
 
@@ -222,8 +246,44 @@ func (s *Shell) flock(ctx context.Context, path string, timeout time.Duration) (
 	return lock, err
 }
 
+// agentAPILock contains all the information required to unlock an Agent API
+// lock-service lock.
+type agentAPILock struct {
+	client     *lock.Client
+	key, token string
+}
+
+func (l *agentAPILock) Unlock() error {
+	return l.client.Unlock(context.Background(), l.key, l.token)
+}
+
+// lockWithAgentAPI acquires a lock in the Agent API lock service.
+func (s *Shell) lockWithAgentAPI(ctx context.Context, path string, timeout time.Duration) (*agentAPILock, error) {
+	absolutePathToLock, err := filepath.Abs(path)
+	if err != nil {
+		return nil, fmt.Errorf("Failed to find absolute path to lock \"%s\" (%v)", path, err)
+	}
+
+	ctx, cancel := context.WithTimeout(ctx, timeout)
+	defer cancel()
+
+	token, err := s.lockClient.Lock(ctx, absolutePathToLock)
+	if err != nil {
+		return nil, fmt.Errorf("Failed to acquire lock for %q: %v", path, err)
+	}
+
+	return &agentAPILock{
+		client: s.lockClient,
+		key:    absolutePathToLock,
+		token:  token,
+	}, err
+}
+
 // Create a cross-process file-based lock based on pid files
-func (s *Shell) LockFile(ctx context.Context, path string, timeout time.Duration) (LockFile, error) {
+func (s *Shell) LockFile(ctx context.Context, path string, timeout time.Duration) (Unlocker, error) {
+	if s.lockClient != nil {
+		return s.lockWithAgentAPI(ctx, path, timeout)
+	}
 	return s.flock(ctx, path, timeout)
 }
 
diff --git a/bootstrap/shell/shell_test.go b/bootstrap/shell/shell_test.go
index a5e35a3a60..7bffe40916 100644
--- a/bootstrap/shell/shell_test.go
+++ b/bootstrap/shell/shell_test.go
@@ -131,7 +131,7 @@ func TestContextCancelTerminates(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
-	sh, err := shell.New()
+	sh, err := shell.New(ctx, shell.Config{})
 	if err != nil {
 		t.Fatalf("shell.New() error = %v", err)
 	}
@@ -165,7 +165,7 @@ func TestInterrupt(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
-	sh, err := shell.New()
+	sh, err := shell.New(ctx, shell.Config{})
 	if err != nil {
 		t.Fatalf("shell.New() error = %v", err)
 	}
@@ -190,7 +190,7 @@ func TestInterrupt(t *testing.T) {
 }
 
 func TestDefaultWorkingDirFromSystem(t *testing.T) {
-	sh, err := shell.New()
+	sh, err := shell.New(context.Background(), shell.Config{})
 	if err != nil {
 		t.Fatalf("shell.New() error = %v", err)
 	}
@@ -231,7 +231,7 @@ func TestWorkingDir(t *testing.T) {
 		t.Fatalf("os.Getwd() error = %v", err)
 	}
 
-	sh, err := shell.New()
+	sh, err := shell.New(context.Background(), shell.Config{})
 	if err != nil {
 		t.Fatalf("shell.New() error = %v", err)
 	}
@@ -353,7 +353,7 @@ func TestAcquiringLockHelperProcess(t *testing.T) {
 }
 
 func newShellForTest(t *testing.T) *shell.Shell {
-	sh, err := shell.New()
+	sh, err := shell.New(context.Background(), shell.Config{})
 	if err != nil {
 		t.Fatalf("shell.New() error = %v", err)
 	}
@@ -362,7 +362,7 @@ func newShellForTest(t *testing.T) *shell.Shell {
 }
 
 func TestRunWithoutPrompt(t *testing.T) {
-	sh, err := shell.New()
+	sh, err := shell.New(context.Background(), shell.Config{})
 	if err != nil {
 		t.Fatalf("shell.New() error = %v", err)
 	}
diff --git a/bootstrap/shell/test.go b/bootstrap/shell/test.go
index a4c62a7ccd..9b60817640 100644
--- a/bootstrap/shell/test.go
+++ b/bootstrap/shell/test.go
@@ -1,6 +1,7 @@
 package shell
 
 import (
+	"context"
 	"io"
 	"os"
 	"runtime"
@@ -11,7 +12,7 @@ import (
 
 // NewTestShell creates a minimal shell suitable for tests.
 func NewTestShell(t *testing.T) *Shell {
-	sh, err := New()
+	sh, err := New(context.Background(), Config{})
 	if err != nil {
 		t.Fatalf("shell.New() error = %v", err)
 	}
diff --git a/bootstrap/ssh_test.go b/bootstrap/ssh_test.go
index 705db89b83..60cb2c3501 100644
--- a/bootstrap/ssh_test.go
+++ b/bootstrap/ssh_test.go
@@ -18,7 +18,7 @@ func init() {
 func TestFindingSSHTools(t *testing.T) {
 	t.Parallel()
 
-	sh, err := shell.New()
+	sh, err := shell.New(context.Background(), shell.Config{})
 	if err != nil {
 		t.Fatalf("shell.New() error = %v", err)
 	}
diff --git a/clicommand/agent_start.go b/clicommand/agent_start.go
index d415db2ff1..a4bd751900 100644
--- a/clicommand/agent_start.go
+++ b/clicommand/agent_start.go
@@ -963,10 +963,10 @@ var AgentStartCommand = cli.Command{
 		pool := agent.NewAgentPool(workers)
 
 		// Agent-wide shutdown hook. Once per agent, for all workers on the agent.
-		defer agentShutdownHook(l, cfg)
+		defer agentShutdownHook(ctx, l, cfg)
 
 		// Once the shutdown hook has been setup, trigger the startup hook.
-		if err := agentStartupHook(l, cfg); err != nil {
+		if err := agentStartupHook(ctx, l, cfg); err != nil {
 			l.Fatal("%s", err)
 		}
 
@@ -1052,17 +1052,17 @@ func handlePoolSignals(ctx context.Context, l logger.Logger, pool *agent.AgentPo
 	return signals
 }
 
-func agentStartupHook(log logger.Logger, cfg AgentStartConfig) error {
-	return agentLifecycleHook("agent-startup", log, cfg)
+func agentStartupHook(ctx context.Context, log logger.Logger, cfg AgentStartConfig) error {
+	return agentLifecycleHook(ctx, "agent-startup", log, cfg)
 }
-func agentShutdownHook(log logger.Logger, cfg AgentStartConfig) {
-	_ = agentLifecycleHook("agent-shutdown", log, cfg)
+func agentShutdownHook(ctx context.Context, log logger.Logger, cfg AgentStartConfig) {
+	_ = agentLifecycleHook(ctx, "agent-shutdown", log, cfg)
 }
 
 // agentLifecycleHook looks for a hook script in the hooks path
 // and executes it if found. Output (stdout + stderr) is streamed into the main
 // agent logger. Exit status failure is logged and returned for the caller to handle
-func agentLifecycleHook(hookName string, log logger.Logger, cfg AgentStartConfig) error {
+func agentLifecycleHook(ctx context.Context, hookName string, log logger.Logger, cfg AgentStartConfig) error {
 	// search for hook (including .bat & .ps1 files on Windows)
 	p, err := hook.Find(cfg.HooksPath, hookName)
 	if err != nil {
@@ -1072,7 +1072,7 @@ func agentLifecycleHook(hookName string, log logger.Logger, cfg AgentStartConfig
 		}
 		return nil
 	}
-	sh, err := shell.New()
+	sh, err := shell.New(ctx, shell.Config{})
 	if err != nil {
 		log.Error("creating shell for %q hook: %v", hookName, err)
 		return err
diff --git a/clicommand/agent_start_test.go b/clicommand/agent_start_test.go
index 1f105bc3c2..aa01841511 100644
--- a/clicommand/agent_start_test.go
+++ b/clicommand/agent_start_test.go
@@ -1,6 +1,7 @@
 package clicommand
 
 import (
+	"context"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -50,7 +51,7 @@ func TestAgentStartupHook(t *testing.T) {
 		defer closer()
 		filepath := writeAgentHook(t, hooksPath, "agent-startup")
 		log := logger.NewBuffer()
-		err := agentStartupHook(log, cfg(hooksPath))
+		err := agentStartupHook(context.Background(), log, cfg(hooksPath))
 
 		if assert.NoError(t, err, log.Messages) {
 			assert.Equal(t, []string{
@@ -64,14 +65,14 @@ func TestAgentStartupHook(t *testing.T) {
 		defer closer()
 
 		log := logger.NewBuffer()
-		err := agentStartupHook(log, cfg(hooksPath))
+		err := agentStartupHook(context.Background(), log, cfg(hooksPath))
 		if assert.NoError(t, err, log.Messages) {
 			assert.Equal(t, []string{}, log.Messages)
 		}
 	})
 	t.Run("with bad hooks path", func(t *testing.T) {
 		log := logger.NewBuffer()
-		err := agentStartupHook(log, cfg("zxczxczxc"))
+		err := agentStartupHook(context.Background(), log, cfg("zxczxczxc"))
 
 		if assert.NoError(t, err, log.Messages) {
 			assert.Equal(t, []string{}, log.Messages)
@@ -95,7 +96,7 @@ func TestAgentShutdownHook(t *testing.T) {
 		defer closer()
 		filepath := writeAgentHook(t, hooksPath, "agent-shutdown")
 		log := logger.NewBuffer()
-		agentShutdownHook(log, cfg(hooksPath))
+		agentShutdownHook(context.Background(), log, cfg(hooksPath))
 
 		assert.Equal(t, []string{
 			"[info] " + prompt + " " + filepath, // prompt
@@ -107,12 +108,12 @@ func TestAgentShutdownHook(t *testing.T) {
 		defer closer()
 
 		log := logger.NewBuffer()
-		agentShutdownHook(log, cfg(hooksPath))
+		agentShutdownHook(context.Background(), log, cfg(hooksPath))
 		assert.Equal(t, []string{}, log.Messages)
 	})
 	t.Run("with bad hooks path", func(t *testing.T) {
 		log := logger.NewBuffer()
-		agentShutdownHook(log, cfg("zxczxczxc"))
+		agentShutdownHook(context.Background(), log, cfg("zxczxczxc"))
 		assert.Equal(t, []string{}, log.Messages)
 	})
 }