diff --git a/.github/workflows/go.yml b/.github/workflows/go.yml
index 68151fb..91e4dd7 100644
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@@ -19,9 +19,6 @@ jobs:
 
       - name: Set up uv
         uses: astral-sh/setup-uv@v3
-        with:
-          enable-cache: true
-          python-version: "3.11"
 
       - name: Validate router configs
         run: |
diff --git a/multipart_ops.go b/multipart_ops.go
index ee56f1a..3f5ec30 100644
--- a/multipart_ops.go
+++ b/multipart_ops.go
@@ -49,7 +49,13 @@ func (c *router) UploadPart(ctx context.Context, in *s3.UploadPartInput, optFns
 		)
 		// UploadPart typically handles large chunks (5MB-5GB), use streaming
 		if in.ContentLength == nil || *in.ContentLength >= c.maxBufferBytes {
-			r1, r2, err = teeBody(ctx, in.Body)
+			// For large bodies, we can only support parallel actions (Mirror, BestEffort).
+			// Fallback requires buffering or seeking, which we can't do for generic streams.
+			if action == config.ActFallback {
+				return nil, fmt.Errorf("%s: fallback strategy is not supported for large or unknown-length streams", op)
+			}
+			tolerant := (action == config.ActBestEffort)
+			r1, r2, err = teeBody(ctx, in.Body, tolerant)
 		} else {
 			r1, r2, err = drainBody(ctx, in.Body)
 		}
diff --git a/ops.go b/ops.go
index 7c2bd7c..502ad2c 100644
--- a/ops.go
+++ b/ops.go
@@ -56,22 +56,30 @@ func (c *router) PutObject(
 	primB, secB := c.cfg.PhysicalBuckets(bucket)
 	inPrimary, inSecondary := *in, *in
 	inPrimary.Bucket, inSecondary.Bucket = aws.String(primB), aws.String(secB)
-	if action == config.ActMirror && in.Body != nil {
+	if (action == config.ActMirror || action == config.ActBestEffort || action == config.ActFallback) && in.Body != nil {
 		var (
 			r1, r2 io.Reader
 			err    error
 		)
 		// If ContentLength is not provided, S3 use chunked transfer encoding.
 		if in.ContentLength == nil || *in.ContentLength >= c.maxBufferBytes {
-			r1, r2, err = teeBody(ctx, in.Body)
+			// For large bodies, we can only support parallel actions (Mirror, BestEffort).
+			// Fallback requires buffering or seeking, which we can't do for generic streams.
+			if action == config.ActFallback {
+				return nil, fmt.Errorf("%s: fallback strategy is not supported for large or unknown-length streams", op)
+			}
+			tolerant := (action == config.ActBestEffort)
+			r1, r2, err = teeBody(ctx, in.Body, tolerant)
 		} else {
 			r1, r2, err = drainBody(ctx, in.Body)
 		}
 		if err != nil {
-			return nil, fmt.Errorf("%s: failed to split body for mirror: %w", op, err)
+			return nil, fmt.Errorf("%s: failed to split body for %s: %w", op, action, err)
+		}
+		if r1 != nil && r2 != nil {
+			inPrimary.Body = r1
+			inSecondary.Body = r2
 		}
-		inPrimary.Body = r1
-		inSecondary.Body = r2
 	}
 	return dispatch(ctx, action,
 		func(ctx context.Context, st store.Store, in *s3.PutObjectInput) (*s3.PutObjectOutput, error) {
diff --git a/router.go b/router.go
index 3192c38..fc612ee 100644
--- a/router.go
+++ b/router.go
@@ -116,10 +116,10 @@ func doParallel[I any, T any](
 		return out, nil
 	}
 	// best-effort: fire-and-forget secondary
-	out, err := op(ctx, s1, in1)
 	go func() {
 		_, _ = op(ctx, s2, in2)
 	}()
+	out, err := op(ctx, s1, in1)
 	return out, err
 }
 
@@ -134,24 +134,72 @@ func drainBody(ctx context.Context, r io.Reader) (io.ReadSeeker, io.ReadSeeker,
 	return bytes.NewReader(data), bytes.NewReader(data), nil
 }
 
-func teeBody(ctx context.Context, r io.Reader) (io.ReadCloser, io.ReadCloser, error) {
+// tolerantWriter wraps an io.Writer and ignores errors from the underlying writer.
+type tolerantWriter struct {
+	w      io.Writer
+	failed bool
+}
+
+func (t *tolerantWriter) Write(p []byte) (n int, err error) {
+	if t.failed {
+		return len(p), nil
+	}
+	n, err = t.w.Write(p)
+	if err != nil {
+		t.failed = true
+		// Act as if we wrote everything to keep MultiWriter happy.
+		return len(p), nil
+	}
+	return n, nil
+}
+
+func teeBody(ctx context.Context, r io.Reader, tolerantSecondary bool) (io.ReadCloser, io.ReadCloser, error) {
 	pr1, pw1 := io.Pipe()
 	pr2, pw2 := io.Pipe()
 	go func() {
 		defer pw1.Close()
 		defer pw2.Close()
 
-		select {
-		case <-ctx.Done():
-			err := ctx.Err()
-			pw1.CloseWithError(err)
-			pw2.CloseWithError(err)
-			return
-		default:
-			_, err := io.Copy(io.MultiWriter(pw1, pw2), r)
-			if err != nil {
+		var w2 io.Writer = pw2
+		if tolerantSecondary {
+			w2 = &tolerantWriter{w: pw2}
+		}
+		mw := io.MultiWriter(pw1, w2)
+
+		buf := make([]byte, 32*1024)
+		for {
+			select {
+			case <-ctx.Done():
+				err := ctx.Err()
 				pw1.CloseWithError(err)
 				pw2.CloseWithError(err)
+				return
+			default:
+			}
+
+			nr, er := r.Read(buf)
+			if nr > 0 {
+				nw, ew := mw.Write(buf[0:nr])
+				if ew != nil {
+					// Check if error is from pw1
+					// If tolerantWriter wrapped pw2, it won't return error.
+					// So any error here means pw1 failed (or tolerantWriter itself failed unexpectedly).
+					pw1.CloseWithError(ew)
+					pw2.CloseWithError(ew)
+					return
+				}
+				if nr != nw {
+					pw1.CloseWithError(io.ErrShortWrite)
+					pw2.CloseWithError(io.ErrShortWrite)
+					return
+				}
+			}
+			if er != nil {
+				if er != io.EOF {
+					pw1.CloseWithError(er)
+					pw2.CloseWithError(er)
+				}
+				return
 			}
 		}
 	}()
diff --git a/router_ops_test.go b/router_ops_test.go
new file mode 100644
index 0000000..9aba5cd
--- /dev/null
+++ b/router_ops_test.go
@@ -0,0 +1,190 @@
+package s3router
+
+import (
+	"context"
+	"io"
+	"strings"
+	"sync"
+	"testing"
+
+	"github.com/aws/aws-sdk-go-v2/service/s3"
+	"github.com/wilbeibi/s3router/config"
+)
+
+type mockBodyStore struct {
+	name string
+	t    *testing.T
+	// Optional: Simulate error for primary/secondary
+	fail bool
+	// Optional: WaitGroup to signal completion
+	wg *sync.WaitGroup
+}
+
+func (m *mockBodyStore) GetObject(ctx context.Context, in *s3.GetObjectInput, optFns ...func(*s3.Options)) (*s3.GetObjectOutput, error) {
+	return nil, nil
+}
+func (m *mockBodyStore) PutObject(ctx context.Context, in *s3.PutObjectInput, optFns ...func(*s3.Options)) (*s3.PutObjectOutput, error) {
+	if m.wg != nil {
+		defer m.wg.Done()
+	}
+	if in.Body == nil {
+		m.t.Errorf("[%s] PutObject body is nil", m.name)
+		return nil, nil
+	}
+	// Simulate reading the body
+	data, err := io.ReadAll(in.Body)
+	if err != nil {
+		m.t.Errorf("[%s] failed to read body: %v", m.name, err)
+		return nil, err
+	}
+
+	if m.fail {
+		return nil, io.EOF // Simulate error
+	}
+
+	expected := "hello world"
+	if string(data) != expected {
+		m.t.Errorf("[%s] got body %q, want %q", m.name, string(data), expected)
+	} else {
+		// m.t.Logf("[%s] successfully read body", m.name)
+	}
+	return &s3.PutObjectOutput{}, nil
+}
+func (m *mockBodyStore) HeadObject(ctx context.Context, in *s3.HeadObjectInput, optFns ...func(*s3.Options)) (*s3.HeadObjectOutput, error) {
+	return nil, nil
+}
+func (m *mockBodyStore) DeleteObject(ctx context.Context, in *s3.DeleteObjectInput, optFns ...func(*s3.Options)) (*s3.DeleteObjectOutput, error) {
+	return nil, nil
+}
+func (m *mockBodyStore) DeleteObjects(ctx context.Context, in *s3.DeleteObjectsInput, optFns ...func(*s3.Options)) (*s3.DeleteObjectsOutput, error) {
+	return nil, nil
+}
+func (m *mockBodyStore) ListObjectsV2(ctx context.Context, in *s3.ListObjectsV2Input, optFns ...func(*s3.Options)) (*s3.ListObjectsV2Output, error) {
+	return nil, nil
+}
+func (m *mockBodyStore) CreateMultipartUpload(ctx context.Context, in *s3.CreateMultipartUploadInput, optFns ...func(*s3.Options)) (*s3.CreateMultipartUploadOutput, error) {
+	return nil, nil
+}
+func (m *mockBodyStore) UploadPart(ctx context.Context, in *s3.UploadPartInput, optFns ...func(*s3.Options)) (*s3.UploadPartOutput, error) {
+	return nil, nil
+}
+func (m *mockBodyStore) CompleteMultipartUpload(ctx context.Context, in *s3.CompleteMultipartUploadInput, optFns ...func(*s3.Options)) (*s3.CompleteMultipartUploadOutput, error) {
+	return nil, nil
+}
+func (m *mockBodyStore) ListParts(ctx context.Context, in *s3.ListPartsInput, optFns ...func(*s3.Options)) (*s3.ListPartsOutput, error) {
+	return nil, nil
+}
+func (m *mockBodyStore) AbortMultipartUpload(ctx context.Context, in *s3.AbortMultipartUploadInput, optFns ...func(*s3.Options)) (*s3.AbortMultipartUploadOutput, error) {
+	return nil, nil
+}
+
+func stringPtr(s string) *string {
+	return &s
+}
+
+func TestPutObject_BestEffort_Concurrent(t *testing.T) {
+	cfgYaml := `
+endpoints:
+  primary: http://p
+  secondary: http://s
+buckets:
+  testbucket:
+    primary: p
+    secondary: s
+rules:
+  - bucket: testbucket
+    prefix:
+      "*":
+        PutObject: best-effort
+        "*": primary
+`
+	cfg, err := config.Load(strings.NewReader(cfgYaml))
+	if err != nil {
+		t.Fatalf("failed to load config: %v", err)
+	}
+
+	var wg sync.WaitGroup
+	wg.Add(2)
+
+	primary := &mockBodyStore{name: "primary", t: t, wg: &wg}
+	secondary := &mockBodyStore{name: "secondary", t: t, wg: &wg}
+
+	r, err := New(cfg, primary, secondary)
+	if err != nil {
+		t.Fatalf("New failed: %v", err)
+	}
+
+	// Use a pipe to simulate a stream
+	pr, pw := io.Pipe()
+	go func() {
+		pw.Write([]byte("hello world"))
+		pw.Close()
+	}()
+
+	ctx := context.Background()
+	_, err = r.PutObject(ctx, &s3.PutObjectInput{
+		Bucket: stringPtr("testbucket"),
+		Key:    stringPtr("obj"),
+		Body:   pr,
+	})
+	if err != nil {
+		t.Fatalf("PutObject failed: %v", err)
+	}
+
+	// Wait for both primary (which finishes before PutObject returns)
+	// and secondary (which finishes async) to complete.
+	wg.Wait()
+}
+
+func TestPutObject_Fallback_SmallBody(t *testing.T) {
+	// Fallback should work for small bodies by buffering
+	cfgYaml := `
+endpoints:
+  primary: http://p
+  secondary: http://s
+buckets:
+  testbucket:
+    primary: p
+    secondary: s
+rules:
+  - bucket: testbucket
+    prefix:
+      "*":
+        PutObject: fallback
+        "*": primary
+`
+	cfg, err := config.Load(strings.NewReader(cfgYaml))
+	if err != nil {
+		t.Fatalf("failed to load config: %v", err)
+	}
+
+	primary := &mockBodyStore{name: "primary", t: t, fail: true} // Primary fails
+	secondary := &mockBodyStore{name: "secondary", t: t}
+
+	r, err := New(cfg, primary, secondary)
+	if err != nil {
+		t.Fatalf("New failed: %v", err)
+	}
+
+	bodyContent := "hello world"
+	contentLength := int64(len(bodyContent))
+	// ContentLength is optional but drainBody uses it to decide buffering if available.
+	// If nil, it checks maxBufferBytes which is large by default.
+	// So drainBody will buffer "hello world" only if ContentLength is set and small.
+
+	ctx := context.Background()
+	_, err = r.PutObject(ctx, &s3.PutObjectInput{
+		Bucket:        stringPtr("testbucket"),
+		Key:           stringPtr("obj"),
+		Body:          strings.NewReader(bodyContent),
+		ContentLength: &contentLength,
+	})
+
+	// Even if it is strings.NewReader (seekable), drainBody reads it all.
+	// Primary mock reads it all (fails).
+	// Secondary mock should receive a fresh reader with same content.
+
+	if err != nil {
+		t.Fatalf("PutObject failed: %v", err)
+	}
+}
diff --git a/router_test.go b/router_test.go
index 8958de4..5449ef2 100644
--- a/router_test.go
+++ b/router_test.go
@@ -124,7 +124,7 @@ func TestTeeBody(t *testing.T) {
 	ctx := context.Background()
 	want := []byte("stream‑content")
 
-	pr1, pr2, err := teeBody(ctx, bytes.NewReader(want))
+	pr1, pr2, err := teeBody(ctx, bytes.NewReader(want), false)
 	if err != nil {
 		t.Fatalf("teeBody error: %v", err)
 	}