diff --git a/client_internal_test.go b/client_internal_test.go
new file mode 100644
index 0000000..68221ad
--- /dev/null
+++ b/client_internal_test.go
@@ -0,0 +1,50 @@
+package quickwit
+
+import (
+	"net/http"
+	"testing"
+)
+
+// The default client's transport must size its idle-connection pool to the
+// worker count, so raising SetConcurrent does not get throttled by the stdlib
+// default of MaxIdleConnsPerHost = 2.
+func TestHTTPClient_DefaultTransportSizedToConcurrent(t *testing.T) {
+	const concurrent = 16
+
+	c := NewClient("http://example/api/v1/test")
+	c.SetConcurrent(concurrent)
+
+	got := c.httpClient()
+	tr, ok := got.Transport.(*http.Transport)
+	if !ok {
+		t.Fatalf("transport = %T, want *http.Transport", got.Transport)
+	}
+	if tr.MaxIdleConnsPerHost != concurrent {
+		t.Errorf("MaxIdleConnsPerHost = %d, want %d", tr.MaxIdleConnsPerHost, concurrent)
+	}
+	if tr.MaxIdleConns < concurrent {
+		t.Errorf("MaxIdleConns = %d, want >= %d", tr.MaxIdleConns, concurrent)
+	}
+}
+
+// The default client is built once and reused, so workers share one connection
+// pool rather than each creating its own.
+func TestHTTPClient_DefaultClientCached(t *testing.T) {
+	c := NewClient("http://example/api/v1/test")
+
+	if c.httpClient() != c.httpClient() {
+		t.Error("httpClient returned different default clients across calls")
+	}
+}
+
+// A user-supplied client is used verbatim, untouched by the default tuning.
+func TestHTTPClient_UserClientPassthrough(t *testing.T) {
+	custom := &http.Client{}
+
+	c := NewClient("http://example/api/v1/test")
+	c.SetHTTPClient(custom)
+
+	if c.httpClient() != custom {
+		t.Error("httpClient did not return the user-supplied client")
+	}
+}
diff --git a/quickwit.go b/quickwit.go
index 1b1957c..acac19d 100644
--- a/quickwit.go
+++ b/quickwit.go
@@ -38,6 +38,8 @@ type Client struct {
 	discard             bool
 	concurrent          int
 	ingestBuffer        chan any
+	defaultClient       *http.Client
+	onceDefaultClient   sync.Once
 	onceSetup           sync.Once
 	onceClose           sync.Once
 	stopWg              sync.WaitGroup
@@ -94,10 +96,33 @@ func (c *Client) OnDiscard(f OnDiscardFunc) {
 }
 
 func (c *Client) httpClient() *http.Client {
-	if c.client == nil {
-		return http.DefaultClient
+	if c.client != nil {
+		return c.client
 	}
-	return c.client
+	// When no client is supplied, fall back to a tuned default instead of
+	// http.DefaultClient. Its transport's MaxIdleConnsPerHost defaults to 2,
+	// which would close (and force a fresh handshake on) every connection
+	// beyond the first two when SetConcurrent raises the worker count. Sizing
+	// the idle pool to the worker count lets each worker keep its connection
+	// hot for reuse. Built once, lazily, so the pool is shared across workers.
+	c.onceDefaultClient.Do(func() {
+		c.defaultClient = c.newDefaultClient()
+	})
+	return c.defaultClient
+}
+
+func (c *Client) newDefaultClient() *http.Client {
+	concurrent := c.getConcurrent()
+
+	t := http.DefaultTransport.(*http.Transport).Clone()
+	t.MaxIdleConnsPerHost = concurrent
+	if t.MaxIdleConns < concurrent {
+		t.MaxIdleConns = concurrent
+	}
+
+	// No client-level timeout: the per-request context deadline from
+	// getIngestTimeout already bounds each flush, matching prior behavior.
+	return &http.Client{Transport: t}
 }
 
 func (c *Client) getMaxDelay() time.Duration {