diff --git a/src/clob/client.rs b/src/clob/client.rs
index 2697bf02..99aebb7e 100644
--- a/src/clob/client.rs
+++ b/src/clob/client.rs
@@ -368,6 +368,16 @@ pub struct Config {
     /// This is primarily useful for testing.
     #[builder(into)]
     geoblock_host: Option<String>,
+    /// A pre-configured [`reqwest::Client`] to use for HTTP requests. When provided,
+    /// the supplied client is used as-is — callers should include appropriate default
+    /// headers (e.g. `User-Agent`, `Content-Type: application/json`) on their client.
+    ///
+    /// This is useful for latency-sensitive use cases that need control over connection
+    /// pooling, TCP keep-alive, HTTP/2 window sizing, TLS, proxies, or timeouts.
+    ///
+    /// If `None` (the default), the client builds a standard [`reqwest::Client`]
+    /// internally.
+    http_client: Option<ReqwestClient>,
     #[cfg(feature = "heartbeats")]
     #[builder(default = Duration::from_secs(5))]
     /// How often the [`Client`] will automatically submit heartbeats. The default is five (5) seconds.
@@ -379,6 +389,7 @@ impl Default for Config {
         Self {
             use_server_time: false,
             geoblock_host: None,
+            http_client: None,
             #[cfg(feature = "heartbeats")]
             heartbeat_interval: Duration::from_secs(5),
         }
@@ -1194,7 +1205,10 @@ impl Client<Unauthenticated> {
         headers.insert("Connection", HeaderValue::from_static("keep-alive"));
         headers.insert("Content-Type", HeaderValue::from_static("application/json"));
 
-        let client = ReqwestClient::builder().default_headers(headers).build()?;
+        let client = match config.http_client.clone() {
+            Some(custom) => custom,
+            None => ReqwestClient::builder().default_headers(headers).build()?,
+        };
 
         let geoblock_host = Url::parse(
             config
@@ -1563,7 +1577,7 @@ impl<K: Kind> Client<Authenticated<K>> {
         let request = self
             .client()
             .request(Method::DELETE, format!("{}order", self.host()))
-            .json(&json!({ "orderId": order_id }))
+            .json(&json!({ "orderID": order_id }))
             .build()?;
         let headers = self.create_headers(&request).await?;
 
diff --git a/tests/clob.rs b/tests/clob.rs
index f4bacadb..46f50837 100644
--- a/tests/clob.rs
+++ b/tests/clob.rs
@@ -49,6 +49,36 @@ mod unauthenticated {
 
     use super::*;
 
+    #[tokio::test]
+    async fn custom_http_client_should_be_used() -> anyhow::Result<()> {
+        let server = MockServer::start();
+
+        let custom = reqwest::Client::builder()
+            .tcp_nodelay(true)
+            .pool_max_idle_per_host(10)
+            .default_headers({
+                let mut h = reqwest::header::HeaderMap::new();
+                h.insert("User-Agent", "rs_clob_client".parse().unwrap());
+                h.insert("Content-Type", "application/json".parse().unwrap());
+                h
+            })
+            .build()?;
+
+        let config = Config::builder().http_client(custom).build();
+        let client = Client::new(&server.base_url(), config)?;
+
+        let mock = server.mock(|when, then| {
+            when.method(httpmock::Method::GET).path("/");
+            then.status(StatusCode::OK).body("\"OK\"");
+        });
+
+        let response = client.ok().await?;
+        assert_eq!(response, "OK");
+        mock.assert();
+
+        Ok(())
+    }
+
     #[tokio::test]
     async fn ok_should_succeed() -> anyhow::Result<()> {
         let server = MockServer::start();
@@ -1826,7 +1856,7 @@ mod authenticated {
                 .header(POLY_ADDRESS, client.address().to_string().to_lowercase())
                 .header(POLY_API_KEY, API_KEY)
                 .header(POLY_PASSPHRASE, PASSPHRASE)
-                .json_body(json!({ "orderId": "1" }));
+                .json_body(json!({ "orderID": "1" }));
             then.status(StatusCode::OK).json_body(json!({
                     "canceled": [],
                     "notCanceled": {
@@ -1862,7 +1892,7 @@ mod authenticated {
                 .header(POLY_ADDRESS, client.address().to_string().to_lowercase())
                 .header(POLY_API_KEY, API_KEY)
                 .header(POLY_PASSPHRASE, PASSPHRASE)
-                .json_body(json!({ "orderId": "1" }));
+                .json_body(json!({ "orderID": "1" }));
             then.status(StatusCode::OK).json_body(json!({
                     "canceled": [],
                     "not_canceled": {