diff --git a/Cargo.toml b/Cargo.toml
index 8ecfc4c..ffb9a1c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -40,3 +40,6 @@ features = ["connect"]
 [dependencies.futures-util]
 version = "0.3.31"
 features = ["sink", "std"]
+
+[dependencies.url]
+version = "2.5.4"
diff --git a/src/v1/api.rs b/src/v1/api.rs
index c53f989..458dc34 100644
--- a/src/v1/api.rs
+++ b/src/v1/api.rs
@@ -43,6 +43,7 @@ use reqwest::multipart::{Form, Part};
 use reqwest::{Client, Method, Response};
 use serde::Serialize;
 use serde_json::Value;
+use url::Url;
 
 use std::error::Error;
 use std::fs::{create_dir_all, File};
@@ -62,9 +63,10 @@ pub struct OpenAIClientBuilder {
     headers: Option<HeaderMap>,
 }
 
+#[derive(Debug)]
 pub struct OpenAIClient {
     api_endpoint: String,
-    api_key: String,
+    api_key: Option<String>,
     organization: Option<String>,
     proxy: Option<String>,
     timeout: Option<u64>,
@@ -111,14 +113,13 @@ impl OpenAIClientBuilder {
     }
 
     pub fn build(self) -> Result<OpenAIClient, Box<dyn Error>> {
-        let api_key = self.api_key.ok_or("API key is required")?;
         let api_endpoint = self.api_endpoint.unwrap_or_else(|| {
             std::env::var("OPENAI_API_BASE").unwrap_or_else(|_| API_URL_V1.to_owned())
         });
 
         Ok(OpenAIClient {
             api_endpoint,
-            api_key,
+            api_key: self.api_key,
             organization: self.organization,
             proxy: self.proxy,
             timeout: self.timeout,
@@ -133,7 +134,10 @@ impl OpenAIClient {
     }
 
     async fn build_request(&self, method: Method, path: &str) -> reqwest::RequestBuilder {
-        let url = format!("{}/{}", self.api_endpoint, path);
+        let url = self
+            .build_url_with_preserved_query(path)
+            .unwrap_or_else(|_| format!("{}/{}", self.api_endpoint, path));
+
         let client = Client::builder();
 
         #[cfg(feature = "rustls")]
@@ -153,9 +157,11 @@ impl OpenAIClient {
 
         let client = client.build().unwrap();
 
-        let mut request = client
-            .request(method, url)
-            .header("Authorization", format!("Bearer {}", self.api_key));
+        let mut request = client.request(method, url);
+
+        if let Some(api_key) = &self.api_key {
+            request = request.header("Authorization", format!("Bearer {}", api_key));
+        }
 
         if let Some(organization) = &self.organization {
             request = request.header("openai-organization", organization);
@@ -775,7 +781,22 @@ impl OpenAIClient {
         let url = Self::query_params(limit, None, after, None, "batches".to_string());
         self.get(&url).await
     }
+    fn build_url_with_preserved_query(&self, path: &str) -> Result<String, url::ParseError> {
+        let (base, query_opt) = match self.api_endpoint.split_once('?') {
+            Some((b, q)) => (b.trim_end_matches('/'), Some(q)),
+            None => (self.api_endpoint.trim_end_matches('/'), None),
+        };
 
+        let full_path = format!("{}/{}", base, path.trim_start_matches('/'));
+        let mut url = Url::parse(&full_path)?;
+
+        if let Some(query) = query_opt {
+            for (k, v) in url::form_urlencoded::parse(query.as_bytes()) {
+                url.query_pairs_mut().append_pair(&k, &v);
+            }
+        }
+        Ok(url.to_string())
+    }
     fn query_params(
         limit: Option<i64>,
         order: Option<String>,