diff --git a/openai-client/build.gradle.kts b/openai-client/build.gradle.kts
index 48a3321e..feedfc01 100644
--- a/openai-client/build.gradle.kts
+++ b/openai-client/build.gradle.kts
@@ -48,6 +48,7 @@ kotlin {
                 implementation(kotlin("test-common"))
                 implementation(kotlin("test-annotations-common"))
                 implementation(libs.coroutines.test)
+                implementation(libs.ktor.client.mock)
             }
         }
         val jvmMain by getting
diff --git a/openai-client/src/commonMain/kotlin/com.aallam.openai.client/internal/HttpClient.kt b/openai-client/src/commonMain/kotlin/com.aallam.openai.client/internal/HttpClient.kt
index 135d3e64..ab1a106a 100644
--- a/openai-client/src/commonMain/kotlin/com.aallam.openai.client/internal/HttpClient.kt
+++ b/openai-client/src/commonMain/kotlin/com.aallam.openai.client/internal/HttpClient.kt
@@ -48,7 +48,11 @@ internal fun createHttpClient(config: OpenAIConfig): HttpClient {
         install(Auth) {
             bearer {
                 loadTokens {
-                    BearerTokens(accessToken = config.token, refreshToken = "")
+                    BearerTokens(accessToken = config.token, refreshToken = null)
+                }
+                // In the event of a 401, do NOT clear the token; just return the old token - OpenAI tokens do not have a refresh mechanism
+                refreshTokens {
+                    oldTokens
                 }
             }
         }
diff --git a/openai-client/src/commonTest/kotlin/com/aallam/openai/client/misc/TestHttpClientAuth.kt b/openai-client/src/commonTest/kotlin/com/aallam/openai/client/misc/TestHttpClientAuth.kt
new file mode 100644
index 00000000..6f93a6be
--- /dev/null
+++ b/openai-client/src/commonTest/kotlin/com/aallam/openai/client/misc/TestHttpClientAuth.kt
@@ -0,0 +1,86 @@
+package com.aallam.openai.client.misc
+
+import com.aallam.openai.client.OpenAIConfig
+import com.aallam.openai.client.internal.createHttpClient
+import io.ktor.client.engine.mock.*
+import io.ktor.client.request.*
+import io.ktor.http.*
+import kotlinx.coroutines.test.runTest
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNotNull
+
+/**
+ * Tests for HttpClient authentication behavior, specifically token handling
+ * when receiving 401 responses.
+ */
+class TestHttpClientAuth {
+
+    /**
+     * Verifies that the authentication token is NOT cleared when a 401 response
+     * is received from the API. This test ensures that the refreshTokens callback
+     * returns the old tokens instead of null (which would clear the token).
+     *
+     * To verify the test is working correctly:
+     * 1. Run the test - it should pass
+     * 2. Comment out the refreshTokens block in HttpClient.kt
+     * 3. Run the test again - it should fail
+     */
+    @Test
+    fun testTokenNotClearedOn401() = runTest {
+        val testToken = "test-token-12345"
+        var requestCount = 0
+        val capturedAuthHeaders = mutableListOf<String?>()
+
+        // Create a mock engine that simulates:
+        // 1. First request: Returns 401 (triggers token refresh)
+        // 2. Second request: Should still have the token (not cleared)
+        val mockEngine = MockEngine { request ->
+            requestCount++
+            val authHeader = request.headers[HttpHeaders.Authorization]
+            capturedAuthHeaders.add(authHeader)
+
+            when (requestCount) {
+                1 -> {
+                    // First request: return 401 to trigger refresh
+                    respond(
+                        content = """{"error": {"message": "Invalid token", "type": "invalid_request_error"}}""",
+                        status = HttpStatusCode.Unauthorized,
+                        headers = headersOf(HttpHeaders.ContentType, "application/json")
+                    )
+                }
+                2 -> {
+                    // Second request: should succeed with same token
+                    respond(
+                        content = """{"data": []}""",
+                        status = HttpStatusCode.OK,
+                        headers = headersOf(HttpHeaders.ContentType, "application/json")
+                    )
+                }
+                else -> error("Unexpected request count: $requestCount")
+            }
+        }
+
+        val config = OpenAIConfig(token = testToken, engine = mockEngine)
+        val httpClient = createHttpClient(config)
+
+        try {
+            // Make a request that will trigger 401 and then retry
+            httpClient.get("/test")
+
+            // Verify we made 2 requests (initial + retry after 401)
+            assertEquals(2, requestCount, "Should have made 2 requests (initial + retry)")
+
+            // Verify first request had the token
+            assertNotNull(capturedAuthHeaders[0], "First request should have Authorization header")
+            assertEquals("Bearer $testToken", capturedAuthHeaders[0])
+
+            // Verify second request STILL has the token (not cleared)
+            assertNotNull(capturedAuthHeaders[1], "Second request should still have Authorization header")
+            assertEquals("Bearer $testToken", capturedAuthHeaders[1],
+                "Token should NOT be cleared after 401 response")
+        } finally {
+            httpClient.close()
+        }
+    }
+}
\ No newline at end of file