diff --git a/public/scripts/custom-request.js b/public/scripts/custom-request.js
index 69c1ab882..888a09745 100644
--- a/public/scripts/custom-request.js
+++ b/public/scripts/custom-request.js
@@ -82,7 +82,6 @@ export class TextCompletionService {
      */
     static createRequestData({ stream = false, prompt, max_tokens, model, api_type, api_server, temperature, min_p, ...props }) {
         const payload = {
-            ...props,
             stream,
             prompt,
             max_tokens,
@@ -92,6 +91,7 @@ export class TextCompletionService {
             api_server: api_server ?? getTextGenServer(api_type),
             temperature,
             min_p,
+            ...props,
         };
 
         // Remove undefined values to avoid API errors
@@ -391,7 +391,6 @@ export class ChatCompletionService {
      */
     static createRequestData({ stream = false, messages, model, chat_completion_source, max_tokens, temperature, custom_url, reverse_proxy, proxy_password, ...props }) {
         const payload = {
-            ...props,
             stream,
             messages,
             model,
@@ -401,6 +400,9 @@ export class ChatCompletionService {
             custom_url,
             reverse_proxy,
             proxy_password,
+            use_makersuite_sysprompt: true,
+            claude_use_sysprompt: true,
+            ...props,
         };
 
         // Remove undefined values to avoid API errors
diff --git a/public/scripts/extensions/shared.js b/public/scripts/extensions/shared.js
index dfd4bc2c2..0568cbb24 100644
--- a/public/scripts/extensions/shared.js
+++ b/public/scripts/extensions/shared.js
@@ -306,9 +306,10 @@ export class ConnectionManagerRequestService {
      * @param {boolean?} [custom.includePreset=true]
      * @param {boolean?} [custom.includeInstruct=true]
      * @param {Partial<InstructSettings>?} [custom.instructSettings] Override instruct settings
+     * @param {Record<string, any>} [overridePayload] - Override payload for the request
      * @returns {Promise<import('../custom-request.js').ExtractedData | (() => AsyncGenerator<import('../custom-request.js').StreamResponse>)>} If not streaming, returns extracted data; if streaming, returns a function that creates an AsyncGenerator
      */
-    static async sendRequest(profileId, prompt, maxTokens, custom = this.defaultSendRequestParams) {
+    static async sendRequest(profileId, prompt, maxTokens, custom = this.defaultSendRequestParams, overridePayload = {}) {
         const { stream, signal, extractData, includePreset, includeInstruct, instructSettings } = { ...this.defaultSendRequestParams, ...custom };
 
         const context = SillyTavern.getContext();
@@ -338,6 +339,7 @@ export class ConnectionManagerRequestService {
                         custom_url: profile['api-url'],
                         reverse_proxy: proxyPreset?.url,
                         proxy_password: proxyPreset?.password,
+                        ...overridePayload,
                     }, {
                         presetName: includePreset ? profile.preset : undefined,
                     }, extractData, signal);
@@ -354,6 +356,7 @@ export class ConnectionManagerRequestService {
                         model: profile.model,
                         api_type: selectedApiMap.type,
                         api_server: profile['api-url'],
+                        ...overridePayload,
                     }, {
                         instructName: includeInstruct ? profile.instruct : undefined,
                         presetName: includePreset ? profile.preset : undefined,