support chat completions json_object with tool call

for anthropic and openai-format models that do not natively
support structured output.

Author: sachinpad

packages/proxy/src/proxy.ts

@@ -1713,6 +1713,7 @@ async function fetchOpenAI(
         delete bodyData.response_format;
         break;
       case "json_schema":
+      case "json_object":
         if (
           bodyData.model.startsWith("gpt") ||
           bodyData.model.startsWith("o1") ||
@@ -1734,8 +1735,20 @@ async function fetchOpenAI(
             function: {
               name: "json",
               description: "Output the result in JSON format",
-              parameters: responseFormatParsed.data.json_schema.schema,
-              strict: responseFormatParsed.data.json_schema.strict,
+              parameters:
+                responseFormatParsed.data.type === "json_schema"
+                  ? responseFormatParsed.data.json_schema.schema
+                  : {
+                      type: "object",
+                      description:
+                        "A flexible schema that accepts any JSON object.",
+                      properties: {},
+                      additionalProperties: true,
+                    },
+              strict:
+                responseFormatParsed.data.type === "json_schema"
+                  ? responseFormatParsed.data.json_schema.strict
+                  : false,
             },
           },
         ];
@@ -1745,6 +1758,11 @@ async function fetchOpenAI(
     }
   }
 
+  console.log("fetching openai:", {
+    fullURL: fullURL.toString(),
+    headers,
+    body: JSON.stringify(bodyData),
+  });
   const proxyResponse = await fetch(
     fullURL.toString(),
     method === "POST"
@@ -2113,7 +2131,10 @@ async function fetchAnthropicChatCompletions({
 
   let isStructuredOutput = false;
   const parsed = responseFormatSchema.safeParse(oaiParams.response_format);
-  if (parsed.success && parsed.data.type === "json_schema") {
+  if (
+    parsed.success &&
+    (parsed.data.type === "json_schema" || parsed.data.type === "json_object")
+  ) {
     isStructuredOutput = true;
     if (params.tools || params.tool_choice) {
       throw new ProxyBadRequestError(
@@ -2124,7 +2145,15 @@ async function fetchAnthropicChatCompletions({
       {
         name: "json",
         description: "Output the result in JSON format",
-        input_schema: parsed.data.json_schema.schema,
+        input_schema:
+          parsed.data.type === "json_schema"
+            ? parsed.data.json_schema.schema
+            : {
+                type: "object",
+                description: "A flexible schema that accepts any JSON object.",
+                properties: {},
+                additionalProperties: true,
+              },
       },
     ];
     params.tool_choice = { type: "tool", name: "json" };
@@ -2155,6 +2184,15 @@ async function fetchAnthropicChatCompletions({
     delete params.model;
   }
 
+  console.log("fetching anthropic:", {
+    fullURL: fullURL.toString(),
+    headers,
+    body: JSON.stringify({
+      messages,
+      system,
+      ...params,
+    }),
+  });
   const proxyResponse = await fetch(fullURL.toString(), {
     method: "POST",
     headers,