diff --git a/changelog.d/fixes/8083-responses-input-items-status.md b/changelog.d/fixes/8083-responses-input-items-status.md
new file mode 100644
index 0000000000..d184d8dbee
--- /dev/null
+++ b/changelog.d/fixes/8083-responses-input-items-status.md
@@ -0,0 +1 @@
+- fix(translator): set `status: "completed"` on translated OpenAI Responses `input` items so strict Responses-compatible upstreams stop rejecting them with 400 MissingParameter input.status (#8083)
diff --git a/open-sse/translator/request/openai-responses/toResponses.ts b/open-sse/translator/request/openai-responses/toResponses.ts
index 859f2d60d7..f91b66f918 100644
--- a/open-sse/translator/request/openai-responses/toResponses.ts
+++ b/open-sse/translator/request/openai-responses/toResponses.ts
@@ -120,6 +120,7 @@ export function openaiToOpenAIResponsesRequest(
         type: "message",
         role: "developer",
         content: buildResponsesTextParts(msg.content),
+        status: "completed",
       });
       continue;
     }
@@ -185,6 +186,7 @@ export function openaiToOpenAIResponsesRequest(
         type: "message",
         role: "user",
         content,
+        status: "completed",
       });
     }
 
@@ -223,6 +225,7 @@ export function openaiToOpenAIResponsesRequest(
           type: "message",
           role: "assistant",
           content: outputContent,
+          status: "completed",
         });
       }
 
@@ -241,6 +244,7 @@ export function openaiToOpenAIResponsesRequest(
             call_id: clampCallId(toString(toolCall.id).trim() || generateToolCallId()),
             name: fnName,
             arguments: toString(fn.arguments, "{}"),
+            status: "completed",
           });
         }
       }
@@ -255,6 +259,7 @@ export function openaiToOpenAIResponsesRequest(
             call_id: clampCallId(`call_${fnName}`),
             name: fnName,
             arguments: toString(fc.arguments, "{}"),
+            status: "completed",
           });
         }
       }
@@ -276,6 +281,7 @@ export function openaiToOpenAIResponsesRequest(
                   return c;
                 })
               : String(msg.content ?? ""),
+        status: "completed",
       });
     }
 
@@ -285,6 +291,7 @@ export function openaiToOpenAIResponsesRequest(
         type: "function_call_output",
         call_id: clampCallId(`call_${toString(msg.name)}`),
         output: typeof msg.content === "string" ? msg.content : String(msg.content ?? ""),
+        status: "completed",
       });
     }
   }
diff --git a/tests/unit/responses-input-item-status-8083.test.ts b/tests/unit/responses-input-item-status-8083.test.ts
new file mode 100644
index 0000000000..ddbedc9500
--- /dev/null
+++ b/tests/unit/responses-input-item-status-8083.test.ts
@@ -0,0 +1,55 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+// Kept in its own file rather than growing the frozen
+// tests/unit/translator-openai-responses-req.test.ts (file-size ratchet).
+const { openaiToOpenAIResponsesRequest } = await import(
+  "../../open-sse/translator/request/openai-responses.ts"
+);
+
+// --- Issue #8083: strict Responses-compatible upstreams reject items whose
+// `type` is set without an accompanying `status`, returning
+// 400 MissingParameter input.status. `status` is optional per OpenAI's own
+// schema, so setting it to "completed" on translated history items (which by
+// construction always represent an already-completed prior turn) is a safe
+// superset fix that also satisfies stricter third-party validators.
+test("Chat -> Responses sets status:completed on every input item (#8083)", () => {
+  const result = openaiToOpenAIResponsesRequest(
+    "gpt-4o",
+    {
+      messages: [
+        { role: "system", content: "Rules" },
+        // Mid-conversation developer turn -> developer-role message item.
+        { role: "developer", content: "Follow up instruction" },
+        { role: "user", content: "Hello" },
+        {
+          role: "assistant",
+          content: "Done",
+          tool_calls: [
+            { id: "call_1", type: "function", function: { name: "read_file", arguments: "{}" } },
+          ],
+        },
+        { role: "tool", tool_call_id: "call_1", content: "ok" },
+        // Deprecated function_call / function role pair.
+        {
+          role: "assistant",
+          function_call: { name: "legacy_fn", arguments: "{}" },
+        },
+        { role: "function", name: "legacy_fn", content: "legacy ok" },
+      ],
+    },
+    false,
+    null
+  ) as Record<string, unknown>;
+
+  const input = result.input as Array<Record<string, unknown>>;
+  assert.ok(input.length > 0, "input array must not be empty");
+  for (const item of input) {
+    assert.equal(
+      item.status,
+      "completed",
+      `input item of type "${item.type}" is missing status:"completed" — strict Responses-compatible ` +
+        `upstreams reject this with 400 MissingParameter input.status (#8083)`
+    );
+  }
+});
diff --git a/tests/unit/translator-openai-responses-req.test.ts b/tests/unit/translator-openai-responses-req.test.ts
index 9618961bcc..b12038606b 100644
--- a/tests/unit/translator-openai-responses-req.test.ts
+++ b/tests/unit/translator-openai-responses-req.test.ts
@@ -360,22 +360,26 @@ test("Chat -> Responses converts messages, tool calls, tool outputs, tools and p
         { type: "input_image", image_url: "https://example.com/cat.png", detail: "high" },
         { type: "input_file", file_data: "abc", filename: "doc.txt" },
       ],
+      status: "completed",
     },
     {
       type: "message",
       role: "assistant",
       content: [{ type: "output_text", text: "Done" }],
+      status: "completed",
     },
     {
       type: "function_call",
       call_id: "call_1",
       name: "read_file",
       arguments: '{"path":"/tmp/a"}',
+      status: "completed",
     },
     {
       type: "function_call_output",
       call_id: "call_1",
       output: [{ type: "input_text", text: "ok" }],
+      status: "completed",
     },
   ]);
   assert.deepEqual((result as any).tools, [
@@ -520,6 +524,7 @@ test("Chat -> Responses converts assistant image_url history parts to output_tex
         { type: "output_text", text: "I inspected the screenshot." },
         { type: "output_text", text: "[Image: https://example.com/scope.png]" },
       ],
+      status: "completed",
     },
   ]);
   assert.equal(JSON.stringify(result).includes('"image_url"'), false);