diff --git a/changelog.d/fixes/6704-unwrap-bare-function-tool.md b/changelog.d/fixes/6704-unwrap-bare-function-tool.md
new file mode 100644
index 0000000000..85b21b7c5b
--- /dev/null
+++ b/changelog.d/fixes/6704-unwrap-bare-function-tool.md
@@ -0,0 +1 @@
+- **fix(sse):** unwrap bare `{function:{…}}` tools so OpenAI-shape clients no longer have tools silently dropped in Claude translation. (thanks @samir-abis)
diff --git a/open-sse/translator/request/openai-to-claude.ts b/open-sse/translator/request/openai-to-claude.ts
index ec75bb5834..ff5dc4b6d5 100644
--- a/open-sse/translator/request/openai-to-claude.ts
+++ b/open-sse/translator/request/openai-to-claude.ts
@@ -363,7 +363,15 @@ export function openaiToClaudeRequest(model, body, stream) {
   if (body.tools && Array.isArray(body.tools)) {
     result.tools = body.tools
       .map((tool) => {
-        const toolData = tool.type === "function" && tool.function ? tool.function : tool;
+        // Function-shaped tools arrive in two flavors from real clients:
+        //   (a) openai-spec: { type: "function", function: { name, ... } }
+        //   (b) bare/loose:  { function: { name, ... } }   (no parent `type`)
+        // Unwrap `tool.function` whenever it is present, regardless of the
+        // parent `type` field — some OpenAI-shape clients omit the wrapper's
+        // `type: "function"` entirely. Previously that bare shape fell
+        // through to `toolData = tool` (the wrapper itself, with no `.name`),
+        // producing an empty `originalName` and silently dropping the tool.
+        const toolData = tool.function ?? tool;
         const originalName = typeof toolData.name === "string" ? toolData.name.trim() : "";
 
         if (!originalName) {
diff --git a/tests/unit/openai-to-claude-bare-tool.test.ts b/tests/unit/openai-to-claude-bare-tool.test.ts
new file mode 100644
index 0000000000..848d0c75e5
--- /dev/null
+++ b/tests/unit/openai-to-claude-bare-tool.test.ts
@@ -0,0 +1,65 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+const { openaiToClaudeRequest } = await import(
+  "../../open-sse/translator/request/openai-to-claude.ts"
+);
+
+// Regression: some OpenAI-shape clients send a tool as a BARE
+// `{ function: { name, description, parameters } }` object, omitting the
+// spec-required `type: "function"` parent wrapper. Before this fix, the
+// tools-mapping in openai-to-claude.ts only unwrapped `tool.function` when
+// `tool.type === "function"` was ALSO true, so a bare-function tool fell
+// through with `toolData === tool` (the wrapper itself, which has no
+// `.name`) — `originalName` came out empty and the tool was silently
+// dropped from the translated request (worse than a 400: the caller has no
+// idea the tool never made it upstream).
+
+test("openaiToClaudeRequest: bare {function:{...}} tool (no parent type) is NOT dropped", () => {
+  const request = {
+    messages: [{ role: "user", content: "hi" }],
+    tools: [
+      {
+        function: {
+          name: "get_weather",
+          description: "Get the current weather",
+          parameters: { type: "object", properties: { city: { type: "string" } } },
+        },
+      },
+    ],
+  };
+
+  const translated = openaiToClaudeRequest("claude-sonnet-4", request, false);
+
+  assert.ok(Array.isArray(translated.tools), "expected translated.tools to be an array");
+  assert.equal(translated.tools.length, 1, "expected the bare-function tool to survive translation");
+
+  const tool = translated.tools[0];
+  assert.match(tool.name, /get_weather$/, "expected the original tool name to be preserved (prefixed)");
+  assert.equal(tool.description, "Get the current weather");
+  assert.deepEqual(tool.input_schema, {
+    type: "object",
+    properties: { city: { type: "string" } },
+  });
+});
+
+test("openaiToClaudeRequest: spec-shape {type:'function', function:{...}} tool still converts (no regression)", () => {
+  const request = {
+    messages: [{ role: "user", content: "hi" }],
+    tools: [
+      {
+        type: "function",
+        function: {
+          name: "get_weather",
+          description: "Get the current weather",
+          parameters: { type: "object", properties: { city: { type: "string" } } },
+        },
+      },
+    ],
+  };
+
+  const translated = openaiToClaudeRequest("claude-sonnet-4", request, false);
+
+  assert.equal(translated.tools.length, 1);
+  assert.match(translated.tools[0].name, /get_weather$/);
+});