diff --git a/pipeline_llm/inference.py b/pipeline_llm/inference.py
index 9a44a02..1470738 100644
--- a/pipeline_llm/inference.py
+++ b/pipeline_llm/inference.py
@@ -298,6 +298,23 @@ async def _render_headers(tmpl, ns):
     return out
 
 
+def _join_url(api_base, path):
+    """api_base + path 拼接（2026-09-05 404 教训）：模板 path 若把 base_url
+    已有的路径前缀带上（提取 LLM 给 /api/v1/tasks/...，端点又是 .../api/v1），
+    朴素字符串相加会双前缀 404——重叠段去重后再拼。"""
+    base = (api_base or '').rstrip('/')
+    p = (path or '').strip()
+    if not base:
+        return p
+    if not p.startswith('/'):
+        p = '/' + p
+    from urllib.parse import urlparse
+    bp = urlparse(base).path.rstrip('/')
+    if bp and p.startswith(bp + '/'):
+        p = p[len(bp):]
+    return base + p
+
+
 async def _build_upstream_body(ctx, payload):
     """请求体模板渲染（uapi data 模板同款）。
 
@@ -348,7 +365,7 @@ async def _call_upstream_chat(ctx, payload):
     if path.startswith('http://') or path.startswith('https://'):
         url = path
     else:
-        url = (ctx.get('api_base') or '').rstrip('/') + path
+        url = _join_url(ctx.get('api_base'), path)
     headers = await _render_headers(profile.get('headers', ''), ns)
     body = await _build_upstream_body(ctx, payload)
     timeout = int(_fnum(ctx.get('timeout')) or _TOTAL_TIMEOUT)
@@ -500,7 +517,7 @@ async def _async_query_once(ctx, qprofile, task_id, ns, timeout):
     if path.startswith('http://') or path.startswith('https://'):
         url = path
     else:
-        url = (ctx.get('api_base') or '').rstrip('/') + path
+        url = _join_url(ctx.get('api_base'), path)
     headers = await _render_headers(qprofile.get('headers', ''), ns)
     method = (qprofile.get('method') or 'GET').upper()
     status, data = await _http_request(method, url, headers, None, timeout)
@@ -541,7 +558,7 @@ async def _async_inference(ctx, payload, req_timeout):
     if path.startswith('http://') or path.startswith('https://'):
         url = path
     else:
-        url = (ctx.get('api_base') or '').rstrip('/') + path
+        url = _join_url(ctx.get('api_base'), path)
     headers = await _render_headers(profile.get('headers', ''), ns)
     try:
         status, data = await _http_request('POST', url, headers, body, step_timeout)