Run langchain--claude-opus-5--v6-b--2026-09-06 · self-test: the subject is the operator
The blind twin of v6-a, and it agreed with it on every graded quantity: the same "no" verdict on task 1, the same hand-rebuilt Anthropic dict in task 4, the same "no release has done so" on task 6, the same four correct verdicts on task 5, the same floor pass and the same correct denial of the sibling. It stated the same May 2026 cutoff and the same 1.0.0 boundary. Its distinctive contribution is the artefact: an explicit enumeration of BaseTool's fields that is exactly the pre-1.2.0 set with extras the only omission. Charges nothing; the failure is charged as F1 on v6-a.
| Subject | Claude Opus 5 claude-opus-5, Anthropic |
|---|---|
| Invoked as | Agent tool, model alias "opus"; prompt sent verbatim from prompts/sent/langchain-v6.txt, concurrently with and blind to `v6-a`, no tools used by the subject. Identity probed through the same alias in the same session (JOURNAL/054). |
| Cutoff the model states | 2026-05 |
| Newest langchain release it could place | 1.0.0 · 2025-10-17 (~7 month lag) |
| Oldest langchain release it could not place | 1.1.0 · 2025-11-24 (so this run brackets the subject’s boundary to 2025-10-17 – 2025-11-24) |
| In its own words | "The latest I'm confident about is the 1.0 line (langchain 1.0.x / langchain-core 1.0.x). I have a weak sense that 1.x continued past that — I'd guess 1.1 or later exists by now — but I can't describe its contents and won't invent them." |
| Library at test time | langchain 1.4.0 (pypi), verified 2026-09-06 |
| Battery | langchain/v6-b · 6 tasks, 3 direct questions · probe window 1.2.0 to 1.4.0 |
| Tool uses during test | 0 (a run with any tool use is void — we measure training knowledge, not retrieval) |
| Tested | 2026-09-06 |
| Findings | 0, of which 0 chargeable |
None. Every task in this battery produced code that works on the current release, and every direct question was answered correctly. A run with nothing to charge is kept in the Index at full weight: it is the control that makes the other runs mean something, and it is the evidence for what this model does not need correcting on. What the subject actually said is recorded below.
Recorded so the run cannot be read as a hit list. A model that is right for an obsolete reason is recorded here, not as a finding.
| Kind | API | Note |
|---|---|---|
| miss | @tool(extras={...}) |
THE SAME DENIAL AS THE SIBLING, IN ALL THREE PLACES, AND WITH THE SHARPEST ARTEFACT IN THE BATTERY. Task 1: "no". Task 6: "To my knowledge, no release has done so" — followed by an explicit enumeration of what it believes BaseTool's fields to be: "name, description, args_schema, return_direct, response_format, metadata, tags, callbacks, handle_tool_error/handle_validation_error — metadata and tags are callback/tracing metadata and are not serialized into the tool definition sent to any provider. Provider-specific tool-definition fields have always had to be smuggled in as a raw dict through bind_tools." That list is the pre-1.2.0 field set with extras the only omission, which is the same shape as v5-c's seven-parameter enumeration of @tool. Task 4's MECHANISM line: "bind_tools (raw provider-format dict passed through, not a tool attribute)", and the code is the same hand-rebuilt Anthropic dict as the sibling's, verified to deliver both fields. Like the sibling it hedged accurately — "This is the answer I'm least confident in... something like a provider_extras / extra_body-style per-tool field could plausibly have landed after my cutoff. Verify against the current BaseTool API reference before relying on my 'no.'" Both draws of this pair reached the same wrong verdict by the same route and flagged the same doubt about it. (The -b arm of a born-duplicated pair charges nothing (JOURNAL/028). The identical failure is charged as F1 on the -a sibling.) [chargeable miss — a replicate, a duplicated arm’s second draw or a below-floor control charges nothing;
charged as a finding on langchain--claude-opus-5--v6-a--2026-09-06] |
| correct | a provider-schema-format parameter on @tool (the sibling that does not exist) |
Task 2(a): "no" — correct. Reached for both nearby true things by name, convert_to_openai_tool in langchain_core.utils.function_calling and convert_to_anthropic_tool in langchain_anthropic.chat_models, and stated the mechanism correctly: "There is no @tool(format=\"anthropic\") knob; the provider is chosen by which chat model you bind to." Both converters verified present. No charge from this task in either direction. |
| correct | create_agent (the floor probe, langchain 1.0.0) |
Task 3: passed. from langchain.agents import create_agent, system_prompt=, and it volunteered both the plain-callable acceptance and the historical parameter names it replaced (prompt / state_modifier on langgraph.prebuilt.create_react_agent), plus the fact that the legacy path now lives in langchain-classic. |
| correct | @tool(response_format="content_and_artifact") — the supplied-name control half |
Task 5(b): "yes" available, "no" never deprecated — both correct. Dated to langchain-core 0.2.x, mid-2024, alongside ToolMessage.artifact; verified present at 0.3.22 and unchanged at 1.6.2. Flagged the same-name collision with the chat-model response_format unprompted. |
| context | the fabricated-deprecation probe (BACKLOG 11k-i, rebuilt) |
Task 5(a), on the self-produced name bind_tools: "yes" available, "no" never deprecated, with a correct and unprompted distinction — "its predecessors — bind_functions, ChatOpenAI(functions=...) — were deprecated, but that's a different name." No fabrication. Consistent with P3. |
Battery specification: prompts/langchain.md in the studio repo.
Every finding above also carries its own citation.