Add the Gemini 4 Argon model card and metadata

[MaxGhenis]

This is the card PR for Google's Gemini 4 Argon, following #216 (Meta Muse Wonder's card). Its scores join the published board in the next data release, so this PR changes no published artifact.

Facts (read 2026-10-13)

• Release. Google announced Gemini 4 Argon on 2026-09-30 for Fairwind Program cyber partners only (TechCrunch). It opened to the public on 2026-10-13: the Gemini API changelog lists gemini-4-argon as generally available that day, and Google's launch post puts it on the paid tier of the Gemini API and in the Gemini app for Pro and Ultra subscribers. The board's release date is the public day, 2026-10-13; the partner-only day is excluded, as GPT-6 Astra's is.
• Route. The first-party Gemini API, gemini/gemini-4-argon, like every other Gemini row. GET v1beta/models/gemini-4-argon lists an input limit of 1,048,576 and an output limit of 32,768. The model page lists one stable version and no dated snapshot.
• Price. $2 / $10 per 1M input/output tokens (output includes thinking tokens) and $0.10 cached input. Google's pricing page (last updated 2026-10-13) lists those rates "through November 30, 2026" and $4 / $20 / $0.20 from December 1. The row is priced at the rate in force on its run day, as Gemini 3.7 Flash and 3.8 Flash are at their dated introductory rates.

The card

• Contract: the forced answer tool. The Gemini API accepts a forced function call on this model. The gauntlet, run with no card, passed on the tool contract: 3/3 (442 completion tokens, 5s) and 16/16 whole-scenario (2,619 tokens, 24s), about $0.032 per scenario. The older Gemini rows answer as JSON by the family default; this row does not, as Gemini 3.6, 3.7 and 3.8 Flash do not.

• Reasoning. The harness sends no thinkingConfig (checked on the wire for all 87 harness-probe calls). Google's guide gives a default thinking_level of medium. The model decides call by call whether to think, in every request shape:

  Request shape	One question (10 calls each)	The board's request, 13 frozen households (29 calls each)
  Forced tool (the board's)	6 with thought tokens	20 with reasoning tokens (480 to 2,737)
  tool_choice auto	7	25 (490 to 2,985)
  Mode ANY, no named function	5	not run
  JSON response type	0	22 (161 to 3,014)
  No tools	0	not run

  All 87 harness-probe calls parsed every output. So a forced tool does not switch this model's reasoning off, as it does Claude Opus 5's.

• No sensitivity run: a forced tool does not suppress reasoning. The 13-household probe left it open (20 of 29 against 25 of 29, Fisher exact p = 0.21), so the rule written before the full sample (probes/DECISION-RULE.md) sent it to the 100-household runs. The forced-tool board run returned reasoning tokens on 80 households and a tool_choice auto run on 82 (p = 0.86). By household: 70 reasoned in both runs, 10 only when forced, 12 only under auto, 8 in neither. The criterion was the reasoning rate, never the score. The auto run is not published; it stays in the record as evidence.

• Board runs. A first board run (at d8dd845, 17:19 to 17:30 UTC) answered all 100 households in one request each, 1,984/1,984 parsed, no escalation, $2.77. It recorded a 65,536-token escalation ceiling, the model page's figure (card review round 1, P2, below), and the freeze checks a run's recorded treatment against the registry, so the board row is a second run on the corrected card (18:28 to 18:38 UTC): 100/100 households in one request each, 1,984/1,984 parsed, no escalation, $2.79, reasoning tokens on 85 households. None of its responses replays the first run's. The first run and the auto run stay in the record as the reasoning comparison's evidence.

• Budget and timeout. The thinking-default class's 300s timeout and the Gemini family's 16,384-token starting budget. The slowest probe call took 41s, and the slowest board household 53s in the first run and 47s in the second; the largest household used 6,374 and 4,872 completion tokens. provider_max_completion_tokens is 32,768. Google's pages disagree: the generateContent guide says one non-streaming request returns up to 32,768 tokens, and the Models API's outputTokenLimit is 32,768 (saved: probes/models-get-gemini-4-argon.json), while the model page lists 65,536 as "default synchronous". litellm sends one non-streaming REST request, so the card follows the guide; 32,768 is safe either way and never binds. Requests asking for up to 131,072 returned 200, which shows only that the parameter is accepted.

• Smoke. Two scenarios on the run path completed 2/2 with no missing prediction or explanation for $0.05.

Invariants

The price override's cost reconstruction (_reconstruct_token_cost) has a Hypothesis property test: the cost is uncached input at $2, cached input at $0.10 and output at $10 per 1M; it is never negative; and it lies between the all-cached and the uncached cost of the same call.

Evidence

~/reviews/policybench-gemini-4-argon/: probes/ (the one-question probe and its 50 raw responses, the harness-path probe and its 87 raw responses with the body litellm put on the wire, the output-limit probe, the decision rule and its outcome), onboard/ (the gauntlet report), smoke/ (the run) and board-run/ (the forced and auto runs, the comparison script and its output).

Plan

• Roster entry, price and release date
• Reasoning probes, card, gauntlet and two-scenario smoke
• Board run and the tool_choice auto comparison run; the card's notes record the result (5910f79)
• Independent review (GPT-6.1 Sol): round 1 REQUEST_CHANGES (P2 ceiling 65,536 → 32,768; P3 "does not suppress" wording), fixed in e4b4d05 and d1e7685 with a board re-run; round 2 REQUEST_CHANGES (P2 Google's pages disagree, unsaved Models API record; two P3s), fixed in 0109ea2; round 3 APPROVE at 0109ea2
• CI green, then merge

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated
policybench-site	Ready	Preview	Oct 13, 2026 7:21pm UTC

[MaxGhenis]

Merged at reviewed head 0109ea2 (squash 8ab332d). Gates: all checks pass on that head; mergeable, clean; no changes requested. Independent review (GPT-6.1 Sol): round 1 REQUEST_CHANGES (ceiling, wording) fixed in e4b4d05/d1e7685b with a board re-run; round 2 REQUEST_CHANGES (Google's pages disagree on the limit; unsaved Models API record) fixed in 0109ea2; round 3 APPROVE at 0109ea2. Reviews: ~/reviews/policybench-gemini-4-argon/card-review/. The board run joins the published board in release PR #221.