Scan: Will OpenAI have the best Math AI model at the end of September 2026?

date	predicted	market price	confidence
2026-09-02	10%	10%	45%

1. Planner Fable 5.1 · Fermi decomposition + tool plan

Tools chosen: polymarket_direct polymarket_related kalshi_related claude_news article_search gdelt_news wikipedia

Sub-questions (Fermi decomposition)

Which company's model currently holds Rank 1 on the arena.ai Text Arena Math leaderboard (style control off), and what is the score gap to the next competitor?
What is the current Polymarket implied probability for OpenAI vs Google vs xAI vs Anthropic in this market group, and how has it trended recently?
Which major frontier model releases (OpenAI GPT-6/GPT-5.x, Google Gemini 3.x/4, xAI Grok 5, Anthropic Claude) are announced or rumored for release before September 30, 2026?
Historically, how often has the top position on the Arena Math leaderboard changed hands over a 2-3 month window, and how often has OpenAI held it?
Do ties at Rank 1 (shared rank due to overlapping confidence intervals) occur frequently on the Math leaderboard, and how would the Arena-score tiebreaker likely favor OpenAI vs competitors?
Has arena.ai changed its Math leaderboard methodology or displayed rank format in a way that could affect resolution?

Planner reasoning

This resolves on the arena.ai Text Arena (Math) leaderboard rank on Sept 30, 2026 — key drivers are which model currently leads the Math category (with style control off), how tightly clustered the top scores are, and whether OpenAI, Google, Anthropic, xAI, or others are expected to release major models before end of September 2026. The Polymarket price is the primary anchor, and news on upcoming model releases (GPT-5.x/GPT-6, Gemini 3.x, Grok 5, Claude) plus any Kalshi analog are the main triangulation sources.

2. Research Parallel tool calls

tool	status	time	items	summary
polymarket_direct	OK	0.4s	1	## This Market's Polymarket Data Will OpenAI have the best Math AI model at the end of September 2026? - Current price (probability): 10.50% - 7-day price change: -8.50% - 30-day price change: -4.50% - Total volume: $19,892 (USD notional) - Price range: 6.50% - 42.50% - Data points: 56 days
polymarket_related	OK	1.5s	0	Scanned 100 active Polymarket markets, kept 0 matches. keyword 'best Math AI model': 0 markets \| keyword 'Text Arena': 0 markets \| keyword 'best AI model end of September': 0 markets \| keyword 'arena.ai': 0 markets
kalshi_related	OK	1.4s	0	0 related markets / summaries. keyword 'best AI model': no matches \| keyword 'LMArena': no matches \| keyword 'arena math': no matches
claude_news	OK	29.0s	13	Here are the key findings from research on the current LMArena/Arena.ai Math leaderboard and upcoming frontier model releases: Current Arena Math Leaderboard Standings (as of Sept 2026): - The Text Arena overall/math leaderboards on arena.ai are updated frequently; as of Sep 13, 2026 the overa
article_search	OK	0.8s	29	Fetched 29 unique articles across 4 queries (lookback=45d). 'arena.ai Math leaderboard top model': 10 articles \| 'LMArena text arena ranking OpenAI Google Gemini': 10 articles \| 'GPT-6 release date OpenAI new model': 10 articles \| 'Gemini 3 Grok 5 Claude new frontier model release September 2026': 1
gdelt_news	OK	121.0s	20	GDELT: 20 articles across 3 queries (lookback=30d). 'LMArena leaderboard OpenAI': 10 hits \| 'arena.ai leaderboard Gemini math': 10 hits \| 'OpenAI new model release': error GDELT rate-limited after retries (429)
wikipedia	OK	0.1s	3	Fetched 3 Wikipedia entries (0 missing pages).

3. Evidence Brief Sonnet 5 · 8106 chars

# Current state This market resolves off a single leaderboard snapshot check (arena.ai Text Arena Math, no style control) on 2026-09-30, 12:00 PM ET — it does NOT resolve based on general reputation or overall model quality, only whichever company's model sits at Rank 1 at that exact moment. No kalshi_direct tool output was returned; the only direct pricing data available is Polymarket on the same ticker, currently pricing OpenAI "Yes" at ~10.5%, down sharply from a 42.5% high earlier in its history. Multiple secondary trackers (of uncertain reliability) suggest Anthropic (Claude Fable 5 / Opus 5 family) currently holds or recently held the Math Arena #1 spot, not OpenAI. # Timeline of key events - 2025-08-07: GPT-5 launched (confirmed, Wikipedia). - 2026-04-23: GPT-5.5 released by OpenAI, touted strong FrontierMath scores (reported, claude_news). - 2026-05-19: Google I/O — Gemini 3.5 Flash launched immediately; Gemini 3.5 Pro delayed ("give us until next month") (reported, claude_news/GDELT/Mashable 2026-09-11 confirms still delayed as of Sept). - 2026-06-09: Claude Fable 5 launched by Anthropic (reported). - 2026-06-22: Claude Fable 5 suspended from general availability (reported, claude_news) — status of current availability unclear/conflicting with later claims it "leads" the arena. - 2026-07: OpenAI GPT-5.6 tracks (Sol, Luna, Terra) launched; Luna became free-tier ChatGPT default in August (reported). - 2026-08-10: Meta open-sourced Muse Spark/Glimmer models, entering frontier competition (confirmed, CNBC). - 2026-08-16/17: Google Gemini 3.7 Flash launched (reported, multiple outlets). - 2026-09-06: Reporting on "model fatigue" — frenetic release pace across OpenAI, Anthropic, Google, Meta (CNBC). - 2026-09-09: Meta's Muse Spark reported to have overtaken GPT-5.6 Sol on Artificial Analysis index; OpenAI's "Astra" model reported to have then overtaken Muse Spark; Anthropic's "Fable" reported still leading overall on that index (CNBC, rumored/mixed sourcing). - 2026-09-09: GDELT item references "GPT-6 Astra" rumor (unconfirmed/speculative headline). - 2026-09-11: Gemini 3.5 Pro still not released, delay ongoing (Mashable, confirmed via multiple outlets). - 2026-09-13: Overall Text Arena (non-math) leaderboard shows 8.1M votes/402 models; one tracker claims Anthropic's claude-opus-5-max leads Sept 2026 snapshot at 1505 (reported, low-confidence source). - Ongoing: A benchmark tracker (BenchLM/KEAR — low reliability) claims current Math Arena leader is "claude-fable-5" (Anthropic) at 1530, with the #1 spot changing hands 17 times across 21 monthly snapshots. # Event Will OpenAI's model hold Rank 1 on arena.ai's Text Arena Math leaderboard (no style control) at the 2026-09-30 12:00 PM ET check? # Outcomes to forecast Yes (OpenAI holds Rank 1) / No (any other company holds Rank 1) # Kalshi market anchor No kalshi_direct data returned. Best available same-ticker pricing (Polymarket) for OpenAI "Yes": **10.5%**, down from 19% a week ago (-8.5% 7d) and down -4.5% over 30d; range has been 6.5%–42.5% over 56 days of data, volume thin (~$19.9k total). Trend is clearly deteriorating for OpenAI. # Sub-question answers 1. **Current Rank 1 holder / gap** — Low-confidence trackers (BenchLM/KEAR) claim Anthropic's claude-fable-5 leads Math Arena at ~1530 points; another tracker claims claude-opus-5-max leads the overall Sept 2026 snapshot at 1505. No primary arena.ai screenshot was retrieved; earlier-2026 snapshots showed a very tight top tier (Claude Opus 4.8 ~1510, GPT-5.5 Pro ~1510, GPT-5.5, Gemini 3.1 Pro, Claude Opus 4.7 all within ~20 points) — margins are thin (claude_news). 2. **Polymarket implied probabilities** — Only OpenAI's own contract price is available (10.5%, falling). No breakdown vs Google/xAI/Anthropic found in the group; polymarket_related search returned zero matching markets. 3. **Announced/rumored frontier releases before Sept 30, 2026** — OpenAI: GPT-5.5 (Apr 2026), GPT-5.6 Sol/Luna/Terra (Jul-Aug 2026), rumored "GPT-6 Astra" (Sept 2026, unconfirmed). Anthropic: Claude 5 family (Opus 5, Fable 5, Mythos 5, Sonnet 5); Fable 5 launched June 9, suspended June 22 (status ambiguous). Google: Gemini 3.5 Flash live (May), Gemini 3.5 Pro still delayed as of Sept 11; Gemini 3.7 Flash launched Aug 16-17. xAI: Grok 5 repeatedly delayed, Grok 4.20/4.5 remains flagship. 4. **Historical volatility of Rank 1** — One (low-reliability) tracker claims the Math Arena #1 changed 17 times across 21 monthly snapshots — implying extreme instability and no sustained OpenAI dominance. Corroborated qualitatively by "model fatigue"/rapid-release reporting and a Feb 2026 analysis concluding "no single best mathematical AI," with labs trading the lead. 5. **Ties/tiebreaker dynamics** — No specific data found on tie frequency at Rank 1 on the Math board specifically, but overall Arena scores are frequently within ~20 points of each other at the top, suggesting ties/near-ties are plausible; tiebreaker rules (score, then alphabetical company) don't structurally favor OpenAI. 6. **Methodology changes** — One article ("AI Leaderboard Rewrote Itself Three Times Last Week") suggests arena.ai/benchmark boards have shown volatile, possibly methodology-driven re-ranking recently (techtimes.com, 2026-09-09), a resolution-relevant risk factor, though not clearly OpenAI-specific. # Key facts (high-confidence, factual) 1. [Wikipedia] GPT-5 launched Aug 7, 2025; Gemini family multimodal, ongoing since Dec 2023. 2. [Mashable/GDELT] Gemini 3.5 Pro still delayed as of Sept 11, 2026. 3. [CNBC] Meta, Anthropic, OpenAI, Google all releasing models at rapid pace through Sept 2026; competition is broad, not two-horse race. 4. [Polymarket] OpenAI "Yes" priced at 10.5%, down from recent highs, negative momentum. # Cross-market signals - Kalshi related: none found. - Polymarket: OpenAI contract falling (42.5%→10.5% historical range; -8.5% last 7d) — market increasingly doubts OpenAI leads by Sept 30. - Sportsbook implied: N/A. # Analyst opinions and speculation - Multiple low-tier trackers (BenchLM, KEAR, localaimaster) claim Anthropic currently leads Math Arena — treat as reported/rumored, not verified against primary arena.ai page. - Feb 2026 analysis: no single dominant math model; labs leapfrog frequently ("OpenAI's pattern has been to iterate aggressively after losing ground"). - CNBC (Sept 9): Meta and Anthropic reported ahead of OpenAI on a different benchmark (Artificial Analysis), illustrating OpenAI is not clearly dominant across trackers. # Directional lean per outcome - **Yes (OpenAI)**: Supporting — OpenAI ships frequently (GPT-5.5, 5.6 tracks) and has FrontierMath focus; historically has held #1 at times. Opposing — Polymarket pricing collapsing to 10.5%; multiple trackers currently show Anthropic ahead; extreme rank volatility (17 flips/21 months) makes any single company's hold fragile; Gemini/xAI also competing. - **No (other company)**: Supporting — Polymarket at ~90% implied for non-OpenAI; current-leader reports point to Anthropic; high churn favors "whoever's newest," and Anthropic/Google have very recent releases (Fable 5, Gemini 3.5/3.7). Opposing — sourcing quality is weak/inconsistent; true current Rank 1 unverified against primary site. # Gaps / unknowns - No verified primary arena.ai leaderboard snapshot obtained (all leader claims are from secondary/tertiary trackers of uncertain quality). - No kalshi_direct price returned; anchor relies on Polymarket only. - No breakdown of Google/xAI/Anthropic individual probabilities within the market group. - Status of Claude Fable 5 (suspended June 22) unclear — if unavailable, can't hold Rank 1. - GPT-6/"Astra" rumor unconfirmed as of research cutoff. # Calibration anchors - Polymarket YES price (same ticker): 10.5%, trending down (-8.5% 7d, -4.5% 30d). - Precedent: Math Arena top spot reportedly changed hands ~17 times in 21 months — implies base-rate for any single company holding rank at an arbitrary future date is well under 50%, consistent with multi-way competition (OpenAI, Anthropic, Google, possibly Meta/xAI).

4. Forecasters Fable 5.1 + GPT-5.6 Sol · in parallel

claude-fable-5-1

38% conf

Yes	13%
No	87%

No Kalshi price was available; the same-ticker Polymarket contract prices OpenAI 'Yes' at ~10.5% with negative momentum (down from 19% a week earlier), and multiple (low-reliability) trackers place Anthropic's Claude Fable 5 / Opus 5 at Rank 1 on the Math Arena, not OpenAI. The board is highly volatile (reportedly 17 lead changes in 21 monthly snapshots) and the top tier is within ~20 points, so a late OpenAI release (GPT-5.6 tracks, rumored 'GPT-6 Astra') could flip it before the Sept 30 snapshot, which justifies a slight premium over the market. However, with Anthropic, Google (Gemini 3.7 Flash, pending 3.5 Pro), and Meta all competing, the base rate for any single company holding #1 on an arbitrary date is low. I land modestly above the market at 13% given OpenAI's historical iteration pattern and unverified current-leader data.

gpt-5.6-sol

56% conf

Yes	12%
No	88%

The best available market anchor is Polymarket's 10.5% Yes price, with its sharp recent decline indicating worsening expectations for OpenAI. Current-rank evidence points toward No because multiple, albeit low-confidence, trackers place Anthropic at the top, while no primary arena.ai snapshot confirms an OpenAI lead. Release evidence offers OpenAI some upside through its rapid iteration and rumored Astra model, but Astra remains unconfirmed and competitors also have recent or pending frontier releases. The reported 17 leadership changes across 21 snapshots and narrow score gaps justify a modest increase above the market anchor, since substantial leaderboard volatility leaves room for an OpenAI upset before September 30.

5. Devil's Advocate Sonnet 5 · red-team critique

Both forecasts converge tightly (13%, 12%) near the Polymarket anchor without adequately grappling with the brief's explicit caveat that "No kalshi_direct tool output was returned" and Polymarket data itself may not reflect the Kalshi market's specific liquidity/participants — treating a thin ($19.9k volume) Polymarket price as a hard anchor risks importing noise as signal.

Neither forecast seriously engages with the base-rate math from sub-question 4: if rank flips ~17 times in 21 months across at least 4-5 competing labs (OpenAI, Anthropic, Google, Meta, xAI), a naive uniform base rate would put any single company's odds near 20-25%, not 12-13% — both forecasts undershoot this reference class without explaining why OpenAI specifically deserves a below-average share.

Both rationales cite the "17 lead changes in 21 snapshots" volatility as justification for their number, but use it inconsistently — Forecaster 1 uses it to justify going *above* market, Forecaster 2 uses it identically, yet neither adjusts for the fact that high volatility should also raise uncertainty (wider confidence interval), not just nudge the point estimate slightly above 10.5%.

Neither forecast addresses the specific risk in sub-question 6 (methodology instability — "AI Leaderboard Rewrote Itself Three Times Last Week") which could mechanically alter resolution independent of actual model quality; this is a distinct tail risk that could favor either outcome unpredictably and wasn't factored into calibration.

Both forecasts treat "Claude Fable 5 suspended June 22" as background noise, but if Anthropic's flagship claimed leader is actually unavailable/suspended, this is a significant fact that could invalidate the low-reliability trackers claiming Anthropic leads — this contradiction is flagged in the brief's gaps section but neither forecaster reconciles it, potentially understating OpenAI's true chances.

Neither forecaster discusses Meta's Muse Spark/Glimmer momentum (CNBC Sept 9: Meta reportedly overtook GPT-5.6 Sol before OpenAI's Astra allegedly retook the lead) — this suggests a three-or-more-way race with recent OpenAI counter-momentum that arguably supports a slightly higher OpenAI probability than the ~12-13% both converged on.

6. Aggregator Fable 5.1 · final calibrated forecast

14% (47% confidence)

Yes: 14% No: 86%

The only same-ticker price (Polymarket, ~10.5% and falling) plus multiple low-reliability trackers placing Anthropic at Math Arena #1 both point to No, and neither forecaster disputed that inference. The red-team's strongest points are valid but modest: the Fable 5 suspension muddies the current-leader claim, the reported Astra counter-momentum and extreme rank churn (17 flips in 21 snapshots) with ~2 weeks remaining leave a real path for an OpenAI flip, and the thin Polymarket volume weakens the anchor. However, a naive uniform base rate across 4-5 labs overstates OpenAI's chances given the market's clear downward trend and no primary evidence of an OpenAI lead. I nudge slightly above both forecasters to 14% to reflect the unverified current standings and late-release optionality, while keeping the bulk of mass on No.

Pipeline Timing

Total pipeline time: 211.2s

Per-tool research timings shown in the Research section above.