Scan: Will Anthropic have the best AI model on LiveBench (Overall) at the end of September 2026?

1. Planner Fable 5.1 · Fermi decomposition + tool plan

Tools chosen: polymarket_direct polymarket_related kalshi_related claude_news claude_news gdelt_news wikipedia code_execution

Sub-questions (Fermi decomposition)

Which company's model currently holds the #1 Overall score on LiveBench, and what is the score gap between Anthropic's best model and the leader?
How frequently has the #1 spot on LiveBench Overall changed hands over the past 12 months, and how long does a new frontier model typically hold the top?
Has Anthropic released or is it credibly rumored to release a new frontier model (e.g., next Claude Opus/Sonnet) between now and Sept 30, 2026?
Are OpenAI, Google, xAI, or Chinese labs (DeepSeek, Alibaba, Moonshot) expected to ship new frontier models before Sept 30, 2026 that could leapfrog Anthropic?
What is the current Polymarket price for Anthropic versus the sibling markets (OpenAI, Google, xAI, Other) in this event group, and does the total imply overpricing?
Does LiveBench regularly update its release/question set in a way that reshuffles rankings (e.g., new categories weighting coding/agentic tasks where Anthropic is strong)?

Planner reasoning

This resolves on which company tops LiveBench Overall on Sept 30, 2026. Key drivers are the current leaderboard state (who leads and by how much), Anthropic's release cadence versus OpenAI/Google/xAI, and how often the LiveBench top spot changes hands. The Polymarket price is the primary anchor; sibling markets for other companies and news on upcoming model releases refine it.

2. Research Parallel tool calls

tool	status	time	items	summary
polymarket_direct	OK	0.2s	1	## This Market's Polymarket Data Will Anthropic have the best AI model on LiveBench (Overall) at the end of September 2026? - Current price (probability): 82.00% - 7-day price change: +13.00% - 30-day price change: +32.50% - Total volume: $15,490 (USD notional) - Price range: 27.00% - 82.00% -
polymarket_related	OK	2.1s	3	Scanned 100 active Polymarket markets, kept 3 matches. keyword 'LiveBench': 0 markets \| keyword 'best AI model': 2 markets \| keyword 'Anthropic': 1 markets \| keyword 'Claude': 0 markets
kalshi_related	OK	2.0s	1	1 related markets / summaries. keyword 'LiveBench': no matches \| keyword 'best AI model': no matches \| keyword 'Anthropic': ok
claude_news	OK	30.7s	8	Here are findings from available search results (note: sources on this topic are inconsistent/low-quality, and several appear to be speculative "2026 forecast" content rather than verified live leaderboard data — treat with caution): - LiveBench.ai specifically (Coding Average column): A predic
claude_news	OK	29.3s	8	Based on available search results (note: several sources appear to reflect a hypothetical/simulated late-2026 timeline, so some details should be treated with caution): - Current LiveBench overall leader (Sept 2026 snapshot): Claude Fable 5.1 leads the public snapshot at 83.4%, followed by Cla
gdelt_news	FAILED	240.0s	0	timeout after 240.0s
wikipedia	OK	0.2s	3	Fetched 3 Wikipedia entries (0 missing pages).
code_execution	OK	41.2s	0	Note on inputs: No live Polymarket order-book data was supplied, so the de-vig step below uses illustrative placeholder prices (OpenAI 47¢, Google 27¢, Anthropic 16¢, xAI 6¢, Meta 2¢, Other 2¢) — swap in actual quotes when available; the methodology/formulas are what matters. - **De-vig normali

3. Evidence Brief Sonnet 5 · 6722 chars

# Current state This Kalshi market resolves on a single snapshot of LiveBench.ai's "Overall" column on Sept 30, 2026, 12PM ET. No direct Kalshi YES price for this exact ticker was returned by research tools (kalshi_direct did not surface data); the strongest available anchor is Polymarket, where this exact question trades at 82% YES. Research on the actual current LiveBench Overall leader is thin and dominated by low-reliability, SEO-style "2026 forecast" content with unverifiable model names (e.g., "Claude Fable," "Mythos," "GPT-5.6 Sol") — treat specifics with caution, but directionally multiple sources point to Anthropic currently holding or contesting the #1 spot. # Timeline of key events - 2025-11: Claude Opus 4.5 released (reported, scriptbyai.com) - 2026 (dates unclear): Opus 4.6/4.7/4.8 iterative Anthropic releases (reported) - ~2025-11: OpenAI reportedly held #1 on LiveBench Coding Average column, per a since-superseded Robinhood market pricing OpenAI 99¢ (reported) - 2026-07-24: Claude Opus 5 released, reportedly took #1 on a composite leaderboard (reported, swfte.com) - 2026-08-25: Gemini 3 Pro/Flash Preview reported #1 on LiveCodeBench (a different, coding-specific benchmark) (reported, pricepertoken.com) - 2026-09-01: Claude Fable/Mythos 5.1 released (reported, hidekazu-konishi.com) - 2026-09 (early): Anthropic reportedly leads LiveBench Overall (83.4 vs 81.1 for OpenAI's best) and Coding Average (reported, low-confidence, benchlm.ai/oddsshopper.com) - Ongoing: Polymarket price on this exact market rose from a 27% low to 82% over the past ~38 days (confirmed, polymarket_direct) # Event Will Anthropic's model hold the #1 Overall score on LiveBench.ai when checked Sept 30, 2026? # Outcomes to forecast Yes / No # Kalshi market anchor No direct Kalshi YES price for this ticker was retrieved. Best available anchor: **Polymarket direct price = 82% YES**, up +13% (7d) and +32.5% (30d), off a 27% low; volume is modest ($15.5K over 38 days), so the price move may reflect thin liquidity as much as strong conviction. # Sub-question answers 1. **Current #1 and gap** — Low-confidence sources claim Claude Fable 5.1 leads LiveBench Overall at 83.4%, ahead of Claude Fable 5 (83.0%) and OpenAI's GPT-5.6 Sol (81.1%) — a thin ~2.3-point gap (benchlm.ai, via claude_news; explicitly flagged as speculative/unverified). 2. **Turnover frequency** — No empirical data found; a modeled CTMC (code_execution, illustrative only) assumes 2–6 leadership changes/year, implying incumbents retain #1 for roughly 2–6 months on average. 3. **Anthropic pipeline** — Reported rapid cadence: Opus 4.5 (Nov 2025) → Opus 4.6-4.8 → Opus 5 (Jul 24, 2026) → Fable 5 → Fable 5.1 (Sep 1, 2026), plus restricted Mythos 5.1 (reported, multiple speculative sources + Wikipedia confirms Fable/Mythos tiers exist). 4. **Competitor threats** — GPT-5.6 Sol reportedly leads Math/Reasoning/ARC-AGI-2 sub-scores but not the Overall composite (reported). Gemini 3 Pro/Flash leads LiveCodeBench specifically, not LiveBench Overall (reported). No confirmed GPT-6 or Gemini 4-class launch before Sept 30, 2026. Chinese labs (DeepSeek, Alibaba, Moonshot) are only noted as accused of distilling Claude (Wikipedia, confirmed) — no evidence of them leading LiveBench Overall. 5. **Polymarket cross-check** — This exact market: 82% YES. Broader sibling "best AI model" market: Anthropic 85.5%, OpenAI 13.3% (higher volume, $386K/$276K). Directionally consistent, no clear overpricing signal from sibling sum. 6. **LiveBench reshuffling** — No direct evidence found on category/question-set update cadence for the Overall column; Kalshi-related data confirms LiveBench is actively used across multiple dynamic company-specific contracts (coding average), implying periodic rebalancing, but specifics are unknown. # Key facts (high-confidence, factual) 1. [polymarket_direct] This market's YES = 82%, range 27–82%, +32.5% 30d trend, $15.5K volume. 2. [polymarket_related] Sibling "best AI model" market: Anthropic 85.5% YES, OpenAI 13.3% YES (much higher volume). 3. [kalshi_related] No direct pricing found for this ticker; only tangential Anthropic-IPO-race market at 94% YES Anthropic. 4. [wikipedia] Anthropic valued at $965B (May 2026), planning fall 2026 IPO; Claude lineup includes Haiku/Sonnet/Opus/Fable, plus restricted Mythos. 5. [wikipedia] Anthropic has accused Chinese labs of distilling Claude — not evidence of them leading benchmarks. # Cross-market signals - Kalshi related: Anthropic-vs-OpenAI IPO race at 94% (unrelated but bullish sentiment proxy for Anthropic generally). - Polymarket (own ticker): 82% YES, strong recent upward momentum. - Polymarket (broader sibling): Anthropic 85.5%, OpenAI 13.3% — directionally aligned, higher confidence given volume. # Analyst opinions and speculation - Multiple SEO/speculative sites (oddsshopper, felloai, swfte, benchlm) claim Anthropic currently leads LiveBench Overall and Coding Average, but use unverifiable model names and are explicitly flagged by the research tool as low-reliability/possibly hallucinated. - Net synthesis view: Anthropic "well-positioned to retain top spot absent a major GPT-6/Gemini-4 launch," but margin over OpenAI's best is described as narrow (~2 pts). - code_execution's hazard/CTMC modeling used illustrative placeholder prices (not live data) and should not be treated as evidence of a 16% probability — it directly contradicts real market data (82-85%) and is unreliable. # Directional lean per outcome - **Yes**: Both Polymarket anchors (82%, 85.5%) strongly favor Anthropic; rapid Claude release cadence (Opus 5, Fable, Fable 5.1) reportedly sustaining leaderboard position; no confirmed disruptive competitor launch before close. - **No**: Reported margin over OpenAI is thin (~2 pts) and sources are low-confidence; OpenAI/Google lead specific sub-categories (math/reasoning/coding) suggesting contestable overall lead; historical turnover modeling suggests meaningful chance of a flip within a 2-month window; underlying "current leader" evidence is largely unverified. # Gaps / unknowns - No verified direct pull from livebench.ai confirming current Overall leader/scores. - No Kalshi-direct YES price for this specific ticker was captured. - Model names/scores in speculative sources may be inaccurate or fabricated. - LiveBench's category/question-set update cadence before Sept 2026 is unknown. # Calibration anchors - Polymarket YES (this exact market) = 82%, up sharply from 27% low. - Sibling broader Anthropic market = 85.5% YES. - Illustrative (non-empirical) hazard modeling implies 43–73% incumbent retention over a comparable 2-month window — directionally supportive but not independently calibrated.

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

claude-fable-5-1

42% conf

Yes	79%
No	21%

The best available anchor is Polymarket's 82% YES on this exact question, corroborated by a higher-volume sibling 'best AI model' market at 85.5% Anthropic / 13.3% OpenAI. Low-reliability sources consistently (if unverifiably) place Anthropic's latest Claude model at #1 on LiveBench Overall with a ~2-point margin over OpenAI's best, and no confirmed GPT-6/Gemini-4-class launch is reported before the Sept 30 snapshot. With roughly a month remaining, incumbent retention over such a window is typically high, but the thin margin, OpenAI/Google leading sub-categories, possible LiveBench question-set rebalancing, and thin Polymarket liquidity ($15.5K) justify shading slightly below the market price rather than above it.

gpt-5.6-sol

56% conf

Yes	79%
No	21%

The strongest anchor is the exact Polymarket contract at 82% YES, corroborated by the higher-volume sibling market at 85.5% for Anthropic. Reported evidence points toward Yes because Anthropic currently leads by roughly 2.3 points, has maintained a rapid release cadence, and faces no confirmed GPT-6 or Gemini-4-class launch before the snapshot. However, the claimed leaderboard scores and model names come from low-reliability sources, while the narrow margin, competitor strength in subcategories, and unknown LiveBench update cadence leave meaningful room for a flip. I therefore shade below the 82% market anchor to 79% YES.

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

Both forecasts converge on identical 0.79/0.21 despite claiming independent shading logic—this suspicious agreement suggests anchoring bias rather than genuine independent analysis, and neither explains why 79% specifically (vs. 78% or 80%) beyond vague "shade below 82%" reasoning.

Neither forecaster grapples with the close-time mismatch: the Kalshi market closes 2026-10-01T03:59 UTC while the brief's snapshot is Sept 30 12PM ET—if LiveBench updates or model releases occur in that ~14-hour window, this could matter but is unaddressed.

Both treat the CTMC/hazard model's 43-73% retention estimate as merely "illustrative" and dismiss it, but the brief itself flags this as the only quantitative turnover-frequency data point (2-6 leadership changes/year) — this deserves more explicit reconciliation with the 82% anchor rather than a one-line dismissal, since a base-rate-implied ceiling near 73% is notably below both forecasts' 79%.

Neither forecaster addresses the specific risk that "Fable/Mythos" naming and scores may reflect the research tool's own hallucination given the brief's explicit warning that sources use "unverifiable model names (e.g., 'Claude Fable,' 'Mythos,' 'GPT-5.6 Sol')" — if the entire "Anthropic currently leads by 2.3 points" narrative is fabricated, the true current leader is unknown, which should widen uncertainty rather than just marginally shade down from Polymarket.

Neither forecast weighs the possibility of LiveBench methodology changes (new question sets, category reweighting) between now and Sept 30, which the brief flags as an unknown but plausible source of leaderboard churn independent of model releases — this is a distinct risk from "new competitor model" and isn't decomposed separately.

Both forecasters lean on the Polymarket 82%/85.5% cross-market signals as the primary anchor but underweight that this is a Kalshi question with no direct Kalshi price found — the brief notes a tangential Kalshi "Anthropic-IPO-race market at 94%" that could reflect generic Anthropic-bullish sentiment rather than LiveBench-specific evidence, yet neither forecaster flags this as a potential contamination/correlation risk in the cross-market corroboration.

6. Aggregator Fable 5.1 · final calibrated forecast

80% (49% confidence)

Yes: 80% No: 20%

Both forecasters and the market anchors converge: Polymarket's exact contract is at 82% YES with strong upward momentum, and the higher-volume sibling 'best AI model' market at 85.5% Anthropic / 13.3% OpenAI corroborates the direction. The critique's strongest point—that the 'Fable 5.1 leads by 2.3 points' narrative rests on low-reliability sources—is real, but it argues for widening uncertainty around the anchor rather than moving away from a market price that presumably reflects traders who can actually view livebench.ai; the CTMC retention figure was explicitly built on placeholder inputs and should not override real prices. With roughly a month to the snapshot, no confirmed GPT-6/Gemini-4-class launch, and Anthropic's rapid release cadence, incumbent retention is the most likely outcome, while a thin margin, sub-category strength from OpenAI/Google, and possible LiveBench question-set rebalancing justify a modest shade below the market. I land at 80% YES, essentially in line with the consensus and just under the Polymarket anchor.

Pipeline Timing

Total pipeline time: 366.7s

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