Anthropic · proprietary on Arena · first on Arena 3 October 2025

claude-sonnet-4-5-20250929-thinking-32k

4 days in first place

It held first place on Arena in WebDev (4 days).

Embed

Who held first place

<iframe src="https://jesseahawkins.com/frontier/embed/" title="Frontier: who held first place on each Arena leaderboard, and for how long" width="100%" height="560" style="border:0;max-width:100%" loading="lazy"></iframe>

Credits LMArena.

The open-weights catch-up

<iframe src="https://jesseahawkins.com/frontier/embed/catch-up/" title="Frontier: the days until open weights matched each closed leader" width="100%" height="900" style="border:0;max-width:100%" loading="lazy"></iframe>

Credits LMArena.

The saturation clock

<iframe src="https://jesseahawkins.com/frontier/embed/clock/" title="Frontier: the days from each benchmark’s release to a model at 90%" width="100%" height="640" style="border:0;max-width:100%" loading="lazy"></iframe>

Credits Epoch AI.

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Cite

This page

Jesse Hawkins, “claude-sonnet-4-5-20250929-thinking-32k · Frontier”, jesseahawkins.com, data retrieved 30 Oct 2026. https://jesseahawkins.com/frontier/claude-sonnet-4-5-20250929-thinking-32k/. Data: LMArena, Arena leaderboard dataset, revision 4491b06, CC BY 4.0; Epoch AI, Capabilities & benchmarking, CC BY 4.0.

BibTeX

@misc{hawkins2026frontierclaudesonnet4520250929thinking32k,
  author = {Hawkins, Jesse},
  title = {{claude-sonnet-4-5-20250929-thinking-32k · Frontier}},
  year = {2026},
  howpublished = {\url{https://jesseahawkins.com/frontier/claude-sonnet-4-5-20250929-thinking-32k/}},
  note = {Data: LMArena, Arena leaderboard dataset, revision 4491b06, CC BY 4.0; Epoch AI, Capabilities \& benchmarking, CC BY 4.0, retrieved 2026-10-30}
}

Arena · LMArena

LMArena, "Arena leaderboard dataset", Hugging Face, revision 4491b06. https://huggingface.co/datasets/lmarena-ai/leaderboard-dataset. CC BY 4.0.

Benchmarks · Epoch AI

Epoch AI, 'Capabilities & benchmarking'. Published online at epoch.ai. Retrieved from 'https://epoch.ai/benchmarks' [online resource]. CC BY 4.0.

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Post on X

Text: best place 4

last on the board 11 August 2026

1st10th

On the board: 3 October 2025 to 11 August 2026
Score: 1433 (1431–1436) on 11 August 2026 · 82,549 votes

WebDev: 4 days in first place

last on the board 11 August 2026

1st10th

On the board: 12 November 2025 to 11 August 2026
Score: 1392 (1384–1400) on 11 August 2026 · 12,803 votes
First place: 12 November 2025 to 16 November 2025 · 4 days
Catch-up: Open weights matched it on 22 December 2025, 40 days after it first took first place: glm-4.7.

Epoch AI: Claude Sonnet 4.5

released 29 September 2025 · API access

Chess Puzzles 10.0%
EBR-bench 2.4%
FrontierMath-2025-02-28-Private 15.2%
FrontierMath-Tier-4-2025-07-01-Private 4.2%
FrontierMath-Tier-4-v2-Private 2.4%
FrontierMath-Tiers-1-3-v2-Private 23.9%
GPQA diamond 82.3%
MATH level 5 97.7%
Mystery Game Puzzles 17.0%
OTIS Mock AIME 2024-2025 77.8%
SWE-Bench verified 71.3%
SimpleQA Verified 30.7%

When each vendor retires it

every model’s dates

Anthropic 30 Nov 2026 claude-sonnet-4-5-20250929 · 61 days’ notice, from the deprecation on 30 Sep 2026
Amazon Bedrock 8 Apr 2027 anthropic.claude-sonnet-4-5-20250929-v1:0 · 182 days’ notice, from the deprecation on 8 Oct 2026

Sources

Arena scores come from people voting between two anonymous answers. First place is the highest score; the top two are often within each other’s margin of error. LMArena, Arena leaderboard dataset, revision 4491b06, retrieved 30 October 2026; Epoch AI, Capabilities & benchmarking, retrieved 30 October 2026. Both CC BY 4.0. Retirement dates: each vendor’s own deprecation page, quoted and kept, listed with the record.