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How Kimi K3.1 Pro stacks up against Claude Opus 5.5 and GPT-6 Astra

Updated 6:14 PM ET · 5:15 PM ETConfirmed

Technology Desk

In Short: Anthropic released Claude Opus 5.5, its new flagship model, priced at $4 per million input tokens and $20 per million output tokens, a 20% reduction from its previous model.

Anthropic launched Claude Opus 5.5, its new flagship general-release model, on September 22, 2026. The model is priced at $4 per million input tokens and $20 per million output tokens, a 20% reduction from its predecessor, Opus 5.

According to Anthropic, Claude Opus 5.5 performs at the same level as Claude Fable 5.1 on most tasks and costs about 40% less to run than Opus 5.

CEO Dario Amodei emphasized the importance of 'pacing the frontier,' suggesting that progress should be slowed to ensure safety practices stay ahead of capabilities.

On Anthropic’s own benchmark table, Claude Opus 5.5 leads GPT-6 Astra in agentic coding, knowledge work, and multidisciplinary reasoning.

An August preprint introducing BenchBench-Protocol, a test of 149 modifications scientists made to published wet-lab protocols, found Kimi K3 and GPT-5.6 Sol statistically indistinguishable on single attempts; over 10 attempts, Kimi K3 scored higher.

On CursorBench 4.0, which recreates real coding sessions from the Cursor editor, Sonnet 5.5 scores 55.5 percent versus 34.1 percent, landing just two points below Opus 5.5 (57.8 percent).

Claude Haiku 5.5, launched on Tuesday, is positioned as the model of choice for high-volume, cost-sensitive tasks. It scores 72.4% on OSWorld 2.1, a test of how well AI agents complete real computer tasks, compared to 15.7% for Haiku 4.5 and 48.9% for OpenAI’s GPT-6 Luna.

According to Artificial Analysis’s Intelligence Index, Claude Opus 5.5 sits at 58, Claude Sonnet 5.5 at 56, and both GPT-6 Astra and Gemini 4 Argon land at 53.

On Terminal-Bench 4.0, Kimi K3.1 Pro scores 65.7%, Opus 5.5 scores 66.4%, and Astra scores 58.2%.

Anthropic reported a $183 billion valuation in September following its latest funding round, largely due to Claude’s popularity among enterprise customers.

Muse Wonder ranks sixth on Artificial Analysis's benchmark at 77.44, behind GPT-5.6 Sol and Claude Opus 4.8, even as Meta charges up to $100 a month for its most capable tier.

According to Anthropic, at these levels of capability, benchmark margins have become less reliable guides to real-world differences. In their own use, the gap between Opus 5.5 and Claude Fable 5.1 is narrower than these scores suggest.

What this adds

Background

What's confirmed

• Anthropic launched Claude Opus 5.5, its new flagship general-release model, on September 22, 2026. The model is priced at $4 per million input tokens and $20 per million output tokens, a 20% reduction from its predecessor, Opus 5.
• According to Anthropic, Claude Opus 5.5 performs at the same level as Claude Fable 5.1 on most tasks and costs about 40% less to run than Opus 5.
• CEO Dario Amodei emphasized the importance of 'pacing the frontier,' suggesting that progress should be slowed to ensure safety practices stay ahead of capabilities.
• On Anthropic’s own benchmark table, Claude Opus 5.5 leads GPT-6 Astra in agentic coding, knowledge work, and multidisciplinary reasoning.
• An August preprint introducing BenchBench-Protocol, a test of 149 modifications scientists made to published wet-lab protocols, found Kimi K3 and GPT-5.6 Sol statistically indistinguishable on single attempts; over 10 attempts, Kimi K3 scored higher.
• On CursorBench 4.0, which recreates real coding sessions from the Cursor editor, Sonnet 5.5 scores 55.5 percent versus 34.1 percent, landing just two points below Opus 5.5 (57.8 percent).
• Claude Haiku 5.5, launched on Tuesday, is positioned as the model of choice for high-volume, cost-sensitive tasks. It scores 72.4% on OSWorld 2.1, a test of how well AI agents complete real computer tasks, compared to 15.7% for Haiku 4.5 and 48.9% for OpenAI’s GPT-6 Luna.
• According to Artificial Analysis’s Intelligence Index, Claude Opus 5.5 sits at 58, Claude Sonnet 5.5 at 56, and both GPT-6 Astra and Gemini 4 Argon land at 53.
• On Terminal-Bench 4.0, Kimi K3.1 Pro scores 65.7%, Opus 5.5 scores 66.4%, and Astra scores 58.2%.
• Anthropic reported a $183 billion valuation in September following its latest funding round, largely due to Claude’s popularity among enterprise customers.
• Muse Wonder ranks sixth on Artificial Analysis's benchmark at 77.44, behind GPT-5.6 Sol and Claude Opus 4.8, even as Meta charges up to $100 a month for its most capable tier.
• According to Anthropic, at these levels of capability, benchmark margins have become less reliable guides to real-world differences. In their own use, the gap between Opus 5.5 and Claude Fable 5.1 is narrower than these scores suggest.

What's still developing

• That is a stronger raw score than the comparison would predict for a “cheaper” model, and it is one reason Sonnet 5.5 shows up ahead of Opus 5.5 on BenchLM’s October 2026 coding leaderboard, where Sonnet 5.5 scored 84.2 against Opus 5.5’s 82.6, even though BenchLM still lists Opus 5.5 first in its overall coding ranking once other weighting factors are folded in.
• ⚠️ Note: the official model card benchmarks against Opus 4.6 Max, GPT-5.4 xHigh, and Gemini 3.1 Pro High — not Opus 4.7 or GPT-5.5.
• After submitting, check your inbox for "Confirm your subscription to The Kingy Brief" and open its confirmation link.
• DeepSeek V4 is not the “1T param, Engram memory” model rumored earlier — it’s a 1.6T MoE with hybrid sparse attention that: AI changes, original tests and one practical thing to try.
• It generates output more than 30 percent faster, costs up to 30 percent less per task, and nearly matches Opus 5.5 on several benchmarks.
• It approaches the benchmark numbers achieved by the considerably more expensive Sonnet 5.5 and beats the recently released GPT-6 Luna across all benchmarks shared by Anthropic.
• Meanwhile, developers can get started with Claude-Haiku-5.5 on the Claude Platform.
• Muse’s spiral tells you something different: it saw valid words and claimed them, with no apparent model of what “valid” meant given the scoring rules.
• Kimi K2.6, an open-weights model from Chinese startup Moonshot AI, won the challenge outright: 22 match points, 7-1-0.
• The company also wrote that the model “scored higher than any human candidate ever” on the “notoriously difficult” exam given to prospective engineering employees.

Sources

• Kingy AIlink
• R&D Worldlink
• Startupfortunelink
• Shatteredlink
• News9Livelink
• Kingylink
• The-Decoderlink
• Androidauthoritylink
• Thetechportallink
• The Indian Expresslink
• Tech-Insiderlink
• Therundownlink
• Thinkpollink
• Zdnetlink
• WarpBeat — background on Kimi K3.1 Pro Closes In on Claude Opus 5.5 in AI Benchmarking link
• WarpBeat — background on How Kimi K3.1 Pro stacks up against Claude Opus 5.5 and GPT-6 Astra link
• Code Scrapper — video link