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Claude Opus 4.5 vs K2 Horizon 375B-A23B

Claude Opus 4.5 and K2 Horizon 375B-A23B are closely matched at 37.7 and 38.5 on the LLM Stats Score.

Anthropic · Institute of Foundation Models · Updated for 2026

Which is better?

Claude Opus 4.5 and K2 Horizon 375B-A23B are closely matched on the overall LLM Stats Score at 37.7 and 38.5.

In the 1 individual benchmarks reported for both models, K2 Horizon 375B-A23B wins 1; this is a narrower head-to-head signal than the composite indexes.

Based on current LLM Stats indexes, shared benchmarks, pricing, and model metadata for 2026.

Choose Claude Opus 4.5

  • you want predictable pricing at $5.00/M input and $25.00/M output

Choose K2 Horizon 375B-A23B

  • you value its reported benchmark strengths — it wins 1 of 1 exact shared results
  • you want the most recent training data — it shipped Sep 2026
  • you need open weights you can self-host or fine-tune

At a glance

The differences that matter most.

Claude Opus 4.5
Anthropic
K2 Horizon 375B-A23B
Institute of Foundation Models
Core performance indexes
LLM Stats Score
37.7
#88
38.5
#83
Reasoning
39.5
#73
37.3
#87
Coding
27.7
#80
21.2
#114
Agents
17.5
#99
23.9
#74
Cost, coverage & limits
Benchmark wins
0 of 1
1 of 1
Input price
$5.00 / M
— / M
Output price
$25.00 / M
— / M
Context window
200,000
—

Capability indexes

Additional strengths measured across groups of related public benchmarks

2 shared
Index
Claude Opus 4.5
K2 Horizon 375B-A23B
Math
32.4#66
29.7#89
Tool use
20.8#70
22.3#62
Conservative TrueSkill rating · higher is betterHow scores work

Individual benchmarks

11 reported for Claude Opus 4.5 · 18 for K2 Horizon 375B-A23B

1 shared

Claude Opus 4.5 outperforms in 0 benchmarks, while K2 Horizon 375B-A23B is better at 1 benchmark (GPQA).

K2 Horizon 375B-A23B significantly outperforms across most benchmarks.

Fri Oct 30 2026 • llm-stats.com

Human preference

Blind head-to-head votes and playground preference scores

Context Window

Maximum input and output token capacity

Only Claude Opus 4.5 specifies input context (200,000 tokens). Only Claude Opus 4.5 specifies output context (64,000 tokens).

Anthropic
Claude Opus 4.5
Input200,000 tokens
Output64,000 tokens
Institute of Foundation Models
K2 Horizon 375B-A23B
Input- tokens
Output- tokens
Fri Oct 30 2026 • llm-stats.com

Input capabilities

Documented input modalities across available providers

Claude Opus 4.5 supports multimodal inputs, whereas K2 Horizon 375B-A23B does not.

Claude Opus 4.5 can handle both text and other forms of data like images, making it suitable for multimodal applications.

Claude Opus 4.5

Text
Images
Audio
Video

K2 Horizon 375B-A23B

Text
Images
Audio
Video

License

Usage and distribution terms

Claude Opus 4.5 is licensed under a proprietary license, while K2 Horizon 375B-A23B uses Apache 2.0.

License differences may affect how you can use these models in commercial or open-source projects.

Claude Opus 4.5

Proprietary

Closed source

K2 Horizon 375B-A23B

Apache 2.0

Open weights

Release Timeline

When each model was launched

Claude Opus 4.5 was released on 2025-11-24, while K2 Horizon 375B-A23B was released on 2026-09-03.

K2 Horizon 375B-A23B is 9 months newer than Claude Opus 4.5.

Claude Opus 4.5

Nov 24, 2025

11 months ago

K2 Horizon 375B-A23B

Sep 3, 2026

1 months ago

9mo newer

Knowledge Cutoff

When training data ends

Claude Opus 4.5 has a documented knowledge cutoff of 2025-03-31, while K2 Horizon 375B-A23B's cutoff date is not specified.

We can confirm Claude Opus 4.5's training data extends to 2025-03-31, but cannot make a direct comparison without K2 Horizon 375B-A23B's cutoff date.

Claude Opus 4.5

Mar 2025

K2 Horizon 375B-A23B

—

Outputs Comparison

Notice missing or incorrect data?

Judge for yourself.

Run your own prompts against Claude Opus 4.5 and K2 Horizon 375B-A23B side-by-side, then vote on the output you prefer.

Claude Opus 4.5
✓ Preferred
K2 Horizon 375B-A23B
Open in Playground

FAQ

Common questions about Claude Opus 4.5 vs K2 Horizon 375B-A23B.

Which is better, Claude Opus 4.5 or K2 Horizon 375B-A23B?

Claude Opus 4.5 and K2 Horizon 375B-A23B are closely matched on the LLM Stats Score at 37.7 and 38.5. Claude Opus 4.5 is made by Anthropic and K2 Horizon 375B-A23B is made by Institute of Foundation Models. The best choice depends on your use case — compare their capability indexes, individual benchmarks, pricing, and limits above.

How does Claude Opus 4.5 compare to K2 Horizon 375B-A23B in benchmarks?

Claude Opus 4.5 scores Tau2 Telecom: 98.2%, MMMLU: 90.8%, Tau2 Retail: 88.9%, GPQA: 87.0%, SWE-Bench Verified: 80.9%. K2 Horizon 375B-A23B scores GPQA: 87.3%, AA-LCR: 76.0%, OmniScience (non-hallucination rate): 74.7%, BrowseComp: 72.8%, Terminal-Bench 2.1: 70.2%.

What are the context window sizes for Claude Opus 4.5 and K2 Horizon 375B-A23B?

Claude Opus 4.5 supports 200K tokens and K2 Horizon 375B-A23B supports an unknown number of tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.

What are the main differences between Claude Opus 4.5 and K2 Horizon 375B-A23B?

Key differences include LLM Stats Score (37.7 vs 38.5), multimodal support (yes vs no), licensing (Proprietary vs Apache 2.0). See the full comparison above for benchmark-by-benchmark results.

Who makes Claude Opus 4.5 and K2 Horizon 375B-A23B?

Claude Opus 4.5 is developed by Anthropic and K2 Horizon 375B-A23B is developed by Institute of Foundation Models.

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