Model Comparison

Claude Sonnet 4.5 vs Step-3.5-Flash

Step-3.5-Flash significantly outperforms across most benchmarks. Step-3.5-Flash is 34.3x cheaper per token.

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Performance Benchmarks

Comparative analysis across standard metrics

1 benchmarks

Claude Sonnet 4.5 outperforms in 0 benchmarks, while Step-3.5-Flash is better at 1 benchmark (AIME 2025).

Step-3.5-Flash significantly outperforms across most benchmarks.

Thu Apr 16 2026 • llm-stats.com

Arena Performance

Human preference votes

Pricing Analysis

Price comparison per million tokens

Step-3.5-Flash costs less

For input processing, Claude Sonnet 4.5 ($3.00/1M tokens) is 30.0x more expensive than Step-3.5-Flash ($0.10/1M tokens).

For output processing, Claude Sonnet 4.5 ($15.00/1M tokens) is 37.5x more expensive than Step-3.5-Flash ($0.40/1M tokens).

In conclusion, Claude Sonnet 4.5 is more expensive than Step-3.5-Flash.*

* Using a 3:1 ratio of input to output tokens

Lowest available price from all providers
Thu Apr 16 2026 • llm-stats.com
Anthropic
Claude Sonnet 4.5
Input tokens$3.00
Output tokens$15.00
Best providerAnthropic
StepFun
Step-3.5-Flash
Input tokens$0.10
Output tokens$0.40
Best providerStepFun
Notice missing or incorrect data?Start an Issue→

Context Window

Maximum input and output token capacity

Claude Sonnet 4.5 accepts 200,000 input tokens compared to Step-3.5-Flash's 65,536 tokens. Claude Sonnet 4.5 can generate longer responses up to 64,000 tokens, while Step-3.5-Flash is limited to 8,192 tokens.

Anthropic
Claude Sonnet 4.5
Input200,000 tokens
Output64,000 tokens
StepFun
Step-3.5-Flash
Input65,536 tokens
Output8,192 tokens
Thu Apr 16 2026 • llm-stats.com

Input Capabilities

Supported data types and modalities

Claude Sonnet 4.5 supports multimodal inputs, whereas Step-3.5-Flash does not.

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

Claude Sonnet 4.5

Text
Images
Audio
Video

Step-3.5-Flash

Text
Images
Audio
Video

License

Usage and distribution terms

Claude Sonnet 4.5 is licensed under a proprietary license, while Step-3.5-Flash uses Apache 2.0.

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

Claude Sonnet 4.5

Proprietary

Closed source

Step-3.5-Flash

Apache 2.0

Open weights

Release Timeline

When each model was launched

Claude Sonnet 4.5 was released on 2025-09-29, while Step-3.5-Flash was released on 2026-02-02.

Step-3.5-Flash is 4 months newer than Claude Sonnet 4.5.

Claude Sonnet 4.5

Sep 29, 2025

6 months ago

Step-3.5-Flash

Feb 2, 2026

2 months ago

4mo newer

Knowledge Cutoff

When training data ends

Claude Sonnet 4.5 has a documented knowledge cutoff of 2025-01-31, while Step-3.5-Flash's cutoff date is not specified.

We can confirm Claude Sonnet 4.5's training data extends to 2025-01-31, but cannot make a direct comparison without Step-3.5-Flash's cutoff date.

Claude Sonnet 4.5

Jan 2025

Step-3.5-Flash

—

Provider Availability

Claude Sonnet 4.5 is available from Anthropic. Step-3.5-Flash is available from StepFun.

Claude Sonnet 4.5

anthropic logo
Anthropic
Input Price:Input: $3.00/1MOutput Price:Output: $15.00/1M

Step-3.5-Flash

stepfun logo
StepFun
Input Price:Input: $0.10/1MOutput Price:Output: $0.40/1M
* Prices shown are per million tokens

Outputs Comparison

Notice missing or incorrect data?Start an Issue discussion→

Key Takeaways

Anthropic
Larger context window (200,000 tokens)
Supports multimodal inputs
StepFun
Less expensive input tokens
Less expensive output tokens
Has open weights
Higher AIME 2025 score (97.3% vs 87.0%)

Detailed Comparison

AI Model Comparison Table
Feature
Anthropic
Claude Sonnet 4.5
StepFun
Step-3.5-Flash

FAQ

Common questions about Claude Sonnet 4.5 vs Step-3.5-Flash

Step-3.5-Flash significantly outperforms across most benchmarks. Claude Sonnet 4.5 is made by Anthropic and Step-3.5-Flash is made by StepFun. The best choice depends on your use case — compare their benchmark scores, pricing, and capabilities above.
Claude Sonnet 4.5 scores MMMLU: 89.1%, AIME 2025: 87.0%, TAU-bench Retail: 86.2%, GPQA: 83.4%, MMMUval: 77.8%. Step-3.5-Flash scores AIME 2025: 97.3%, Tau-bench: 88.2%, LiveCodeBench v6: 86.4%, IMO-AnswerBench: 85.4%, SWE-Bench Verified: 74.4%.
Step-3.5-Flash is 30.0x cheaper for input tokens. Claude Sonnet 4.5 costs $3.00/M input and $15.00/M output via anthropic. Step-3.5-Flash costs $0.10/M input and $0.40/M output via stepfun.
Claude Sonnet 4.5 supports 200K tokens and Step-3.5-Flash supports 66K tokens. A larger context window lets you process longer documents, conversations, or codebases in a single request.
Key differences include context window (200K vs 66K), input pricing ($3.00 vs $0.10/M), multimodal support (yes vs no), licensing (Proprietary vs Apache 2.0). See the full comparison above for benchmark-by-benchmark results.
Claude Sonnet 4.5 is developed by Anthropic and Step-3.5-Flash is developed by StepFun.