Claude Mythos 5.1 vs Step-3.5-Flash
Claude Mythos 5.1 leads the LLM Stats Score 45.1 to 37.3. Step-3.5-Flash is 114.3x cheaper per token.
Anthropic · StepFun · Updated for 2026
Which is better?
Claude Mythos 5.1 leads the overall LLM Stats Score 45.1 to 37.3, ranking #31 overall.
On price, Step-3.5-Flash is roughly 114.3x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.
Claude Mythos 5.1 also accepts a larger context window (1,000,000 input tokens), making it the stronger choice for long documents and large codebases.
Based on current LLM Stats indexes, shared benchmarks, pricing, and model metadata for 2026.
Choose Claude Mythos 5.1
- overall performance matters — it scores 45.1 and ranks #31 on LLM Stats
- your work emphasizes reasoning and coding — it leads those capability indexes
- you process long inputs — it offers a 1,000,000 token context window
- you want the most recent training data — it shipped Sep 2026
Choose Step-3.5-Flash
- cost matters — it's about 114.3x cheaper per token
- you need open weights you can self-host or fine-tune
At a glance
The differences that matter most.
Individual benchmarks
1 reported for Claude Mythos 5.1 · 7 for Step-3.5-Flash
Claude Mythos 5.1 and Step-3.5-Flashdon't have any common benchmark datasets to compare. They may have been evaluated on different testing suites.
Human preference
Blind head-to-head votes and playground preference scores
Pricing Analysis
Price comparison per million tokens
For input processing, Claude Mythos 5.1 ($10.00/1M tokens) is 100.0x more expensive than Step-3.5-Flash ($0.10/1M tokens).
For output processing, Claude Mythos 5.1 ($50.00/1M tokens) is 125.0x more expensive than Step-3.5-Flash ($0.40/1M tokens).
In conclusion, Claude Mythos 5.1 is more expensive than Step-3.5-Flash.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
Claude Mythos 5.1 accepts 1,000,000 input tokens compared to Step-3.5-Flash's 65,536 tokens. Claude Mythos 5.1 can generate longer responses up to 128,000 tokens, while Step-3.5-Flash is limited to 8,192 tokens.
Input capabilities
Documented input modalities across available providers
Claude Mythos 5.1 supports multimodal inputs, whereas Step-3.5-Flash does not.
Claude Mythos 5.1 can handle both text and other forms of data like images, making it suitable for multimodal applications.
Claude Mythos 5.1
Step-3.5-Flash
License
Usage and distribution terms
Claude Mythos 5.1 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.
Proprietary
Closed source
Apache 2.0
Open weights
Release Timeline
When each model was launched
Claude Mythos 5.1 was released on 2026-09-01, while Step-3.5-Flash was released on 2026-02-02.
Claude Mythos 5.1 is 7 months newer than Step-3.5-Flash.
Sep 1, 2026
1 weeks ago
7mo newerFeb 2, 2026
7 months ago
Knowledge Cutoff
When training data ends
Neither model specifies a knowledge cutoff date.
Unable to compare the recency of their training data.
Provider Availability
Claude Mythos 5.1 is available from Anthropic. Step-3.5-Flash is available from StepFun.
Claude Mythos 5.1
Step-3.5-Flash
Outputs Comparison
Judge for yourself.
Run your own prompts against Claude Mythos 5.1 and Step-3.5-Flash side-by-side, then vote on the output you prefer.
FAQ
Common questions about Claude Mythos 5.1 vs Step-3.5-Flash.