Claude Mythos Preview vs Claude Sonnet 5.5
Claude Mythos Preview and Claude Sonnet 5.5 are closely matched at 54.5 and 58.5 on the LLM Stats Score. Claude Sonnet 5.5 is 12.5x cheaper per token.
Anthropic · Anthropic · Updated for 2026
Which is better?
Claude Mythos Preview and Claude Sonnet 5.5 are closely matched on the overall LLM Stats Score at 54.5 and 58.5.
In the 3 individual benchmarks reported for both models, Claude Sonnet 5.5 wins 2; this is a narrower head-to-head signal than the composite indexes.
On price, Claude Sonnet 5.5 is roughly 12.5x cheaper per token on a blended 3:1 input/output basis, which adds up quickly at production volume.
Based on current LLM Stats indexes, shared benchmarks, pricing, and model metadata for 2026.
Choose Claude Mythos Preview
- you want predictable pricing at $25.00/M input and $125.00/M output
Choose Claude Sonnet 5.5
- you value its reported benchmark strengths — it wins 2 of 3 exact shared results
- cost matters — it's about 12.5x cheaper per token
At a glance
The differences that matter most.
Capability indexes
Additional strengths measured across groups of related public benchmarks
Individual benchmarks
16 reported for Claude Mythos Preview · 47 for Claude Sonnet 5.5
Claude Mythos Preview outperforms in 1 benchmarks (SWE-Bench Multimodal), while Claude Sonnet 5.5 is better at 2 benchmarks (SWE-bench Multilingual, SWE-Bench Pro).
Claude Sonnet 5.5 shows notably better performance in the majority of benchmarks.
Human preference
Blind head-to-head votes and playground preference scores
Pricing Analysis
Price comparison per million tokens
For input processing, Claude Mythos Preview ($25.00/1M tokens) is 12.5x more expensive than Claude Sonnet 5.5 ($2.00/1M tokens).
For output processing, Claude Mythos Preview ($125.00/1M tokens) is 12.5x more expensive than Claude Sonnet 5.5 ($10.00/1M tokens).
In conclusion, Claude Mythos Preview is more expensive than Claude Sonnet 5.5.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
Only Claude Sonnet 5.5 specifies input context (1,000,000 tokens). Only Claude Sonnet 5.5 specifies output context (128,000 tokens).
Input capabilities
Documented input modalities across available providers
Both Claude Mythos Preview and Claude Sonnet 5.5 support multimodal inputs.
They are both capable of processing various types of data, offering versatility in application.
Claude Mythos Preview
Claude Sonnet 5.5
License
Usage and distribution terms
Both models are licensed under proprietary licenses.
Both models have usage restrictions defined by their respective organizations.
Proprietary
Closed source
Proprietary
Closed source
Release Timeline
When each model was launched
Claude Sonnet 5.5 was released on 2026-09-28, while Claude Mythos Preview's release date is not specified.
We can confirm Claude Sonnet 5.5's release timeline, but cannot make a direct age comparison without Claude Mythos Preview's release date.
—
Sep 28, 2026
1 weeks ago
Knowledge Cutoff
When training data ends
Claude Sonnet 5.5 has a documented knowledge cutoff of 2026-06-01, while Claude Mythos Preview's cutoff date is not specified.
We can confirm Claude Sonnet 5.5's training data extends to 2026-06-01, but cannot make a direct comparison without Claude Mythos Preview's cutoff date.
—
Jun 2026
Provider Availability
Claude Mythos Preview is available from Anthropic. Claude Sonnet 5.5 is available from Anthropic.
Claude Mythos Preview
Claude Sonnet 5.5
Outputs Comparison
Judge for yourself.
Run your own prompts against Claude Mythos Preview and Claude Sonnet 5.5 side-by-side, then vote on the output you prefer.
FAQ
Common questions about Claude Mythos Preview vs Claude Sonnet 5.5.