Claude Mythos 5.1 vs Claude Opus 4.5
Claude Mythos 5.1 leads the LLM Stats Score 45.1 to 38.3. Claude Opus 4.5 is 2.0x cheaper per token.
Anthropic · Anthropic · Updated for 2026
Which is better?
Claude Mythos 5.1 leads the overall LLM Stats Score 45.1 to 38.3, ranking #31 overall.
On price, Claude Opus 4.5 is roughly 2.0x 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 Claude Opus 4.5
- cost matters — it's about 2.0x cheaper per token
At a glance
The differences that matter most.
Individual benchmarks
1 reported for Claude Mythos 5.1 · 11 for Claude Opus 4.5
Claude Mythos 5.1 and Claude Opus 4.5don'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 2.0x more expensive than Claude Opus 4.5 ($5.00/1M tokens).
For output processing, Claude Mythos 5.1 ($50.00/1M tokens) is 2.0x more expensive than Claude Opus 4.5 ($25.00/1M tokens).
In conclusion, Claude Mythos 5.1 is more expensive than Claude Opus 4.5.*
* 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 Claude Opus 4.5's 200,000 tokens. Claude Mythos 5.1 can generate longer responses up to 128,000 tokens, while Claude Opus 4.5 is limited to 64,000 tokens.
Input capabilities
Documented input modalities across available providers
Both Claude Mythos 5.1 and Claude Opus 4.5 support multimodal inputs.
They are both capable of processing various types of data, offering versatility in application.
Claude Mythos 5.1
Claude Opus 4.5
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 Mythos 5.1 was released on 2026-09-01, while Claude Opus 4.5 was released on 2025-11-24.
Claude Mythos 5.1 is 9 months newer than Claude Opus 4.5.
Sep 1, 2026
1 weeks ago
9mo newerNov 24, 2025
9 months ago
Knowledge Cutoff
When training data ends
Claude Opus 4.5 has a documented knowledge cutoff of 2025-03-31, while Claude Mythos 5.1'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 Claude Mythos 5.1's cutoff date.
—
Mar 2025
Provider Availability
Claude Mythos 5.1 is available from Anthropic. Claude Opus 4.5 is available from Anthropic.
Claude Mythos 5.1
Claude Opus 4.5
Outputs Comparison
Judge for yourself.
Run your own prompts against Claude Mythos 5.1 and Claude Opus 4.5 side-by-side, then vote on the output you prefer.
FAQ
Common questions about Claude Mythos 5.1 vs Claude Opus 4.5.