Claude Mythos 5.1 vs Claude Opus 4.8
Claude Mythos 5.1 and Claude Opus 4.8 are closely matched at 45.1 and 51.0 on the LLM Stats Score. Claude Opus 4.8 is 2.0x cheaper per token.
Anthropic · Anthropic · Updated for 2026
Which is better?
Claude Mythos 5.1 and Claude Opus 4.8 are closely matched on the overall LLM Stats Score at 45.1 and 51.0.
In the 1 individual benchmarks reported for both models, Claude Mythos 5.1 wins 1; this is a narrower head-to-head signal than the composite indexes.
On price, Claude Opus 4.8 is roughly 2.0x 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 5.1
- 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
Choose Claude Opus 4.8
- 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 · 27 for Claude Opus 4.8
Claude Mythos 5.1 outperforms in 1 benchmarks (Terminal-Bench 4.0), while Claude Opus 4.8 is better at 0 benchmarks.
Claude Mythos 5.1 significantly outperforms across most benchmarks.
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 4.8 ($5.00/1M tokens).
For output processing, Claude Mythos 5.1 ($50.00/1M tokens) is 2.0x more expensive than Claude Opus 4.8 ($25.00/1M tokens).
In conclusion, Claude Mythos 5.1 is more expensive than Claude Opus 4.8.*
* Using a 3:1 ratio of input to output tokens
Context Window
Maximum input and output token capacity
Both models have the same input context window of 1,000,000 tokens. Both models can generate responses up to 128,000 tokens.
Input capabilities
Documented input modalities across available providers
Both Claude Mythos 5.1 and Claude Opus 4.8 support multimodal inputs.
They are both capable of processing various types of data, offering versatility in application.
Claude Mythos 5.1
Claude Opus 4.8
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 4.8 was released on 2026-05-28.
Claude Mythos 5.1 is 3 months newer than Claude Opus 4.8.
Sep 1, 2026
1 weeks ago
3mo newerMay 28, 2026
3 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. Claude Opus 4.8 is available from Anthropic, DeepInfra, Vertex AI.
Claude Mythos 5.1
Claude Opus 4.8
Outputs Comparison
Judge for yourself.
Run your own prompts against Claude Mythos 5.1 and Claude Opus 4.8 side-by-side, then vote on the output you prefer.
FAQ
Common questions about Claude Mythos 5.1 vs Claude Opus 4.8.