Claude Mythos
Open timelineCurrent models
Official catalog- Claude Mythos 5.1Restricted access
Claude Mythos 5.1
Mythos 5.1 shares the Fable 5.1 model with different safeguards and restricted access.
- Available only through trusted access programs, initially to selected US organizations in cyberdefense and life sciences.
Access at announcement
Available only through trusted access programs, initially to selected US organizations in cyberdefense and life sciences.
Announcements & evaluations
6 sourcesCurrent leaderboards
Intelligence Index v4.3.2. This is a checked snapshot; older method versions are not directly comparable.
View scoresUpdate date not stated
Update date not stated
| Claude Opus 5.5max with fallback | 58 |
|---|---|
| Claude Sonnet 5.5max with fallback | 56 |
| GPT-6 Astramax | 53 |
| Gemini 4 Argonhigh | 53 |
| GPT-6.1 Solmax | 52 |
| Qwen3.8 Max (0902) | 45 |
| Muse Spark 1.3max | 48 |
| GLM-5.3max | 45 |
| GLM-5.3low | 34 |
| GLM-5.3-Flash | 42 |
Text preference scores. Preliminary entries and uncertainty are retained; compare within this board.
View scoresOct 2, 2026
Data updated ·
| Gemini 4 Argonhigh; preliminary | 1525±9 |
|---|---|
| Claude Opus 5.5high | 1504±9 |
| Claude Fable 5.1max | 1501±6 |
| Gemini 3.8 Flashhigh; preliminary | 1495±5 |
| Muse Spark 1.3max | 1494±6 |
WebDev preference scores. Preliminary entries and uncertainty are retained; compare within this board.
View scoresOct 1, 2026
Data updated ·
| Claude Opus 5.5max | 1815+16/-16 |
|---|---|
| Claude Sonnet 5.5xhigh | 1786+18/-18 |
| GPT-6.1 Solmax | 1758+17/-17 |
| Gemini 4 Argonhigh; preliminary | 1680+13/-13 |
| Qwen3.8 Max (0902)preliminary | 1670+8/-8 |
Agent Arena measures Net Improvement, not task success rate. Scores depend on the listed configuration.
View scoresOct 2, 2026
Data updated ·
| Claude Fable 5.1max | 14.31%±1.90% |
|---|---|
| Claude Opus 5.5high | 13.82%±2.17% |
| Claude Sonnet 5.5max | 12.52%±3.09% |
| GPT-6 Astramax | 12.27%±2.23% |
| GPT-6.1 Solmax | 11.23%±2.76% |
TH1.1 task-completion time horizons. Model-specific chart values were not read; no scores are copied.
Data updated ·