Model comparison
Claude Mythos 5.1 vs Gemini 3.1 Pro
Anthropic against Google, compared on context, price, and verified benchmark results.
Catalog record checked September 5, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below
Anthropic
Claude Mythos 5.1
Frontier
Gemini 3.1 Pro
Frontier
| Specification | Claude Mythos 5.1 | Gemini 3.1 Pro |
|---|---|---|
| Provider | Anthropic | |
| Tier | Frontier | Frontier |
| Context window | Not verifiedUnverified | 1.05M |
| Max output | Not verifiedUnverified | 66K |
| Input / 1M tokens | $10 | Winner: $2 |
| Output / 1M tokens | $50 | Winner: $12 |
| Weights | Closed | Closed |
| Parameters | cyber/bio research variant of Fable 5.1 | Not disclosedUnverified |
| Reasoning levels | adaptive | low, medium, high |
| Modalities | text, image | text, image, video, audio, pdf |
| API model id | claude-mythos-5 | gemini-3.1-pro-preview |
| Released | September 1, 2026 | February 19, 2026 |
| Artificial Analysis Intelligence Index (2026-08-14) | Not verifiedUnverified | 60 |
| SWE-bench Verified (2026-02) | Not verifiedUnverified | 80.6 |
| GPQA Diamond (2026-02) | Not verifiedUnverified | 94.3 |
| Humanity's Last Exam (2026-02) | Not verifiedUnverified | 44.4 |
| Terminal-Bench 2.1 (2026-07) | Not verifiedUnverified | 73.8 |
Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Bold indicates the better figure where one is objectively better. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.
Benchmark receipts
- 2026-08-14: Artificial AnalysisComposite index blending reasoning, knowledge, and coding evals into one 0–100 score. Comparability: directly comparable — AA occasionally rebaselines the index scale between snapshots — a score captured on one date is only comparable to same-snapshot scores (check measuredAt).
- 2026-07: Google DeepMind model evaluation report (vendor, Terminus-2; own Feb report separately reported TB 2.0 = 68.5 — versions preserved)Agentic terminal work: multi-step tasks executed in a sandboxed shell environment. Comparability: comparable with caveat — Scores across Terminal-Bench major versions (v1 vs v2) are NOT comparable; harness configuration (container, time limits) also shifts results.
- 2026-02: Google DeepMind model evaluation report (vendor, no tools; 51.4 with search+code)Real GitHub issue resolution: does the model's patch pass the hidden tests. Comparability: comparable with caveat — Post-audit vendor claims and pre-audit scores sit on different task trust levels; scaffolding (agent harness, compute budget) also dominates results. Never aggregate across scaffolds.
Pricing tiers: Claude Mythos 5.1: Starts at $10/$50 per MTok — priced with Fable 5.1, which shares the same underlying model. API id claude-mythos-5 replaced the deprecated claude-mythos-preview. · Gemini 3.1 Pro: $2/$12 per MTok (≤200K); $4/$18 (>200K). Still 'Preview' as of 2026-08-29; 3.5 Pro not yet released.
Claude Mythos 5.1
Claude Mythos 5.1 is Anthropic's most capable model for cybersecurity and biology research — the Fable 5.1 model with fewer cyber/bio safeguards, restricted to vetted US organisations.
Best for
- Cyber-defence research
- Biology research
- Claude Security workloads
Watch out
Invite-only (vetted US organisations, verification programmes); 30-day data retention applies by default. Same underlying model as Fable 5.1 — most teams should just use Fable.
Gemini 3.1 Pro
Gemini 3.1 Pro is Google's current flagship Pro model with record benchmark scores and a 1M-token context.
Best for
- Very long documents
- Multimodal reasoning
- Frontier knowledge work
Watch out
Still in Preview; 3.5 Pro is 'coming soon' but unreleased as of 2026-08-29.
When the cheaper one wins
Gemini 3.1 Pro is cheaper on output at $12 per million tokens against $50 for Claude Mythos 5.1 — about 4.2×. Use the cheaper tier for classification, extraction, summarisation, and any task where the expensive model’s extra score does not change the accepted output. The expensive one only pays if your hardest task actually fails on the cheap tier. These are standard-tier API rates, excluding batch and cache discounts.
Run the model pickerEvidence confidence: Medium
How strong and complete the evidence behind this comparison is — not a prediction of which model is better.
- Pricing verified on both sides — Input and output rates are verified for both models.
- 2/5 core specs verified on both sides — Not published for at least one side: context window, max output, parameter count.
- No shared named benchmark — No benchmark has been measured on both models.
- Verified within the last 90 days — Newest catalog check was 6 days ago.
- Both models carry source citations — Each side has at least two catalog sources on record.
Source receipts
Each catalog figure was checked against the provider or an independent second source on the date shown.
- Claude Mythos 5.1: Anthropic — Claude Mythos (accessed 2026-09-03)
- Claude Mythos 5.1: Anthropic — model deprecations (claude-mythos-5) (accessed 2026-09-03)
- Gemini 3.1 Pro: Google Cloud — Gemini 3.1 Pro (accessed 2026-08-29)
- Gemini 3.1 Pro: TechCrunch — Gemini 3.1 Pro (accessed 2026-08-29)
Related comparisons
- Claude Fable 5.1 vs Claude Mythos 5.1
- Claude Fable 5.1 vs Gemini 3.1 Pro
- Claude Fable 5 vs Claude Mythos 5.1
- Claude Fable 5 vs Gemini 3.1 Pro
- Claude Haiku 4.5 vs Claude Mythos 5.1
- Claude Mythos 5.1 vs Claude Opus 5
Diving deeper on one model? Claude Mythos 5.1 · Gemini 3.1 Pro
Common questions
Claude Mythos 5.1 vs Gemini 3.1 Pro
Answered from the verified figures on this page rather than general guidance.
Is Claude Mythos 5.1 or Gemini 3.1 Pro cheaper for input?
Gemini 3.1 Pro is cheaper at $2 per million input tokens, against $10 for Claude Mythos 5.1 — roughly 5.0× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Mythos 5.1 has tiered pricing: Starts at $10/$50 per MTok — priced with Fable 5.1, which shares the same underlying model. API id claude-mythos-5 replaced the deprecated claude-mythos-preview. Gemini 3.1 Pro has tiered pricing: $2/$12 per MTok (≤200K); $4/$18 (>200K). Still 'Preview' as of 2026-08-29; 3.5 Pro not yet released.
Is Claude Mythos 5.1 or Gemini 3.1 Pro cheaper for output?
Gemini 3.1 Pro is cheaper at $12 per million output tokens, against $50 for Claude Mythos 5.1 — roughly 4.2× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Mythos 5.1 has tiered pricing: Starts at $10/$50 per MTok — priced with Fable 5.1, which shares the same underlying model. API id claude-mythos-5 replaced the deprecated claude-mythos-preview. Gemini 3.1 Pro has tiered pricing: $2/$12 per MTok (≤200K); $4/$18 (>200K). Still 'Preview' as of 2026-08-29; 3.5 Pro not yet released.
Do Claude Mythos 5.1 and Gemini 3.1 Pro support the same reasoning levels?
Claude Mythos 5.1 exposes adaptive, while Gemini 3.1 Pro exposes low, medium, high.
Should I use Claude Mythos 5.1 or Gemini 3.1 Pro?
Both sit in the frontier tier, so the choice usually comes down to price and context rather than capability. Claude Mythos 5.1 suits cyber-defence research; Gemini 3.1 Pro suits very long documents.
Next step
Choosing between them
The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.
- Input price: Gemini 3.1 Pro costs $2 per 1M tokens versus $10 for Claude Mythos 5.1 — a 5x difference at the headline tier.
Choosing a harness rather than a model — Cursor, Copilot, Claude Code, Windsurf, or Lovable? Compare agentic harnesses · Latest releases.