Model comparison
Claude Mythos 5.1 vs NVIDIA Nemotron 3 Ultra
Anthropic against NVIDIA, compared on context, price, and verified benchmark results.
Catalog record checked September 3, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below
Anthropic
Claude Mythos 5.1
Frontier
NVIDIA
NVIDIA Nemotron 3 Ultra
Frontier · Open weights
| Specification | Claude Mythos 5.1 | NVIDIA Nemotron 3 Ultra |
|---|---|---|
| Provider | Anthropic | NVIDIA |
| Tier | Frontier | Frontier |
| Context window | Not verifiedUnverified | 1M |
| Max output | Not verifiedUnverified | Not verifiedUnverified |
| Input / 1M tokens | $10 | Winner: $0.50 |
| Output / 1M tokens | $50 | Winner: $2.20 |
| Weights | Closed | Open |
| Parameters | cyber/bio research variant of Fable 5.1 | 550B total / 55B active (MoE) |
| Reasoning levels | adaptive | low, high, max |
| Modalities | text, image | text |
| API model id | claude-mythos-5 | nemotron-3-ultra-550b-a55b |
| Released | September 1, 2026 | June 4, 2026 |
| Artificial Analysis Intelligence Index (2026-08-14) | Not verifiedUnverified | 54 |
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).
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. · NVIDIA Nemotron 3 Ultra: Open weights (weights + data + recipes); $0.50/$2.20 per MTok is the third-party hosted rate (OpenRouter). 550B/55B MoE.
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.
NVIDIA Nemotron 3 Ultra
Nemotron 3 Ultra is NVIDIA's open-weight (550B/55B) frontier MoE with a 1M-token context.
Best for
- Open-weight frontier
- Self-hosting on NVIDIA GPUs
- Reasoning
Watch out
Top US open-weight until Thinking Machines Inkling; verify hosted pricing.
When the cheaper one wins
NVIDIA Nemotron 3 Ultra is cheaper on output at $2.20 per million tokens against $50 for Claude Mythos 5.1 — about 23×. 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.
- 3/5 core specs verified on both sides — Not published for at least one side: context window, max output.
- No shared named benchmark — No benchmark has been measured on both models.
- Verified within the last 90 days — Newest catalog check was 8 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)
- NVIDIA Nemotron 3 Ultra: NVIDIA — Nemotron (accessed 2026-08-29)
- NVIDIA Nemotron 3 Ultra: NVIDIA Nemotron 3 Ultra (accessed 2026-08-29)
Related comparisons
- Claude Fable 5.1 vs Claude Mythos 5.1
- Claude Fable 5.1 vs NVIDIA Nemotron 3 Ultra
- Claude Fable 5 vs Claude Mythos 5.1
- Claude Fable 5 vs NVIDIA Nemotron 3 Ultra
- 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 · NVIDIA Nemotron 3 Ultra
Common questions
Claude Mythos 5.1 vs NVIDIA Nemotron 3 Ultra
Answered from the verified figures on this page rather than general guidance.
Is Claude Mythos 5.1 or NVIDIA Nemotron 3 Ultra cheaper for input?
NVIDIA Nemotron 3 Ultra is cheaper at $0.50 per million input tokens, against $10 for Claude Mythos 5.1 — roughly 20× 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. NVIDIA Nemotron 3 Ultra has tiered pricing: Open weights (weights + data + recipes); $0.50/$2.20 per MTok is the third-party hosted rate (OpenRouter). 550B/55B MoE.
Is Claude Mythos 5.1 or NVIDIA Nemotron 3 Ultra cheaper for output?
NVIDIA Nemotron 3 Ultra is cheaper at $2.20 per million output tokens, against $50 for Claude Mythos 5.1 — roughly 23× 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. NVIDIA Nemotron 3 Ultra has tiered pricing: Open weights (weights + data + recipes); $0.50/$2.20 per MTok is the third-party hosted rate (OpenRouter). 550B/55B MoE.
Do Claude Mythos 5.1 and NVIDIA Nemotron 3 Ultra support the same reasoning levels?
Claude Mythos 5.1 exposes adaptive, while NVIDIA Nemotron 3 Ultra exposes low, high, max.
Should I use Claude Mythos 5.1 or NVIDIA Nemotron 3 Ultra?
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; NVIDIA Nemotron 3 Ultra suits open-weight frontier.
Can I self-host Claude Mythos 5.1 or NVIDIA Nemotron 3 Ultra?
NVIDIA Nemotron 3 Ultra publishes open weights, but self-hosting and third-party provider access depend on the licence, hardware, serving support, and availability. Claude Mythos 5.1 is a closed model whose supported access paths are controlled by its provider.
Next step
Choosing between them
The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.
- Input price: NVIDIA Nemotron 3 Ultra costs $0.50 per 1M tokens versus $10 for Claude Mythos 5.1 — a 20x difference at the headline tier.
- Deployment: NVIDIA Nemotron 3 Ultra publishes weights you can self-host; the other is API-only.
Choosing a harness rather than a model — Cursor, Copilot, Claude Code, Windsurf, or Lovable? Compare agentic harnesses · Latest releases.