Model comparison

Claude Mythos 5.1 vs Gemini 3.1 Pro

Anthropic against Google, compared on context, price, and attributed benchmark results.

Recorded profile verification October 1, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below

Anthropic

Claude Mythos 5.1

Frontier

Google

Gemini 3.1 Pro

Frontier

AI model capability comparison
Specification	Claude Mythos 5.1	Gemini 3.1 Pro
Provider
Provider	Anthropic	Google
Tier
Tier	Frontier	Frontier
Context window
Context window	1M	Winner: 1.05M
Max output
Max output	Winner: 128K	66K
Input / 1M tokens
Input / 1M tokens	$10	Winner: $2
Output / 1M tokens
Output / 1M tokens	$50	Winner: $12
Weights
Weights	Closed	Closed
Parameters
Parameters	Not verifiedUnverified	Not verifiedUnverified
Reasoning levels
Reasoning levels	low, medium, high, xhigh, max	low, medium, high
Modalities
Modalities	text, image	text, image, video, audio, pdf
API model id
API model id	claude-mythos-5-1	gemini-3.1-pro-preview
Released
Released	September 1, 2026	February 19, 2026
SWE-bench Verified · source date Gemini 3.1 Pro: 2026-02
SWE-bench Verified · source date Gemini 3.1 Pro: 2026-02	Not verifiedUnverified	80.6
GPQA Diamond · source date Gemini 3.1 Pro: 2026-02
GPQA Diamond · source date Gemini 3.1 Pro: 2026-02	Not verifiedUnverified	94.3
Humanity's Last Exam · source date Gemini 3.1 Pro: 2026-02
Humanity's Last Exam · source date Gemini 3.1 Pro: 2026-02	Not verifiedUnverified	44.4
Terminal-Bench 2.1 · source date Gemini 3.1 Pro: 2026-07
Terminal-Bench 2.1 · source date Gemini 3.1 Pro: 2026-07	Not verifiedUnverified	73.8

Dates beside benchmark scores refer to the linked source’s publication or capture date unless that source explicitly states when it measured the result. A shared URL alone does not establish comparable runs; unverified setups are marked. Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.

Benchmark receipts

Where each score comes from, and how far it can be compared across models.

Source date2026-07
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.
Comparable with caveatNot comparable with Terminal-Bench 3.0 or 4.0 (different task sets) or v1; harness configuration (container, time limits) also shifts results.
Source date2026-02
Google DeepMind model evaluation report (vendor, no tools; 51.4 with search+code)
Frontier-knowledge ceiling: extremely hard multi-domain questions written to be near-impossible without deep expertise.
Comparable with caveatSubset/tool configurations (text-only vs with-tools) differ between vendors and materially change scores; must match configuration to compare.
Source date2026-02
Google DeepMind model evaluation report (vendor, no tools, pass@1)
Graduate-level science reasoning: multiple-choice questions written by domain PhDs.
Comparable with caveatDo not treat a fixed two-point band as universal measurement uncertainty; it depends on run count and evaluation setup. Chain-of-thought, prompt, and tool policy must match. The small pool limits fine-grained conclusions, and frontier scores can be near ceiling; Artificial Analysis dropped it from its Intelligence Index in v4.3.
Source date2026-02
Google DeepMind model evaluation report (vendor, Thinking High, avg of 10 runs, +0.6 disclosed adjustment)
Real GitHub issue resolution: does the model's patch pass the hidden tests.
Comparable with caveatPost-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: Standard $10/$50 per MTok, sharing Fable 5.1's specifications/pricing. Cache reads $0.25; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Invite-only for vetted US organisations; API ID claude-mythos-5-1. Retirement not sooner than September 1, 2027; this is a minimum commitment, not an announced shutdown.

Gemini 3.1 Pro: The current Gemini developer guide lists $2/$12 per MTok below 200K input and $4/$18 above 200K, including thinking output. It leaves the exact 200K boundary unspecified; confirm that boundary and other processing/cache tiers before budgeting. The exact API ID remains gemini-3.1-pro-preview. Restricted Gemini 4 Argon is a separate preview and does not make this endpoint stable.

FrontierRecord checked October 1, 2026

Claude Mythos 5.1

Anthropic describes Claude Mythos 5.1 as its 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 for vetted US organisations through trusted access programmes, with 30-day retention required by default for safety monitoring. Adaptive thinking cannot be disabled and forced tool use errors. Shared underlying model does not make Fable benchmark results Mythos observations; safeguards and access differ.

FrontierRecord checked October 1, 2026

Gemini 3.1 Pro

Gemini 3.1 Pro Preview is Google's multimodal Pro endpoint with a 1,048,576-token input limit and 65,536-token output limit.

Best for

Very long documents
Multimodal reasoning
Frontier knowledge work

Watch out

This API endpoint remains Preview. A separate customtools endpoint is optimized for bash/custom-tool workflows and can behave differently on other tasks. Keep endpoint, thinking level and benchmark version matched; restricted Gemini 4 Argon access is a separate lifecycle.

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. This compares standard short-context token rates, not total cost per accepted task. Include input, cache, context tiers, schedules, retries and review in your pilot.

Run the model picker

Evidence 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.
4/5 core specs verified on both sides — Not published for at least one side: parameter count.
No directly aligned benchmark setup — No benchmark has matching cited sources, source dates, units, effort and recorded run details on both models.
Verified within the last 90 days — Older of the two catalog checks was 25 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: Claude model overview — whole-profile source check October 1 (accessed 2026-10-01)
Claude Mythos 5.1: Claude current API pricing, caching and inference geography (accessed 2026-10-01)
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)
Claude Mythos 5.1: Anthropic — Mythos 5.1 overview (1M context, 128K output, claude-mythos-5-1) (accessed 2026-09-26)
Claude Mythos 5.1: Anthropic selectable effort levels (separate from adaptive thinking mode) (accessed 2026-10-01)
Gemini 3.1 Pro: Google primary profile — whole-record source check October 1 (accessed 2026-10-01)
Gemini 3.1 Pro: Gemini current API pricing and cache-storage tiers (accessed 2026-10-01)
Gemini 3.1 Pro: Gemini developer guide — exact Preview rates and boundary limitation (accessed 2026-10-01)
Gemini 3.1 Pro: Gemini API 3.1 Pro Preview — exact endpoint and customtools scope (accessed 2026-10-01)
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

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. Estimate both input and output token volume for your workload. These are base rates; Claude Mythos 5.1: Standard $10/$50 per MTok, sharing Fable 5.1's specifications/pricing. Cache reads $0.25; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Invite-only for vetted US organisations; API ID claude-mythos-5-1. Retirement not sooner than September 1, 2027; this is a minimum commitment, not an announced shutdown. Gemini 3.1 Pro: The current Gemini developer guide lists $2/$12 per MTok below 200K input and $4/$18 above 200K, including thinking output. It leaves the exact 200K boundary unspecified; confirm that boundary and other processing/cache tiers before budgeting. The exact API ID remains gemini-3.1-pro-preview. Restricted Gemini 4 Argon is a separate preview and does not make this endpoint stable.

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. Estimate both input and output token volume for your workload. These are base rates; Claude Mythos 5.1: Standard $10/$50 per MTok, sharing Fable 5.1's specifications/pricing. Cache reads $0.25; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Invite-only for vetted US organisations; API ID claude-mythos-5-1. Retirement not sooner than September 1, 2027; this is a minimum commitment, not an announced shutdown. Gemini 3.1 Pro: The current Gemini developer guide lists $2/$12 per MTok below 200K input and $4/$18 above 200K, including thinking output. It leaves the exact 200K boundary unspecified; confirm that boundary and other processing/cache tiers before budgeting. The exact API ID remains gemini-3.1-pro-preview. Restricted Gemini 4 Argon is a separate preview and does not make this endpoint stable.

Which has the larger context window, Claude Mythos 5.1 or Gemini 3.1 Pro?

Gemini 3.1 Pro accepts 1.05M tokens against 1M for Claude Mythos 5.1. This only matters if you routinely send very long documents or large codebases.

Do Claude Mythos 5.1 and Gemini 3.1 Pro support the same reasoning levels?

Claude Mythos 5.1 exposes low, medium, high, xhigh, max, while Gemini 3.1 Pro exposes low, medium, high.

Should I use Claude Mythos 5.1 or Gemini 3.1 Pro?

Both are classified in our frontier tier; this editorial grouping does not imply equal capability. Claude Mythos 5.1 is a candidate for cyber-defence research; Gemini 3.1 Pro is a candidate for very long documents. Compare accuracy, tool reliability, latency and cost on representative tasks.

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.
Context: Gemini 3.1 Pro takes 1.05M against 1M for Claude Mythos 5.1 — only decisive if your prompts approach the smaller window.

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