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BenchLM

Claude Mythos 5.1 vs Claude Opus 5.5

Decision reading

At least one model is not scored in the current public ranking lane, so the page does not name an overall quality winner.

1 results are shared. Category rows resting on Estimated evidence or different benchmark sets are marked directional and do not name a winner.

Anthropic logo
Model A
Claude Mythos 5.1

Anthropic

—

Evidence status unavailable

90% interval unavailable

Anthropic logo
Model B
Claude Opus 5.5

Anthropic

81.03/100

Estimated · Public rank #5

90% interval 56.1–92.5

Updated September 22, 2026. We do not rank this pair: at least one has no public score. Public scores include evidence status and uncertainty.

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Which one for your work

Recommendations appear only when a shared evidence basis or an explicit operating constraint supports the call. Secondary and unsupported use cases stay disclosed below the initial list.

No workload recommendation clears the current evidence threshold.

Use the matched evidence, workload costs, and sourced specifications below instead of treating a point score as a universal answer.

Show secondary and unsupported calls

  • Coding work

    Code generation, repair, and software-engineering tasks

    Not enough matched evidence

    Claude Mythos 5.1 is not ranked on the public lane for coding, so no winner is named for coding.

    Confidence: limited

  • Agentic work

    Tool use, computer use, and multi-step task completion

    Not enough matched evidence

    Claude Mythos 5.1 is not ranked on the public lane for agentic, so no winner is named for agentic.

    Confidence: limited

  • Long documents

    Prompts that approach the documented context limit

    No clear pick

    The documented context windows are equal.

    Confidence: documented

  • Chat turn cost

    1K fresh input + 500 output tokens

    Not enough matched evidence

    A complete comparable API-rate estimate is not available for both models.

    Confidence: listed-rates

  • Cache-heavy agent loop cost

    200K cached + 20K fresh input + 10K output tokens

    Not enough matched evidence

    A complete comparable API-rate estimate is not available for both models.

    Confidence: listed-rates

  • Repository review cost

    50K fresh input + 3K output tokens

    Not enough matched evidence

    A complete comparable API-rate estimate is not available for both models.

    Confidence: listed-rates

Which one for a specific job

Choose a job from the LLM Selector's task catalog to see the category row it rests on, under the same basis rules as the table below. A directional row stays directional; choosing a job never creates a winner.

The same task catalog as the LLM Selector. Each job names the evidence surface it rests on; nothing here adds a new score.

—Claude Mythos 5.180.1Claude Opus 5.5

Not comparable · BenchAlign

The coding row is not comparable on the public lane: at least one model is not measured or not ranked there.

Coding scores combine specific tasks and setups. Match the editor, harness, and effort to your workflow.

Open the coding leaderboardShortlist models for this job

What is actually comparable

Shared results can support a head-to-head reading. Results present for only one model describe coverage, not superiority.

Shared results
1
Claude Mythos 5.1 only
0
Claude Opus 5.5 only
46
Like-for-like categories
0 / 8

Category results, on a stated basis

Each row shows the public-lane category score for both models: the BenchAlign lane for agentic, coding, and knowledge, and the weighted public rows elsewhere, with the same rank each model page reports. A row is like-for-like only when both scores rest on Supported evidence or the same weighted set. Directional and not-comparable rows remain visible, but they never receive a winner.

Agentic

Not comparable
Claude Mythos 5.1
Not ranked
Claude Opus 5.5
82.9
Supported · #1/157
Basis
BenchAlign lane · 1 vs 11 public rows
Reading
Not comparable

Coding

Not comparable
Claude Mythos 5.1
Not ranked
Claude Opus 5.5
80.1
Supported · #2/159
Basis
BenchAlign lane · 0 vs 9 public rows
Reading
Not comparable

Reasoning

Not comparable
Claude Mythos 5.1
Not ranked
Claude Opus 5.5
78.5
#4/17
Basis
Provisional lane · 0 vs 0 weighted rows
Reading
Not comparable

Multimodal

Not comparable
Claude Mythos 5.1
Not ranked
Claude Opus 5.5
88.8
#3/50
Basis
Provisional lane · 0 vs 1 weighted rows
Reading
Not comparable

Knowledge

Not comparable
Claude Mythos 5.1
Not ranked
Claude Opus 5.5
81.8
Estimated · #4/189
Basis
BenchAlign lane · 0 vs 16 public rows
Reading
Not comparable

Multilingual

Not comparable
Claude Mythos 5.1
Not ranked
Claude Opus 5.5
Not ranked
Basis
Provisional lane · 0 vs 0 weighted rows
Reading
Not comparable

Instruction following

Not comparable
Claude Mythos 5.1
Not ranked
Claude Opus 5.5
Not ranked
Basis
Provisional lane · 0 vs 0 weighted rows
Reading
Not comparable

Math

Not comparable
Claude Mythos 5.1
Not ranked
Claude Opus 5.5
Not ranked
Basis
Provisional lane · 0 vs 0 weighted rows
Reading
Not comparable

Ranks count the models scored in each category’s lane, so the agentic, coding, and knowledge denominators (BenchAlign) differ from the provisional-lane categories. Unranked scores sit on the lane’s scale but never name a winner. Like-for-like rows within 0.5 points read as a practical tie.

Shape of the matched evidence

Only shared public evidence is shown. Sparse evidence stays a ruled list rather than being closed into a radar shape.

A shared-evidence shape is not available.

BenchLM does not draw a radar or infer missing axes when the matched evidence is too sparse.

What each workload costs

Three fixed token mixes turn per-token rates into comparable decisions. Each scenario states context fit and whether cached input had to fall back to the published list-input rate.

Chat turn

1K fresh input + 500 output tokens

Claude Mythos 5.1
API rate not published
Fits in one request
Claude Opus 5.5
$0.014
Fits in one request

Claude Mythos 5.1 has no comparable published API token rate.

Repository review

50K fresh input + 3K output tokens

Claude Mythos 5.1
API rate not published
Fits in one request
Claude Opus 5.5
$0.26
Fits in one request

Claude Mythos 5.1 has no comparable published API token rate.

Cache-heavy agent loop

200K cached + 20K fresh input + 10K output tokens

Claude Mythos 5.1
API rate not published
Fits in one request
Cached-input rate unavailable
Claude Opus 5.5
$0.32
Fits in one request

Claude Mythos 5.1 has no comparable published API token rate.

Specification differences

Sourced differences are shown directly. Missing facts stay explicit instead of being inferred from a model name or family.

Reasoning profile

Claude Mythos 5.1

Reasoning

Claude Opus 5.5

Reasoning

Weight access

Claude Mythos 5.1

Proprietary

Claude Opus 5.5

Proprietary

License

Claude Mythos 5.1

Proprietary

Claude Opus 5.5

Proprietary

Release date

Claude Mythos 5.1

2026-09-01

Claude Opus 5.5

2026-09-22

If you already use one of these models
Deployment change
Both entries list Anthropic as the provider. Confirm endpoint, model ID, limits, and feature support before switching.
Quality signal
At least one model is not scored in the current public ranking lane, so the page does not name an overall quality winner.
Workload cost
A complete comparable API-rate estimate is not available for both models.
Context tradeoff
Both models list 1M.

Run the same representative tasks against both endpoints before changing production traffic.

Benchmark evidence

The full public result ledger is available for audit without forcing a wide desktop table onto a phone.

Browse raw public benchmark evidence47 rows

Agentic

  • Terminal-Bench 4.0

    Claude Mythos 5.160.90%
    Source
    Claude Opus 5.566.40%
    Source

    Claude Opus 5.5 leads this result

  • Terminal-Bench-Science 0.1

    Claude Mythos 5.1—
    Claude Opus 5.558.7%
    Source

    Not directly comparable

  • AutomationBench

    Claude Mythos 5.1—
    Claude Opus 5.540.0%
    Source

    Not directly comparable

  • HLE w/ tools

    Claude Mythos 5.1—
    Claude Opus 5.567.7%
    Source

    Not directly comparable

  • OSWorld 2.0

    Claude Mythos 5.1—
    Claude Opus 5.548.7%
    Source

    Not directly comparable

  • LAB all-pass (Harvey held-out)

    Claude Mythos 5.1—
    Claude Opus 5.58.3%
    Source

    Not directly comparable

  • LAB criterion-pass (Harvey held-out)

    Claude Mythos 5.1—
    Claude Opus 5.591.2%
    Source

    Not directly comparable

  • Toolathlon-Verified

    Claude Mythos 5.1—
    Claude Opus 5.577.8%
    Source

    Not directly comparable

  • Toolathlon Verified Pass@3

    Claude Mythos 5.1—
    Claude Opus 5.582.4%
    Source

    Not directly comparable

  • Toolathlon Verified Pass³

    Claude Mythos 5.1—
    Claude Opus 5.572.2%
    Source

    Not directly comparable

  • Toolathlon Verified avg. turns

    Claude Mythos 5.1—
    Claude Opus 5.526.9 turns
    Source

    Not directly comparable

Coding

  • FrontierCode 1.1 Main

    Claude Mythos 5.1—
    Claude Opus 5.554.4%
    Source

    Not directly comparable

  • cursorBench40

    Claude Mythos 5.1—
    Claude Opus 5.557.8%
    Source

    Not directly comparable

  • SWE-bench Pro

    Claude Mythos 5.1—
    Claude Opus 5.589.9%
    Source

    Not directly comparable

  • SWE Multilingual

    Claude Mythos 5.1—
    Claude Opus 5.593.9%
    Source

    Not directly comparable

  • SWE Multimodal

    Claude Mythos 5.1—
    Claude Opus 5.561.4%
    Source

    Not directly comparable

  • DeepSWE

    Claude Mythos 5.1—
    Claude Opus 5.574.2%
    Source

    Not directly comparable

  • FrontierCode 1.1 Extended

    Claude Mythos 5.1—
    Claude Opus 5.563.6%
    Source

    Not directly comparable

  • FrontierSWE v2

    Claude Mythos 5.1—
    Claude Opus 5.562.3%
    Source

    Not directly comparable

  • ProgramBench

    Claude Mythos 5.1—
    Claude Opus 5.591.2%
    Source

    Not directly comparable

Multimodal

  • Chartography (tools)

    Claude Mythos 5.1—
    Claude Opus 5.589.0%
    Source

    Not directly comparable

  • Chartography (no tools)

    Claude Mythos 5.1—
    Claude Opus 5.564.4%
    Source

    Not directly comparable

  • BenchCAD Vision2Code (no tools)

    Claude Mythos 5.1—
    Claude Opus 5.50.730
    Source

    Not directly comparable

  • BenchCAD Vision2Code (tools)

    Claude Mythos 5.1—
    Claude Opus 5.50.962
    Source

    Not directly comparable

  • Biomedical image analysis

    Claude Mythos 5.1—
    Claude Opus 5.571.4%
    Source

    Not directly comparable

  • OfficeQA

    Claude Mythos 5.1—
    Claude Opus 5.578.9%
    Source

    Not directly comparable

  • OfficeQA Pro

    Claude Mythos 5.1—
    Claude Opus 5.567.7%
    Source

    Not directly comparable

Knowledge

  • HLE w/o tools

    Claude Mythos 5.1—
    Claude Opus 5.564.4%
    Source

    Not directly comparable

  • HealthBench (raw)

    Claude Mythos 5.1—
    Claude Opus 5.568.1%
    Source

    Not directly comparable

  • HealthBench (length-adjusted)

    Claude Mythos 5.1—
    Claude Opus 5.560.6%
    Source

    Not directly comparable

  • HealthBench Professional

    Claude Mythos 5.1—
    Claude Opus 5.565.6%
    Source

    Not directly comparable

  • HealthBench Professional (raw)

    Claude Mythos 5.1—
    Claude Opus 5.577.1%
    Source

    Not directly comparable

  • BioMysteryBench (human-solvable)

    Claude Mythos 5.1—
    Claude Opus 5.589.3%
    Source

    Not directly comparable

  • BioMysteryBench (human-difficult)

    Claude Mythos 5.1—
    Claude Opus 5.550.0%
    Source

    Not directly comparable

  • SpatialBench Verified

    Claude Mythos 5.1—
    Claude Opus 5.572.0%
    Source

    Not directly comparable

  • SingleCellBench

    Claude Mythos 5.1—
    Claude Opus 5.561.2%
    Source

    Not directly comparable

  • Morphology-to-molecule matching

    Claude Mythos 5.1—
    Claude Opus 5.534.0%
    Source

    Not directly comparable

  • Medicinal chemistry

    Claude Mythos 5.1—
    Claude Opus 5.563.5%
    Source

    Not directly comparable

  • Protein Design

    Claude Mythos 5.1—
    Claude Opus 5.560.2%
    Source

    Not directly comparable

  • Protein Design library ranking

    Claude Mythos 5.1—
    Claude Opus 5.556.0%
    Source

    Not directly comparable

  • De novo protein-binder design

    Claude Mythos 5.1—
    Claude Opus 5.582.6%
    Source

    Not directly comparable

  • Protocols (troubleshooting)

    Claude Mythos 5.1—
    Claude Opus 5.573.7%
    Source

    Not directly comparable

  • Protocols (understanding)

    Claude Mythos 5.1—
    Claude Opus 5.569.0%
    Source

    Not directly comparable

Multilingual

  • GMMLU

    Claude Mythos 5.1—
    Claude Opus 5.594.3%
    Source

    Not directly comparable

  • MILU

    Claude Mythos 5.1—
    Claude Opus 5.593.1%
    Source

    Not directly comparable

Math

  • ArXivMath Aug. 2026 (no tools)

    Claude Mythos 5.1—
    Claude Opus 5.591.2%
    Source

    Not directly comparable

  • ArXivMath Aug. 2026 (tools)

    Claude Mythos 5.1—
    Claude Opus 5.596.9%
    Source

    Not directly comparable

Questions

Which is better, Claude Mythos 5.1 or Claude Opus 5.5?

At least one model is not scored in the current public ranking lane, so the page does not name an overall quality winner. The page therefore keeps the decision tied to the specific documented workload.

Which is better for coding, Claude Mythos 5.1 or Claude Opus 5.5?

Claude Mythos 5.1 is not ranked on the public lane for coding, so no winner is named for coding.

Which is better for agentic tasks, Claude Mythos 5.1 or Claude Opus 5.5?

Claude Mythos 5.1 is not ranked on the public lane for agentic tasks, so no winner is named for agentic tasks.

Which costs less, Claude Mythos 5.1 or Claude Opus 5.5?

Both models do not have comparable published API token rates, so this page does not name a universal price winner.

Which has the larger context window, Claude Mythos 5.1 or Claude Opus 5.5?

Both models list the same context window, 1M.

Related comparisons

Compare API pricing Read the methodology Open the model selector

Last updated September 22, 2026

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