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
Claude Mythos 5.1 vs Claude Sonnet 5.5
Updated September 28, 2026. We do not rank this pair: at least one has no public score. Public scores include evidence status and uncertainty.
Both of these models will change. Get the price, version and retirement notices for the pair, each with its source. Follow model changes
Share or export
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.
- Shared results
- 1
- Claude Mythos 5.1 only
- 0
- Claude Sonnet 5.5 only
- 46
- Like-for-like categories
- 0 / 8
Estimated: Claude Sonnet 5.5How the comparison works
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
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: limitedLong documents
Prompts that approach the documented context limit
No clear pick
The documented context windows are equal.
Confidence: documentedChat 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-ratesCache-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-ratesRepository 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 5.179.6Claude Sonnet 5.5
Not comparable · BenchAlign v5.7
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.
Same basis rules as the category table below
What is actually comparable
Shared results can support a head-to-head reading. Results present for only one model describe coverage, not superiority.
1 Shared
46 Claude Sonnet 5.5 only
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.
Category results, on a stated basis
Each row shows the public-lane category score for both models: the BenchAlign v5.7 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 Sonnet 5.5
- 66.1
- Supported · #10/111
- Basis
- BenchAlign v5.7 lane · 1 vs 11 public rows
- Reading
- Not comparable
Coding
Not comparable- Claude Mythos 5.1
- Not ranked
- Claude Sonnet 5.5
- 79.6
- Estimated · #3/136
- Basis
- BenchAlign v5.7 lane · 0 vs 9 public rows
- Reading
- Not comparable
Reasoning
Not comparable- Claude Mythos 5.1
- Not ranked
- Claude Sonnet 5.5
- 79.2
- #7/27
- Basis
- Provisional lane · 0 vs 0 weighted rows
- Reading
- Not comparable
Multimodal
Not comparable- Claude Mythos 5.1
- Not ranked
- Claude Sonnet 5.5
- 83.3
- Unranked · 7 rankable rows
- Basis
- Provisional lane · 0 vs 1 weighted rows
- Reading
- Not comparable
Knowledge
Not comparable- Claude Mythos 5.1
- Not ranked
- Claude Sonnet 5.5
- 80.9
- Supported · #6/160
- Basis
- BenchAlign v5.7 lane · 0 vs 16 public rows
- Reading
- Not comparable
Multilingual
Not comparable- Claude Mythos 5.1
- Not ranked
- Claude Sonnet 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 Sonnet 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 Sonnet 5.5
- Not ranked
- Basis
- Provisional lane · 0 vs 0 weighted rows
- Reading
- Not comparable
| Category | Claude Mythos 5.1 | Claude Sonnet 5.5 | Basis | Reading |
|---|---|---|---|---|
| Agentic | Not ranked | 66.1Supported · #10/111 | Not comparableBenchAlign v5.7 lane · 1 vs 11 public rows | Not comparable |
| Coding | Not ranked | 79.6Estimated · #3/136 | Not comparableBenchAlign v5.7 lane · 0 vs 9 public rows | Not comparable |
| Reasoning | Not ranked | 79.2#7/27 | Not comparableProvisional lane · 0 vs 0 weighted rows | Not comparable |
| Multimodal | Not ranked | 83.3Unranked · 7 rankable rows | Not comparableProvisional lane · 0 vs 1 weighted rows | Not comparable |
| Knowledge | Not ranked | 80.9Supported · #6/160 | Not comparableBenchAlign v5.7 lane · 0 vs 16 public rows | Not comparable |
| Multilingual | Not ranked | Not ranked | Not comparableProvisional lane · 0 vs 0 weighted rows | Not comparable |
| Instruction following | Not ranked | Not ranked | Not comparableProvisional lane · 0 vs 0 weighted rows | Not comparable |
| Math | Not ranked | Not ranked | Not comparableProvisional lane · 0 vs 0 weighted rows | Not comparable |
Ranks count the models scored in each category’s lane, so the agentic, coding, and knowledge denominators (BenchAlign v5.7) differ from the provisional-lane categories. Unranked scores sit on the provisional lane’s scale but never name a winner. Like-for-like rows within 0.5 points read as a practical tie.
Supported evidence per lane · bars run 0–100Methodology
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 Sonnet 5.5
- $0.007
- 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 Sonnet 5.5
- $0.13
- 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 Sonnet 5.5
- $0.18
- Fits in one request
Claude Mythos 5.1 has no comparable published API token rate.
Cached input falls back to the list input rate only where a cached rate is unpublished
Specification differences
Sourced differences are shown directly. Missing facts stay explicit instead of being inferred from a model name or family.
SpecificationClaude Mythos 5.1Claude Sonnet 5.5
Context window
Maximum documented context; output-token limits may be lower.
Claude Mythos 5.1
Claude Sonnet 5.5
API model ID
Claude Mythos 5.1
Not sourced
Claude Sonnet 5.5
claude-sonnet-5-5
Anthropic Claude Sonnet 5.5 model documentationCached-input rate
A missing cached-input rate falls back to the listed input rate only in the stated workload estimate.
Claude Mythos 5.1
No comparable hosted API rate
Anthropic Fable 5.1 and Mythos 5.1 launchClaude Sonnet 5.5
$0.2 per 1M cached input tokens
Claude API pricingDocumented inputs
Claude Mythos 5.1
Not sourced
Claude Sonnet 5.5
Documented outputs
Claude Mythos 5.1
Not sourced
Claude Sonnet 5.5
Provider availability
Claude Mythos 5.1
Limited Access · Cyber Verification Program, Life Sciences Verification Program, Claude Security
Anthropic Fable 5.1 and Mythos 5.1 launchClaude Sonnet 5.5
Generally Available · Claude API, Amazon Bedrock, Google Cloud, Microsoft Foundry, Claude Platform on AWS
Anthropic Claude Sonnet 5.5 model documentationReasoning profile
Claude Mythos 5.1
Reasoning
Claude Sonnet 5.5
Reasoning
Weight access
Claude Mythos 5.1
Proprietary
Claude Sonnet 5.5
Proprietary
License
Claude Mythos 5.1
Proprietary
Claude Sonnet 5.5
Proprietary
Release date
Claude Mythos 5.1
2026-09-01
Claude Sonnet 5.5
2026-09-28
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.
Questions
Which is better, Claude Mythos 5.1 or Claude Sonnet 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 Sonnet 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 Sonnet 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 Sonnet 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 Sonnet 5.5?
Both models list the same context window, 1M.
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%SourceClaude Sonnet 5.570.60%SourceClaude Sonnet 5.5 leads this result
HLE w/ tools
Claude Mythos 5.1—Claude Sonnet 5.564.5%SourceNot directly comparable
DRACO
Claude Mythos 5.1—Claude Sonnet 5.587.0%SourceNot directly comparable
Terminal-Bench-Science 0.1
Claude Mythos 5.1—Claude Sonnet 5.559.9%SourceNot directly comparable
LAB all-pass (Harvey held-out)
Claude Mythos 5.1—Claude Sonnet 5.510.0%SourceNot directly comparable
LAB criterion-pass (Harvey held-out)
Claude Mythos 5.1—Claude Sonnet 5.593.1%SourceNot directly comparable
Toolathlon Verified Pass@3
Claude Mythos 5.1—Claude Sonnet 5.585.2%SourceNot directly comparable
Toolathlon Verified Pass³
Claude Mythos 5.1—Claude Sonnet 5.568.5%SourceNot directly comparable
Toolathlon Verified avg. turns
Claude Mythos 5.1—Claude Sonnet 5.531.6 turnsSourceNot directly comparable
AutomationBench (Zapier 1.0.6)
Claude Mythos 5.1—Claude Sonnet 5.544.7%SourceNot directly comparable
Toolathlon-Verified
Claude Mythos 5.1—Claude Sonnet 5.577.8%SourceNot directly comparable
Coding
FrontierCode 1.1 Main
Claude Mythos 5.1—Claude Sonnet 5.546.2%SourceNot directly comparable
cursorBench40
Claude Mythos 5.1—Claude Sonnet 5.555.5%SourceNot directly comparable
SWE-bench Pro
Claude Mythos 5.1—Claude Sonnet 5.581.3%SourceNot directly comparable
SWE Multilingual
Claude Mythos 5.1—Claude Sonnet 5.590.3%SourceNot directly comparable
SWE Multimodal
Claude Mythos 5.1—Claude Sonnet 5.554.3%SourceNot directly comparable
DeepSWE
Claude Mythos 5.1—Claude Sonnet 5.571.0%SourceNot directly comparable
FrontierCode 1.1 Extended
Claude Mythos 5.1—Claude Sonnet 5.559.1%SourceNot directly comparable
ProgramBench
Claude Mythos 5.1—Claude Sonnet 5.579.7%SourceNot directly comparable
FrontierSWE v2
Claude Mythos 5.1—Claude Sonnet 5.561.9%SourceNot directly comparable
Multimodal
Chartography (no tools)
Claude Mythos 5.1—Claude Sonnet 5.561.6%SourceNot directly comparable
Chartography (tools)
Claude Mythos 5.1—Claude Sonnet 5.590.2%SourceNot directly comparable
BenchCAD Vision2Code (no tools)
Claude Mythos 5.1—Claude Sonnet 5.50.747SourceNot directly comparable
BenchCAD Vision2Code (tools)
Claude Mythos 5.1—Claude Sonnet 5.50.963SourceNot directly comparable
Biomedical image analysis
Claude Mythos 5.1—Claude Sonnet 5.572.2%SourceNot directly comparable
OfficeQA
Claude Mythos 5.1—Claude Sonnet 5.576.9%SourceNot directly comparable
OfficeQA Pro
Claude Mythos 5.1—Claude Sonnet 5.565.6%SourceNot directly comparable
Knowledge
HealthBench (raw)
Claude Mythos 5.1—Claude Sonnet 5.569.4%SourceNot directly comparable
HealthBench (length-adjusted)
Claude Mythos 5.1—Claude Sonnet 5.565.4%SourceNot directly comparable
HealthBench Professional (raw)
Claude Mythos 5.1—Claude Sonnet 5.577.1%SourceNot directly comparable
HealthBench Professional
Claude Mythos 5.1—Claude Sonnet 5.569.2%SourceNot directly comparable
BioMysteryBench (human-solvable)
Claude Mythos 5.1—Claude Sonnet 5.589.2%SourceNot directly comparable
BioMysteryBench (human-difficult)
Claude Mythos 5.1—Claude Sonnet 5.544.7%SourceNot directly comparable
SpatialBench Verified
Claude Mythos 5.1—Claude Sonnet 5.572.5%SourceNot directly comparable
SingleCellBench
Claude Mythos 5.1—Claude Sonnet 5.559.1%SourceNot directly comparable
Protein Design
Claude Mythos 5.1—Claude Sonnet 5.551.0%SourceNot directly comparable
Morphology-to-molecule matching
Claude Mythos 5.1—Claude Sonnet 5.525.0%SourceNot directly comparable
Medicinal chemistry
Claude Mythos 5.1—Claude Sonnet 5.565.3%SourceNot directly comparable
Protein Design library ranking
Claude Mythos 5.1—Claude Sonnet 5.554.8%SourceNot directly comparable
De novo protein-binder design
Claude Mythos 5.1—Claude Sonnet 5.582.3%SourceNot directly comparable
Protocols (troubleshooting)
Claude Mythos 5.1—Claude Sonnet 5.567.3%SourceNot directly comparable
Protocols (understanding)
Claude Mythos 5.1—Claude Sonnet 5.566.6%SourceNot directly comparable
HLE w/o tools
Claude Mythos 5.1—Claude Sonnet 5.556.9%SourceNot directly comparable
Multilingual
Math
47 public results · 1 shared
Watch Claude Mythos 5.1 vs Claude Sonnet 5.5
One weekly email when material rank, price, or benchmark evidence changes make this matchup worth revisiting.
Read a sample issueJoin 2,000+ readers.
Last updated September 28, 2026