ModelSpec is an analysis of alternatives for AI models: it decides which models fit a job from your requirements, sourced benchmarks and real cost, and shows its work.

Claude Opus 5.5 vs Claude Sonnet 5.5 for Coding (balanced), as of 2026-09-23

Find an active coding model with room for a repository that balances coding strength against task cost.

Worked example as of 2026-09-23, from the public data image.

What the evidence says

The evidence can't separate them for this job.

Claude Sonnet 5.5 has a 48% chance of matching or beating Claude Opus 5.5 on this job's objective.

probability bands: a model joins the leader when P(its score >= the leader's) >= 0.25 under the score posteriors; a weighted capability with an 80% interval wider than 2.8 is not enough evidence

Decision status: partial. P(best) and score intervals retain the full ranked lineup for this job, including models beyond this pair and models with thin evidence. Models with unknown objective values remain unranked and are outside this probability. P(best) is not a head-to-head probability.

Scores and score intervals use the objective's dimensionless normalised units. Cost per task is in USD for the selected offering and the applied spec's task size. When task size is omitted, the engine uses its documented default. Unavailable means the engine returned no value.

Model	Score	Score interval	P(best), ranked job lineup	Cost per task, USD	Selected offering: provider / region / tier	Capability estimates and intervals
Claude Opus 5.5	0.894595	[0.657556, 1.131633]	22%	0.24	anthropic / global / standard	software_engineering: 1.300758259; interval [0.373384859, 2.22813166]; benchmarks 4; direct benchmarks 2
Claude Sonnet 5.5	0.884067	[0.636213, 1.131921]	27%	0.12	anthropic / global / standard	software_engineering: 1.005798442; interval [0.036112567, 1.975484317]; benchmarks 3; direct benchmarks 2

Coding strength first, cost as a real second term.

Requirements

model.class = text-generator: Coding work needs a model that generates text and code.
model.lifecycle = active: An active model is still supported by its lab or provider.
model.context_window >= 200000: A large repository needs room for code, tests, and instructions.

Preferences

software_engineering: Prefer stronger evidence on real software-engineering tasks.
-offering.cost_per_task: Among strong coders, prefer the cheaper task.

Applied template spec

spec_version

where

model.class = text-generator
model.lifecycle = active
model.context_window >= 200000

optimize

weights

software_engineering: 0.7
-offering.cost_per_task: 0.3

Evidence for Claude Opus 5.5

Benchmark	Version	Measurement	Unit	Published interval	Evidence date	Measurement conditions	Provenance
arena_webdev	webdev / overall, latest split, revision 1880dbebff5b	1818.41	Arena score (Elo scale)	Unavailable	2026-09-23	Effort: Unavailable Subcategory: Unavailable Harness: Unavailable Measured by: independent_evaluator Sample size: Unavailable	Source
cursorbench_4	CursorBench 4.0	57.8	percent	Unavailable	2026-09-30	Effort: max Subcategory: Unavailable Harness: Unavailable Measured by: benchmark_author Sample size: Unavailable	Source
swe_bench_multilingual	SWE-bench Multilingual	93.9	percent	Unavailable	2026-09-22	Effort: max Subcategory: Unavailable Harness: Unavailable Measured by: provider_self_report Sample size: Unavailable	Source
swe_bench_multimodal	SWE-bench Multimodal	61.4	percent	Unavailable	2026-09-22	Effort: max Subcategory: Unavailable Harness: Unavailable Measured by: provider_self_report Sample size: Unavailable	Source
swe_bench_pro	SWE-bench Pro	89.9	percent	Unavailable	2026-09-22	Effort: max Subcategory: Unavailable Harness: Unavailable Measured by: provider_self_report Sample size: Unavailable	Source
terminal_bench_v4_0	Terminal-Bench 4.0	66.4	percent	Unavailable	2026-09-22	Effort: xhigh Subcategory: Unavailable Harness: Unavailable Measured by: provider_self_report Sample size: Unavailable	Source

Missing facts for Claude Opus 5.5

model.hardware_fit_indeterminate: unknown
model.languages: unknown
model.parameters_total: unknown
origin.base_lineage: not_disclosed
origin.weights_hosting: not_disclosed
offering.api_model_id: unknown
offering.data.zero_retention: requires_contract
offering.private_deployment: unknown
offering.router_slug: unknown
offering.speed.throughput: unknown
offering.speed.time_to_first_token: unknown

Evidence for Claude Sonnet 5.5

Benchmark	Version	Measurement	Unit	Published interval	Evidence date	Measurement conditions	Provenance
cursorbench_4	CursorBench 4.0	55.5	percent	Unavailable	2026-09-28	Effort: Unavailable Subcategory: Unavailable Harness: Unavailable Measured by: provider_self_report Sample size: Unavailable	Source
frontiercode_v1_1	FrontierCode 1.1 (Main)	46.2	percent	Unavailable	2026-09-28	Effort: max Subcategory: Unavailable Harness: Unavailable Measured by: provider_self_report Sample size: Unavailable	Source
terminal_bench_v4_0	Terminal-Bench 4.0	70.6	percent	Unavailable	2026-09-28	Effort: Unavailable Subcategory: Unavailable Harness: Unavailable Measured by: provider_self_report Sample size: Unavailable	Source

Missing facts for Claude Sonnet 5.5

feature.structured_output: not_disclosed
licence.fine_tuning: not_disclosed
licence.user_cap: not_disclosed
model.fits_hardware: unknown
model.hardware_fit_indeterminate: unknown
model.languages: unknown
model.parameters_total: unknown
model.weights_openness: not_disclosed
origin.base_lineage: not_disclosed
origin.weights_hosting: not_disclosed
offering.api_model_id: unknown
offering.data.zero_retention: requires_contract
offering.private_deployment: unknown
offering.router_slug: unknown
offering.speed.throughput: unknown
offering.speed.time_to_first_token: unknown

What this template teaches

A 70/30 blend keeps capability in charge while letting a large price gap decide close calls.

Decision dec_522f407374f23603bb2a189d on public snapshot snap_05a963d2477ac2fb.

Read the full dated job answer.

The live board uses current data. This link applies the template to its full lineup.

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