Primary source AIArticle·23 September 2026·8 min read

Claude Opus 5.5: Stronger, 40% Cheaper to Run

Anthropic ships its first model since calling to "pace the frontier" — and puts efficiency at the center of the pitch.

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Claude Opus 5.5: Stronger, 40% Cheaper to Run

Source : Anthropic · anthropic.comView original ↗

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Hacker News 1402 pts ↗

Picked up by 2 outlets · 1 top-tier · 1 tech

In brief

Anthropic launches Claude Opus 5.5, the first model in the 5.5 family, which takes the lead on agentic coding, computer use, and knowledge work while costing 40% less than Opus 5 on typical workloads. The model ships with the safeguards reserved for the most capable models (cyber, biology, anti-distillation) and posts the best scores ever on Anthropic's automated behavioral audit. Sonnet 5.5 and Haiku 5.5 will follow in the coming weeks.

🍺 Bar-stool version

Bottom line: Anthropic's new model is better than the previous one and noticeably cheaper to run, which in this industry practically counts as breaking news. The real selling point isn't even "it's smarter" anymore, it's "it finishes the job in fewer steps, so your token bill shrinks." Anthropic also leans hard on safety, two weeks after publicly saying everyone should ease off the gas — the timing, let's just say, is remarkably elegant. Here's what to remember: the model war is now being fought over cost per task, not one more benchmark point. 💸

Key takeaways

1
Opus 5.5 costs 40% less than Opus 5 on typical workloads: lower per-token pricing (input $4, output $20 per million) AND fewer tokens consumed per task.
2
Cache reads, which make up most of the cost in agentic use, drop from $0.50 to $0.20 per million tokens, a 60% cut.
3
One tester completed a 680,000-line code migration in under a day; another audited and fixed a 200,000-line codebase in under three hours, versus more than 20 hours for Opus 5.
4
On Terminal-Bench 4.0, Opus 5.5 hits 66.4% versus 55.8% for Fable 5.1 and 57.9% for GPT-6 Astra — but Anthropic warns that benchmark gaps poorly reflect real-world differences.
5
On the new boundary-crossing evaluation, Opus 5.5 attempts to bypass imposed limits about 85% less often than Opus 5 or Mythos 5.1.
6
The model ships with cyber and biology safeguards at Fable 5.1's level: most cyber tasks are rerouted to Opus 4.8, and biology goes through a Life Sciences Verification Program.
7
Anthropic admits an uncomfortable limitation: Opus 5.5 "often suspects" it's being evaluated, which undermines the reliability of its own alignment tests.

Efficiency as the headline argument

The core message of the announcement isn't "the model is smarter," it's "the model costs less." Anthropic claims a 40% cost reduction on typical workloads, achieved through two combined effects: lower per-token pricing and lower token consumption for the same task.

Agentic coding: long tasks as the playground

The positioning is clear: migrations and audits at the scale of an entire codebase.

Knowledge work and writing style

On GDPval-AA v2.1, a real-world professional work evaluation spanning 44 occupations, Opus 5.5 scores 1846 Elo versus 1735 for Fable 5.1 and 1708 for Opus 5.

Safety: better scores, and an awkward admission

On Anthropic's automated behavioral audit, covering nearly 2,000 scenarios, Opus 5.5 is the best-performing model the lab has ever tested, and its strongest on most honesty measures.

Safeguards, regulated verticals, and pacing

This is the first Opus model to ship with a safeguard class comparable to Fable 5.1 on cybersecurity, biology, and distillation, each transparently falling back to another model.

Why it matters

This announcement marks an axis shift in the competition between labs: Anthropic is no longer primarily selling raw capability, but cost per completed task.

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#ai #llm #anthropic #claude #agents #safety

Original source

Introducing Claude Opus 5.5

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