Opus 5.5: Frontier Coding That Finishes the Job
Happycapy brings Anthropic's Opus 5.5 to your browser, an agent built to carry long, multi-step work from a single prompt to a finished result.
What is Opus 5.5?
Opus 5.5 is Anthropic's newest frontier model and the first in the Claude 5.5 family. It leads in agentic coding, computer use, and knowledge work, and is a major step up from Opus 5 on complex, long-horizon tasks.
Where earlier models stall partway through a hard job, Opus 5.5 keeps going. It plans, writes and runs code, uses a browser and tools, checks its own work, and stays reliable across long, multi-step runs, from codebase-wide migrations and audits to carrying a bigger build end to end. That reliability across a whole task, not just a single answer, is what separates it most from Opus 5.
On Happycapy, Opus 5.5 runs entirely in your browser with no setup. Describe what you want, and it builds, previews, and refines the result for you, turning frontier intelligence into work you can ship the same day.
How Opus 5.5 performs
Across agentic coding, computer use, and knowledge work, Opus 5.5 sits at the cost-to-score frontier, higher scores for less spend, with the clearest gains on the long, multi-step tasks it was built for. Figures reported by Anthropic.
Terminal-Bench 4.0
Accuracy vs CostTerminal-Bench 4.0 measures how well a model can complete complex, multi-step professional tasks within a command line interface. Opus 5.5 at default effort beats Opus 5 at max effort for about a fifth of the cost. It matches GPT-6 Astra at about 40% of the cost.
Source: Anthropic (anthropic.com/claude-opus-5-5). GDPval-AA by Artificial Analysis, AutomationBench by Zapier, WANDR by Perplexity.
Built on Happycapy with Opus 5.5
Games, interactive 3D, and scroll-driven sites, each built from a prompt in the browser. No setup, no local tools, just the finished thing running.
Blueprint
An interactive architecture study that animates a courtyard museum from line drawing to built form, with axonometric, elevation, and plan views. Built with Three.js.
What Opus 5.5 is best at
One frontier model that plans, codes, and carries a task to the finish, with the reliability long, multi-step work demands.
Agentic coding
Writes, runs, and debugs across a full codebase, and leads on hard software benchmarks like Terminal-Bench 4.0 and CursorBench, a clear step up from Opus 5.
Long, multi-step work
Stays on task across long runs, from codebase-wide migrations and audits to carrying a bigger build end to end, without losing the thread.
Knowledge work
Handles research, analysis, and professional deliverables, and posts a leading score on GDPval, which rates economically valuable knowledge work.
Computer use
Operates a browser and tools to complete real, multi-step workflows on its own, improving on Opus 5 on the OSWorld computer-use benchmark.
Who Opus 5.5 is for
From a quick build to a codebase-wide migration, Opus 5.5 meets you wherever the work gets long.
Engineering teams
Hand off migrations, refactors, and codebase-wide audits, and get work that holds up across a whole repository.
Builders and indie devs
Carry a build from a single prompt to a working app, with an agent that keeps going through the messy middle.
Analysts and professionals
Offload research, data analysis, and business workflows to a model that reasons through long, involved tasks.
Anyone with long tasks
Jobs that take many steps and do not fit in one prompt are where Opus 5.5 pulls ahead of earlier models.
What people are building with Opus 5.5
Games, 3D scenes, dashboards, and animations that builders shared on X, most from a single prompt. A snapshot of what Opus 5.5 ships in one pass.
Opus 5.5 FAQ
Everything you need to know about running Anthropic's Opus 5.5 on Happycapy.
What is Opus 5.5?
Opus 5.5 is Anthropic's newest frontier model and the first in the Claude 5.5 family. It leads in agentic coding, computer use, and knowledge work, and is a major step up from Opus 5 on complex, long, multi-step tasks.
How do I use Opus 5.5 on Happycapy?
Sign in, select Opus 5.5, and describe what you want to build. Happycapy runs it end to end in your browser, then previews and refines the result, with no setup required.
What is Opus 5.5 best at?
It excels at agentic coding across a full codebase, long multi-step runs such as codebase-wide migrations and audits, knowledge work and analysis, and computer use, staying reliable where the task takes many steps. The Happycapy use cases gallery collects real builds you can open and remix as a starting point.
How does Opus 5.5 compare with Opus 5?
On benchmarks reported by Anthropic, Opus 5.5 improves on Opus 5 across the board: Terminal-Bench 4.0 rises to 66.4% from 52.3%, CursorBench 4.0 to 57.8% from 46.6%, FrontierCode v1.1 to 54.6% from 48.0%, OSWorld 2.0 to 81.8% from 74.0%, and its GDPval knowledge-work Elo to 1846 from 1708.
How much does Opus 5.5 cost on Happycapy?
Via the Claude API, Opus 5.5 is priced at $4 per million input tokens and $20 per million output tokens, about 20% below Opus 5. On Happycapy, Opus 5.5 is a premium model on paid plans; create a free account to explore the platform first, then upgrade to run it.
Can Opus 5.5 handle long, multi-step tasks?
Yes. Opus 5.5 is built to stay reliable across long runs, including codebase-wide migrations and audits and larger builds carried end to end, which is where it separates most from earlier models.
What inputs and context does Opus 5.5 support?
Opus 5.5 accepts text and images and supports a 1M-token context window, enough to hold an entire codebase, long documents, or a full project brief in view at once.
Give Opus 5.5 the hard part
Point Opus 5.5 at a long, multi-step build and let it carry the work end to end. Just describe what you want and let it run.