How to Use Claude Opus 5.5: Practical Coding Guide

Claude Opus 5.5 arrived on 22 September 2026 as the first model in Anthropic’s Claude 5.5 family. It matches Claude Fable 5.1 on most tasks while costing 40% less to run than Opus 5 on typical workloads. Developers and knowledge workers now get stronger agentic coding, clearer writing, and faster output without raising their bills.

This guide shows how to access Opus 5.5, choose the right effort level, write effective prompts, and run long coding tasks. All details come from Anthropic’s official announcement and documentation.

Access Claude Opus 5.5

Opus 5.5 is available on Claude.ai for Pro, Max, and Team subscribers. Open a new chat and select Claude Opus 5.5 from the model picker if it appears. On Claude Code, update the tool and use the model ID claude-opus-5-5 or the alias that resolves to it.

API users call the model as claude-opus-5-5. Pricing sits at $4 per million input tokens and $20 per million output tokens. Cache reads drop to $0.20 per million. Fast mode costs $8 input and $40 output for up to 2.5x speed. Pro, Max, and Team plans also receive higher five-hour usage limits.

If you work inside Google Antigravity, check our earlier guide on accessing Claude Opus 5.5 in Google Antigravity.

Set the Effort Level

Thinking is always on in Opus 5.5. You cannot disable it. The effort parameter controls how deeply the model reasons before it answers. The default is medium.

Start most tasks at medium. It delivers quality close to Opus 5 at high effort for less cost. Raise effort only when a task fails or needs deeper analysis.

Effort	Best for	Notes
low	Classification, short rewrites, lookups	Fastest and cheapest
medium	Daily coding, drafting, document review	Default; start here
high	Multi-file changes, analytical reports	Solid quality step-up
xhigh	Long agentic coding, hard debugging	Used for peak benchmark scores
max	Research-grade reasoning	Highest quality; uses far more tokens

Anthropic recommends testing levels on your own work rather than copying settings from Opus 5.

Prompt for Long Tasks

Opus 5.5 handles multi-step work better than earlier Opus models. Give the full task in one message. State what finished looks like and when the model should stop and ask.

Example prompt for a coding migration:

Migrate the payment endpoints from the old client library to the new one.
Done means every endpoint uses the new client, the old client files are deleted, and the test suite passes.
Stop and ask only if a test fails for a reason you cannot explain.

Delete lines that say “think carefully,” “think step by step,” or “maximum reasoning.” Opus 5.5 already decides how much to think. Removing those instructions often makes replies start sooner with no clear quality loss.

For Claude Code, place stop rules in your CLAUDE.md file. Specify which actions need confirmation and which can continue. When a long run finishes, read the summary first before asking follow-up questions.

Run Coding and Knowledge Work

Early testers completed large migrations faster and with fewer tokens. One team audited a 200,000-line codebase in under three hours. Another finished a 680,000-line migration in less than a day. On Terminal-Bench 4.0, Opus 5.5 scores 66.4% at xhigh effort. On FrontierCode it leads at default settings while using fewer tokens than competitors.

Writing is clearer and leads with the key point. Testers noted it feels more natural over long sessions. For knowledge work, start at medium effort and raise only for complex analysis.

Practical Tips

• Begin every new project at medium effort and measure token use.
• Name the finish line in the first message.
• Use subagents for lookups and keep the main agent on medium or high.
• Check the System Card for safety details if your work touches biology or cybersecurity.
• Monitor your usage limits on Pro and Max plans; they stretch further because the model uses fewer tokens.

Conclusion

Claude Opus 5.5 lowers the cost of frontier coding and knowledge work while improving speed and clarity. Access it through Claude.ai, Claude Code, or the API. Start at medium effort, hand over complete tasks with clear done criteria, and remove outdated thinking instructions. The result is stronger output at roughly 40% lower cost on typical jobs.

Sources: Anthropic announcement (22 September 2026), Claude Platform pricing and model docs, Opus 5.5 System Card.