Claude Opus 5.5 Is Live: Fable-Class Results for Less Than Opus 5

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Key Takeaways

• Fable-class results at an Opus price: 66.4% on Terminal-Bench 4.0, ahead of Fable 5.1 (55.8%) and Opus 5 (52.3%); it beats Fable 5.1 on most coding, knowledge-work and computer-use benchmarks
• Lower prices across the board: $4 input / $20 output per 1M tokens (Opus 5: $5 / $25), cache reads down from $0.50 to $0.20; Anthropic says typical workloads cost about 40% less than on Opus 5
• Faster output: Anthropic says it generates output more than 30% faster than Opus 5
• Live on APIYI: claude-opus-5-5 and claude-opus-5-5-thinking, on both the OpenAI-compatible and native Anthropic endpoints, with all four billing items matching the provider
• Four breaking changes: thinking can’t be disabled, forced tool use returns 400, thinking blocks are bound to the model and conversation, and computer use needs the new toolset; the default effort drops from high to medium

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Background

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In Detail

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Core Features

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Performance Highlights

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For Developers: Four Breaking Changes

• Progress text written between tool calls now comes back in thinking blocks (empty by default; set thinking.display: "updates" to see it)
• The safety classifiers cover more ground: besides cybersecurity, biology requests and attempts to extract the reasoning process may also be declined (stop_reason: "refusal"); high-risk cybersecurity requests are routed by Anthropic to Claude Opus 4.8

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Technical Specs

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Using It

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Recommended Scenarios

1. Agentic coding: large code migrations, repo-wide refactors and terminal automation, where the gains are largest
2. Knowledge work: reports, research, spreadsheets and documents, with a clear lead on GDPval-AA
3. Computer use and automation: 81.8% on OSWorld 2.0, a good fit for browser and desktop workflows
4. Replacing most Fable 5.1 workloads: outside the hardest reasoning tasks, similar or better results at 40% of the price

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Code Examples

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Native Anthropic Format

import anthropic

client = anthropic.Anthropic(
    api_key="your-apiyi-key",
    base_url="https://api.apiyi.com"
)

message = client.messages.create(
    model="claude-opus-5-5",
    max_tokens=64000,
    output_config={"effort": "high"},  # default is medium; raise it explicitly for coding
    messages=[
        {
            "role": "user",
            "content": "Migrate this module from callbacks to async/await, add tests, and explain the trade-off at each step."
        }
    ]
)

for block in message.content:
    if block.type == "text":
        print(block.text)

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OpenAI-Compatible Format

from openai import OpenAI

client = OpenAI(
    api_key="your-apiyi-key",
    base_url="https://api.apiyi.com/v1"
)

response = client.chat.completions.create(
    model="claude-opus-5-5",
    messages=[
        {"role": "user", "content": "Find the root cause of this production bug step by step and propose a fix."}
    ]
)

print(response.choices[0].message.content)

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Five Checks When Migrating from Opus 5

1. Change the model name: claude-opus-5 → claude-opus-5-5
2. Remove thinking-off settings: drop thinking: {"type": "disabled"}; set effort to low if you need low latency
3. Remove forced tool use: switch tool_choice to auto, check the reply actually contains a tool call, and retry if not
4. Set effort explicitly: the default is now medium; start coding and agent work at high or xhigh
5. Keep history append-only: pass thinking blocks back unchanged and don’t edit system / tools / earlier messages between requests

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Pricing and Availability

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Pricing

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Groups and Endpoints

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Stack with Top-Up Promotions

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Summary

1. Opus 5 users: change the model name to upgrade, but run the five checks above first, especially thinking-off settings, forced tool use and the effort default
2. Fable 5.1 users: move most workloads to Opus 5.5 for an evaluation round first, at about 40% of the cost
3. Coding / agent workflows: set effort to high or xhigh explicitly and leave max_tokens room for thinking