Claude Opus 5 to Opus 5.5: Model ID, Claude Code Setup, and API Migration
Start Here: The New ID and Migration Changes
The exact Claude API model ID for Opus 5.5 is claude-opus-5-5. Anthropic’s supplied model documentation lists its release as September 22, 2026, with status Active (latest). If you are maintaining an Opus 5 integration, treat this as a migration review—not just a model-name replacement.
Anthropic identifies four breaking changes for code already running on Opus 5:
- Thinking cannot be disabled. Opus 5.5 uses always-on adaptive thinking.
- Forced tool use returns an error. Review any workflow that requires the model to invoke a tool.
- Thinking blocks are tied to the model and conversation. Review how your application stores and reuses those blocks before changing models.
- The earlier
computer_20251124computer-use tool is not accepted on the Claude API and Google Cloud. Check the tool configuration if your application uses that version.
There is also a response-shape change: text between tool calls is returned in thinking blocks whose text is empty at the default display setting. Anthropic warns that applications streaming this text as progress updates can go quiet between tool calls until they select a display value that returns the text.
These changes come from the official Opus 5.5 overview. They are Anthropic specifications, not confirmation that every intermediary exposes the same features.
llmapi.pro availability is a separate question. The supplied subscription page explicitly lists claude-opus-5-5. Its setup and model-directory pages still recommend claude-opus-5. Before switching, consult the live catalog rather than interpreting an older recommendation as a complete availability list.
Official Opus 5.5 Specifications
The supplied Anthropic model overview and Opus 5.5 model page establish the following:
| Item | Official Opus 5.5 specification |
|---|---|
| Claude API model ID | claude-opus-5-5 |
| Context window | 1M tokens |
| Maximum output | 128K tokens |
| Thinking | Adaptive, always on |
| Default effort | medium |
| Input and output | Text and images → text |
The official model page separately documents a 300K output-token limit for the Message Batches API with the output-300k-2026-03-24 beta header. Do not treat that batch-specific capability as the ordinary maximum output or as proof of llmapi.pro support.
For migration planning, distinguish the model’s documented limits from your application’s chosen request limits. Check both before running a representative workload.
Anthropic Availability Versus the llmapi.pro Catalog
Anthropic lists Opus 5.5 on the Claude API, Amazon Bedrock, Google Cloud, Microsoft Foundry, and Claude Platform on AWS. Those are official platform listings; they do not establish availability through llmapi.pro.
The supplied llmapi.pro evidence is more specific:
- The Claude Code setup guide documents the relay configuration and an Opus 5 launch command.
- The model directory lists common model names, including
claude-opus-5, and directs readers to the full live models page. - The subscription page explicitly includes
claude-opus-5-5in its subscription model list and identifiesGET /v1/modelsas the authoritative subscription-availability list.
The supported conclusion is that llmapi.pro lists Opus 5.5 for subscriptions. That listing is not a successful request test, a guarantee of uninterrupted availability, or verification of every official feature and token limit.
Open the model directory and follow its live-list link before changing your configuration. For subscription-specific inclusion and current terms, use the subscription page. Keep those checks separate from the official specifications above.
Preserve the Documented Opus 5 Claude Code Setup
For an existing Opus 5 workflow, retain the setup documented by llmapi.pro. Its Claude Code instructions use ANTHROPIC_AUTH_TOKEN and the base URL https://llmapi.pro without /v1.
Replace YOUR_API_KEY with your own key locally. Do not paste a real key into shared documentation or troubleshooting messages.
macOS and Linux
export ANTHROPIC_BASE_URL="https://llmapi.pro"
export ANTHROPIC_AUTH_TOKEN="YOUR_API_KEY"
claude --model claude-opus-5
Windows PowerShell
$env:ANTHROPIC_BASE_URL = "https://llmapi.pro"
$env:ANTHROPIC_AUTH_TOKEN = "YOUR_API_KEY"
claude --model claude-opus-5
These examples preserve the documented Opus 5 model selection while correcting this guide’s authentication-variable example to match the supplied site setup instructions.
For persistence instructions, consult that setup page rather than adding credentials to a project file as part of the migration.
Select Opus 5.5 After Checking Availability
The llmapi.pro subscription page says listed model IDs can be entered into Claude Code’s model field. After checking the live list and configuring your environment, the corresponding launch command is:
claude --model claude-opus-5-5
This combines the documented claude --model command pattern with the model ID explicitly listed on the subscription page. It is a configuration example, not a report of a successful request or a feature-compatibility test.
Keep the older model selection available while evaluating the migration:
claude --model claude-opus-5
The supplied setup guide also warns that Claude Code’s built-in /model menu is not the site’s model catalog. Use the documented launch flag for explicit selection rather than treating menu visibility as an availability check.
Audit API Integrations Before Changing the Model Field
The following is a suggested review checklist, not a tested migration procedure or a report of observed llmapi.pro behavior.
| Review area | Official change | Suggested check |
|---|---|---|
| Thinking configuration | Thinking cannot be disabled | Find requests that attempt to turn thinking off |
| Tool selection | Forced tool use returns an error | Identify workflows that depend on forced invocation |
| Stored conversation state | Thinking blocks are tied to model and conversation | Inspect block replay and cross-model history handling |
| Computer use | computer_20251124 is not accepted on the Claude API and Google Cloud |
Identify the configured computer-use tool version |
| Progress display | Inter-tool text moves into thinking blocks, empty at the default display setting | Test the progress UI as well as the final answer |
| Effort | Opus 5.5 defaults to medium |
Make the intended effort policy part of the migration review |
Anthropic says effort controls thinking depth, but the supplied overview does not show a complete request example establishing its JSON placement. It also does not provide the exact replacement computer-use schema or the display-setting syntax needed for progress text.
Accordingly, this revision does not retain the previous article’s standalone top-level effort example as a verified request. Nor does it invent replacement payloads. Open the migration and feature references linked from the official Opus 5.5 page before implementing those changes.
The same evidence boundary applies to a full Messages API smoke test: the supplied excerpts support the model ID and the Claude Code setup above, but do not establish a complete, tested HTTP request and response contract. Use the relevant API reference before assembling a production request.
Validate the Migration and Check Current Pricing
For your own evaluation, choose a small set of representative tasks and compare the existing configuration with the proposed Opus 5.5 configuration. Suggested checks include:
- Whether the selected model accepts your request and tool configuration.
- Whether conversation-history handling works across the migration boundary.
- Whether progress updates remain visible between tool calls.
- Whether output length and the selected effort policy suit the workload.
These are illustrative checks, not benchmarks or claims that Opus 5.5 will improve a particular application.
For current official pricing, consult the Anthropic Opus 5.5 page. For llmapi.pro subscription pricing and inclusion, consult the site’s plans page; for the live model catalog, start with the model directory.
The practical migration path is to verify availability, select claude-opus-5-5, and review the four breaking changes plus the progress-text change before replacing an existing Opus 5 integration.