Use Sonnet 5.5 in Claude Code: model, effort and access

To select Sonnet 5.5 explicitly in Claude Code, use claude --model claude-sonnet-5-5 for a new session or /model claude-sonnet-5-5 inside a session, on a provider that accepts that model ID. First check the client version and your account’s model permissions. Anthropic’s current documentation requires Claude Code v2.1.284 or later for Sonnet 5.5.

This guide separates three things that are easy to confuse: the client recognizing the model, the provider serving it, and the account being allowed to use it. The instructions were checked against Claude Code’s model configuration documentation on September 29, 2026. They do not establish that every subscription or third-party endpoint has access.

Check and select the model

In your terminal:

claude --version
claude update
claude --model claude-sonnet-5-5 --effort medium

claude update changes the installed client. Follow your organization’s software-management process if the installation is managed. In an existing interactive session, use:

/model claude-sonnet-5-5
/status

Check the displayed model and provider rather than assuming the command succeeded. Do not use the generated answer’s self-description as proof of the serving model; the client state and response metadata are more useful evidence.

The short alias sonnet is convenient, but its meaning depends on the provider and client version. The current documentation maps it to Sonnet 5.5 for the Anthropic API while some cloud-provider aliases still resolve to older Sonnet models. A full model name makes your intent explicit, but you must still use the identifier and access route supported by that provider.

Why changing the default is not enough

Claude Code’s default model is not necessarily the newest Sonnet. Current documentation lists Opus 5.5 as the default for several account/provider categories. Selecting Sonnet is a deliberate action. If an organization restricts model choices, the available list may differ from examples in a public guide.

An environment variable such as ANTHROPIC_DEFAULT_SONNET_MODEL can also change what the alias resolves to. Before editing configuration, inspect the applicable user, project and managed settings. Keep a note of the old value so you can undo a local experiment. Avoid overwriting a shared team’s provider settings to fix one session.

Use explicit selection for a reproducible test, then choose whether a persistent default is appropriate. A one-off test does not require changing every repository or every agent definition.

Pick effort for the task

The Sonnet 5.5 API defaults to high effort. Claude Code’s model configuration describes medium as Sonnet 5.5’s default there. Those statements refer to different entry points, so they are not interchangeable.

For a well-specified code change, medium is a reasonable documented starting point. Increase effort only when the task and results justify it. Use /effort in the interactive client or --effort when launching, subject to your account’s restrictions. Managed effort caps can limit the effective setting even when you requested something higher; record the applied configuration where it is available.

The effort guide explains why a higher label is not automatically a better result. Start with an isolated branch, explicit acceptance criteria and a reviewable diff. The model still needs permission to run tools and you still need to inspect the changes before merging them.

Separate subscription access from API billing

A Claude subscription login and an API key are different access routes. A message saying the organization disabled subscription access for Claude Code is an account-policy block, not proof that the Sonnet model is down. Ask the administrator to review the approved access route; do not attempt to bypass a managed restriction.

During preparation for this guide, our local Claude Code v2.1.281 run returned that organization-access message and did not execute a Sonnet task. It was also below the documented minimum version. We therefore do not claim a successful model test, timing result or cost measurement from that attempt. The command examples above are documentation-verified instructions.

If an approved API route is available, its requests follow API billing rather than becoming free because you also have a subscription. Check the exact endpoint, model, account and current rates before testing. See the Sonnet API cost guide for the vendor rate-card calculation.

Troubleshoot the actual failure

Do not use a 404 as proof of a global outage or a 429 as proof of a subscription cancellation. Save a redacted error body, timestamp and client version. Never post tokens, full environment dumps or private repository context with a support request.

For native request changes, use the Sonnet 5.5 API migration checklist. For deciding whether to switch from an older model at all, see Sonnet 5 versus 5.5.