I tried Claude Sonnet 5.5 which became available for selection in Kiro
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Introduction
On October 3, 2026, Claude Sonnet 5.5 became available in Kiro as an Experimental preview.
Anthropic released Claude Sonnet 5.5 on September 28, 2026. According to the announcement on the same day, it is available on various platforms including Amazon Web Services.
Anthropic has announced that it is more than 30% faster than Sonnet 5 and up to 30% lower cost for most tasks.
This article introduces how to select Claude Sonnet 5.5 in the Kiro CLI and the responses actually obtained.
Selecting in the Kiro IDE
In the IDE's model selector, Claude Sonnet 5.5 was listed as an Experimental preview. The notation showed 1.3x Credit and 1M context window.
Selecting in the Kiro CLI
Running kiro-cli chat --list-models with kiro-cli 2.26.1, here are the relevant lines extracted.
...
claude-sonnet-5 1.30x credits Claude Sonnet 5 model with 1M context window
...
qwen3-coder-next 0.05x credits Experimental preview of Qwen3 Coder Next
claude-sonnet-5.5 1.30x credits Experimental preview of Claude Sonnet 5.5 model with 1M context window
claude-sonnet-5.5 has the same 1.30x as Sonnet 5. Switching models does not change the credit multiplier per model.
Running with --model claude-sonnet-5.5 specified, a response was obtained.
kiro-cli chat --no-interactive --model claude-sonnet-5.5 "1文で自己紹介してください"
私はKiroです。ターミナル上でコーディング、システム操作、AWS管理、開発ワークフローを支援するAIエージェントです。
Enabling in a Model Governance-Enabled Environment
In environments with model governance enabled, models that can be used are explicitly specified using a whitelist approach. Sonnet 5.5 will not automatically become available, and members cannot select it until it is checked in the approved list.
The procedure for opening "Manage approved list" from "Model availability" in the admin screen is described in the Opus 5.5 article.
In the approved list as well, Sonnet 5.5 was at the bottom of the list. Check the box and click "Save list".
Summary
Claude Sonnet 5.5 is now available as an Experimental preview in both the Kiro IDE and CLI.
The credit multiplier for Sonnet 5.5 is the same as the conventional Sonnet 5, and according to Anthropic, it has also recorded results comparable to Opus 5.5 on some benchmarks.
Please take advantage of Sonnet 5.5, which can be expected to offer cost-effective usage, in Kiro as well.
