Models changelog

Claude Sonnet 5.5 is now available with experimental support across the Kiro IDE, CLI, Crew, and Web for Pro, Pro+, Pro Max, and Power customers in us-east-1 (IAD) and eu-central-1 (FRA). It's Anthropic's fastest Sonnet model to date and a clear upgrade over Sonnet 5: output is more than 30% faster, real-world knowledge work approaches Opus 5.5 performance, and clearer writing makes it a stronger collaborator. Claude Sonnet 5.5 includes a 1M-token context window, adaptive thinking on by default, and a 1.3x credit multiplier. To load the latest model list, restart the IDE or CLI, run kirocrew restart for Crew, or refresh Web in your browser. Learn more ->

Claude Opus 5.5 is now available with experimental support across the Kiro IDE, CLI, Crew, and Web for Pro, Pro+, Pro Max, and Power customers in us-east-1 (IAD) and eu-central-1 (FRA). Anthropic reports stronger performance on long, complex coding tasks and clearer communication than prior models. Claude Opus 5.5 includes a 1M-token context window and has a 2.0x credit multiplier. To load the latest model list, restart the IDE or CLI, run kirocrew restart for Crew, or refresh Web in your browser. Learn more ->

Claude Fable 5.1 is beginning to roll out in Preview across Kiro clients for Kiro Enterprise organizations. Anthropic's most capable agentic coding model traces problems to root causes, maintains context and intent across complex tasks, and improves reliability for multi-file refactors and long autonomous runs. It has a 1M context window and a 6x credit multiplier. Inference runs only in US East (N. Virginia) (us-east-1).

Availability is limited during the Preview rollout. Organizations with access can enable Fable 5.1 through model governance. After model access management is enabled, administrators can add Fable 5.1 from Manage approved list and make it available to their users.

All Fable 5.1 traffic is retained for up to 30 days (unless otherwise required by law) for automated offline abuse detection. Classifier-flagged traffic will be subject to potential human review performed by AWS, and we may review flagged traffic for abuse. Learn more ->

GPT-5.6 Sol, Terra, and Luna now support a 1M token context window, up from 272K, in the Kiro IDE, CLI, and Web. Entire codebases, long-form documents, and extended multi-turn agent histories fit in a single request, so repository-scale refactors, end-to-end debugging, and long-horizon agentic tasks run without chunking or losing earlier context. Credit multipliers for the GPT-5.6 family are updated with this launch and follow the two-tier context model OpenAI and Amazon Bedrock use: requests up to 272K tokens bill at the short context rate (Sol 4.4x, Terra 2.2x, Luna 1.1x), and requests above 272K tokens bill at double that rate. 1M context is rolling out gradually with experimental support to Kiro Pro, Pro+, Pro Max, and Power customers. Restart your IDE or CLI, or refresh Kiro Web, to see the updated models. Learn more ->

OpenAI reduced prices for GPT‑5.6 Terra and Luna, and we’re passing those savings on to Kiro customers. Updated credit multipliers reflect OpenAI’s new pricing and are live now.

• GPT‑5.6 Luna drops from 0.6x to 0.1x
• GPT‑5.6 Terra drops from 1.2x to 1.0x
• GPT‑5.6 Sol remains unchanged at 2.4x

GPT‑5.6 Sol, Terra, and Luna are available with experimental support to Kiro Pro, Pro+, Pro Max, and Power customers. See the original launch post for full details on GPT‑5.6 in Kiro.

Claude Opus 5 is now available in the Kiro IDE, CLI, and Web. It's a meaningful step up from Opus 4.8 on the hardest agentic coding tasks — setting new state-of-the-art results on leading coding benchmarks, more than doubling Opus 4.8's performance while approaching Fable 5 at half the cost. Excels at multi-file features, large refactors, and end-to-end feature work, completing full tasks rather than leaving stubs or placeholders. Opus 5 verifies its own work and iterates carefully until it succeeds. Multi-agent coordination sees meaningful gains with fewer conflicts between parallel agents. For code review, it finds a high rate of real bugs with low false positives and stays accurate at lower effort settings. Claude Opus 5 is rolling out gradually with experimental support to Kiro Pro, Pro+, Pro Max, and Power customers in us-east-1 and eu-central-1 with cross-region inference. 1M context window. 2.2x credit multiplier. Restart your IDE or CLI to access it from the model selector. Learn more ->

Claude Opus 4.8 and Claude Sonnet 5 are now available in the Kiro IDE and CLI across AWS GovCloud (US-East) and AWS GovCloud (US-West). Opus 4.8 brings stronger self-verification, efficient tool calling, and better follow-through on complex multi-step tasks, with a 1M context window and 2.2x credit multiplier. Sonnet 5 approaches Opus 4.8 on reasoning and agentic coding at lower cost, with a 1M context window, 1.3x credit multiplier, and experimental support. Update to the latest IDE or CLI version, then restart it to access the models from the model selector. Learn more ->

OpenAI models are available in Kiro for the first time. GPT-5.6 Sol, Terra, and Luna bring three tiers of frontier intelligence to the IDE, CLI, and Web — each tuned for a different point on the performance-cost curve. Sol is the flagship, built for the hardest multi-step work: spec-driven implementation, long-horizon refactors, and complex terminal tasks. It scores 80 on the Coding Agent Index and 88.8% on Terminal-Bench 2.1. Terra is the balanced option for routine multi-step development at a fraction of flagship cost. Luna is the fastest, lowest-cost tier for high-frequency tasks where throughput matters most. All three run longer without supervision and can write lightweight programs that coordinate tools and process intermediate results, reducing round-trips and dead ends. Hidden chain-of-thought means you see final output only. 272K context window across all tiers. Kiro credit multipliers: Sol 2.4x, Terra 1.2x, Luna 0.6x. Experimental support is rolling out to Pro, Pro+, Pro Max, and Power customers in us-east-1 and eu-central-1 with cross-region inference. Learn more ->

Claude Sonnet 5 is now available in the Kiro IDE, CLI, and Web. It's Anthropic's most agentic Sonnet model yet, a substantial upgrade from Sonnet 4.6 with stronger reasoning, tool use, and coding that approaches Opus 4.8 performance at Sonnet-class pricing. Plans before it edits, runs longer without supervision, and checks its own output without being asked. Sonnet 5 is rolling out gradually with experimental support to Kiro Pro, Pro+, Pro Max, and Power customers in the AWS US-East-1 (Northern Virginia) and AWS Europe (Frankfurt) regions, with cross-region inference support. It ships with the full 1M context window, 1.3x credit multiplier, the same as Sonnet 4.6. Restart your IDE or CLI to access it from the model selector. Learn more ->

OpenAI GPT-5.4 and NVIDIA Nemotron 3 Super 120B are now available in the Kiro IDE and CLI for AWS GovCloud (US-West). GPT-5.4 supports complex reasoning, coding, document analysis, and multi-step agentic workflows with a 272K context window and 1.2x credit multiplier. Nemotron 3 Super 120B is an open weight option with a 256K context window, 32K maximum output, and 0.25x credit multiplier. Update to the latest IDE or CLI version, then restart it to access the models from the model selector. Learn more ->