July 7th, 2026

Breaking Changes:

• ⚠️ (all, smithy-rs#4692) Upgrade MSRV to Rust 1.94.1.

New this release:

• 🎉 (client, smithy-rs#4726, @mark-creamer-amazon) Add keys() JMESPath function support for union shapes in waiter matchers. This enables waiters to match on the active variant of a union using keys(unionField) with the allStringEquals or anyStringEquals comparators.
• 🐛 (server, @lauzadis) Soften the server codegen's handling of unknown codegen configuration keys: log a warning instead of throwing IllegalArgumentException. This makes server codegen forward-compatible with smithy-build.json files that carry keys recognized by other tools or by future server codegen versions, matching the lenient behavior already used for client codegen settings.
• 🐛 (all, aws-sdk-rust#1433, aws-sdk-rust#1418, @iconara) Update the User-Agent header to contain the same information as the x-amz-user-agent header (including AppName, environment metadata, business metrics, etc.)
• 🐛 (all, smithy-rs#4729) Fix codegen emitting integer literals for f64/f32 non-zero default value comparisons in serializers. When a Smithy model specifies a non-zero @default on a Double or Float member using a JSON integer (e.g., 1 instead of 1.0), the generated "skip if default" check produced if value != 1 which fails to compile in Rust. The fix appends _f64/_f32 type suffixes to the rendered default value.

Contributors
Thank you for your contributions! ❤

• @iconara (aws-sdk-rust#1418, aws-sdk-rust#1433)
• @lauzadis
• @mark-creamer-amazon (smithy-rs#4726)