July 23rd, 2026

New this release:

• 🐛 (client, smithy-rs#4749) Fix two retry-behavior bugs:

  • Under Retry Behavior 2.1, adaptive retry mode now acquires a client-side rate-limiter send token before every send, including retries. Previously a retry computed a rate-limiter delay but sent without acquiring a token, so the adaptive rate limiter under-throttled retried requests. Pre-2.1 adaptive behavior — still the default today, until 2.1 becomes the default (see aws-sdk-rust#1431) — is unchanged.
  • Honor the server-directed x-amz-retry-after header on responses that are retryable purely by HTTP status (e.g. a bare 500). This is enabled by a new ClassifyRetry::classify_retry_v2, which additionally receives the RetryAction accumulated by earlier-running classifiers and can refine it. It has a default implementation that delegates to classify_retry, so existing classifiers are unaffected.

• 🐛 (client, smithy-rs#4741, @mark-creamer-amazon) Fix keys() JMESPath codegen for union shapes by using the symbol provider's resolved variant names instead of raw member names. This correctly handles modeled Unknown members (which get renamed to avoid colliding with the synthetic Unknown unit variant) and preserves the original wire name in the match output.

• 🐛 (client, @lauzmata) Fix endpoint rules codegen emitting invalid Rust when a templated static segment
  is a single character requiring escape in a Rust char literal (e.g. ', ",
  \). Previously produced out.push('''); in internals.rs; now always emits
  out.push_str(...) with proper string escaping.

• (client) Replace the hardcoded 5-second identity cache load_timeout with a pessimistic timeout derived from the configured RetryConfig and TimeoutConfig. The new default ensures the inner credential provider's retry strategy has enough time to exhaust all configured attempts before the cache kills the resolution future. With default settings (3 attempts, 3.1s connect timeout), the derived timeout is approximately 22 seconds. Customers who explicitly set load_timeout are unaffected.

  If you rely on the legacy 5-second timeout behavior, you can restore it explicitly:

  use aws_smithy_runtime::client::identity::IdentityCache;
  use std::time::Duration;
  
  IdentityCache::lazy()
      .load_timeout(Duration::from_secs(5))
      .build()

Contributors
Thank you for your contributions! ❤

• @lauzmata
• @mark-creamer-amazon (smithy-rs#4741)