August 12th, 2026

New this release:

• 🎉 (all, smithy-rs#4758) Blob now stores its contents as Bytes and provides from_maybe_shared and into_bytes methods to avoid copies in Bytes-based protocol paths.

• 🎉 (client) Add opt-in capture of selected operation-input members for telemetry. Naming input members via
  Config::builder().emit_input_attributes([...]) makes the SDK capture those members' values into
  the ConfigBag (as CapturedTelemetryAttributes) during read_before_execution, before the input
  is consumed by serialization. Any interceptor can then read a value via
  cfg.load::<CapturedTelemetryAttributes>(), without threading it through a task_local!. Only
  string-valued, non-@sensitive members are eligible; capture is off by default.

  use aws_smithy_types::telemetry::CapturedTelemetryAttributes;
  
  // Opt in to capturing the S3 `Bucket` input member.
  let config = aws_sdk_s3::Config::builder()
      .emit_input_attributes(["Bucket"])
      // ...
      .build();
  
  // In any interceptor, read the captured value off the config bag — no `task_local!`.
  if let Some(bucket) = cfg
      .load::<CapturedTelemetryAttributes>()
      .and_then(|a| a.get("Bucket"))
  {
      // use `bucket`
  }

• 🎉 (client) Emit captured telemetry attributes and transfer sizes on the built-in client metrics. Values
  selected via emit_input_attributes([...]) are now attached as attributes on
  smithy.client.call.duration and smithy.client.call.attempt.duration. The operation-duration metric additionally
  carries the outcome as error.type (a coarse category, set only on failure) and the raw
  http.status_code when a response was received. Real transferred-byte counts are recorded on their
  own histograms, smithy.client.call.request.size / smithy.client.call.response.size, counted per
  frame and emitted when the body completes — so a streaming body reports its true size rather than the
  0 that content-length reports for it.

  // The same opt-in that captures a member now also emits it on the built-in metrics.
  let config = aws_sdk_s3::Config::builder()
      .emit_input_attributes(["Bucket"])
      // ...
      .build();
  
  // `smithy.client.call.duration` is now emitted with, e.g.:
  //   rpc.service="S3", rpc.method="GetObject", Bucket="my-bucket",
  //   error.type="connector" (on failure), http.status_code=200
  //
  // and body sizes on their own instruments, e.g.:
  //   smithy.client.call.response.size { rpc.service="S3", rpc.method="GetObject" } = 1024

• 🎉 (client) Add support for configuring additional server names in TLS certificate verification.
  When standard hostname verification fails, the client retries verification against
  each configured additional server name. This is useful when a server presents a
  certificate whose Subject Alternative Names (SANs) do not include the hostname used
  to connect, but do include an alternative name the client has been configured to accept.

• 🐛 (server, smithy-rs#4731, @hsbakshi) Fix RPC v2 CBOR server routing to use the verbatim Smithy operation shape name, matching the URI sent by spec-compliant clients.

  For operations whose modeled name starts lowercase, regeneration changes the accepted route from the previous capitalized form (for example, GetFoo) to the spec-compliant verbatim form (getFoo). Operations already modeled with an uppercase initial are unchanged.

  Set rpcV2CborAddCapitalizedRoute to true to also register the legacy capitalized route during migration.

• 🐛 (server, smithy-rs#4743, @takenoko-gohan) Fix server codegen referencing MakeSensitive at the wrong module path. The type is located at instrumentation::sensitivity::MakeSensitive, so generating a sensitive status-code formatter
  previously failed to compile (E0425).

• 🐛 (server) Make DefaultMetricsPlugin's Service impl generic over the request body type instead of
  hardcoding hyper::body::Incoming. The plugin only reads request extensions (operation name,
  service name, request ID) and never touches the body, so it composes with any body type. This
  fixes a compilation error when using DefaultMetricsPlugin with request bodies other than
  hyper::body::Incoming.

• (client, smithy-rs#4764) Improve discoverability of the retry token bucket: the config::retry module docs, the retry_config builder method, and the TokenBucket type now point to RetryPartition::custom().token_bucket(...) for sizing or isolating the bucket.

Contributors
Thank you for your contributions! ❤

• @hsbakshi (smithy-rs#4731)
• @takenoko-gohan (smithy-rs#4743)