Java 26 warning from reflective mutation of Byte Buddy AgentBuilder.Default.transformations under JEP 500

[unalpolat]

Describe the bug

When running the OpenTelemetry Java agent on Java 26, the JVM emits the following warning during startup:

From inspection of the packaged agent jar, this appears to come from OpenTelemetry reflectively replacing Byte Buddy's final transformations field on AgentBuilder$Default.

This is especially relevant on Java 26 because of JEP 500, which warns about reflective mutation of final fields:
https://openjdk.org/jeps/500

In Byte Buddy, AgentBuilder.Default declares the field:

protected final List<Transformation> transformations;

Byte Buddy AgentBuilder.java#L10717

OpenTelemetry Java agent, net.bytebuddy.agent.builder.AgentBuilderUtil reflectively accesses and mutates this field:

OpenTelemetry AgentBuilderUtil.java#L135

WARNING: Final field transformations in class net.bytebuddy.agent.builder.AgentBuilder$Default has been mutated reflectively by class net.bytebuddy.agent.builder.AgentBuilderUtil in unnamed module @4e08711f (file:/otel.jar)

Steps to reproduce

Run an application with the OpenTelemetry Java agent on Java 26.

Example startup shape:

java -javaagent:/path/to/otel.jar -jar app.jar
On startup, the JVM emits:

WARNING: Final field transformations in class net.bytebuddy.agent.builder.AgentBuilder$Default has been mutated reflectively by class net.bytebuddy.agent.builder.AgentBuilderUtil in unnamed module @4e08711f (file:/otel.jar)

Expected behavior

Ideally the agent should avoid reflective mutation of final fields on Java 26+, or have a compatibility path that does not trigger JEP 500 warnings.

At minimum, it would be helpful to know:

• whether this warning is expected and safe
• whether there is a plan to remove this reflective final-field mutation
• whether there is a supported workaround besides JVM flags such as: --enable-final-field-mutation=ALL-UNNAMED, --illegal-final-field-mutation=allow

Actual behavior

The application starts with the JVM warning above when the OpenTelemetry Java agent is enabled on Java 26.

Javaagent or library instrumentation version

v2.26.1

Environment

JDK: 26
OS: Alpine 3.23
Embedded Byte Buddy: 1.18.7
Base image: eclipse-temurin:26-jre-alpine

Additional context

No response

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