Support for Parallel Tool Execution with Custom Models

[omricarmi4]

I am using adk-java version 0.5.0 with a custom model implementation (wrapping GPT-4.1 / GPT-5.1 via LangChain4j).

When these models return multiple tool calls in a single turn (Parallel Function Calling), the LlmAgent in the Java ADK executes them sequentially. This results in significant, avoidable latency compared to concurrent execution.

I have verified that this exact architecture works correctly in the Python ADK (v1.10.0) using the LiteLLM wrapper. In the Python environment, the same models successfully trigger parallel tool execution, drastically reducing the total response time.

I attempted to enforce parallelism using the RunConfig builder in Java, but it did not result in concurrent execution:

Java

RunConfig runConfig = RunConfig.builder()
    .setToolExecutionMode(ToolExecutionMode.PARALLEL)
    .build(); 
// Passed this config to the agent runner

Question Is parallel tool execution currently supported for custom model implementations in the Java ADK? If so, is there a specific configuration required beyond ToolExecutionMode.PARALLEL? If not, is this a planned enhancement for an upcoming release?