Stream: git-wasmtime

Topic: wasmtime / issue #13705 C API support status for Async Co...

Wasmtime GitHub notifications bot (Jun 22 2026 at 07:20):

rudikone opened issue #13705:

Hello.

I'm evaluating Wasmtime as an embedding runtime from Java through the public Wasmtime C API.

I noticed that Async Component Model support (component-model-async) appears to be available in the Rust API, including APIs such as:

• Func::call_concurrent
• Func::start_call_concurrent
• Func::finish_call_concurrent
• Store::run_concurrent
• func_wrap_concurrent
• native handling of component-model future<T> and stream<T>

At the same time, I cannot find equivalent functionality in the public C API.

From the documentation it looks like the C API currently exposes the older async mechanism based on:

• wasmtime_config_async_support_set
• wasmtime_func_call_async
• wasmtime_call_future_t

which solves host-side asynchronous execution, but does not appear to expose the Async Component Model scheduler or guest task APIs.

Questions:

1. Is exposing Async Component Model functionality in the C API part of the current roadmap?

2. Is there already an issue tracking support for:

   • call_concurrent
   • run_concurrent
   • concurrent guest Tasks
   • component-model future / stream
   • func_wrap_concurrent

3. Is the current recommendation for non-Rust embedders to:

   • use Rust as an adapter layer and expose custom FFI,
   • or wait for first-class C API support?

4. Are there known architectural blockers preventing a direct mapping of the Async Component Model APIs into the C API?

The motivation is support for WASI 0.3 style component composition from Java without introducing an intermediate Rust host layer.

Thanks.

Wasmtime GitHub notifications bot (Jun 29 2026 at 14:00):

alexcrichton added the wasmtime:c-api label to Issue #13705.

Wasmtime GitHub notifications bot (Jun 29 2026 at 14:00):

alexcrichton added the wasm-proposal:component-model-async label to Issue #13705.

Wasmtime GitHub notifications bot (Jun 29 2026 at 14:01):

alexcrichton commented on issue #13705:

Yes *_concurrent functions aren't exposed just yet in the C API. There'll need to be some work necessary to get those exposed, but my hope is that it's relatively similar to StoreContextMut<'_, ..> and how it's exposed. No one's lined up to do this just yet, however.

Last updated: Jul 29 2026 at 05:03 UTC