Remote functions - CoreWeave Docs

The examples on this page omit auth. To authenticate with your W&B API key, install cwsandbox[wandb] and pass auth=AuthStrategy.WANDB to Sandbox.run(), Sandbox(), or Sandbox.session(). See Get started.

This tutorial shows you how to run Python functions inside a sandbox using remote functions. You can call sandbox-executed code as if it were a local function instead of constructing shell command strings. It’s for developers who want to invoke compute in a sandbox directly from their Python code and collect typed results.

Define and call a remote function

Decorate a function with @session.function() to call it inside the sandbox with .remote(). The call returns a reference you resolve with .result():

from cwsandbox import Sandbox, SandboxDefaults

with Sandbox.session(SandboxDefaults()) as session:
    @session.function()
    def add(x: int, y: int) -> int:
        return x + y

    result = add.remote(2, 3).result()  # 5

Run functions in parallel with `.map()`

Use .map() to dispatch many invocations at once and collect their results. Independent calls run concurrently instead of one at a time:

@session.function()
def square(x: int) -> int:
    return x * x

refs = square.map([(1,), (2,), (3,)])
results = [r.result() for r in refs]  # [1, 4, 9]

Next steps

You can now invoke Python functions inside a sandbox as if they were local calls, and fan out work in parallel with .map(). For serialization modes, .local() testing, and more, see the Remote functions guide.

Last modified on September 30, 2026

​Define and call a remote function

​Run functions in parallel with .map()

​Next steps

Define and call a remote function

Run functions in parallel with `.map()`

Next steps