---
source: https://iinventedlight.com/library/notes/rust-async-await-futures.md
title: "Async, await, and Futures in Rust"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "MIT OR Apache-2.0 (rust-lang/book; Copyright (c) 2010 The Rust Project Developers); additional cited sources under MIT OR Apache-2.0; prose restates cited source lines in own words"
license_family: rust-mit
attribution: "Summary by iinventedlight (AI-assisted). Sources: The Rust Project (The Rust Programming Language book), Fundamentals of Asynchronous Programming: Async, Await, Futures, and Streams, MIT OR Apache-2.0; The Rust Project (The Rust Programming Language book), Futures and the Async Syntax, MIT OR Apache-2.0; The Rust Standard Library, Future trait, MIT OR Apache-2.0. Notices: The Rust Programming Language book (rust-lang/book): Copyright (c) 2010 The Rust Project Developers; MIT OR Apache-2.0, used under MIT (https://github.com/rust-lang/book/blob/main/LICENSE-MIT). The Rust Standard Library docs (rust-lang/rust): Copyright (c) The Rust Project Contributors; MIT OR Apache-2.0, used under MIT (https://github.com/rust-lang/rust/blob/master/LICENSE-MIT)."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-09
status: published
approved_by: "Cole Withington, 2026-11-09 13:40 PT: \"Yes, publish all 15 Rust drafts\""
checked_on: 2026-11-09
as_of: 2026-11-09
confidence: medium
untested: "No Rust code was run for this note; only the fetched documentation pages were read."
category: coding-references
topic_area: "code-systems: Rust async"
tags: [rust, async, await, futures]
client: Librarian
sources:
  - id: S1
    title: "Fundamentals of Asynchronous Programming: Async, Await, Futures, and Streams"
    publisher: The Rust Project (The Rust Programming Language book)
    url: https://doc.rust-lang.org/book/ch17-00-async-await.html
    accessed: 2026-11-09
    license: "MIT OR Apache-2.0"
  - id: S2
    title: "Futures and the Async Syntax"
    publisher: The Rust Project (The Rust Programming Language book)
    url: https://doc.rust-lang.org/book/ch17-01-futures-and-syntax.html
    accessed: 2026-11-09
    license: "MIT OR Apache-2.0"
  - id: S3
    title: "Future trait"
    publisher: The Rust Standard Library
    url: https://doc.rust-lang.org/std/future/trait.Future.html
    accessed: 2026-11-09
    license: "MIT OR Apache-2.0"
---
# Async, await, and Futures in Rust

**Answer:** Futures are lazy and don't do anything until you use `await`. An `async fn` desugars to a function that returns a future of its return type.

## Futures

A future represents an asynchronous computation commonly obtained by `async`. A future is a value that may not be ready now but will become ready later.

## Claims

- id: C1
  claim: Asynchronous programming is a core challenge covered in the Rust book.
  source: S1
  evidence: "Asynchronous Programming: Async, Await, Futures, and Streams Many operations we ask the computer to do"

- id: C2
  claim: Futures in Rust are lazy until you await them.
  source: S2
  evidence: "futures in Rust are lazy: they don't do anything until you ask them to with"
- id: C3
  claim: Writing async fn is equivalent to returning a future.
  source: S2
  evidence: "writing async fn is equivalent to writing a function that returns a future of the"
- id: C4
  claim: A future represents an asynchronous computation.
  source: S3
  evidence: "A future represents an asynchronous computation, commonly obtained by use of async ."

## Sources

- [S1] Fundamentals of Asynchronous Programming: Async, Await, Futures, and Streams. The Rust Project (The Rust Programming Language book). https://doc.rust-lang.org/book/ch17-00-async-await.html . License: MIT OR Apache-2.0. Accessed 2026-11-09.
- [S2] Futures and the Async Syntax. The Rust Project (The Rust Programming Language book). https://doc.rust-lang.org/book/ch17-01-futures-and-syntax.html . License: MIT OR Apache-2.0. Accessed 2026-11-09.
- [S3] Future trait. The Rust Standard Library. https://doc.rust-lang.org/std/future/trait.Future.html . License: MIT OR Apache-2.0. Accessed 2026-11-09.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted). Sources and notices: The Rust Programming Language book (rust-lang/book): Copyright (c) 2010 The Rust Project Developers; MIT OR Apache-2.0, used under MIT (https://github.com/rust-lang/book/blob/main/LICENSE-MIT). The Rust Standard Library docs (rust-lang/rust): Copyright (c) The Rust Project Contributors; MIT OR Apache-2.0, used under MIT (https://github.com/rust-lang/rust/blob/master/LICENSE-MIT). Text was condensed and changed from the originals.

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