diff --git a/.cargo/config.toml b/.cargo/config.toml
index e9a242c..aa3925b 100644
--- a/.cargo/config.toml
+++ b/.cargo/config.toml
@@ -3,3 +3,9 @@
 # * AWS auth environment variables, for running the wstd-aws integration tests.
 # * . directory is available at .
 runner = "wasmtime run -Shttp --env AWS_ACCESS_KEY_ID --env AWS_SECRET_ACCESS_KEY --env AWS_SESSION_TOKEN --dir .::."
+
+[target.wasm32-wasip3]
+# wasmtime is given:
+# * AWS auth environment variables, for running the wstd-aws integration tests.
+# * . directory is available at .
+runner = "wasmtime run -Shttp -Sp3 --env AWS_ACCESS_KEY_ID --env AWS_SECRET_ACCESS_KEY --env AWS_SESSION_TOKEN --dir .::."
diff --git a/.github/actions/install-rust/action.yml b/.github/actions/install-rust/action.yml
index 0d11907..57cc11c 100644
--- a/.github/actions/install-rust/action.yml
+++ b/.github/actions/install-rust/action.yml
@@ -31,6 +31,11 @@ runs:
         rustup update "${{ steps.select.outputs.version }}" --no-self-update
         rustup default "${{ steps.select.outputs.version }}"
 
+        # Required for -Zbuild-std for the wasip3 target.
+        if [ "${{ inputs.toolchain }}" = "nightly" ]; then
+          rustup component add rust-src
+        fi
+
         # Save disk space by avoiding incremental compilation. Also turn down
         # debuginfo from 2 to 0 to help save disk space.
         cat >> "$GITHUB_ENV" <<EOF
diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 1362609..9e2f537 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -51,9 +51,13 @@ jobs:
     - name: check
       run: cargo check --workspace --all --bins --examples
 
-    - name: wstd tests
+    - name: wstd p2 tests
       run: cargo test -p wstd -p wstd-axum --target wasm32-wasip2 -- --nocapture
 
+    - name: wstd p3 tests
+      if: matrix.rust == 'nightly'
+      run: cargo test -p wstd -p wstd-axum --target wasm32-wasip3 -Z build-std=std,panic_abort -- --nocapture
+
     - name: test-programs tests
       run: cargo test -p test-programs -- --nocapture
       if: steps.creds.outcome == 'success'
@@ -90,4 +94,3 @@ jobs:
     - run: ./publish bump
     # Make sure the tree is publish-able as-is
     - run: ./publish verify
-
diff --git a/Cargo.toml b/Cargo.toml
index 386afa8..fc43b0f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -27,13 +27,18 @@ http.workspace = true
 itoa.workspace = true
 pin-project-lite.workspace = true
 slab.workspace = true
-wasip2.workspace = true
 wstd-macro.workspace = true
 
 # optional
 serde = { workspace = true, optional = true }
 serde_json = { workspace = true, optional = true }
 
+[target.'cfg(target_env = "p2")'.dependencies]
+wasip2.workspace = true
+
+[target.'cfg(target_env = "p3")'.dependencies]
+wasip3.workspace = true
+
 [dev-dependencies]
 anyhow.workspace = true
 clap.workspace = true
@@ -95,13 +100,13 @@ test-programs = { path = "test-programs" }
 tower-service = "0.3.3"
 ureq = { version = "3.1", default-features = false, features = ["json"] }
 wasip2 = "1.0"
-wstd = { path = ".", version = "=0.6.8" }
+wasip3 = "0.8"
+wstd = { path = ".", version = "=0.6.8", default-features = false }
 wstd-axum = { path = "./axum", version = "=0.6.8" }
 wstd-axum-macro = { path = "./axum/macro", version = "=0.6.8" }
 wstd-macro = { path = "./macro", version = "=0.6.8" }
 
 [package.metadata.docs.rs]
-all-features = true
 targets = [
     "wasm32-wasip2"
 ]
diff --git a/axum/Cargo.toml b/axum/Cargo.toml
index 154a021..74141e9 100644
--- a/axum/Cargo.toml
+++ b/axum/Cargo.toml
@@ -13,7 +13,7 @@ rust-version.workspace = true
 [dependencies]
 axum.workspace = true
 tower-service.workspace = true
-wstd.workspace = true
+wstd = { workspace = true, features = ["json"] }
 wstd-axum-macro.workspace = true
 
 [dev-dependencies]
diff --git a/axum/examples/hello_world.rs b/axum/examples/hello_world.rs
index 90a9cbd..8cf124c 100644
--- a/axum/examples/hello_world.rs
+++ b/axum/examples/hello_world.rs
@@ -1,3 +1,6 @@
+#![cfg_attr(not(target_env = "p2"), no_main)]
+#![cfg(target_env = "p2")]
+
 //! Run with
 //!
 //! ```sh
diff --git a/axum/examples/hello_world_nomacro.rs b/axum/examples/hello_world_nomacro.rs
index f3068d1..44744e5 100644
--- a/axum/examples/hello_world_nomacro.rs
+++ b/axum/examples/hello_world_nomacro.rs
@@ -1,3 +1,6 @@
+#![cfg_attr(not(target_env = "p2"), no_main)]
+#![cfg(target_env = "p2")]
+
 //! Run with
 //!
 //! ```sh
diff --git a/axum/examples/weather.rs b/axum/examples/weather.rs
index 5163fcc..f404c0f 100644
--- a/axum/examples/weather.rs
+++ b/axum/examples/weather.rs
@@ -1,3 +1,6 @@
+#![cfg_attr(not(target_env = "p2"), no_main)]
+#![cfg(target_env = "p2")]
+
 //! This demo app shows a Axum based wasi-http server making an arbitrary
 //! number of http requests as part of serving a single response.
 //!
diff --git a/axum/src/lib.rs b/axum/src/lib.rs
index 3272b91..d113410 100644
--- a/axum/src/lib.rs
+++ b/axum/src/lib.rs
@@ -1,3 +1,4 @@
+#![cfg(target_env = "p2")]
 //! Support for the [`axum`] web server framework in wasi-http components, via
 //! [`wstd`].
 //!
diff --git a/examples/complex_http_client.rs b/examples/complex_http_client.rs
index 703e931..7dadebf 100644
--- a/examples/complex_http_client.rs
+++ b/examples/complex_http_client.rs
@@ -1,3 +1,6 @@
+#![cfg_attr(not(target_env = "p2"), no_main)]
+#![cfg(target_env = "p2")]
+
 use anyhow::{Result, anyhow};
 use clap::{ArgAction, Parser};
 use std::str::FromStr;
diff --git a/examples/http_client.rs b/examples/http_client.rs
index f4465a8..6850d60 100644
--- a/examples/http_client.rs
+++ b/examples/http_client.rs
@@ -1,3 +1,6 @@
+#![cfg_attr(not(target_env = "p2"), no_main)]
+#![cfg(target_env = "p2")]
+
 use anyhow::{Result, anyhow};
 use clap::{ArgAction, Parser};
 use wstd::http::{Body, BodyExt, Client, Method, Request, Uri};
diff --git a/examples/http_server.rs b/examples/http_server.rs
index 8449f83..5486f0c 100644
--- a/examples/http_server.rs
+++ b/examples/http_server.rs
@@ -1,3 +1,6 @@
+#![cfg_attr(not(target_env = "p2"), no_main)]
+#![cfg(target_env = "p2")]
+
 use anyhow::{Context, Result};
 use futures_lite::stream::{once_future, unfold};
 use http_body_util::{BodyExt, StreamBody};
diff --git a/examples/http_server_proxy.rs b/examples/http_server_proxy.rs
index ccad608..77bb231 100644
--- a/examples/http_server_proxy.rs
+++ b/examples/http_server_proxy.rs
@@ -1,3 +1,6 @@
+#![cfg_attr(not(target_env = "p2"), no_main)]
+#![cfg(target_env = "p2")]
+
 //! Run the example with:
 //! ```sh
 //! cargo build --example http_server_proxy --target=wasm32-wasip2
diff --git a/examples/tcp_echo_server.rs b/examples/tcp_echo_server.rs
index f1dd895..3e8aef2 100644
--- a/examples/tcp_echo_server.rs
+++ b/examples/tcp_echo_server.rs
@@ -1,3 +1,6 @@
+#![cfg_attr(not(target_env = "p2"), no_main)]
+#![cfg(target_env = "p2")]
+
 use wstd::io;
 use wstd::iter::AsyncIterator;
 use wstd::net::TcpListener;
diff --git a/examples/tcp_stream_client.rs b/examples/tcp_stream_client.rs
index 2e93faf..c14b267 100644
--- a/examples/tcp_stream_client.rs
+++ b/examples/tcp_stream_client.rs
@@ -1,3 +1,6 @@
+#![cfg_attr(not(target_env = "p2"), no_main)]
+#![cfg(target_env = "p2")]
+
 use wstd::io::{self, AsyncRead, AsyncWrite};
 use wstd::net::TcpStream;
 
diff --git a/src/lib.rs b/src/lib.rs
index ebc673d..c3442aa 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -55,30 +55,44 @@
 //! These are unique capabilities provided by WASI 0.2, and because this library
 //! is specific to that are exposed from here.
 
+#[cfg(target_env = "p2")]
 pub mod future;
+#[cfg(target_env = "p2")]
 #[macro_use]
 pub mod http;
+#[cfg(target_env = "p2")]
 pub mod io;
 pub mod iter;
+#[cfg(target_env = "p2")]
 pub mod net;
+#[cfg(target_env = "p2")]
 pub mod rand;
+#[cfg(target_env = "p2")]
 pub mod runtime;
+#[cfg(target_env = "p2")]
 pub mod task;
+#[cfg(target_env = "p2")]
 pub mod time;
 
-pub use wstd_macro::attr_macro_http_server as http_server;
-pub use wstd_macro::attr_macro_main as main;
-pub use wstd_macro::attr_macro_test as test;
+#[cfg(target_env = "p2")]
+pub use wstd_macro::{
+    attr_macro_http_server as http_server, attr_macro_main as main, attr_macro_test as test,
+};
 
-// Re-export the wasip2 crate for use only by `wstd-macro` macros. The proc
-// macros need to generate code that uses these definitions, but we don't want
-// to treat it as part of our public API with regards to semver, so we keep it
-// under `__internal` as well as doc(hidden) to indicate it is private.
+// Re-export the active WASI backend crate for use only by `wstd-macro` macros.
+// The proc macros need to generate code that uses these definitions, but we
+// don't want to treat it as part of our public API with regards to semver, so
+// we keep it under `__internal` as well as doc(hidden) to indicate it is
+// private.
 #[doc(hidden)]
 pub mod __internal {
+    #[cfg(target_env = "p2")]
     pub use wasip2;
+    #[cfg(target_env = "p3")]
+    pub use wasip3;
 }
 
+#[cfg(target_env = "p2")]
 pub mod prelude {
     pub use crate::future::FutureExt as _;
     pub use crate::io::AsyncRead as _;
diff --git a/tests/http_first_byte_timeout.rs b/tests/http_first_byte_timeout.rs
index 5fd47be..fb22cd3 100644
--- a/tests/http_first_byte_timeout.rs
+++ b/tests/http_first_byte_timeout.rs
@@ -1,3 +1,5 @@
+#![cfg(target_env = "p2")]
+
 use wstd::http::{Body, Client, Request, error::ErrorCode};
 
 #[wstd::main]
diff --git a/tests/http_get.rs b/tests/http_get.rs
index e7a3a5a..5660e0e 100644
--- a/tests/http_get.rs
+++ b/tests/http_get.rs
@@ -1,3 +1,5 @@
+#![cfg(target_env = "p2")]
+
 use std::error::Error;
 use wstd::http::{Body, Client, HeaderValue, Request};
 
diff --git a/tests/http_get_json.rs b/tests/http_get_json.rs
index a4f42b6..5596e0b 100644
--- a/tests/http_get_json.rs
+++ b/tests/http_get_json.rs
@@ -1,3 +1,5 @@
+#![cfg(target_env = "p2")]
+
 use serde::Deserialize;
 use std::error::Error;
 use wstd::http::{Body, Client, Request};
diff --git a/tests/http_handle_error_code.rs b/tests/http_handle_error_code.rs
index 6affb90..0bbdd1d 100644
--- a/tests/http_handle_error_code.rs
+++ b/tests/http_handle_error_code.rs
@@ -1,3 +1,5 @@
+#![cfg(target_env = "p2")]
+
 use wstd::http::{Body, Client, Request, error::ErrorCode};
 
 /// Test that `outgoing_handler::handle` errors are properly propagated.
diff --git a/tests/http_post.rs b/tests/http_post.rs
index 5de184d..522c47b 100644
--- a/tests/http_post.rs
+++ b/tests/http_post.rs
@@ -1,3 +1,5 @@
+#![cfg(target_env = "p2")]
+
 use std::error::Error;
 use wstd::http::{Client, HeaderValue, Request};
 
diff --git a/tests/http_post_json.rs b/tests/http_post_json.rs
index f9fcf07..1dc07f2 100644
--- a/tests/http_post_json.rs
+++ b/tests/http_post_json.rs
@@ -1,3 +1,5 @@
+#![cfg(target_env = "p2")]
+
 use serde::{Deserialize, Serialize};
 use std::error::Error;
 use wstd::http::{Body, Client, HeaderValue, Request};
diff --git a/tests/http_timeout.rs b/tests/http_timeout.rs
index 96d40de..04f60fc 100644
--- a/tests/http_timeout.rs
+++ b/tests/http_timeout.rs
@@ -1,3 +1,5 @@
+#![cfg(target_env = "p2")]
+
 use wstd::future::FutureExt;
 use wstd::http::{Body, Client, Request};
 use wstd::time::Duration;
diff --git a/tests/sleep.rs b/tests/sleep.rs
index eb55ea0..ac8c72a 100644
--- a/tests/sleep.rs
+++ b/tests/sleep.rs
@@ -1,3 +1,5 @@
+#![cfg(target_env = "p2")]
+
 use std::error::Error;
 use wstd::task::sleep;
 use wstd::time::Duration;