diff --git a/crates/factor-outbound-http/src/wasi.rs b/crates/factor-outbound-http/src/wasi.rs
index 908aa825d..9b80e1df2 100644
--- a/crates/factor-outbound-http/src/wasi.rs
+++ b/crates/factor-outbound-http/src/wasi.rs
@@ -10,7 +10,7 @@ use std::{
     time::Duration,
 };
 
-use bytes::Bytes;
+use bytes::{Buf, Bytes};
 use futures::channel::oneshot;
 use http::{
     HeaderMap, Uri,
@@ -138,6 +138,7 @@ impl p3::WasiHttpHooks for InstanceHttpHooks {
             url.full = Empty,
             http.request.method = %request.method(),
             otel.name = %request.method(),
+            http.response.body.size = Empty,
             http.response.status_code = Empty,
             server.address = Empty,
             server.port = Empty,
@@ -216,6 +217,8 @@ impl p3::WasiHttpHooks for InstanceHttpHooks {
                                 body,
                                 sleep: None,
                                 timeout: between_bytes_timeout,
+                                byte_count: 0,
+                                span: Some(Span::current()),
                             }
                             .boxed_unsync()
                         }),
@@ -246,6 +249,8 @@ pin_project_lite::pin_project! {
         #[pin]
         sleep: Option<tokio::time::Sleep>,
         timeout: Duration,
+        byte_count: u64,
+        span: Option<Span>,
     }
 }
 
@@ -258,9 +263,33 @@ impl<B: Body<Error = p2_types::ErrorCode>> Body for BetweenBytesTimeoutBody<B> {
         cx: &mut Context<'_>,
     ) -> Poll<Option<Result<Frame<Self::Data>, Self::Error>>> {
         let mut me = self.project();
-        match me.body.poll_frame(cx) {
+        match me.body.as_mut().poll_frame(cx) {
             Poll::Ready(value) => {
                 me.sleep.as_mut().set(None);
+
+                let mut record_body_size_once = |body_size: u64| {
+                    if let Some(span) = me.span.take() {
+                        span.record("http.response.body.size", body_size);
+                    }
+                };
+
+                match &value {
+                    Some(Ok(frame)) => {
+                        if let Some(data) = frame.data_ref() {
+                            *me.byte_count += data.remaining() as u64;
+                        }
+                        if me.body.as_ref().is_end_stream() {
+                            record_body_size_once(*me.byte_count);
+                        }
+                    }
+                    None => {
+                        record_body_size_once(*me.byte_count);
+                    }
+                    Some(Err(e)) => {
+                        tracing::warn!("error reading response body: {e:?}");
+                    }
+                }
+
                 Poll::Ready(value.map(|v| v.map_err(p2_to_p3_error_code)))
             }
             Poll::Pending => {