diff --git a/changelog.d/source_chunk_size_config.feature.md b/changelog.d/source_chunk_size_config.feature.md
new file mode 100644
index 0000000000000..2e4fd8a9e8921
--- /dev/null
+++ b/changelog.d/source_chunk_size_config.feature.md
@@ -0,0 +1,2 @@
+Add `--chunk-size` / `VECTOR_CHUNK_SIZE` to configure the source sender batch size and source output buffer base capacity (defaults to 1000 events).
+authors: sakateka
diff --git a/lib/vector-core/src/source_sender/builder.rs b/lib/vector-core/src/source_sender/builder.rs
index 7f9f5d522497a..d0533f085e503 100644
--- a/lib/vector-core/src/source_sender/builder.rs
+++ b/lib/vector-core/src/source_sender/builder.rs
@@ -5,8 +5,8 @@ use vector_common::histogram;
 use vector_common::internal_event::DEFAULT_OUTPUT;
 
 use super::{
-    CHUNK_SIZE, LAG_TIME_NAME, Output, OutputMetrics, SEND_BATCH_LATENCY_NAME, SEND_LATENCY_NAME,
-    SourceSender, SourceSenderItem,
+    LAG_TIME_NAME, Output, OutputMetrics, SEND_BATCH_LATENCY_NAME, SEND_LATENCY_NAME, SourceSender,
+    SourceSenderItem, chunk_size,
 };
 use crate::config::{ComponentKey, OutputId, SourceOutput};
 
@@ -22,7 +22,7 @@ pub struct Builder {
 impl Default for Builder {
     fn default() -> Self {
         Self {
-            buf_size: CHUNK_SIZE,
+            buf_size: chunk_size(),
             default_output: None,
             named_outputs: Default::default(),
             output_metrics: OutputMetrics::new(
diff --git a/lib/vector-core/src/source_sender/mod.rs b/lib/vector-core/src/source_sender/mod.rs
index 24eb23688c0a1..d188fd1822ffe 100644
--- a/lib/vector-core/src/source_sender/mod.rs
+++ b/lib/vector-core/src/source_sender/mod.rs
@@ -17,7 +17,30 @@ pub use errors::SendError;
 use output::{Output, OutputMetrics};
 pub use sender::{SourceSender, SourceSenderItem};
 
-pub const CHUNK_SIZE: usize = 1000;
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+/// Default number of events batched per source send, and the base used for source output buffer
+/// sizing. Used when the chunk size has not been configured at startup.
+pub const DEFAULT_CHUNK_SIZE: usize = 1000;
+
+static CHUNK_SIZE: AtomicUsize = AtomicUsize::new(0);
+
+/// Returns the configured source sender chunk size, or [`DEFAULT_CHUNK_SIZE`] if unset.
+#[must_use]
+pub fn chunk_size() -> usize {
+    match CHUNK_SIZE.load(Ordering::Relaxed) {
+        0 => DEFAULT_CHUNK_SIZE,
+        size => size,
+    }
+}
+
+/// Sets the process-wide source sender chunk size. Must be called at most once, before the
+/// topology is built. Panics if called more than once.
+pub fn set_chunk_size(size: usize) {
+    CHUNK_SIZE
+        .compare_exchange(0, size, Ordering::Acquire, Ordering::Relaxed)
+        .unwrap_or_else(|_| panic!("double chunk_size initialization"));
+}
 
 #[cfg(any(test, feature = "test"))]
 const TEST_BUFFER_SIZE: usize = 100;
diff --git a/lib/vector-core/src/source_sender/output.rs b/lib/vector-core/src/source_sender/output.rs
index 4593f64a3b7a9..144b724304aba 100644
--- a/lib/vector-core/src/source_sender/output.rs
+++ b/lib/vector-core/src/source_sender/output.rs
@@ -24,7 +24,7 @@ use vector_common::{
 };
 use vrl::value::Value;
 
-use super::{CHUNK_SIZE, SendError, SourceSenderItem};
+use super::{SendError, SourceSenderItem, chunk_size};
 use crate::{
     EstimatedJsonEncodedSizeOf,
     config::{OutputId, log_schema},
@@ -246,7 +246,7 @@ impl Output {
         S: Stream<Item = E> + Unpin,
         E: Into<Event> + ByteSizeOf,
     {
-        let mut stream = events.ready_chunks(CHUNK_SIZE);
+        let mut stream = events.ready_chunks(chunk_size());
         while let Some(events) = stream.next().await {
             self.send_batch(events).await?;
         }
@@ -270,7 +270,7 @@ impl Output {
         let mut unsent_event_count = UnsentEventCount::new(events.len());
         let send_batch_start = Instant::now();
 
-        for events in array::events_into_arrays(events, Some(CHUNK_SIZE)) {
+        for events in array::events_into_arrays(events, Some(chunk_size())) {
             self.send_inner(events, &mut unsent_event_count, reference)
                 .await
                 .inspect_err(|error| {
diff --git a/lib/vector-core/src/source_sender/tests.rs b/lib/vector-core/src/source_sender/tests.rs
index 6ca446c23b7ad..a5c4d8ffd8de0 100644
--- a/lib/vector-core/src/source_sender/tests.rs
+++ b/lib/vector-core/src/source_sender/tests.rs
@@ -142,7 +142,7 @@ async fn emits_component_discarded_events_total_for_send_batch() {
     let (mut sender, _recv) = SourceSender::new_test_sender_with_options(1, None);
 
     let expected_drop = 100;
-    let events: Vec<Event> = (0..(CHUNK_SIZE + expected_drop))
+    let events: Vec<Event> = (0..(chunk_size() + expected_drop))
         .map(|_| {
             Event::Metric(Metric::new(
                 "name",
@@ -152,7 +152,7 @@ async fn emits_component_discarded_events_total_for_send_batch() {
         })
         .collect();
 
-    // `CHUNK_SIZE` events will be sent into buffer but then the future will not be polled to completion.
+    // `chunk_size()` events will be sent into buffer but then the future will not be polled to completion.
     let res = timeout(
         std::time::Duration::from_millis(100),
         sender.send_batch(events),
diff --git a/src/app.rs b/src/app.rs
index 565937d3dc21d..24733617060c5 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -229,7 +229,7 @@ impl Application {
             );
         }
 
-        let runtime = build_runtime(opts.root.threads, "vector-worker")?;
+        let runtime = build_runtime(opts.root.threads, opts.root.chunk_size, "vector-worker")?;
 
         // Signal handler for OS and provider messages.
         let mut signals = SignalPair::new(&runtime);
@@ -541,7 +541,11 @@ fn get_log_levels(default: &str) -> String {
         .unwrap_or_else(|_| default.into())
 }
 
-pub fn build_runtime(threads: Option<usize>, thread_name: &str) -> Result<Runtime, ExitCode> {
+pub fn build_runtime(
+    threads: Option<usize>,
+    chunk_size: Option<NonZeroUsize>,
+    thread_name: &str,
+) -> Result<Runtime, ExitCode> {
     let mut rt_builder = runtime::Builder::new_multi_thread();
     rt_builder.max_blocking_threads(20_000);
     rt_builder.enable_all().thread_name(thread_name);
@@ -556,7 +560,16 @@ pub fn build_runtime(threads: Option<usize>, thread_name: &str) -> Result<Runtim
         .unwrap_or_else(|_| panic!("double thread initialization"));
     rt_builder.worker_threads(threads);
 
-    debug!(message = "Building runtime.", worker_threads = threads);
+    let chunk_size = chunk_size
+        .map(NonZeroUsize::get)
+        .unwrap_or(vector_lib::source_sender::DEFAULT_CHUNK_SIZE);
+    vector_lib::source_sender::set_chunk_size(chunk_size);
+
+    debug!(
+        message = "Building runtime.",
+        worker_threads = threads,
+        chunk_size
+    );
     Ok(rt_builder.build().expect("Unable to create async runtime"))
 }
 
diff --git a/src/cli.rs b/src/cli.rs
index 5c07193a230b7..d84fe8e350dfb 100644
--- a/src/cli.rs
+++ b/src/cli.rs
@@ -1,6 +1,9 @@
 #![allow(missing_docs)]
 
-use std::{num::NonZeroU64, path::PathBuf};
+use std::{
+    num::{NonZeroU64, NonZeroUsize},
+    path::PathBuf,
+};
 
 use clap::{ArgAction, CommandFactory, FromArgMatches, Parser};
 
@@ -129,6 +132,11 @@ pub struct RootOpts {
     #[arg(short, long, env = "VECTOR_THREADS")]
     pub threads: Option<usize>,
 
+    /// Number of events batched per source send and used as the base for source output buffer sizing
+    /// (source output buffer capacity is this value multiplied by the number of worker threads)
+    #[arg(long, env = "VECTOR_CHUNK_SIZE")]
+    pub chunk_size: Option<NonZeroUsize>,
+
     /// Enable more detailed internal logging. Repeat to increase level. Overridden by `--quiet`.
     #[arg(short, long, action = ArgAction::Count)]
     pub verbose: u8,
diff --git a/src/topology/builder.rs b/src/topology/builder.rs
index d325d1fc070d3..c4d65c54475ab 100644
--- a/src/topology/builder.rs
+++ b/src/topology/builder.rs
@@ -31,7 +31,7 @@ use vector_lib::{
     internal_event::{self, CountByteSize, EventsSent, InternalEventHandle as _, Registered},
     latency::LatencyRecorder,
     schema::Definition,
-    source_sender::{CHUNK_SIZE, SourceSenderItem},
+    source_sender::{SourceSenderItem, chunk_size},
     transform::update_runtime_schema_definition,
 };
 use vector_lib::{gauge, internal_event::GaugeName};
@@ -72,9 +72,8 @@ static ENRICHMENT_TABLES_LOAD_LOCK: LazyLock<AsyncMutex<()>> = LazyLock::new(Asy
 static METRICS_STORAGE: LazyLock<MetricsStorage> = LazyLock::new(MetricsStorage::default);
 
 pub(crate) static SOURCE_SENDER_BUFFER_SIZE: LazyLock<usize> =
-    LazyLock::new(|| *TRANSFORM_CONCURRENCY_LIMIT * CHUNK_SIZE);
+    LazyLock::new(|| *TRANSFORM_CONCURRENCY_LIMIT * chunk_size());
 
-const READY_ARRAY_CAPACITY: NonZeroUsize = NonZeroUsize::new(CHUNK_SIZE * 4).unwrap();
 pub(crate) const TOPOLOGY_BUFFER_SIZE: NonZeroUsize = NonZeroUsize::new(100).unwrap();
 
 static TRANSFORM_CONCURRENCY_LIMIT: LazyLock<usize> = LazyLock::new(|| {
@@ -1299,8 +1298,10 @@ impl Runner {
             .into_stream()
             .filter(move |events| ready(filter_events_type(events, self.input_type)));
 
+        let ready_array_capacity =
+            NonZeroUsize::new(chunk_size() * 4).expect("chunk size is non-zero");
         let mut input_rx =
-            super::ready_arrays::ReadyArrays::with_capacity(input_rx, READY_ARRAY_CAPACITY);
+            super::ready_arrays::ReadyArrays::with_capacity(input_rx, ready_array_capacity);
 
         let mut in_flight = FuturesOrdered::new();
         let mut shutting_down = false;
diff --git a/website/cue/reference/cli.cue b/website/cue/reference/cli.cue
index b570bd823aa77..355cb35a606b3 100644
--- a/website/cue/reference/cli.cue
+++ b/website/cue/reference/cli.cue
@@ -192,6 +192,12 @@ cli: {
 			type:        "integer"
 			env_var:     "VECTOR_THREADS"
 		}
+		"chunk-size": {
+			description: env_vars.VECTOR_CHUNK_SIZE.description
+			default:     env_vars.VECTOR_CHUNK_SIZE.type.uint.default
+			type:        "integer"
+			env_var:     "VECTOR_CHUNK_SIZE"
+		}
 		"internal-log-rate-limit": {
 			_short:      "i"
 			description: env_vars.VECTOR_INTERNAL_LOG_RATE_LIMIT.description
@@ -654,6 +660,15 @@ cli: {
 				unit:    null
 			}
 		}
+		VECTOR_CHUNK_SIZE: {
+			description: """
+				The number of events batched per source send and used as the base for source output buffer sizing.
+				"""
+			type: uint: {
+				default: 1000
+				unit:    "events"
+			}
+		}
 		VECTOR_WATCH_CONFIG: {
 			description: "Watch for changes in the configuration file and reload accordingly"
 			type: bool: default: false