diff --git a/uc-client/Cargo.toml b/uc-client/Cargo.toml
index 9c35614397..f7a1b97f11 100644
--- a/uc-client/Cargo.toml
+++ b/uc-client/Cargo.toml
@@ -23,6 +23,10 @@ tracing = "0.1"
 url = "2.5"
 chrono = { version = "0.4", features = ["serde"] }
 
+[features]
+default = []
+test-utils = []
+
 [dev-dependencies]
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 clap = { version = "4.5", features = ["derive", "env"] }
diff --git a/uc-client/src/commits_client/in_memory.rs b/uc-client/src/commits_client/in_memory.rs
new file mode 100644
index 0000000000..bdd2dca4d5
--- /dev/null
+++ b/uc-client/src/commits_client/in_memory.rs
@@ -0,0 +1,280 @@
+//! In-memory implementation of [`UCCommitsClient`] for testing.
+
+use std::collections::HashMap;
+use std::sync::RwLock;
+
+use crate::error::{Error, Result};
+use crate::models::commits::{Commit, CommitRequest, CommitsRequest, CommitsResponse};
+
+use super::UCCommitsClient;
+
+// ============================================================================
+// TableData
+// ============================================================================
+
+/// In-memory representation of a UC-managed Delta table's commit state.
+struct TableData {
+    /// The highest version that has been ratified (committed) to this table.
+    max_ratified_version: i64,
+    /// Commits that have been registered with UC but not yet published.
+    catalog_commits: Vec<Commit>,
+}
+
+impl TableData {
+    const MAX_UNPUBLISHED_COMMITS: u16 = 50;
+
+    /// Creates a new `TableData` representing a UC Delta table that has just been created.
+    /// The table starts with no commits and version 0.
+    fn new_post_table_create() -> Self {
+        Self {
+            max_ratified_version: 0,
+            catalog_commits: vec![],
+        }
+    }
+
+    /// Returns commits within the requested version range.
+    fn get_commits(&self, request: CommitsRequest) -> Result<CommitsResponse> {
+        let start = request.start_version.unwrap_or(0);
+        let end = request.end_version.unwrap_or(i64::MAX);
+
+        Ok(CommitsResponse {
+            commits: Some(
+                self.catalog_commits
+                    .iter()
+                    .filter(|commit| start <= commit.version && commit.version <= end)
+                    .cloned()
+                    .collect(),
+            ),
+            latest_table_version: self.max_ratified_version,
+        })
+    }
+
+    /// Registers a new commit. Returns an error if the version is not the expected next version
+    /// or if the number of unpublished commits exceeds the maximum.
+    fn commit(&mut self, request: CommitRequest) -> Result<()> {
+        let Some(commit) = request.commit_info else {
+            return Err(Error::UnsupportedOperation(
+                "commit_info is required".to_string(),
+            ));
+        };
+
+        let expected_version = self.max_ratified_version + 1;
+
+        if commit.version != expected_version {
+            return Err(Error::UnsupportedOperation(format!(
+                "Expected commit version {} but got {}",
+                expected_version, commit.version
+            )));
+        }
+
+        if self.catalog_commits.len() as u16 >= Self::MAX_UNPUBLISHED_COMMITS {
+            return Err(Error::MaxUnpublishedCommitsExceeded(
+                Self::MAX_UNPUBLISHED_COMMITS,
+            ));
+        }
+
+        if let Some(v) = request.latest_backfilled_version {
+            self.cleanup_published_commits(v);
+        }
+
+        self.catalog_commits.push(commit);
+        self.max_ratified_version = expected_version;
+
+        Ok(())
+    }
+
+    /// Removes commits that have been published (backfilled) to the Delta log.
+    fn cleanup_published_commits(&mut self, max_published_version: i64) {
+        self.catalog_commits
+            .retain(|commit| max_published_version < commit.version);
+    }
+}
+
+// ============================================================================
+// InMemoryCommitsClient
+// ============================================================================
+
+/// An in-memory implementation of [`UCCommitsClient`] for testing.
+pub struct InMemoryCommitsClient {
+    // table id -> table data
+    tables: RwLock<HashMap<String, TableData>>,
+}
+
+impl InMemoryCommitsClient {
+    pub fn new() -> Self {
+        Self {
+            tables: RwLock::new(HashMap::new()),
+        }
+    }
+
+    pub fn create_table(&self, table_id: impl Into<String>) -> Result<()> {
+        let mut tables = self.tables.write().unwrap();
+        match tables.entry(table_id.into()) {
+            std::collections::hash_map::Entry::Vacant(e) => {
+                e.insert(TableData::new_post_table_create());
+                Ok(())
+            }
+            std::collections::hash_map::Entry::Occupied(e) => Err(Error::UnsupportedOperation(
+                format!("Table {} already exists", e.key()),
+            )),
+        }
+    }
+}
+
+impl Default for InMemoryCommitsClient {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl UCCommitsClient for InMemoryCommitsClient {
+    async fn get_commits(&self, request: CommitsRequest) -> Result<CommitsResponse> {
+        let tables = self.tables.read().unwrap();
+        let table = tables
+            .get(&request.table_id)
+            .ok_or_else(|| Error::TableNotFound(request.table_id.clone()))?;
+        table.get_commits(request)
+    }
+
+    async fn commit(&self, request: CommitRequest) -> Result<()> {
+        let mut tables = self.tables.write().unwrap();
+        let table = tables
+            .get_mut(&request.table_id)
+            .ok_or_else(|| Error::TableNotFound(request.table_id.clone()))?;
+        table.commit(request)
+    }
+}
+
+// ============================================================================
+// Tests
+// ============================================================================
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TABLE_ID: &str = "test-table-id";
+    const TABLE_URI: &str = "s3://bucket/table";
+
+    fn make_commit(version: i64) -> Commit {
+        Commit::new(
+            version,
+            version * 1000,
+            format!("{:020}.json", version),
+            100,
+            version * 1000,
+        )
+    }
+
+    fn commit_request(version: i64, latest_backfilled_version: Option<i64>) -> CommitRequest {
+        CommitRequest::new(
+            TABLE_ID,
+            TABLE_URI,
+            make_commit(version),
+            latest_backfilled_version,
+        )
+    }
+
+    fn get_commits_request() -> CommitsRequest {
+        CommitsRequest::new(TABLE_ID, TABLE_URI)
+    }
+
+    fn extract_commit_versions(commits: &[Commit]) -> Vec<i64> {
+        commits.iter().map(|c| c.version).collect()
+    }
+
+    #[tokio::test]
+    async fn test_commit_and_get_commits() {
+        let client = InMemoryCommitsClient::new();
+
+        // Create table
+        client.create_table(TABLE_ID).unwrap();
+
+        // Insert 10 commits (versions 1-10)
+        for v in 1..=10 {
+            client.commit(commit_request(v, None)).await.unwrap();
+        }
+
+        // Get commits (versions 3-8)
+        let commits_request = get_commits_request()
+            .with_start_version(3)
+            .with_end_version(8);
+        let response = client.get_commits(commits_request).await.unwrap();
+        let commits = response.commits.unwrap();
+        assert_eq!(commits.len(), 6);
+        assert_eq!(extract_commit_versions(&commits), vec![3, 4, 5, 6, 7, 8]);
+        assert_eq!(response.latest_table_version, 10);
+
+        // Insert commit 11 with latest_backfilled_version = 5
+        // This should cleanup commits 1-5 (retain versions >= 6)
+        client.commit(commit_request(11, Some(5))).await.unwrap();
+
+        // Get commits again - should return versions 6-11
+        let response = client.get_commits(get_commits_request()).await.unwrap();
+        let commits = response.commits.unwrap();
+        assert_eq!(extract_commit_versions(&commits), vec![6, 7, 8, 9, 10, 11]);
+        assert_eq!(response.latest_table_version, 11);
+    }
+
+    #[test]
+    fn test_create_table_duplicate_throws() {
+        let client = InMemoryCommitsClient::new();
+        client.create_table(TABLE_ID).unwrap();
+        assert!(matches!(
+            client.create_table(TABLE_ID),
+            Err(Error::UnsupportedOperation(_))
+        ));
+    }
+
+    #[tokio::test]
+    async fn test_get_commits_table_not_found() {
+        assert!(matches!(
+            InMemoryCommitsClient::new()
+                .get_commits(get_commits_request())
+                .await,
+            Err(Error::TableNotFound(_))
+        ));
+    }
+
+    #[tokio::test]
+    async fn test_commit_table_not_found() {
+        assert!(matches!(
+            InMemoryCommitsClient::new()
+                .commit(commit_request(1, None))
+                .await,
+            Err(Error::TableNotFound(_))
+        ));
+    }
+
+    #[tokio::test]
+    async fn test_commit_wrong_version() {
+        let client = InMemoryCommitsClient::new();
+        client.create_table(TABLE_ID).unwrap();
+        assert!(matches!(
+            client.commit(commit_request(5, None)).await,
+            Err(Error::UnsupportedOperation(_))
+        ));
+    }
+
+    #[tokio::test]
+    async fn test_get_commits_empty_table() {
+        let client = InMemoryCommitsClient::new();
+        client.create_table(TABLE_ID).unwrap();
+        let response = client.get_commits(get_commits_request()).await.unwrap();
+        assert!(response.commits.unwrap().is_empty());
+        assert_eq!(response.latest_table_version, 0);
+    }
+
+    #[tokio::test]
+    async fn test_commit_max_unpublished_commits_exceeded() {
+        let client = InMemoryCommitsClient::new();
+        client.create_table(TABLE_ID).unwrap();
+        for v in 1..=50 {
+            client.commit(commit_request(v, None)).await.unwrap();
+        }
+        assert!(matches!(
+            client.commit(commit_request(51, None)).await,
+            Err(Error::MaxUnpublishedCommitsExceeded(_))
+        ));
+    }
+}
diff --git a/uc-client/src/commits_client.rs b/uc-client/src/commits_client/mod.rs
similarity index 95%
rename from uc-client/src/commits_client.rs
rename to uc-client/src/commits_client/mod.rs
index 28e282ec69..199bd5b829 100644
--- a/uc-client/src/commits_client.rs
+++ b/uc-client/src/commits_client/mod.rs
@@ -7,6 +7,12 @@ use crate::error::Result;
 use crate::http::{build_http_client, execute_with_retry, handle_response};
 use crate::models::commits::{CommitRequest, CommitsRequest, CommitsResponse};
 
+#[cfg(any(test, feature = "test-utils"))]
+mod in_memory;
+
+#[cfg(any(test, feature = "test-utils"))]
+pub use in_memory::InMemoryCommitsClient;
+
 /// Trait for UC commits API operations.
 ///
 /// Implementations of this trait are responsible for performing any necessary retries on transient
diff --git a/uc-client/src/error.rs b/uc-client/src/error.rs
index 09e7627733..b98b4df51f 100644
--- a/uc-client/src/error.rs
+++ b/uc-client/src/error.rs
@@ -31,6 +31,9 @@ pub enum Error {
 
     #[error("Max retries exceeded")]
     MaxRetriesExceeded,
+
+    #[error("Max unpublished commits exceeded (max: {0})")]
+    MaxUnpublishedCommitsExceeded(u16),
 }
 
 pub type Result<T> = std::result::Result<T, Error>;
diff --git a/uc-client/src/lib.rs b/uc-client/src/lib.rs
index b93c76c5d0..66c65bfe6e 100644
--- a/uc-client/src/lib.rs
+++ b/uc-client/src/lib.rs
@@ -34,6 +34,9 @@ pub use commits_client::{UCCommitsClient, UCCommitsRestClient};
 pub use config::{ClientConfig, ClientConfigBuilder};
 pub use error::{Error, Result};
 
+#[cfg(any(test, feature = "test-utils"))]
+pub use commits_client::InMemoryCommitsClient;
+
 #[doc(hidden)]
 pub mod prelude {
     pub use crate::client::UCClient;