diff --git a/lib/crates/fabro-cli/src/commands/pr/close.rs b/lib/crates/fabro-cli/src/commands/pr/close.rs
index d3ce2e834..6fbaba0d9 100644
--- a/lib/crates/fabro-cli/src/commands/pr/close.rs
+++ b/lib/crates/fabro-cli/src/commands/pr/close.rs
@@ -34,7 +34,7 @@ async fn close_from(
         &record.owner,
         &record.repo,
         record.number,
-        fabro_github::GITHUB_API_BASE_URL,
+        &fabro_github::github_api_base_url(),
     )
     .await
     .map_err(|err| anyhow::anyhow!("{err}"))?;
diff --git a/lib/crates/fabro-cli/src/commands/pr/create.rs b/lib/crates/fabro-cli/src/commands/pr/create.rs
index 6e3bfddd2..e7726bf8c 100644
--- a/lib/crates/fabro-cli/src/commands/pr/create.rs
+++ b/lib/crates/fabro-cli/src/commands/pr/create.rs
@@ -110,7 +110,7 @@ async fn create_from(
         &owner,
         &repo,
         run_branch,
-        fabro_github::GITHUB_API_BASE_URL,
+        &fabro_github::github_api_base_url(),
     )
     .await
     .map_err(|err| anyhow::anyhow!("{err}"))?;
diff --git a/lib/crates/fabro-cli/src/commands/pr/list.rs b/lib/crates/fabro-cli/src/commands/pr/list.rs
index 18f9b46db..1f1ba0985 100644
--- a/lib/crates/fabro-cli/src/commands/pr/list.rs
+++ b/lib/crates/fabro-cli/src/commands/pr/list.rs
@@ -71,7 +71,7 @@ async fn list_from(
                     &record.owner,
                     &record.repo,
                     record.number,
-                    fabro_github::GITHUB_API_BASE_URL,
+                    &fabro_github::github_api_base_url(),
                 )
                 .await
                 {
diff --git a/lib/crates/fabro-cli/src/commands/pr/merge.rs b/lib/crates/fabro-cli/src/commands/pr/merge.rs
index 31ce05d28..956b72cbe 100644
--- a/lib/crates/fabro-cli/src/commands/pr/merge.rs
+++ b/lib/crates/fabro-cli/src/commands/pr/merge.rs
@@ -36,7 +36,7 @@ async fn merge_from(
         &record.repo,
         record.number,
         &args.method,
-        fabro_github::GITHUB_API_BASE_URL,
+        &fabro_github::github_api_base_url(),
     )
     .await
     .map_err(|err| anyhow::anyhow!("{err}"))?;
diff --git a/lib/crates/fabro-cli/src/commands/pr/view.rs b/lib/crates/fabro-cli/src/commands/pr/view.rs
index 32a931d95..a69338a74 100644
--- a/lib/crates/fabro-cli/src/commands/pr/view.rs
+++ b/lib/crates/fabro-cli/src/commands/pr/view.rs
@@ -35,7 +35,7 @@ async fn view_from(
         &record.owner,
         &record.repo,
         record.number,
-        fabro_github::GITHUB_API_BASE_URL,
+        &fabro_github::github_api_base_url(),
     )
     .await
     .map_err(|err| anyhow::anyhow!("{err}"))?;
diff --git a/lib/crates/fabro-cli/src/commands/preflight.rs b/lib/crates/fabro-cli/src/commands/preflight.rs
index 9baf2ba9a..a72beb26a 100644
--- a/lib/crates/fabro-cli/src/commands/preflight.rs
+++ b/lib/crates/fabro-cli/src/commands/preflight.rs
@@ -153,7 +153,7 @@ async fn mint_github_token(
         &jwt,
         &owner,
         &repo,
-        fabro_github::GITHUB_API_BASE_URL,
+        &fabro_github::github_api_base_url(),
         perms_json,
     )
     .await
diff --git a/lib/crates/fabro-cli/src/commands/repo/init.rs b/lib/crates/fabro-cli/src/commands/repo/init.rs
index d1b39b7b3..2140d7be3 100644
--- a/lib/crates/fabro-cli/src/commands/repo/init.rs
+++ b/lib/crates/fabro-cli/src/commands/repo/init.rs
@@ -206,7 +206,7 @@ async fn check_github_app_installation() {
         &jwt,
         &owner,
         &repo,
-        fabro_github::GITHUB_API_BASE_URL,
+        &fabro_github::github_api_base_url(),
     )
     .await
     {
@@ -229,7 +229,7 @@ async fn check_github_app_installation() {
             if let Ok(app_info) = fabro_github::get_authenticated_app(
                 &client,
                 &jwt,
-                fabro_github::GITHUB_API_BASE_URL,
+                &fabro_github::github_api_base_url(),
             )
             .await
             {
@@ -238,7 +238,7 @@ async fn check_github_app_installation() {
                     && fabro_github::is_app_public(
                         &client,
                         &app_info.slug,
-                        fabro_github::GITHUB_API_BASE_URL,
+                        &fabro_github::github_api_base_url(),
                     )
                     .await
                         == Ok(false);
@@ -281,7 +281,7 @@ async fn check_github_app_installation() {
                     &jwt,
                     &owner,
                     &repo,
-                    fabro_github::GITHUB_API_BASE_URL,
+                    &fabro_github::github_api_base_url(),
                 )
                 .await
                 {
diff --git a/lib/crates/fabro-github/src/lib.rs b/lib/crates/fabro-github/src/lib.rs
index 240239ba5..225b30a4c 100644
--- a/lib/crates/fabro-github/src/lib.rs
+++ b/lib/crates/fabro-github/src/lib.rs
@@ -4,6 +4,11 @@ use serde::Deserialize;
 
 pub const GITHUB_API_BASE_URL: &str = "https://api.github.com";
 
+/// Returns the GitHub API base URL, allowing override via `GITHUB_BASE_URL` env var.
+pub fn github_api_base_url() -> String {
+    std::env::var("GITHUB_BASE_URL").unwrap_or_else(|_| GITHUB_API_BASE_URL.to_string())
+}
+
 /// Detailed information about a pull request from the GitHub API.
 #[derive(Debug, Clone, Deserialize)]
 pub struct PullRequestDetail {
@@ -409,9 +414,9 @@ pub async fn create_pull_request(
     let jwt = sign_app_jwt(&creds.app_id, &creds.private_key_pem)?;
     let client = reqwest::Client::new();
 
+    let base_url = github_api_base_url();
     let token =
-        create_installation_access_token_for_pr(&client, &jwt, owner, repo, GITHUB_API_BASE_URL)
-            .await?;
+        create_installation_access_token_for_pr(&client, &jwt, owner, repo, &base_url).await?;
 
     tracing::debug!(title = %title, head = %head, base = %base, draft, "Creating pull request");
 
@@ -423,7 +428,7 @@ pub async fn create_pull_request(
         "draft": draft,
     });
 
-    let url = format!("{GITHUB_API_BASE_URL}/repos/{owner}/{repo}/pulls");
+    let url = format!("{base_url}/repos/{owner}/{repo}/pulls");
     let auth = format!("Bearer {token}");
     let resp = HttpClient::request(
         &client,
@@ -501,9 +506,9 @@ pub async fn enable_auto_merge(
     let jwt = sign_app_jwt(&creds.app_id, &creds.private_key_pem)?;
     let client = reqwest::Client::new();
 
+    let base_url = github_api_base_url();
     let token =
-        create_installation_access_token_for_pr(&client, &jwt, owner, repo, GITHUB_API_BASE_URL)
-            .await?;
+        create_installation_access_token_for_pr(&client, &jwt, owner, repo, &base_url).await?;
 
     let query = format!(
         r#"mutation {{
@@ -525,7 +530,7 @@ pub async fn enable_auto_merge(
         "Enabling auto-merge"
     );
 
-    let graphql_url = format!("{GITHUB_API_BASE_URL}/graphql");
+    let graphql_url = format!("{base_url}/graphql");
     let auth = format!("Bearer {token}");
     let graphql_body = serde_json::json!({ "query": query });
     let resp = HttpClient::request(
@@ -734,8 +739,8 @@ pub async fn resolve_clone_credentials(
     let jwt = sign_app_jwt(&creds.app_id, &creds.private_key_pem)?;
     let client = reqwest::Client::new();
 
-    let token =
-        create_installation_access_token(&client, &jwt, owner, repo, GITHUB_API_BASE_URL).await?;
+    let base_url = github_api_base_url();
+    let token = create_installation_access_token(&client, &jwt, owner, repo, &base_url).await?;
     Ok((Some("x-access-token".to_string()), Some(token)))
 }
 
diff --git a/lib/crates/fabro-slack/src/client.rs b/lib/crates/fabro-slack/src/client.rs
index 6ed7b6d05..9ab5ca506 100644
--- a/lib/crates/fabro-slack/src/client.rs
+++ b/lib/crates/fabro-slack/src/client.rs
@@ -13,13 +13,17 @@ pub struct PostedMessage {
 #[derive(Clone)]
 pub struct SlackClient {
     bot_token: String,
+    api_base: String,
     http: Client,
 }
 
 impl SlackClient {
     pub fn new(bot_token: String) -> Self {
+        let api_base =
+            std::env::var("SLACK_BASE_URL").unwrap_or_else(|_| SLACK_API_BASE.to_string());
         Self {
             bot_token,
+            api_base,
             http: Client::new(),
         }
     }
@@ -37,7 +41,7 @@ impl SlackClient {
         let body = build_post_message_body(channel, blocks, thread_ts);
         let resp = self
             .http
-            .post(format!("{SLACK_API_BASE}/chat.postMessage"))
+            .post(format!("{}/chat.postMessage", self.api_base))
             .bearer_auth(&self.bot_token)
             .json(&body)
             .send()
@@ -63,7 +67,7 @@ impl SlackClient {
         let body = build_update_message_body(channel, ts, blocks);
         let resp = self
             .http
-            .post(format!("{SLACK_API_BASE}/chat.update"))
+            .post(format!("{}/chat.update", self.api_base))
             .bearer_auth(&self.bot_token)
             .json(&body)
             .send()
diff --git a/lib/crates/fabro-slack/src/connection.rs b/lib/crates/fabro-slack/src/connection.rs
index 9e63dde92..eaf922da9 100644
--- a/lib/crates/fabro-slack/src/connection.rs
+++ b/lib/crates/fabro-slack/src/connection.rs
@@ -61,7 +61,10 @@ pub async fn open_socket_url(
     app_token: &str,
 ) -> Result<String, ConnectionError> {
     let resp = http
-        .post("https://slack.com/api/apps.connections.open")
+        .post(format!(
+            "{}/apps.connections.open",
+            std::env::var("SLACK_BASE_URL").unwrap_or_else(|_| "https://slack.com/api".to_string())
+        ))
         .bearer_auth(app_token)
         .header("Content-Type", "application/x-www-form-urlencoded")
         .send()
diff --git a/lib/crates/fabro-workflow/src/pipeline/initialize.rs b/lib/crates/fabro-workflow/src/pipeline/initialize.rs
index 3dca93db9..8a1bcb73f 100644
--- a/lib/crates/fabro-workflow/src/pipeline/initialize.rs
+++ b/lib/crates/fabro-workflow/src/pipeline/initialize.rs
@@ -219,7 +219,7 @@ async fn mint_github_token(
         &jwt,
         &owner,
         &repo,
-        fabro_github::GITHUB_API_BASE_URL,
+        &fabro_github::github_api_base_url(),
         perms_json,
     )
     .await