diff --git a/src/main_leave.rs b/src/main_leave.rs
index 61a281a..682f951 100644
--- a/src/main_leave.rs
+++ b/src/main_leave.rs
@@ -13,6 +13,12 @@ thread_local! {
         std::cell::RefCell::new(Box::new(rand_chacha::ChaCha20Rng::from_entropy()));
 }
 
+static BASE62: &[u8; 62] = b"\
+0123456789\
+ABCDEFGHIJKLMNOPQRSTUVWXYZ\
+abcdefghijklmnopqrstuvwxyz\
+";
+
 static USED_STDOUT: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(false);
 
 // support "-" to mean stdout.
@@ -500,11 +506,6 @@ fn generate_autoplay_logs<const WRITE_LOGS: bool, const SUMMARIZE: bool, const B
         tick_periods,
     }));
     let batch_size = if BREADTH { 10 } else { 100 };
-    // this is a 5-byte random value generated once per process.
-    let common_game_id_str = std::sync::Arc::new(format!(
-        "{:010x}",
-        RNG.with(|rng| rng.borrow_mut().gen_range(0..1u64 << 40))
-    ));
 
     for thread_id in 0..num_threads {
         let game_config = std::sync::Arc::clone(&game_config);
@@ -518,11 +519,10 @@ fn generate_autoplay_logs<const WRITE_LOGS: bool, const SUMMARIZE: bool, const B
         let logged_games = std::sync::Arc::clone(&logged_games);
         let completed_moves = std::sync::Arc::clone(&completed_moves);
         let mutexed_stuffs = std::sync::Arc::clone(&mutexed_stuffs);
-        let common_game_id_str = std::sync::Arc::clone(&common_game_id_str);
         threads.push(std::thread::spawn(move || {
             RNG.with(|rng| {
                 let mut rng = &mut *rng.borrow_mut();
-                let mut game_id = String::with_capacity(24);
+                let mut game_id = String::with_capacity(8);
                 let mut move_generator = movegen::KurniaMoveGenerator::new(&game_config);
                 let mut game_state = game_state::GameState::new(&game_config);
                 let mut cur_rack_as_vec = if SUMMARIZE {
@@ -623,7 +623,7 @@ fn generate_autoplay_logs<const WRITE_LOGS: bool, const SUMMARIZE: bool, const B
                     }
                 }
                 loop {
-                    let num_prior_games =
+                    let mut num_prior_games =
                         num_processed_games.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
                     if num_prior_games >= num_games {
                         num_processed_games.fetch_sub(1, std::sync::atomic::Ordering::Relaxed);
@@ -634,17 +634,16 @@ fn generate_autoplay_logs<const WRITE_LOGS: bool, const SUMMARIZE: bool, const B
                     num_bingos.iter_mut().for_each(|m| *m = 0);
                     num_turns.iter_mut().for_each(|m| *m = 0);
                     game_id.clear();
-                    write!(
-                        game_id,
-                        "{:08x}{}{:06x}",
-                        std::time::SystemTime::now()
-                            .duration_since(std::time::UNIX_EPOCH)
-                            .unwrap()
-                            .as_secs(),
-                        &common_game_id_str,
-                        num_prior_games.wrapping_add(1)
-                    )
-                    .unwrap();
+                    // random prefix. 62 ** 4 == 14776336, hopefully enough entropy.
+                    for _ in 0..4 {
+                        game_id.push(*BASE62.choose(&mut rng).unwrap() as char);
+                    }
+                    // wrapping sequence number. 62 ** 4 == 14776336.
+                    num_prior_games = num_prior_games.wrapping_add(1);
+                    game_id.push(BASE62[(num_prior_games / (62 * 62 * 62) % 62) as usize] as char);
+                    game_id.push(BASE62[(num_prior_games / (62 * 62) % 62) as usize] as char);
+                    game_id.push(BASE62[(num_prior_games / 62 % 62) as usize] as char);
+                    game_id.push(BASE62[(num_prior_games % 62) as usize] as char);
                     let went_first = rng.gen_range(0..game_config.num_players());
                     game_state.reset_and_draw_tiles(&game_config, &mut rng);
                     game_state.turn = went_first;