diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8bd8fc6..a8cb4cd 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -15,15 +15,27 @@ jobs:
     strategy:
       # https://hexdocs.pm/elixir/compatibility-and-deprecations.html#between-elixir-and-erlang-otp
       matrix:
-        elixir: [1.17, 1.16, 1.15]
-        otp: [26, 25]
         include:
+          # Latest
+          - elixir: 1.19
+            otp: 28
+          - elixir: 1.19
+            otp: 27
+          # 1.18
           - elixir: 1.18
             otp: 27
+          - elixir: 1.18
+            otp: 26
+          # 1.17
           - elixir: 1.17
             otp: 27
-          - elixir: 1.14
-            otp: 25
+          - elixir: 1.17
+            otp: 26
+          # Older supported
+          - elixir: 1.16
+            otp: 26
+          - elixir: 1.15
+            otp: 26
 
     steps:
       - uses: actions/checkout@v5
@@ -56,6 +68,6 @@ jobs:
       - uses: actions/checkout@v5
       - uses: erlef/setup-beam@v1
         with:
-          elixir-version: 1
-          otp-version: 27
+          elixir-version: 1.19
+          otp-version: 28
       - run: mix format --check-formatted
diff --git a/.tool-versions b/.tool-versions
index ef426e5..3d664e3 100644
--- a/.tool-versions
+++ b/.tool-versions
@@ -1,2 +1,2 @@
-elixir 1.18.2-otp-27
-erlang 27.1.2
+elixir 1.19.5-otp-28
+erlang 28.3.1
diff --git a/README.md b/README.md
index 9ad9d8b..7e74dd7 100644
--- a/README.md
+++ b/README.md
@@ -8,14 +8,6 @@
 
 **Hammer** is a rate-limiter for Elixir with pluggable storage backends. Hammer enables users to set limits on actions performed within specified time intervals, applying per-user or global limits on API requests, file uploads, and more.
 
----
-
-> [!NOTE]
->
-> This README is for the unreleased master branch, please reference the [official documentation on hexdocs](https://hexdocs.pm/hammer) for the latest stable release.
-
----
-
 ## Installation
 
 Hammer is [available in Hex](https://hex.pm/packages/hammer). Install by adding `:hammer` to your list of dependencies in `mix.exs`:
diff --git a/lib/hammer/atomic.ex b/lib/hammer/atomic.ex
index 4f472bb..0c67385 100644
--- a/lib/hammer/atomic.ex
+++ b/lib/hammer/atomic.ex
@@ -81,7 +81,7 @@ defmodule Hammer.Atomic do
       def start_link(opts) do
         opts = Keyword.put(opts, :table, @table)
         opts = Keyword.put_new(opts, :clean_period, :timer.minutes(1))
-        opts = Keyword.put_new(opts, :algorithm, @algorithm)
+        opts = Keyword.put_new(opts, :algorithm_module, @algorithm)
         Hammer.Atomic.start_link(opts)
       end
 
@@ -136,7 +136,7 @@ defmodule Hammer.Atomic do
 
     {clean_period, opts} = Keyword.pop!(opts, :clean_period)
     {table, opts} = Keyword.pop!(opts, :table)
-    {algorithm, opts} = Keyword.pop!(opts, :algorithm)
+    {algorithm_module, opts} = Keyword.pop!(opts, :algorithm_module)
     {key_older_than, opts} = Keyword.pop(opts, :key_older_than, :timer.hours(24))
 
     case opts do
@@ -151,10 +151,10 @@ defmodule Hammer.Atomic do
 
     config = %{
       table: table,
-      table_opts: algorithm.ets_opts(),
+      table_opts: algorithm_module.ets_opts(),
       clean_period: clean_period,
       key_older_than: key_older_than,
-      algorithm: algorithm
+      algorithm_module: algorithm_module
     }
 
     GenServer.start_link(__MODULE__, config, gen_opts)
diff --git a/lib/hammer/atomic/leaky_bucket.ex b/lib/hammer/atomic/leaky_bucket.ex
index 6c8a9a6..d4fedeb 100644
--- a/lib/hammer/atomic/leaky_bucket.ex
+++ b/lib/hammer/atomic/leaky_bucket.ex
@@ -86,6 +86,8 @@ defmodule Hammer.Atomic.LeakyBucket do
       MyApp.RateLimit.hit("user_123", 100, 500, 1)
   """
 
+  import Bitwise
+
   @doc false
   @spec ets_opts() :: list()
   def ets_opts do
@@ -99,6 +101,19 @@ defmodule Hammer.Atomic.LeakyBucket do
     ]
   end
 
+  # Pack timestamp (seconds) and fill level into one 64-bit value for atomic CAS.
+  # High 32 bits: timestamp, Low 32 bits: fill level
+  @compile {:inline, pack: 2, unpack: 1}
+  defp pack(timestamp, fill) do
+    (timestamp &&& 0xFFFFFFFF) <<< 32 ||| (fill &&& 0xFFFFFFFF)
+  end
+
+  defp unpack(packed) do
+    timestamp = packed >>> 32 &&& 0xFFFFFFFF
+    fill = packed &&& 0xFFFFFFFF
+    {timestamp, fill}
+  end
+
   @doc """
   Checks if a key is allowed to perform an action, and increment the counter by the given amount.
   """
@@ -110,34 +125,51 @@ defmodule Hammer.Atomic.LeakyBucket do
           cost :: pos_integer()
         ) :: {:allow, non_neg_integer()} | {:deny, non_neg_integer()}
   def hit(table, key, leak_rate, capacity, cost) do
-    # bucket window
     now = System.system_time(:second)
 
     case :ets.lookup(table, key) do
       [{_, atomic}] ->
-        # Get current bucket state
-        current_fill = :atomics.get(atomic, 1)
-        last_update = :atomics.get(atomic, 2)
+        do_hit(atomic, now, leak_rate, capacity, cost)
 
-        leaked = trunc((now - last_update) * leak_rate)
+      [] ->
+        atomic = :atomics.new(2, signed: false)
 
-        # Subtract leakage from current level (don't go below 0)
-        current_fill = max(0, current_fill - leaked)
+        if :ets.insert_new(table, {key, atomic}) do
+          # Initialize with empty bucket at current time
+          initial_packed = pack(now, 0)
+          :atomics.put(atomic, 1, initial_packed)
+          :atomics.put(atomic, 2, now)
+        end
 
-        if current_fill < capacity do
-          final_level = current_fill + cost
+        hit(table, key, leak_rate, capacity, cost)
+    end
+  end
+
+  defp do_hit(atomic, now, leak_rate, capacity, cost) do
+    current_packed = :atomics.get(atomic, 1)
+    {last_update, current_fill} = unpack(current_packed)
+
+    leaked = trunc((now - last_update) * leak_rate)
+
+    # Subtract leakage from current level (don't go below 0)
+    current_fill = max(0, current_fill - leaked)
 
-          :atomics.exchange(atomic, 1, final_level)
-          :atomics.exchange(atomic, 2, now)
+    if current_fill < capacity do
+      final_level = current_fill + cost
+      new_packed = pack(now, final_level)
 
+      case :atomics.compare_exchange(atomic, 1, current_packed, new_packed) do
+        :ok ->
+          # Update slot 2 for cleanup tracking (non-critical, just for age-based cleanup)
+          :atomics.put(atomic, 2, now)
           {:allow, final_level}
-        else
-          {:deny, 1000}
-        end
 
-      [] ->
-        :ets.insert_new(table, {key, :atomics.new(2, signed: false)})
-        hit(table, key, leak_rate, capacity, cost)
+        _current_value ->
+          # CAS failed, another process modified the value; retry
+          do_hit(atomic, now, leak_rate, capacity, cost)
+      end
+    else
+      {:deny, 1000}
     end
   end
 
@@ -151,7 +183,9 @@ defmodule Hammer.Atomic.LeakyBucket do
         0
 
       [{_, atomic}] ->
-        :atomics.get(atomic, 1)
+        packed = :atomics.get(atomic, 1)
+        {_timestamp, fill} = unpack(packed)
+        fill
 
       _ ->
         0
diff --git a/lib/hammer/atomic/token_bucket.ex b/lib/hammer/atomic/token_bucket.ex
index 9437017..eff8335 100644
--- a/lib/hammer/atomic/token_bucket.ex
+++ b/lib/hammer/atomic/token_bucket.ex
@@ -90,6 +90,8 @@ defmodule Hammer.Atomic.TokenBucket do
       MyApp.RateLimit.hit("user_123", 10, 100, 1)
   """
 
+  import Bitwise
+
   @doc false
   @spec ets_opts() :: list()
   def ets_opts do
@@ -103,6 +105,19 @@ defmodule Hammer.Atomic.TokenBucket do
     ]
   end
 
+  # Pack timestamp (seconds) and fill level into one 64-bit value for atomic CAS.
+  # High 32 bits: timestamp, Low 32 bits: fill level
+  @compile {:inline, pack: 2, unpack: 1}
+  defp pack(timestamp, fill) do
+    (timestamp &&& 0xFFFFFFFF) <<< 32 ||| (fill &&& 0xFFFFFFFF)
+  end
+
+  defp unpack(packed) do
+    timestamp = packed >>> 32 &&& 0xFFFFFFFF
+    fill = packed &&& 0xFFFFFFFF
+    {timestamp, fill}
+  end
+
   @doc """
   Checks if a key is allowed to perform an action, and consume the bucket by the given amount.
   """
@@ -114,41 +129,51 @@ defmodule Hammer.Atomic.TokenBucket do
           cost :: pos_integer()
         ) :: {:allow, non_neg_integer()} | {:deny, non_neg_integer()}
   def hit(table, key, refill_rate, capacity, cost \\ 1) do
-    # bucket window
     now = System.system_time(:second)
 
     case :ets.lookup(table, key) do
       [{_, atomic}] ->
-        # Get current bucket state
-        current_fill = :atomics.get(atomic, 1)
-        last_update = :atomics.get(atomic, 2)
-
-        new_tokens = trunc((now - last_update) * refill_rate)
-
-        current_tokens = min(capacity, current_fill + new_tokens)
-
-        if current_tokens >= cost do
-          final_level = current_tokens - cost
-
-          :atomics.exchange(atomic, 1, final_level)
-          :atomics.exchange(atomic, 2, now)
-
-          {:allow, final_level}
-        else
-          {:deny, 1000}
-        end
+        do_hit(atomic, now, refill_rate, capacity, cost)
 
       [] ->
         atomic = :atomics.new(2, signed: false)
 
         if :ets.insert_new(table, {key, atomic}) do
-          :atomics.exchange(atomic, 1, capacity)
+          initial_packed = pack(now, capacity)
+          :atomics.put(atomic, 1, initial_packed)
+          :atomics.put(atomic, 2, now)
         end
 
         hit(table, key, refill_rate, capacity, cost)
     end
   end
 
+  defp do_hit(atomic, now, refill_rate, capacity, cost) do
+    current_packed = :atomics.get(atomic, 1)
+    {last_update, current_fill} = unpack(current_packed)
+
+    new_tokens = trunc((now - last_update) * refill_rate)
+    current_tokens = min(capacity, current_fill + new_tokens)
+
+    if current_tokens >= cost do
+      final_level = current_tokens - cost
+      new_packed = pack(now, final_level)
+
+      case :atomics.compare_exchange(atomic, 1, current_packed, new_packed) do
+        :ok ->
+          # Update slot 2 for cleanup tracking (non-critical, just for age-based cleanup)
+          :atomics.put(atomic, 2, now)
+          {:allow, final_level}
+
+        _current_value ->
+          # CAS failed, another process modified the value; retry
+          do_hit(atomic, now, refill_rate, capacity, cost)
+      end
+    else
+      {:deny, 1000}
+    end
+  end
+
   @doc """
   Returns the current level of the bucket for a given key.
   """
@@ -159,7 +184,9 @@ defmodule Hammer.Atomic.TokenBucket do
         0
 
       [{_, atomic}] ->
-        :atomics.get(atomic, 1)
+        packed = :atomics.get(atomic, 1)
+        {_timestamp, fill} = unpack(packed)
+        fill
 
       _ ->
         0
diff --git a/lib/hammer/ets.ex b/lib/hammer/ets.ex
index 0098056..63935e1 100644
--- a/lib/hammer/ets.ex
+++ b/lib/hammer/ets.ex
@@ -144,8 +144,6 @@ defmodule Hammer.ETS do
     - `:clean_period` - How often to run the cleanup process (in milliseconds). Defaults to 1 minute.
     - `:key_older_than` - Optional maximum age for bucket entries (in milliseconds). Defaults to 24 hours.
       Entries older than this will be removed during cleanup.
-    - `:algorithm` - The rate limiting algorithm to use. Can be `:fixed_window`, `:sliding_window`,
-      `:token_bucket`, or `:leaky_bucket`. Defaults to `:fixed_window`.
     - optional `:debug`, `:spawn_opts`, and `:hibernate_after` GenServer options
   """
   @spec start_link([start_option]) :: GenServer.on_start()