diff --git a/CHANGELOG.md b/CHANGELOG.md
deleted file mode 100644
index e69de29..0000000
diff --git a/README.md b/README.md
index b5f7d71..2e17d72 100644
--- a/README.md
+++ b/README.md
@@ -123,4 +123,3 @@ This feature provides:
 - **Request cancellation**: Long-running requests will timeout and be cancelled
 - **Better resource management**: Prevents hanging connections
 - **Comprehensive timeout coverage**: Sets both receive timeout (per-chunk) and request timeout (complete response)
-- **Feature parity with JS client**: Matches timeout functionality in the JavaScript SDK
diff --git a/lib/supabase/functions.ex b/lib/supabase/functions.ex
index 01c1a28..8309806 100644
--- a/lib/supabase/functions.ex
+++ b/lib/supabase/functions.ex
@@ -25,6 +25,7 @@ defmodule Supabase.Functions do
   - `region`: The Region to invoke the function in.
   - `on_response`: The custom response handler for response streaming.
   - `timeout`: The timeout in milliseconds for the request. Defaults to 15 seconds.
+  - `access_token`: Override the authorization token for this request.
   """
   @type opt ::
           {:body, Fetcher.body()}
@@ -33,6 +34,7 @@ defmodule Supabase.Functions do
           | {:region, region}
           | {:on_response, on_response}
           | {:timeout, pos_integer()}
+          | {:access_token, String.t()}
 
   @type on_response :: ({Fetcher.status(), Fetcher.headers(), body :: Enumerable.t()} ->
                           Supabase.result(Response.t()))
@@ -54,6 +56,24 @@ defmodule Supabase.Functions do
           | :"ca-central-1"
           | :"eu-central-1"
 
+  @doc """
+  Updates the access token for a client
+
+  Creates a new client instance with the updated access token. This provides
+  feature parity with the JavaScript client's `setAuth(token)` method.
+
+  ## Examples
+
+      # Update auth token functionally
+      new_client = Supabase.Functions.update_auth(client, "new_token")
+      {:ok, response} = Supabase.Functions.invoke(new_client, "my-function")
+
+  """
+  @spec update_auth(Client.t(), String.t()) :: Client.t()
+  def update_auth(%Client{} = client, token) when is_binary(token) do
+    %{client | access_token: token}
+  end
+
   @doc """
   Invokes a function
 
@@ -62,6 +82,19 @@ defmodule Supabase.Functions do
   - When you pass in a body to your function, we automatically attach the `Content-Type` header automatically. If it doesn't match any of these types we assume the payload is json, serialize it and attach the `Content-Type` header as `application/json`. You can override this behavior by passing in a `Content-Type` header of your own.
   - Responses are automatically parsed as json depending on the Content-Type header sent by your function. Responses are parsed as text by default.
 
+  ## Authentication
+
+  You can override the authorization token for a specific request using the `access_token` option:
+
+      # Use a different token for this request
+      {:ok, response} = Supabase.Functions.invoke(client, "my-function", access_token: "new_token")
+
+  Alternatively, you can update the client's auth token functionally:
+
+      # Update the client's token
+      new_client = Supabase.Functions.update_auth(client, "new_token")
+      {:ok, response} = Supabase.Functions.invoke(new_client, "my-function")
+
   ## Timeout Support
 
   You can set a timeout for function invocations using the `timeout` option. This sets both the 
@@ -84,6 +117,9 @@ defmodule Supabase.Functions do
       {:ok, response} = Supabase.Functions.invoke(client, "my-function", 
         body: %{data: "value"}, 
         timeout: 30_000)
+
+      # With custom access token
+      {:ok, response} = Supabase.Functions.invoke(client, "my-function", access_token: "custom_token")
   """
   @spec invoke(Client.t(), function :: String.t(), opts) :: Supabase.result(Response.t())
   def invoke(%Client{} = client, name, opts \\ []) when is_binary(name) do
@@ -91,7 +127,14 @@ defmodule Supabase.Functions do
     custom_headers = opts[:headers] || %{}
     timeout = opts[:timeout] || 15_000
 
-    client
+    effective_client =
+      if opts[:access_token] do
+        update_auth(client, opts[:access_token])
+      else
+        client
+      end
+
+    effective_client
     |> Request.new(decode_body?: false)
     |> Request.with_functions_url(name)
     |> Request.with_method(method)
diff --git a/test/supabase/functions_test.exs b/test/supabase/functions_test.exs
index a619ff5..3e17d66 100644
--- a/test/supabase/functions_test.exs
+++ b/test/supabase/functions_test.exs
@@ -257,4 +257,153 @@ defmodule Supabase.FunctionsTest do
       assert response == "chunk1chunk2"
     end
   end
+
+  describe "update_auth/2" do
+    test "returns a new client with updated access token", %{client: client} do
+      new_token = "new_test_token"
+      updated_client = Functions.update_auth(client, new_token)
+
+      assert updated_client.access_token == new_token
+      # Original client should remain unchanged
+      assert client.access_token != new_token
+      # All other fields should remain the same
+      assert updated_client.base_url == client.base_url
+      assert updated_client.api_key == client.api_key
+    end
+
+    test "updated client works with invoke/3", %{client: client} do
+      new_token = "updated_token"
+
+      expect(@mock, :stream, fn request, _opts ->
+        assert Request.get_header(request, "authorization") == "Bearer #{new_token}"
+
+        {:ok,
+         %Finch.Response{
+           status: 200,
+           headers: %{"content-type" => "application/json"},
+           body: ~s({"success": true})
+         }}
+      end)
+
+      updated_client = Functions.update_auth(client, new_token)
+
+      assert {:ok, response} =
+               Functions.invoke(updated_client, "test-function", http_client: @mock)
+
+      assert response.body == %{"success" => true}
+    end
+  end
+
+  describe "access_token option in invoke/3" do
+    test "overrides authorization header with custom token", %{client: client} do
+      custom_token = "custom_auth_token"
+
+      expect(@mock, :stream, fn request, _opts ->
+        assert Request.get_header(request, "authorization") == "Bearer #{custom_token}"
+
+        {:ok,
+         %Finch.Response{
+           status: 200,
+           headers: %{"content-type" => "application/json"},
+           body: ~s({"authorized": true})
+         }}
+      end)
+
+      assert {:ok, response} =
+               Functions.invoke(client, "test-function",
+                 access_token: custom_token,
+                 http_client: @mock
+               )
+
+      assert response.body == %{"authorized" => true}
+    end
+
+    test "works with other options combined", %{client: client} do
+      custom_token = "combined_auth_token"
+      custom_headers = %{"x-custom" => "value"}
+      body_data = %{test: "data"}
+
+      expect(@mock, :stream, fn request, _opts ->
+        assert Request.get_header(request, "authorization") == "Bearer #{custom_token}"
+        assert Request.get_header(request, "x-custom") == "value"
+        assert Request.get_header(request, "content-type") == "application/json"
+
+        {:ok,
+         %Finch.Response{
+           status: 200,
+           headers: %{"content-type" => "application/json"},
+           body: ~s({"success": true})
+         }}
+      end)
+
+      assert {:ok, response} =
+               Functions.invoke(client, "test-function",
+                 access_token: custom_token,
+                 headers: custom_headers,
+                 body: body_data,
+                 http_client: @mock
+               )
+
+      assert response.body == %{"success" => true}
+    end
+
+    test "original client remains unchanged after access_token override", %{client: client} do
+      original_token = client.access_token
+      custom_token = "temporary_override_token"
+
+      expect(@mock, :stream, fn request, _opts ->
+        assert Request.get_header(request, "authorization") == "Bearer #{custom_token}"
+
+        {:ok,
+         %Finch.Response{
+           status: 200,
+           headers: %{"content-type" => "application/json"},
+           body: ~s({"success": true})
+         }}
+      end)
+
+      assert {:ok, _response} =
+               Functions.invoke(client, "test-function",
+                 access_token: custom_token,
+                 http_client: @mock
+               )
+
+      # Original client should be unchanged
+      assert client.access_token == original_token
+    end
+
+    test "nil access_token option uses original client token", %{client: client} do
+      expect(@mock, :stream, fn request, _opts ->
+        assert Request.get_header(request, "authorization") == "Bearer #{client.access_token}"
+
+        {:ok,
+         %Finch.Response{
+           status: 200,
+           headers: %{"content-type" => "application/json"},
+           body: ~s({"success": true})
+         }}
+      end)
+
+      assert {:ok, response} =
+               Functions.invoke(client, "test-function", access_token: nil, http_client: @mock)
+
+      assert response.body == %{"success" => true}
+    end
+
+    test "empty access_token option uses original client token", %{client: client} do
+      expect(@mock, :stream, fn request, _opts ->
+        assert Request.get_header(request, "authorization") == "Bearer #{client.access_token}"
+
+        {:ok,
+         %Finch.Response{
+           status: 200,
+           headers: %{"content-type" => "application/json"},
+           body: ~s({"success": true})
+         }}
+      end)
+
+      assert {:ok, response} = Functions.invoke(client, "test-function", http_client: @mock)
+      assert response.body == %{"success" => true}
+    end
+  end
 end