diff --git a/CHANGELOG.md b/CHANGELOG.md
index 09083b8..7bf44ff 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,13 @@
 # Changelog
 
+## 0.0.1.alpha3 - 2026-07-10
+
+### Added
+
+- `Opencode::Client#update_session` for applying permission rules through
+  OpenCode's session PATCH endpoint. OpenCode appends these rules, so hosts
+  should fingerprint their ordered policy and call this only when it changes.
+
 ## 0.0.1.alpha2 — 2026-05-20
 
 ### Added
diff --git a/README.md b/README.md
index 83bf856..e8e938a 100644
--- a/README.md
+++ b/README.md
@@ -72,6 +72,17 @@ result = client.send_message(session_id, "Quick yes/no: is Ruby fun?")
 # result is the OpenCode response hash; see API docs for fields.
 ```
 
+### Updating session permissions
+
+```ruby
+client.update_session(session_id, permissions: permission_rules)
+```
+
+OpenCode appends PATCHed permission rules and evaluates the last matching
+rule. Hosts should send a complete ordered policy and fingerprint it so the
+same policy is not appended on every turn. This endpoint requires OpenCode
+1.16.1 or newer; the rest of the client remains compatible with 1.15.
+
 ### Lower-level event firehose
 
 If you need raw SSE events (every server tick, todo update, prompt asked/replied), use `stream_events` directly:
@@ -155,7 +166,7 @@ bundle install
 bundle exec rake test
 ```
 
-12-test smoke covers Client end-to-end against WebMock-stubbed OpenCode endpoints.
+16-test smoke covers Client end-to-end against WebMock-stubbed OpenCode endpoints.
 
 ## License
 
diff --git a/lib/opencode/client.rb b/lib/opencode/client.rb
index 5f8f706..6a26732 100644
--- a/lib/opencode/client.rb
+++ b/lib/opencode/client.rb
@@ -144,6 +144,10 @@ module Opencode
       execute(request)
     end
 
+    def update_session(session_id, permissions:)
+      patch("/session/#{session_id}", { permission: permissions })
+    end
+
     def children(session_id)
       uri = build_uri("/session/#{session_id}/children")
       request = Net::HTTP::Get.new(uri)
@@ -434,6 +438,13 @@ module Opencode
       execute(request)
     end
 
+    def patch(path, body)
+      uri = build_uri(path)
+      request = Net::HTTP::Patch.new(uri)
+      request.body = body.to_json
+      execute(request)
+    end
+
     def build_uri(path, scoped: true)
       uri = @uri.dup
       uri.path = path
diff --git a/lib/opencode/version.rb b/lib/opencode/version.rb
index 538607c..e9ec7c5 100644
--- a/lib/opencode/version.rb
+++ b/lib/opencode/version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module Opencode
-  VERSION = "0.0.1.alpha2"
+  VERSION = "0.0.1.alpha3"
 end
diff --git a/test/opencode/smoke_test.rb b/test/opencode/smoke_test.rb
index a1e4109..335b03e 100644
--- a/test/opencode/smoke_test.rb
+++ b/test/opencode/smoke_test.rb
@@ -53,6 +53,24 @@ class SmokeTest < Minitest::Test
     assert_equal SESSION_ID, response[:id]
   end
 
+  def test_update_session_patches_permissions_and_returns_the_updated_session
+    permissions = [
+      { permission: "skill", pattern: "*", action: "deny" },
+      { permission: "skill", pattern: "core-details", action: "allow" }
+    ]
+
+    stub_request(:patch, "#{BASE}/session/#{SESSION_ID}")
+      .with(body: { permission: permissions }.to_json)
+      .to_return(status: 200, body: { id: SESSION_ID, permission: permissions }.to_json,
+                 headers: { "Content-Type" => "application/json" })
+
+    response = @client.update_session(SESSION_ID, permissions: permissions)
+
+    assert_equal SESSION_ID, response[:id]
+    assert_equal permissions, response[:permission]
+    assert_requested :patch, "#{BASE}/session/#{SESSION_ID}", times: 1
+  end
+
   def test_send_message_async_returns_empty_body
     stub_request(:post, "#{BASE}/session/#{SESSION_ID}/prompt_async")
       .to_return(status: 204, body: "")