diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..d700895
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,32 @@
+name: Ruby checks
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  test:
+    runs-on: ubuntu-22.04
+    timeout-minutes: 15
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby: ['2.7', '3.0', '3.1', '3.2', '3.3', '3.4', '4.0', jruby]
+    env:
+      IPGEO_RUN_LIVE_TESTS: 'false'
+      IPGEO_RUN_LIVE_HARDENING: 'false'
+    steps:
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262
+        with:
+          persist-credentials: false
+      - uses: ruby/setup-ruby@de492cf36cbab201753d720ce4f4e336cd688c94
+        with:
+          ruby-version: ${{ matrix.ruby }}
+          bundler-cache: true
+      - run: bundle exec rspec
+      - run: bundle exec rake build
+      - run: bundle exec rake install
diff --git a/.gitignore b/.gitignore
index f0c58df..c8923ad 100755
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,6 @@
 .gems/
 *.gem
 spec/examples.txt
+Gemfile.lock
+vendor/
+pkg/
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index d6b6055..455962e 100755
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -3,7 +3,7 @@
     LANG: "C.UTF-8"
   before_script:
     - ruby -v
-    - bundle config set --local deployment true
+    - bundle config set --local path vendor/bundle
     - bundle install -j $(nproc)
   parallel:
     matrix:
@@ -11,7 +11,7 @@
   image: "ruby:$RUBY_VERSION"
   cache:
     paths:
-      - vendor/ruby
+      - vendor/bundle
     key: 'ruby-$RUBY_VERSION'
 
 gem:
diff --git a/README.md b/README.md
index bb37990..eaa79a3 100644
--- a/README.md
+++ b/README.md
@@ -331,7 +331,7 @@ puts IpgeolocationSdk.to_pretty_json(response.data)
 puts IpgeolocationSdk.to_pretty_json(response.data, :full)
 ```
 
-Compact mode omits `nil` fields. Full mode keeps them.
+Compact mode omits `nil` fields. Full mode keeps them. When serializing a client configuration, both modes replace its API key with `[REDACTED]`. The original key remains available through `config.api_key` and is used for authentication.
 
 ## Errors
 
diff --git a/ipgeolocation_sdk.gemspec b/ipgeolocation_sdk.gemspec
index bf372da..71334de 100755
--- a/ipgeolocation_sdk.gemspec
+++ b/ipgeolocation_sdk.gemspec
@@ -22,6 +22,7 @@ Gem::Specification.new do |s|
 
   s.add_development_dependency "rake", "~> 13.0"
   s.add_development_dependency "rspec", "~> 3.13"
+  s.add_development_dependency "bigdecimal", ">= 1.4"
 
   s.files = [
     "CHANGELOG.md",
diff --git a/lib/ipgeolocation_sdk/client.rb b/lib/ipgeolocation_sdk/client.rb
index 6512034..b46c089 100644
--- a/lib/ipgeolocation_sdk/client.rb
+++ b/lib/ipgeolocation_sdk/client.rb
@@ -28,6 +28,10 @@ def initialize(config, transport = nil)
 
     attr_reader :config
 
+    def inspect
+      "#<#{self.class} config=#{@config.inspect} closed=#{@closed}>"
+    end
+
     def lookup_ip_geolocation(request = nil)
       ensure_open
       typed_request = to_lookup_request(request)
diff --git a/lib/ipgeolocation_sdk/client_config.rb b/lib/ipgeolocation_sdk/client_config.rb
index 1e3c4a7..a4e5fb3 100644
--- a/lib/ipgeolocation_sdk/client_config.rb
+++ b/lib/ipgeolocation_sdk/client_config.rb
@@ -26,6 +26,10 @@ def initialize(
       )
     end
 
+    def inspect
+      "#<#{self.class} #{to_h(mode: JsonOutputMode::FULL).inspect}>"
+    end
+
     private
 
     def normalize_api_key(value)
diff --git a/lib/ipgeolocation_sdk/serde.rb b/lib/ipgeolocation_sdk/serde.rb
index 1971212..4c5694d 100644
--- a/lib/ipgeolocation_sdk/serde.rb
+++ b/lib/ipgeolocation_sdk/serde.rb
@@ -164,6 +164,7 @@ def to_plain_data(value, mode = JsonOutputMode::COMPACT)
           item = value.public_send(name)
           next if normalized_mode == JsonOutputMode::COMPACT && item.nil?
 
+          item = "[REDACTED]" if value.is_a?(IpGeolocationClientConfig) && name == :api_key && !item.nil?
           result[name.to_s] = to_plain_data(item, normalized_mode)
         end
       when Array
diff --git a/lib/ipgeolocation_sdk/transport.rb b/lib/ipgeolocation_sdk/transport.rb
index dd624cd..8e5ee3c 100644
--- a/lib/ipgeolocation_sdk/transport.rb
+++ b/lib/ipgeolocation_sdk/transport.rb
@@ -15,6 +15,16 @@ class HttpResponseData < ValueObject
 
   class NetHttpTransport
     DEFAULT_MAX_RESPONSE_BODY_CHARS = 128 * 1024 * 1024
+    INCOMPLETE_UTF8 = /(?:
+      [\xC2-\xDF] |
+      \xE0[\xA0-\xBF]? |
+      [\xE1-\xEC\xEE-\xEF][\x80-\xBF]? |
+      \xED[\x80-\x9F]? |
+      \xF0(?:[\x90-\xBF][\x80-\xBF]?)? |
+      [\xF1-\xF3][\x80-\xBF]{0,2} |
+      \xF4(?:[\x80-\x8F][\x80-\xBF]?)?
+    )\z/nx.freeze
+    private_constant :INCOMPLETE_UTF8
 
     def initialize(max_response_body_chars: DEFAULT_MAX_RESPONSE_BODY_CHARS)
       raise ArgumentError, "max_response_body_chars must be a positive integer" unless max_response_body_chars.is_a?(Integer) && max_response_body_chars.positive?
@@ -29,9 +39,10 @@ def send_request(request)
       http.open_timeout = request.connect_timeout
       http.read_timeout = request.read_timeout
 
-      response = http.request(build_net_http_request(uri, request))
-      body = response.body
-      body = body.nil? ? read_response_body(response) : normalize_response_text(body.to_s)
+      body = nil
+      response = http.request(build_net_http_request(uri, request)) do |stream|
+        body = read_response_body(stream)
+      end
 
       HttpResponseData.new(
         status_code: response.code.to_i,
@@ -78,22 +89,26 @@ def build_net_http_request(uri, request)
     end
 
     def read_response_body(response)
-      body_parts = []
-
-      response.read_body do |chunk|
-        body_parts << normalize_response_text(chunk.to_s)
+      body = String.new(encoding: Encoding::UTF_8)
+      pending = String.new(encoding: Encoding::BINARY)
+      size = 0
+      append = lambda do |text|
+        normalized = text.force_encoding(Encoding::UTF_8).scrub
+        size += normalized.length
+        if size > @max_response_body_chars
+          raise TransportError, "Response body exceeded max size of #{@max_response_body_chars} characters"
+        end
+        body << normalized
       end
 
-      body_parts.join
-    end
-
-    def normalize_response_text(text)
-      normalized = text.encode(Encoding::UTF_8, invalid: :replace, undef: :replace)
-      if normalized.length > @max_response_body_chars
-        raise TransportError, "Response body exceeded max size of #{@max_response_body_chars} characters"
+      response.read_body do |chunk|
+        bytes = pending << chunk.to_s.b
+        pending = bytes.slice!(INCOMPLETE_UTF8) || String.new(encoding: Encoding::BINARY)
+        append.call(bytes)
       end
+      append.call(pending)
 
-      normalized
+      body
     end
 
     def normalize_headers(headers)
diff --git a/spec/ip_location/client_config_spec.rb b/spec/ip_location/client_config_spec.rb
index 23a3956..343d21e 100644
--- a/spec/ip_location/client_config_spec.rb
+++ b/spec/ip_location/client_config_spec.rb
@@ -28,4 +28,34 @@
       described_class.new(connect_timeout: 0)
     end.to raise_error(IpgeolocationSdk::ValidationError, "connect_timeout must be greater than zero")
   end
+
+  it "redacts the API key in config and client inspection without changing authentication" do
+    config = described_class.new(api_key: "private-test-key")
+    client = IpgeolocationSdk::IpGeolocationClient.new(config)
+
+    expect(config.inspect).to include("[REDACTED]")
+    expect(config.inspect).not_to include("private-test-key")
+    expect(client.inspect).not_to include("private-test-key")
+    expect(config.api_key).to eq("private-test-key")
+  end
+
+  it "redacts configuration keys in hashes and nested JSON in both output modes" do
+    config = described_class.new(api_key: "private-test-key", read_timeout: 15)
+
+    [:compact, :full].each do |mode|
+      expect(config.to_h(mode: mode)).to include("api_key" => "[REDACTED]", "read_timeout" => 15.0)
+      [IpgeolocationSdk.to_json({ config: [config] }, mode),
+       IpgeolocationSdk.to_pretty_json(config, mode)].each do |json|
+        expect(json).to include("[REDACTED]")
+        expect(json).not_to include("private-test-key")
+      end
+    end
+  end
+
+  it "keeps absent API keys absent in compact output and nil in full output" do
+    config = described_class.new(request_origin: "https://ipgeolocation.io")
+
+    expect(config.to_h).not_to have_key("api_key")
+    expect(config.to_h(mode: :full)).to include("api_key" => nil)
+  end
 end
diff --git a/spec/ip_location/client_spec.rb b/spec/ip_location/client_spec.rb
index d323edf..54c42c9 100644
--- a/spec/ip_location/client_spec.rb
+++ b/spec/ip_location/client_spec.rb
@@ -85,6 +85,17 @@ def close
     )
   end
 
+  it "does not inspect request data retained by a custom transport" do
+    response = IpgeolocationSdk::HttpResponseData.new(status_code: 200, body: "{}", headers: {})
+    transport = RecordingTransport.new(response)
+    client = described_class.new(config, transport)
+    client.lookup_ip_geolocation
+
+    expect(transport.requests.first.url).to include("apiKey=paid-key")
+    expect(client.inspect).not_to include("paid-key")
+    expect(client.inspect).to include("[REDACTED]")
+  end
+
   it "requires api_key for bulk lookup" do
     client = described_class.new(api_key: nil, request_origin: "https://ipgeolocation.io", base_url: config.base_url)
 
diff --git a/spec/ip_location/transport_spec.rb b/spec/ip_location/transport_spec.rb
index 58feebd..63aa97c 100644
--- a/spec/ip_location/transport_spec.rb
+++ b/spec/ip_location/transport_spec.rb
@@ -8,13 +8,15 @@
       body: "{\"ip\":\"8.8.8.8\"}",
       to_hash: { "x-test" => ["ok"] }
     )
+    allow(response).to receive(:read_body).and_yield("{\"ip\":\"8.8.8.8\"}".b)
+    expect(response).not_to receive(:body)
 
     http = instance_double("Net::HTTP")
     allow(Net::HTTP).to receive(:new).with("api.ipgeolocation.io", 443).and_return(http)
     allow(http).to receive(:use_ssl=).with(true)
     allow(http).to receive(:open_timeout=).with(5.0)
     allow(http).to receive(:read_timeout=).with(10.0)
-    allow(http).to receive(:request).and_return(response)
+    allow(http).to receive(:request).and_yield(response).and_return(response)
 
     request = IpgeolocationSdk::HttpRequestData.new(
       url: "https://api.ipgeolocation.io/v3/ipgeo?ip=8.8.8.8",
diff --git a/spec/ip_location/transport_streaming_spec.rb b/spec/ip_location/transport_streaming_spec.rb
new file mode 100644
index 0000000..7bfb94a
--- /dev/null
+++ b/spec/ip_location/transport_streaming_spec.rb
@@ -0,0 +1,116 @@
+require "spec_helper"
+require "socket"
+
+RSpec.describe IpgeolocationSdk::NetHttpTransport do
+  let(:request) do
+    IpgeolocationSdk::HttpRequestData.new(
+      url: "http://127.0.0.1/v3/ipgeo",
+      method: "GET", headers: {}, body: nil,
+      connect_timeout: 1.0, read_timeout: 0.1
+    )
+  end
+
+  def stream_response(chunks, limit: 100)
+    response = instance_double("Net::HTTPResponse", code: "200", body: chunks.join, to_hash: {})
+    allow(response).to receive(:read_body) do |&block|
+      chunks.each { |chunk| block.call(chunk) }
+    end
+    http = instance_double("Net::HTTP")
+    allow(Net::HTTP).to receive(:new).and_return(http)
+    allow(http).to receive(:use_ssl=).with(false)
+    allow(http).to receive(:open_timeout=).with(1.0)
+    allow(http).to receive(:read_timeout=).with(0.1)
+    allow(http).to receive(:request) do |_, &block|
+      block.call(response) if block
+      response
+    end
+    described_class.new(max_response_body_chars: limit).send_request(request).body
+  end
+
+  it "preserves UTF-8 characters split at every byte boundary" do
+    text = "東京 café 😀\r\n"
+    chunks = text.b.bytes.map { |byte| byte.chr(Encoding::BINARY) }
+
+    expect(stream_response(chunks, limit: text.length)).to eq(text)
+  end
+
+  it "counts accumulated characters rather than bytes or individual chunks" do
+    expect(stream_response(["東".b, "京".b], limit: 2)).to eq("東京")
+    expect { stream_response(["東".b, "京".b, "!".b], limit: 2) }
+      .to raise_error(IpgeolocationSdk::TransportError, "Response body exceeded max size of 2 characters")
+  end
+
+  it "replaces malformed and incomplete UTF-8 sequences" do
+    expect(stream_response(["a\xFFb\xE6".b, "\x9D".b])).to eq("a\uFFFDb\uFFFD")
+  end
+
+  it "preserves valid text adjacent to consecutive malformed sequences" do
+    bytes = [0x8d, 0xdf, 0x61].pack("C*")
+    expect(stream_response([bytes])).to eq("\uFFFD\uFFFDa")
+    expect(stream_response(bytes.bytes.map { |byte| byte.chr(Encoding::BINARY) })).to eq("\uFFFD\uFFFDa")
+  end
+
+  it "handles invalid UTF-8 prefixes without dropping following text" do
+    [[0xe0, 0x80], [0xed, 0xa0], [0xf0, 0x80], [0xf4, 0x90]].each do |prefix|
+      bytes = (prefix + [0x61]).pack("C*")
+      expected = bytes.dup.force_encoding(Encoding::UTF_8).scrub
+      expect(stream_response(bytes.bytes.map { |byte| byte.chr(Encoding::BINARY) })).to eq(expected)
+    end
+  end
+
+  it "matches whole-body UTF-8 replacement for arbitrary bytes and chunk boundaries" do
+    random = Random.new(1234)
+    100.times do
+      bytes = Array.new(random.rand(1..100)) { random.rand(256) }.pack("C*")
+      chunks = []
+      offset = 0
+      while offset < bytes.bytesize
+        chunk = bytes.byteslice(offset, random.rand(1..8))
+        chunks << chunk
+        offset += chunk.bytesize
+      end
+      expected = bytes.dup.force_encoding(Encoding::UTF_8).scrub
+      expect(stream_response(chunks, limit: expected.length)).to eq(expected)
+    end
+  end
+
+  it "includes the replacement for an incomplete final character in the limit" do
+    expect { stream_response(["a\xE6\x9D".b], limit: 1) }
+      .to raise_error(IpgeolocationSdk::TransportError, "Response body exceeded max size of 1 characters")
+  end
+
+  it "returns an empty UTF-8 string for a response with no body" do
+    result = stream_response([])
+    expect(result).to eq("")
+    expect(result.encoding).to eq(Encoding::UTF_8)
+  end
+
+  it "stops an actual HTTP download at the cumulative limit and closes the connection" do
+    server = TCPServer.new("127.0.0.1", 0)
+    connection_closed = Queue.new
+    worker = Thread.new do
+      socket = server.accept
+      while (line = socket.gets) && line != "\r\n"
+      end
+      socket.write("HTTP/1.1 200 OK\r\nTransfer-Encoding: chunked\r\nConnection: close\r\n\r\n")
+      socket.write("2\r\nab\r\n2\r\ncd\r\n")
+      connection_closed << (IO.select([socket], nil, nil, 2) && socket.read(1).nil?)
+    ensure
+      socket.close if socket && !socket.closed?
+    end
+    local_request = IpgeolocationSdk::HttpRequestData.new(
+      url: "http://127.0.0.1:#{server.addr[1]}/v3/ipgeo",
+      method: "GET", headers: {}, body: nil,
+      connect_timeout: 1.0, read_timeout: 0.1
+    )
+
+    expect { described_class.new(max_response_body_chars: 3).send_request(local_request) }
+      .to raise_error(IpgeolocationSdk::TransportError, "Response body exceeded max size of 3 characters")
+    expect(worker.join(3)).not_to be_nil
+    expect(connection_closed.pop).to be_truthy
+  ensure
+    server.close if server && !server.closed?
+    worker.kill if worker && worker.alive?
+    worker.join if worker
+  end
+end