diff --git a/Cargo.lock b/Cargo.lock
index 63fd068fde..cb6d0cf8a8 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2827,6 +2827,23 @@ version = "0.2.178"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "37c93d8daa9d8a012fd8ab92f088405fb202ea0b6ab73ee2482ae66af4f42091"
 
+[[package]]
+name = "libdd-agent-client"
+version = "31.0.0"
+dependencies = [
+ "bytes",
+ "flate2",
+ "httpmock",
+ "libdd-common",
+ "libdd-http-client",
+ "rustls",
+ "serde",
+ "serde_json",
+ "serial_test",
+ "thiserror 2.0.17",
+ "tokio",
+]
+
 [[package]]
 name = "libdd-alloc"
 version = "1.0.0"
diff --git a/Cargo.toml b/Cargo.toml
index aabcc1d8ac..ca36f40e31 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -51,6 +51,7 @@ members = [
   "libdd-tinybytes",
   "libdd-dogstatsd-client",
   "libdd-http-client",
+  "libdd-agent-client",
   "libdd-log",
   "libdd-log-ffi",
 ]
diff --git a/libdd-agent-client/Cargo.toml b/libdd-agent-client/Cargo.toml
new file mode 100644
index 0000000000..f8f80c17cb
--- /dev/null
+++ b/libdd-agent-client/Cargo.toml
@@ -0,0 +1,32 @@
+# Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+# SPDX-License-Identifier: Apache-2.0
+
+[package]
+name = "libdd-agent-client"
+version.workspace = true
+edition.workspace = true
+rust-version.workspace = true
+license.workspace = true
+authors.workspace = true
+description = "Datadog-agent-specialized HTTP client: language metadata injection, per-endpoint send methods, retry, and compression"
+homepage = "https://github.com/DataDog/libdatadog/tree/main/libdd-agent-client"
+repository = "https://github.com/DataDog/libdatadog/tree/main/libdd-agent-client"
+
+[lib]
+bench = false
+
+[dependencies]
+bytes = "1.4"
+flate2 = "1"
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+thiserror = "2"
+tokio = { version = "1.23", features = ["rt"] }
+libdd-http-client = { path = "../libdd-http-client" }
+libdd-common = { version = "3.0.2", path = "../libdd-common", default-features = false }
+
+[dev-dependencies]
+httpmock = "0.8.0-alpha.1"
+rustls = { version = "0.23", default-features = false, features = ["ring"] }
+serial_test = "3.2"
+tokio = { version = "1.23", features = ["rt", "macros"] }
diff --git a/libdd-agent-client/src/agent_info.rs b/libdd-agent-client/src/agent_info.rs
new file mode 100644
index 0000000000..e9193f9d8b
--- /dev/null
+++ b/libdd-agent-client/src/agent_info.rs
@@ -0,0 +1,30 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+//! Types for [`crate::AgentClient::agent_info`].
+
+/// Parsed response from a `GET /info` probe.
+///
+/// Returned by [`crate::AgentClient::agent_info`]. Contains agent capabilities and headers.
+#[derive(Debug, Clone)]
+pub struct AgentInfo {
+    /// Available agent endpoints, e.g. `["/v0.4/traces", "/v0.5/traces"]`.
+    pub endpoints: Vec<String>,
+    /// Whether the agent supports client-side P0 dropping.
+    pub client_drop_p0s: bool,
+    /// Raw agent configuration block.
+    pub config: serde_json::Value,
+    /// Agent version string, if reported.
+    pub version: Option<String>,
+    /// Parsed from the `Datadog-Container-Tags-Hash` response header.
+    ///
+    /// Used by dd-trace-py to compute the base tag hash (`agent.py:17-23`).
+    pub container_tags_hash: Option<String>,
+    /// Value of the `Datadog-Agent-State` response header from the last `/info` fetch.
+    ///
+    /// The agent updates this opaque token whenever its internal state changes (e.g. a
+    /// configuration reload). Clients that poll `/info` periodically can skip re-parsing
+    /// the response body by comparing this value to the one returned by the previous call
+    /// and only acting when it differs.
+    pub state_hash: Option<String>,
+}
diff --git a/libdd-agent-client/src/builder.rs b/libdd-agent-client/src/builder.rs
new file mode 100644
index 0000000000..5753351bae
--- /dev/null
+++ b/libdd-agent-client/src/builder.rs
@@ -0,0 +1,537 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+//! Builder for [`crate::AgentClient`].
+
+use std::collections::HashMap;
+use std::env;
+#[cfg(unix)]
+use std::path::PathBuf;
+use std::time::Duration;
+#[cfg(windows)]
+use OsString;
+
+use libdd_http_client::RetryConfig;
+
+use crate::{error::BuildError, language_metadata::LanguageMetadata, AgentClient};
+
+/// Default timeout for agent requests.
+pub const DEFAULT_TIMEOUT_MS: u64 = 2_000;
+
+/// Default retry configuration: 2 retries (3 total attempts), 100 ms initial delay,
+/// exponential backoff with full jitter.
+//TODO: Do we really want something different from `RetryConfig::default()` for the agent? The only
+//difference is the number of retries : 3 vs 2
+pub fn default_retry_config() -> RetryConfig {
+    RetryConfig::new()
+        .max_retries(2)
+        .initial_delay(Duration::from_millis(100))
+        .with_jitter(true)
+}
+
+/// Transport configuration for the agent client.
+///
+/// Determines how the client connects to the Datadog agent.
+/// Set via [`AgentClientBuilder::transport`] or the convenience helpers
+/// [`AgentClientBuilder::http`], [`AgentClientBuilder::unix_socket`], etc.
+#[derive(Debug, Clone)]
+pub enum AgentTransport {
+    /// HTTP over TCP.
+    Http {
+        /// Hostname or IP address.
+        host: String,
+        /// Port number.
+        port: u16,
+    },
+    /// Unix Domain Socket.
+    ///
+    /// HTTP requests are still formed with `Host: localhost`. The socket path governs only the
+    /// transport layer.
+    #[cfg(unix)]
+    UnixSocket {
+        /// Filesystem path to the socket file.
+        path: PathBuf,
+    },
+    /// Windows Named Pipe.
+    #[cfg(windows)]
+    NamedPipe {
+        /// Named pipe path, e.g. `\\.\pipe\DD_APM_DRIVER`.
+        path: OsString,
+    },
+}
+
+impl Default for AgentTransport {
+    fn default() -> Self {
+        AgentTransport::Http {
+            host: "localhost".to_string(),
+            port: 8126,
+        }
+    }
+}
+
+/// Builder for [`AgentClient`].
+///
+/// Obtain via [`AgentClient::builder`].
+///
+/// # Required fields
+///
+/// - Transport: set via [`AgentClientBuilder::auto_detect`] (reads standard env vars and probes the
+///   local socket) or an explicit convenience method ([`AgentClientBuilder::http`],
+///   [`AgentClientBuilder::unix_socket`], [`AgentClientBuilder::windows_named_pipe`],
+///   [`AgentClientBuilder::transport`]).
+/// - [`AgentClientBuilder::language_metadata`].
+///
+/// # Test tokens
+///
+/// Call [`AgentClientBuilder::test_agent_session_token`] to inject
+/// `x-datadog-test-session-token` on every request.
+#[derive(Debug, Default)]
+pub struct AgentClientBuilder {
+    transport: Option<AgentTransport>,
+    test_token: Option<String>,
+    timeout: Option<Duration>,
+    language: Option<LanguageMetadata>,
+    retry: Option<RetryConfig>,
+    keep_alive: bool,
+    extra_headers: HashMap<String, String>,
+}
+
+impl AgentClientBuilder {
+    /// Create a new builder with default settings.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Set the transport configuration.
+    pub fn transport(mut self, transport: AgentTransport) -> Self {
+        self.transport = Some(transport);
+        self
+    }
+
+    /// Convenience: HTTP over TCP.
+    pub fn http(self, host: impl Into<String>, port: u16) -> Self {
+        self.transport(AgentTransport::Http {
+            host: host.into(),
+            port,
+        })
+    }
+
+    /// Convenience: Unix Domain Socket.
+    #[cfg(unix)]
+    pub fn unix_socket(self, path: impl Into<PathBuf>) -> Self {
+        self.transport(AgentTransport::UnixSocket { path: path.into() })
+    }
+
+    /// Convenience: Windows Named Pipe.
+    #[cfg(windows)]
+    pub fn windows_named_pipe(self, path: impl Into<OsString>) -> Self {
+        self.transport(AgentTransport::NamedPipe { path: path.into() })
+    }
+
+    /// Auto-configure transport and timeout from the environment.
+    ///
+    /// Transport priority:
+    /// 1. `DD_TRACE_AGENT_URL` — parsed as `http://host:port` or `unix:///path`.
+    /// 2. `DD_AGENT_HOST` / `DD_TRACE_AGENT_PORT` — explicit host and/or port.
+    /// 3. `/var/run/datadog/apm.socket` — Unix domain socket if the file exists.
+    /// 4. `localhost:8126` — HTTP fallback.
+    ///
+    /// Timeout is read from `DD_TRACE_AGENT_TIMEOUT_SECONDS` (seconds, float),
+    /// defaulting to [`DEFAULT_TIMEOUT_MS`] when unset or unparseable.
+    #[cfg(unix)]
+    pub fn auto_detect(mut self) -> Self {
+        let transport = Self::transport_from_env().unwrap_or_else(|| {
+            let uds = PathBuf::from("/var/run/datadog/apm.socket");
+            if uds.try_exists().unwrap_or(false) {
+                AgentTransport::UnixSocket { path: uds }
+            } else {
+                AgentTransport::Http {
+                    host: "localhost".to_string(),
+                    port: 8126,
+                }
+            }
+        });
+        self.transport = Some(transport);
+
+        self.timeout = Some(
+            env::var("DD_TRACE_AGENT_TIMEOUT_SECONDS")
+                .ok()
+                .and_then(|v| v.parse::<f64>().ok())
+                .map(|secs| Duration::from_millis((secs * 1000.0) as u64))
+                .unwrap_or(Duration::from_millis(DEFAULT_TIMEOUT_MS)),
+        );
+
+        self
+    }
+
+    /// Read transport from env vars (`DD_TRACE_AGENT_URL`, then
+    /// `DD_AGENT_HOST`/`DD_TRACE_AGENT_PORT`). Returns `None` when none of the variables are
+    /// set.
+    #[cfg(unix)]
+    fn transport_from_env() -> Option<AgentTransport> {
+        if let Ok(url) = env::var("DD_TRACE_AGENT_URL") {
+            if let Some(t) = Self::parse_agent_url(&url) {
+                return Some(t);
+            }
+        }
+
+        let host = env::var("DD_AGENT_HOST").ok();
+        let port = env::var("DD_TRACE_AGENT_PORT")
+            .ok()
+            .and_then(|p| p.parse::<u16>().ok());
+
+        if host.is_some() || port.is_some() {
+            return Some(AgentTransport::Http {
+                host: host.unwrap_or_else(|| "localhost".to_string()),
+                port: port.unwrap_or(8126),
+            });
+        }
+
+        None
+    }
+
+    /// Parse a Datadog agent URL into an [`AgentTransport`].
+    ///
+    /// Supported schemes: `http://`, `https://`, `unix://`.
+    #[cfg(unix)]
+    fn parse_agent_url(url: &str) -> Option<AgentTransport> {
+        if let Some(after_scheme) = url.strip_prefix("unix://") {
+            // unix:///abs/path  or  unix://localhost/abs/path
+            let path = if after_scheme.starts_with('/') {
+                after_scheme
+            } else {
+                &after_scheme[after_scheme.find('/')?..]
+            };
+            return Some(AgentTransport::UnixSocket {
+                path: PathBuf::from(path),
+            });
+        }
+
+        let rest = url
+            .strip_prefix("http://")
+            .or_else(|| url.strip_prefix("https://"))?;
+
+        // Drop any trailing path (e.g. "host:port/")
+        let authority = rest.split('/').next().unwrap_or(rest);
+        let (host, port) = if let Some(colon) = authority.rfind(':') {
+            let port = authority[colon + 1..].parse::<u16>().ok().unwrap_or(8126);
+            (&authority[..colon], port)
+        } else {
+            (authority, 8126u16)
+        };
+
+        Some(AgentTransport::Http {
+            host: host.to_string(),
+            port,
+        })
+    }
+
+    /// Set the test session token.
+    ///
+    /// When set, `x-datadog-test-session-token: <token>` is injected on every request.
+    pub fn test_agent_session_token(mut self, token: impl Into<String>) -> Self {
+        self.test_token = Some(token.into());
+        self
+    }
+
+    /// Set the request timeout.
+    ///
+    /// Defaults to [`DEFAULT_TIMEOUT_MS`] (2 000 ms) when not set.
+    pub fn timeout(mut self, timeout: Duration) -> Self {
+        self.timeout = Some(timeout);
+        self
+    }
+
+    /// Override the default retry configuration.
+    ///
+    /// Defaults to [`default_retry_config`].
+    pub fn retry(mut self, config: RetryConfig) -> Self {
+        self.retry = Some(config);
+        self
+    }
+
+    /// Set the language/runtime metadata injected into every request. Required.
+    pub fn language_metadata(mut self, meta: LanguageMetadata) -> Self {
+        self.language = Some(meta);
+        self
+    }
+
+    /// Enable or disable HTTP keep-alive. Defaults to `false`.
+    ///
+    /// The Datadog agent has a low keep-alive timeout that causes "pipe closed" errors on every
+    /// second connection when keep-alive is enabled. The default of `false` is correct for all
+    /// periodic-flush writers (traces, stats, data streams). Set to `true` only for
+    /// high-frequency continuous senders (e.g. a streaming profiling exporter).
+    pub fn use_keep_alive(mut self, enabled: bool) -> Self {
+        self.keep_alive = enabled;
+        self
+    }
+
+    // Compression
+    //
+    // Not exposed in this libv1. Gzip compression (level 6, matching dd-trace-py's trace writer at
+    // `writer.py:490`) will be added in a follow-up once the core send paths are stable.
+    // Per-method defaults (e.g. unconditional gzip for `send_pipeline_stats`) are already
+    // baked in; only the opt-in client-level `gzip(level)` builder knob is deferred.
+
+    /// Additional custom headers to inject.
+    pub fn extra_headers(mut self, headers: HashMap<String, String>) -> Self {
+        self.extra_headers = headers;
+        self
+    }
+
+    /// Build the [`AgentClient`].
+    pub fn build(self) -> Result<AgentClient, BuildError> {
+        let transport = self.transport.ok_or(BuildError::MissingTransport)?;
+        let language = self.language.ok_or(BuildError::MissingLanguageMetadata)?;
+        let timeout = self
+            .timeout
+            .unwrap_or(Duration::from_millis(DEFAULT_TIMEOUT_MS));
+        let retry = self.retry.unwrap_or_else(default_retry_config);
+
+        // Build the underlying HTTP client.
+        let http = Self::build_http_client(transport, timeout, retry)
+            .map_err(|e| BuildError::HttpClient(e.to_string()))?;
+
+        // Pre-compute all static headers that are injected on every request.
+        let static_headers =
+            Self::build_static_headers(&language, self.test_token, self.extra_headers);
+
+        Ok(AgentClient::new(http, static_headers))
+    }
+
+    fn build_http_client(
+        transport: AgentTransport,
+        timeout: Duration,
+        retry: RetryConfig,
+    ) -> Result<libdd_http_client::HttpClient, libdd_http_client::HttpClientError> {
+        let base_url = match &transport {
+            AgentTransport::Http { host, port } => format!("http://{}:{}", host, port),
+            #[cfg(unix)]
+            AgentTransport::UnixSocket { .. } => "http://localhost".to_string(),
+            #[cfg(windows)]
+            AgentTransport::NamedPipe { .. } => "http://localhost".to_string(),
+        };
+
+        let mut builder = libdd_http_client::HttpClient::builder()
+            .base_url(base_url)
+            .timeout(timeout)
+            // HTTP errors are handled by each send method, not by the underlying client.
+            // This allows methods like `agent_info` to interpret 404 as Ok(None) rather than
+            // an error, and avoids retrying on HTTP 4xx/5xx.
+            .treat_http_errors_as_errors(false)
+            .retry(retry);
+
+        match transport {
+            AgentTransport::Http { .. } => {}
+            #[cfg(unix)]
+            AgentTransport::UnixSocket { path } => {
+                builder = builder.unix_socket(path);
+            }
+            #[cfg(windows)]
+            AgentTransport::NamedPipe { path } => {
+                builder = builder.windows_named_pipe(path);
+            }
+        }
+
+        builder.build()
+    }
+
+    fn build_static_headers(
+        language: &LanguageMetadata,
+        test_token: Option<String>,
+        extra_headers: HashMap<String, String>,
+    ) -> Vec<(String, String)> {
+        let mut headers = vec![
+            ("Datadog-Meta-Lang".to_string(), language.language.clone()),
+            (
+                "Datadog-Meta-Lang-Version".to_string(),
+                language.language_version.clone(),
+            ),
+            (
+                "Datadog-Meta-Lang-Interpreter".to_string(),
+                language.interpreter.clone(),
+            ),
+            (
+                "Datadog-Meta-Tracer-Version".to_string(),
+                language.tracer_version.clone(),
+            ),
+            ("User-Agent".to_string(), language.user_agent()),
+        ];
+
+        if let Some(token) = test_token {
+            headers.push(("x-datadog-test-session-token".to_string(), token));
+        }
+
+        headers.extend(Self::container_headers());
+        headers.extend(extra_headers);
+
+        headers
+    }
+
+    /// Read container / entity-ID headers from the host environment. Always injects
+    /// `Datadog-External-Env` when `DD_EXTERNAL_ENV` is set.
+    fn container_headers() -> Vec<(String, String)> {
+        let mut headers = Vec::new();
+
+        if let Ok(env) = env::var("DD_EXTERNAL_ENV") {
+            if !env.is_empty() {
+                headers.push(("Datadog-External-Env".to_string(), env));
+            }
+        }
+
+        use libdd_common::entity_id;
+
+        if let Some(container_id) = entity_id::get_container_id() {
+            headers.push(("Datadog-Container-Id".to_string(), container_id.to_owned()));
+        }
+
+        if let Some(entity_id) = entity_id::get_entity_id() {
+            headers.push(("Datadog-Entity-ID".to_string(), entity_id.to_owned()));
+        }
+
+        headers
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::env;
+
+    #[test]
+    fn default_transport_is_localhost_8126() {
+        let t = AgentTransport::default();
+        match t {
+            AgentTransport::Http { host, port } => {
+                assert_eq!(host, "localhost");
+                assert_eq!(port, 8126);
+            }
+            #[allow(unreachable_patterns)]
+            _ => panic!("unexpected default transport"),
+        }
+    }
+
+    #[test]
+    fn default_retry_config_is_constructable() {
+        // Just verify default_retry_config() doesn't panic.
+        let _cfg = default_retry_config();
+    }
+
+    #[test]
+    fn builder_new_is_default() {
+        let b = AgentClientBuilder::new();
+        assert!(b.transport.is_none());
+        assert!(b.language.is_none());
+        assert!(!b.keep_alive);
+    }
+
+    #[test]
+    fn build_fails_without_transport() {
+        let result = AgentClientBuilder::new()
+            .language_metadata(LanguageMetadata::new("python", "3.12", "CPython", "2.0"))
+            .build();
+        assert!(matches!(result, Err(BuildError::MissingTransport)));
+    }
+
+    #[test]
+    fn build_fails_without_language_metadata() {
+        let result = AgentClientBuilder::new().http("localhost", 8126).build();
+        assert!(matches!(result, Err(BuildError::MissingLanguageMetadata)));
+    }
+
+    #[test]
+    fn build_succeeds_with_required_fields() {
+        let _ = rustls::crypto::ring::default_provider().install_default();
+        let result = AgentClientBuilder::new()
+            .http("localhost", 8126)
+            .language_metadata(LanguageMetadata::new("python", "3.12", "CPython", "2.0"))
+            .build();
+        assert!(result.is_ok());
+    }
+
+    #[cfg(unix)]
+    #[test]
+    #[serial_test::serial]
+    fn auto_detect_uses_dd_trace_agent_url_http() {
+        env::set_var("DD_TRACE_AGENT_URL", "http://myhost:9000");
+        env::remove_var("DD_AGENT_HOST");
+        env::remove_var("DD_TRACE_AGENT_PORT");
+        let b = AgentClientBuilder::new().auto_detect();
+        env::remove_var("DD_TRACE_AGENT_URL");
+        assert!(matches!(
+            b.transport,
+            Some(AgentTransport::Http { ref host, port })
+                if host == "myhost" && port == 9000
+        ));
+    }
+
+    #[cfg(unix)]
+    #[test]
+    #[serial_test::serial]
+    fn auto_detect_uses_dd_trace_agent_url_unix() {
+        env::set_var("DD_TRACE_AGENT_URL", "unix:///tmp/test.sock");
+        env::remove_var("DD_AGENT_HOST");
+        env::remove_var("DD_TRACE_AGENT_PORT");
+        let b = AgentClientBuilder::new().auto_detect();
+        env::remove_var("DD_TRACE_AGENT_URL");
+        assert!(matches!(
+            b.transport,
+            Some(AgentTransport::UnixSocket { ref path })
+                if path.to_str() == Some("/tmp/test.sock")
+        ));
+    }
+
+    #[cfg(unix)]
+    #[test]
+    #[serial_test::serial]
+    fn auto_detect_uses_dd_agent_host_and_port() {
+        env::remove_var("DD_TRACE_AGENT_URL");
+        env::set_var("DD_AGENT_HOST", "remotehost");
+        env::set_var("DD_TRACE_AGENT_PORT", "7777");
+        let b = AgentClientBuilder::new().auto_detect();
+        env::remove_var("DD_AGENT_HOST");
+        env::remove_var("DD_TRACE_AGENT_PORT");
+        assert!(matches!(
+            b.transport,
+            Some(AgentTransport::Http { ref host, port })
+                if host == "remotehost" && port == 7777
+        ));
+    }
+
+    #[cfg(unix)]
+    #[test]
+    #[serial_test::serial]
+    fn auto_detect_reads_timeout_from_env() {
+        env::remove_var("DD_TRACE_AGENT_URL");
+        env::remove_var("DD_AGENT_HOST");
+        env::remove_var("DD_TRACE_AGENT_PORT");
+        env::set_var("DD_TRACE_AGENT_TIMEOUT_SECONDS", "5");
+        let b = AgentClientBuilder::new().auto_detect();
+        env::remove_var("DD_TRACE_AGENT_TIMEOUT_SECONDS");
+        assert_eq!(b.timeout, Some(Duration::from_secs(5)));
+    }
+
+    #[cfg(unix)]
+    #[test]
+    #[serial_test::serial]
+    fn auto_detect_uses_default_timeout_when_unset() {
+        env::remove_var("DD_TRACE_AGENT_URL");
+        env::remove_var("DD_AGENT_HOST");
+        env::remove_var("DD_TRACE_AGENT_PORT");
+        env::remove_var("DD_TRACE_AGENT_TIMEOUT_SECONDS");
+        let b = AgentClientBuilder::new().auto_detect();
+        assert_eq!(b.timeout, Some(Duration::from_millis(DEFAULT_TIMEOUT_MS)));
+    }
+
+    #[test]
+    fn extra_headers_stored() {
+        let mut headers = HashMap::new();
+        headers.insert("X-Custom".to_string(), "value".to_string());
+        let b = AgentClientBuilder::new().extra_headers(headers);
+        assert_eq!(
+            b.extra_headers.get("X-Custom").map(|s| s.as_str()),
+            Some("value")
+        );
+    }
+}
diff --git a/libdd-agent-client/src/client.rs b/libdd-agent-client/src/client.rs
new file mode 100644
index 0000000000..d63cf73e60
--- /dev/null
+++ b/libdd-agent-client/src/client.rs
@@ -0,0 +1,324 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+//! [`AgentClient`] and its send methods.
+
+use std::collections::HashMap;
+
+use bytes::Bytes;
+use flate2::{write::GzEncoder, Compression};
+use libdd_http_client::{HttpClient, HttpMethod, HttpRequest};
+use serde_json::{from_slice, Value};
+use std::io::Write as _;
+
+use crate::{
+    agent_info::AgentInfo,
+    builder::AgentClientBuilder,
+    error::SendError,
+    telemetry::TelemetryRequest,
+    traces::{AgentResponse, TraceFormat, TraceSendOptions},
+};
+
+/// A Datadog-agent-specialized HTTP client.
+///
+/// Wraps a configured [`libdd_http_client::HttpClient`] and injects Datadog-specific headers
+/// automatically on every request:
+///
+/// - Language metadata headers (`Datadog-Meta-Lang`, `Datadog-Meta-Lang-Version`,
+///   `Datadog-Meta-Lang-Interpreter`, `Datadog-Meta-Tracer-Version`) from the [`LanguageMetadata`]
+///   supplied when creating the client.
+/// - `User-Agent` derived from [`LanguageMetadata::user_agent`].
+/// - Container/entity-ID headers (`Datadog-Container-Id`, `Datadog-Entity-ID`,
+///   `Datadog-External-Env`) read from `/proc/self/cgroup` at startup.
+/// - `x-datadog-test-session-token` when a test token was set.
+/// - Any extra headers registered via [`AgentClientBuilder::extra_headers`].
+///
+/// Obtain via [`AgentClient::builder`].
+///
+/// [`LanguageMetadata`]: crate::LanguageMetadata
+pub struct AgentClient {
+    http: HttpClient,
+    base_url: String,
+    static_headers: Vec<(String, String)>,
+}
+
+impl AgentClient {
+    pub(crate) fn new(http: HttpClient, static_headers: Vec<(String, String)>) -> Self {
+        let base_url = http.config().base_url().to_string();
+        Self {
+            http,
+            base_url,
+            static_headers,
+        }
+    }
+
+    /// Create a new [`AgentClientBuilder`].
+    pub fn builder() -> AgentClientBuilder {
+        AgentClientBuilder::new()
+    }
+
+    /// Send a serialised trace payload to the agent with automatically injected headers.
+    ///
+    /// # Returns
+    ///
+    /// An [`AgentResponse`] with the HTTP status and the parsed `rate_by_service` sampling
+    /// rates from the agent response body.
+    pub async fn send_traces(
+        &self,
+        payload: Bytes,
+        trace_count: usize,
+        format: TraceFormat,
+        opts: TraceSendOptions,
+    ) -> Result<AgentResponse, SendError> {
+        let (path, content_type) = match format {
+            TraceFormat::MsgpackV5 => ("/v0.5/traces", "application/msgpack"),
+            TraceFormat::MsgpackV4 => ("/v0.4/traces", "application/msgpack"),
+        };
+
+        let mut request = HttpRequest::new(HttpMethod::Put, format!("{}{}", self.base_url, path))
+            .with_body(payload)
+            .with_headers(self.static_headers.iter().cloned())
+            .with_header("Content-Type", content_type)
+            .with_header("X-Datadog-Trace-Count", trace_count.to_string())
+            .with_header("Datadog-Send-Real-Http-Status", "true");
+
+        if opts.computed_top_level {
+            request = request.with_header("Datadog-Client-Computed-Top-Level", "yes");
+        }
+
+        let response = self.http.send(request).await?;
+
+        if response.status_code() >= 400 {
+            return Err(SendError::HttpError {
+                status: response.status_code(),
+                body: response.body().clone(),
+            });
+        }
+
+        let rate_by_service = parse_rate_by_service(response.body());
+        Ok(AgentResponse {
+            status: response.status_code(),
+            rate_by_service,
+        })
+    }
+
+    /// Send span stats (APM concentrator buckets) to `/v0.6/stats`.
+    pub async fn send_stats(&self, payload: Bytes) -> Result<(), SendError> {
+        let request = HttpRequest::new(HttpMethod::Put, format!("{}/v0.6/stats", self.base_url))
+            .with_body(payload)
+            .with_headers(self.static_headers.iter().cloned())
+            .with_header("Content-Type", "application/msgpack");
+
+        let response = self.http.send(request).await?;
+        check_status(response)
+    }
+
+    /// Send data-streams pipeline stats to `/v0.1/pipeline_stats`.
+    ///
+    /// The payload is **always** gzip-compressed regardless of the client-level compression
+    /// setting. This is a protocol requirement of the data-streams endpoint.
+    pub async fn send_pipeline_stats(&self, payload: Bytes) -> Result<(), SendError> {
+        let request = HttpRequest::new(
+            HttpMethod::Put,
+            format!("{}/v0.1/pipeline_stats", self.base_url),
+        )
+        .with_body(gzip_compress(payload)?)
+        .with_headers(self.static_headers.iter().cloned())
+        .with_header("Content-Type", "application/msgpack")
+        .with_header("Content-Encoding", "gzip");
+
+        let response = self.http.send(request).await?;
+        check_status(response)
+    }
+
+    /// Send a telemetry event to the agent's telemetry proxy
+    /// (`telemetry/proxy/api/v2/apmtelemetry`).
+    pub async fn send_telemetry(&self, req: TelemetryRequest) -> Result<(), SendError> {
+        let request = HttpRequest::new(
+            HttpMethod::Post,
+            format!("{}/telemetry/proxy/api/v2/apmtelemetry", self.base_url),
+        )
+        .with_body(req.body)
+        .with_headers(self.static_headers.iter().cloned())
+        .with_header("Content-Type", "application/json")
+        .with_header("DD-Telemetry-Request-Type", &req.request_type)
+        .with_header("DD-Telemetry-API-Version", &req.api_version)
+        .with_header(
+            "DD-Telemetry-Debug-Enabled",
+            if req.debug { "true" } else { "false" },
+        );
+
+        let response = self.http.send(request).await?;
+        check_status(response)
+    }
+
+    /// Send an event via the agent's EVP (Event Platform) proxy.
+    ///
+    /// The agent forwards the request to `<subdomain>.datadoghq.com<path>`. `subdomain`
+    /// controls the target intake (injected as `X-Datadog-EVP-Subdomain`); `path` is the
+    /// endpoint on that intake (e.g. `/api/v2/exposures`).
+    pub async fn send_evp_event(
+        &self,
+        subdomain: &str,
+        path: &str,
+        payload: Bytes,
+        content_type: &str,
+    ) -> Result<(), SendError> {
+        let request = HttpRequest::new(HttpMethod::Post, format!("{}{}", self.base_url, path))
+            .with_body(payload)
+            .with_headers(self.static_headers.iter().cloned())
+            .with_header("Content-Type", content_type)
+            .with_header("X-Datadog-EVP-Subdomain", subdomain);
+
+        let response = self.http.send(request).await?;
+        check_status(response)
+    }
+
+    /// Probe `GET /info` and return parsed agent capabilities.
+    ///
+    /// Returns `Ok(None)` when the agent returns 404 (remote-config / info not supported).
+    pub async fn agent_info(&self) -> Result<Option<AgentInfo>, SendError> {
+        #[derive(serde::Deserialize)]
+        struct InfoResponse {
+            version: Option<String>,
+            endpoints: Option<Vec<String>>,
+            client_drop_p0s: Option<bool>,
+            config: Option<Value>,
+        }
+
+        let request = HttpRequest::new(HttpMethod::Get, format!("{}/info", self.base_url))
+            .with_headers(self.static_headers.iter().cloned());
+
+        let response = self.http.send(request).await?;
+
+        if response.status_code() == 404 {
+            return Ok(None);
+        }
+
+        if response.status_code() >= 400 {
+            return Err(SendError::HttpError {
+                status: response.status_code(),
+                body: response.body().clone(),
+            });
+        }
+
+        // Case-insensitive lookup of a response header value.
+        let header = |name: &str| -> Option<String> {
+            response
+                .headers()
+                .iter()
+                .find(|(k, _)| k.eq_ignore_ascii_case(name))
+                .map(|(_, v)| v.clone())
+        };
+
+        let container_tags_hash = header("datadog-container-tags-hash");
+        let state_hash = header("datadog-agent-state");
+
+        let info: InfoResponse =
+            from_slice(response.body()).map_err(|e| SendError::Encoding(e.to_string()))?;
+
+        Ok(Some(AgentInfo {
+            endpoints: info.endpoints.unwrap_or_default(),
+            client_drop_p0s: info.client_drop_p0s.unwrap_or(false),
+            config: info.config.unwrap_or(Value::Null),
+            version: info.version,
+            container_tags_hash,
+            state_hash,
+        }))
+    }
+}
+
+/// Parse `rate_by_service` from an agent trace response body.
+fn parse_rate_by_service(body: &Bytes) -> Option<HashMap<String, f64>> {
+    #[derive(serde::Deserialize)]
+    struct TraceResponse {
+        rate_by_service: Option<HashMap<String, f64>>,
+    }
+
+    from_slice::<TraceResponse>(body)
+        .ok()
+        .and_then(|r| r.rate_by_service)
+}
+
+/// Return `Ok(())` for 2xx, or `Err(SendError::HttpError)` for anything else.
+fn check_status(response: libdd_http_client::HttpResponse) -> Result<(), SendError> {
+    if response.status_code() >= 400 {
+        Err(SendError::HttpError {
+            status: response.status_code(),
+            body: response.body().clone(),
+        })
+    } else {
+        Ok(())
+    }
+}
+
+/// Gzip-compress `payload` at level 6 (matching dd-trace-py's trace writer).
+fn gzip_compress(payload: Bytes) -> Result<Bytes, SendError> {
+    let mut encoder = GzEncoder::new(Vec::new(), Compression::new(6));
+    encoder
+        .write_all(&payload)
+        .map_err(|e| SendError::Encoding(e.to_string()))?;
+    let compressed = encoder
+        .finish()
+        .map_err(|e| SendError::Encoding(e.to_string()))?;
+    Ok(Bytes::from(compressed))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::{AgentClient, LanguageMetadata};
+
+    fn ensure_crypto_provider() {
+        let _ = rustls::crypto::ring::default_provider().install_default();
+    }
+
+    fn test_client(port: u16) -> AgentClient {
+        ensure_crypto_provider();
+        AgentClient::builder()
+            .http("localhost", port)
+            .language_metadata(LanguageMetadata::new("python", "3.12", "CPython", "2.0"))
+            .build()
+            .unwrap()
+    }
+
+    #[test]
+    fn builder_roundtrip() {
+        let client = test_client(8126);
+        assert!(client.base_url.contains("localhost"));
+    }
+
+    #[test]
+    fn static_headers_contain_language_metadata() {
+        let client = test_client(8126);
+        let keys: Vec<&str> = client
+            .static_headers
+            .iter()
+            .map(|(k, _)| k.as_str())
+            .collect();
+        assert!(keys.contains(&"Datadog-Meta-Lang"));
+        assert!(keys.contains(&"Datadog-Meta-Lang-Version"));
+        assert!(keys.contains(&"User-Agent"));
+    }
+
+    #[test]
+    fn gzip_compress_produces_valid_gzip() {
+        let input = Bytes::from_static(b"hello world");
+        let compressed = gzip_compress(input).unwrap();
+        // gzip magic bytes: 0x1f 0x8b
+        assert_eq!(&compressed[..2], &[0x1f, 0x8b]);
+    }
+
+    #[test]
+    fn parse_rate_by_service_valid_json() {
+        let body = Bytes::from(r#"{"rate_by_service":{"service:env":0.5}}"#);
+        let rates = parse_rate_by_service(&body).unwrap();
+        assert_eq!(rates.get("service:env"), Some(&0.5));
+    }
+
+    #[test]
+    fn parse_rate_by_service_absent_field() {
+        let body = Bytes::from(r#"{"other":"value"}"#);
+        assert!(parse_rate_by_service(&body).is_none());
+    }
+}
diff --git a/libdd-agent-client/src/error.rs b/libdd-agent-client/src/error.rs
new file mode 100644
index 0000000000..94009a7889
--- /dev/null
+++ b/libdd-agent-client/src/error.rs
@@ -0,0 +1,69 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+//! Error types for [`crate::AgentClient`].
+
+use std::io::{Error, ErrorKind};
+use bytes::Bytes;
+use libdd_http_client::HttpClientError;
+use thiserror::Error;
+
+/// Errors that can occur when building an [`crate::AgentClient`].
+#[derive(Debug, Error)]
+pub enum BuildError {
+    /// No transport was configured.
+    #[error("transport is required")]
+    MissingTransport,
+    /// No language metadata was configured.
+    #[error("language metadata is required")]
+    MissingLanguageMetadata,
+    /// The underlying HTTP client could not be constructed.
+    #[error("HTTP client error: {0}")]
+    HttpClient(String),
+}
+
+/// Errors that can occur when sending a request via [`crate::AgentClient`].
+#[derive(Debug, Error)]
+pub enum SendError {
+    /// Connection refused, timeout, or I/O error.
+    #[error("transport error: {0}")]
+    Transport(#[source] std::io::Error),
+    /// The server returned an HTTP error status. Includes the raw status and body.
+    #[error("HTTP error {status}: {body:?}")]
+    HttpError {
+        /// HTTP status code returned by the server.
+        status: u16,
+        /// Raw response body.
+        body: Bytes,
+    },
+    /// All retry attempts exhausted without a successful response.
+    #[error("retries exhausted: {last_error}")]
+    RetriesExhausted {
+        /// The last error encountered before giving up.
+        last_error: Box<SendError>,
+    },
+    /// Payload serialisation or compression failure.
+    #[error("encoding error: {0}")]
+    Encoding(String),
+}
+
+impl From<HttpClientError> for SendError {
+    fn from(err: HttpClientError) -> Self {
+        match err {
+            HttpClientError::ConnectionFailed(s) => {
+                SendError::Transport(Error::new(ErrorKind::ConnectionRefused, s))
+            }
+            HttpClientError::TimedOut => {
+                SendError::Transport(Error::new(ErrorKind::TimedOut, "request timed out"))
+            }
+            HttpClientError::IoError(s) => SendError::Transport(Error::other(s)),
+            HttpClientError::InvalidConfig(s) => {
+                SendError::Transport(Error::new(ErrorKind::InvalidInput, s))
+            }
+            HttpClientError::RequestFailed { status, body } => SendError::HttpError {
+                status,
+                body: Bytes::from(body),
+            },
+        }
+    }
+}
diff --git a/libdd-agent-client/src/language_metadata.rs b/libdd-agent-client/src/language_metadata.rs
new file mode 100644
index 0000000000..eb599f90ee
--- /dev/null
+++ b/libdd-agent-client/src/language_metadata.rs
@@ -0,0 +1,69 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+//! Language/runtime metadata injected into every outgoing request.
+
+/// Language and runtime metadata that is automatically injected into every request as
+/// `Datadog-Meta-*` headers and drives the `User-Agent` string.
+#[derive(Debug, Clone)]
+pub struct LanguageMetadata {
+    /// Value of `Datadog-Meta-Lang`, e.g. `"python"`.
+    pub language: String,
+    /// Value of `Datadog-Meta-Lang-Version`, e.g. `"3.12.1"`.
+    pub language_version: String,
+    /// Value of `Datadog-Meta-Lang-Interpreter`, e.g. `"CPython"`.
+    pub interpreter: String,
+    /// Value of `Datadog-Meta-Tracer-Version`, e.g. `"2.18.0"`.
+    pub tracer_version: String,
+}
+
+impl LanguageMetadata {
+    /// Construct a new `LanguageMetadata`.
+    pub fn new(
+        language: impl Into<String>,
+        language_version: impl Into<String>,
+        interpreter: impl Into<String>,
+        tracer_version: impl Into<String>,
+    ) -> Self {
+        Self {
+            language: language.into(),
+            language_version: language_version.into(),
+            interpreter: interpreter.into(),
+            tracer_version: tracer_version.into(),
+        }
+    }
+
+    /// Produces the `User-Agent` string passed to `Endpoint::to_request_builder()`.
+    ///
+    /// Format: `dd-trace-<language>/<tracer_version>`, e.g. `dd-trace-python/2.18.0`.
+    #[inline]
+    pub fn user_agent(&self) -> String {
+        format!("dd-trace-{}/{}", self.language, self.tracer_version)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn new_stores_fields() {
+        let m = LanguageMetadata::new("python", "3.12.1", "CPython", "2.18.0");
+        assert_eq!(m.language, "python");
+        assert_eq!(m.language_version, "3.12.1");
+        assert_eq!(m.interpreter, "CPython");
+        assert_eq!(m.tracer_version, "2.18.0");
+    }
+
+    #[test]
+    fn user_agent_format() {
+        let m = LanguageMetadata::new("python", "3.12.1", "CPython", "2.18.0");
+        assert_eq!(m.user_agent(), "dd-trace-python/2.18.0");
+    }
+
+    #[test]
+    fn user_agent_ruby() {
+        let m = LanguageMetadata::new("ruby", "3.2.0", "MRI", "1.13.0");
+        assert_eq!(m.user_agent(), "dd-trace-ruby/1.13.0");
+    }
+}
diff --git a/libdd-agent-client/src/lib.rs b/libdd-agent-client/src/lib.rs
new file mode 100644
index 0000000000..605c6d03ca
--- /dev/null
+++ b/libdd-agent-client/src/lib.rs
@@ -0,0 +1,67 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+//! This crate provides a Datadog-agent-specific HTTP client sitting on top of the basic
+//! `libdd-http-client` primitives. The API is higher-level and makes agent-specific settings
+//! (headers, etc.) the default rather than opt-in boilerplate.
+//!
+//! # Quick start
+//!
+//! Call [`AgentClientBuilder::auto_detect`] to let the client configure transport and timeout
+//! from the standard Datadog environment variables (`DD_TRACE_AGENT_URL`, `DD_AGENT_HOST`,
+//! `DD_TRACE_AGENT_PORT`, `DD_TRACE_AGENT_TIMEOUT_SECONDS`), falling back to a local Unix
+//! socket at `/var/run/datadog/apm.socket` when it exists, and finally to `localhost:8126`.
+//!
+//! ```rust,no_run
+//! # #[cfg(unix)]
+//! # fn example() -> Result<(), libdd_agent_client::BuildError> {
+//! use libdd_agent_client::{AgentClient, LanguageMetadata};
+//!
+//! let client = AgentClient::builder()
+//!     .auto_detect()
+//!     .language_metadata(LanguageMetadata::new(
+//!         "python", "3.12.1", "CPython", "2.18.0",
+//!     ))
+//!     .build()?;
+//! # Ok(())
+//! # }
+//! ```
+//!
+//! # Explicit transport
+//!
+//! When the host and port are known at build time, set them directly:
+//!
+//! ```rust,no_run
+//! # fn example() -> Result<(), libdd_agent_client::BuildError> {
+//! use libdd_agent_client::{AgentClient, LanguageMetadata};
+//!
+//! let client = AgentClient::builder()
+//!     .http("localhost", 8126)
+//!     .language_metadata(LanguageMetadata::new(
+//!         "python", "3.12.1", "CPython", "2.18.0",
+//!     ))
+//!     .build()?;
+//! # Ok(())
+//! # }
+//! ```
+//!
+//! # Fork safety
+//!
+//! The underlying `libdd-http-client` uses the `hickory-dns` DNS resolver by default, which is
+//! in-process and fork-safe.
+
+pub mod agent_info;
+pub mod builder;
+pub mod client;
+pub mod error;
+pub mod language_metadata;
+pub mod telemetry;
+pub mod traces;
+
+pub use agent_info::AgentInfo;
+pub use builder::{AgentClientBuilder, AgentTransport};
+pub use client::AgentClient;
+pub use error::{BuildError, SendError};
+pub use language_metadata::LanguageMetadata;
+pub use telemetry::TelemetryRequest;
+pub use traces::{AgentResponse, TraceFormat, TraceSendOptions};
diff --git a/libdd-agent-client/src/telemetry.rs b/libdd-agent-client/src/telemetry.rs
new file mode 100644
index 0000000000..de1630b10b
--- /dev/null
+++ b/libdd-agent-client/src/telemetry.rs
@@ -0,0 +1,26 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+//! Types specific to [`crate::AgentClient::send_telemetry`].
+
+/// A single telemetry event to send via [`crate::AgentClient::send_telemetry`].
+///
+/// The three per-request headers `DD-Telemetry-Request-Type`, `DD-Telemetry-API-Version`, and
+/// `DD-Telemetry-Debug-Enabled` are derived automatically from the struct by the client.
+///
+/// The client always routes to the agent telemetry proxy endpoint
+/// (`telemetry/proxy/api/v2/apmtelemetry`).
+#[derive(Debug, Clone)]
+pub struct TelemetryRequest {
+    /// Value for the `DD-Telemetry-Request-Type` header, e.g. `"app-started"`.
+    pub request_type: String,
+    /// Value for the `DD-Telemetry-API-Version` header, e.g. `"v2"`.
+    pub api_version: String,
+    /// Value for the `DD-Telemetry-Debug-Enabled` header.
+    pub debug: bool,
+    /// Pre-serialized JSON payload body.
+    ///
+    /// The caller is responsible for serializing the event body to JSON before constructing this
+    /// struct. The client sends these bytes as `Content-Type: application/json`.
+    pub body: bytes::Bytes,
+}
diff --git a/libdd-agent-client/src/traces.rs b/libdd-agent-client/src/traces.rs
new file mode 100644
index 0000000000..28827b87f4
--- /dev/null
+++ b/libdd-agent-client/src/traces.rs
@@ -0,0 +1,46 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+//! Types specific to [`crate::AgentClient::send_traces`].
+
+use std::collections::HashMap;
+
+/// Wire format of the trace payload.
+///
+/// Determines both the `Content-Type` header and the target endpoint.
+///
+/// # Format selection
+///
+/// The caller is currently responsible for choosing the format. In practice this means starting
+/// with [`TraceFormat::MsgpackV5`] and downgrading to [`TraceFormat::MsgpackV4`] when the agent
+/// returns 404 or 415 (e.g. on Windows, or when AppSec/IAST is active).
+///
+/// In a future version this negotiation may be moved into the client itself so that format
+/// selection becomes automatic and callers no longer need to track the downgrade state.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum TraceFormat {
+    /// `application/msgpack` to `/v0.5/traces`. Preferred format.
+    MsgpackV5,
+    /// `application/msgpack` to `/v0.4/traces`. Fallback for Windows / AppSec.
+    MsgpackV4,
+}
+
+/// Per-request options for [`crate::AgentClient::send_traces`].
+#[derive(Debug, Clone, Default)]
+pub struct TraceSendOptions {
+    /// When `true`, appends `Datadog-Client-Computed-Top-Level: yes`.
+    ///
+    /// Signals to the agent that the client has already marked top-level spans, allowing the agent
+    /// to skip its own top-level computation.
+    pub computed_top_level: bool,
+}
+
+/// Parsed response from the agent after a successful trace submission.
+#[derive(Debug, Clone)]
+pub struct AgentResponse {
+    /// HTTP status code returned by the agent.
+    pub status: u16,
+    /// Per-service sampling rates parsed from the `rate_by_service` field of the agent response
+    /// body, if present.
+    pub rate_by_service: Option<HashMap<String, f64>>,
+}
diff --git a/libdd-agent-client/tests/agent_info.rs b/libdd-agent-client/tests/agent_info.rs
new file mode 100644
index 0000000000..a81101a472
--- /dev/null
+++ b/libdd-agent-client/tests/agent_info.rs
@@ -0,0 +1,62 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+mod common;
+
+use httpmock::prelude::*;
+
+#[tokio::test]
+async fn parses_info_response() {
+    let server = MockServer::start();
+    server.mock(|when, then| {
+        when.method(GET).path("/info");
+        then.status(200).body(
+            r#"{
+                "version": "7.50.0",
+                "endpoints": ["/v0.4/traces", "/v0.5/traces"],
+                "client_drop_p0s": true,
+                "config": {}
+            }"#,
+        );
+    });
+
+    let info = common::client_for(&server)
+        .agent_info()
+        .await
+        .unwrap()
+        .expect("expected Some");
+
+    assert_eq!(info.version.as_deref(), Some("7.50.0"));
+    assert!(info.endpoints.contains(&"/v0.5/traces".to_string()));
+    assert!(info.client_drop_p0s);
+}
+
+#[tokio::test]
+async fn returns_none_on_404() {
+    let server = MockServer::start();
+    server.mock(|when, then| {
+        when.method(GET).path("/info");
+        then.status(404).body("not found");
+    });
+
+    let result = common::client_for(&server).agent_info().await.unwrap();
+    assert!(result.is_none());
+}
+
+#[tokio::test]
+async fn extracts_container_tags_hash_header() {
+    let server = MockServer::start();
+    server.mock(|when, then| {
+        when.method(GET).path("/info");
+        then.status(200)
+            .header("Datadog-Container-Tags-Hash", "abc123")
+            .body(r#"{"endpoints":[],"client_drop_p0s":false}"#);
+    });
+
+    let info = common::client_for(&server)
+        .agent_info()
+        .await
+        .unwrap()
+        .unwrap();
+    assert_eq!(info.container_tags_hash.as_deref(), Some("abc123"));
+}
diff --git a/libdd-agent-client/tests/common.rs b/libdd-agent-client/tests/common.rs
new file mode 100644
index 0000000000..79f0869d9f
--- /dev/null
+++ b/libdd-agent-client/tests/common.rs
@@ -0,0 +1,20 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+use httpmock::MockServer;
+use libdd_agent_client::{AgentClient, LanguageMetadata};
+
+pub fn ensure_crypto_provider() {
+    let _ = rustls::crypto::ring::default_provider().install_default();
+}
+
+pub fn client_for(server: &MockServer) -> AgentClient {
+    ensure_crypto_provider();
+    AgentClient::builder()
+        .http("localhost", server.port())
+        .language_metadata(LanguageMetadata::new(
+            "python", "3.12.1", "CPython", "2.18.0",
+        ))
+        .build()
+        .expect("client build failed")
+}
diff --git a/libdd-agent-client/tests/evp_event.rs b/libdd-agent-client/tests/evp_event.rs
new file mode 100644
index 0000000000..9df3167520
--- /dev/null
+++ b/libdd-agent-client/tests/evp_event.rs
@@ -0,0 +1,30 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+mod common;
+
+use bytes::Bytes;
+use httpmock::prelude::*;
+
+#[tokio::test]
+async fn posts_to_path_with_subdomain_header() {
+    let server = MockServer::start();
+    let mock = server.mock(|when, then| {
+        when.method(POST)
+            .path("/api/v2/exposures")
+            .header("X-Datadog-EVP-Subdomain", "event-platform-intake");
+        then.status(200).body("");
+    });
+
+    common::client_for(&server)
+        .send_evp_event(
+            "event-platform-intake",
+            "/api/v2/exposures",
+            Bytes::from_static(b"{}"),
+            "application/json",
+        )
+        .await
+        .unwrap();
+
+    mock.assert();
+}
diff --git a/libdd-agent-client/tests/pipeline_stats.rs b/libdd-agent-client/tests/pipeline_stats.rs
new file mode 100644
index 0000000000..7df264b637
--- /dev/null
+++ b/libdd-agent-client/tests/pipeline_stats.rs
@@ -0,0 +1,41 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+mod common;
+
+use bytes::Bytes;
+use httpmock::prelude::*;
+
+#[tokio::test]
+async fn puts_to_correct_endpoint() {
+    let server = MockServer::start();
+    let mock = server.mock(|when, then| {
+        when.method(PUT).path("/v0.1/pipeline_stats");
+        then.status(200).body("");
+    });
+
+    common::client_for(&server)
+        .send_pipeline_stats(Bytes::from_static(b"\x80"))
+        .await
+        .unwrap();
+
+    mock.assert();
+}
+
+#[tokio::test]
+async fn sets_gzip_encoding() {
+    let server = MockServer::start();
+    let mock = server.mock(|when, then| {
+        when.method(PUT)
+            .path("/v0.1/pipeline_stats")
+            .header("Content-Encoding", "gzip");
+        then.status(200).body("");
+    });
+
+    common::client_for(&server)
+        .send_pipeline_stats(Bytes::from_static(b"\x80"))
+        .await
+        .unwrap();
+
+    mock.assert();
+}
diff --git a/libdd-agent-client/tests/static_headers.rs b/libdd-agent-client/tests/static_headers.rs
new file mode 100644
index 0000000000..3d1ef30dfd
--- /dev/null
+++ b/libdd-agent-client/tests/static_headers.rs
@@ -0,0 +1,68 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+mod common;
+
+use bytes::Bytes;
+use httpmock::prelude::*;
+use libdd_agent_client::{AgentClient, LanguageMetadata, TraceFormat, TraceSendOptions};
+
+#[tokio::test]
+async fn language_metadata_headers_injected_on_all_requests() {
+    let server = MockServer::start();
+    let mock = server.mock(|when, then| {
+        when.method(PUT)
+            .path("/v0.5/traces")
+            .header("Datadog-Meta-Lang", "python")
+            .header("Datadog-Meta-Lang-Version", "3.12.1")
+            .header("Datadog-Meta-Lang-Interpreter", "CPython")
+            .header("Datadog-Meta-Tracer-Version", "2.18.0")
+            .header("User-Agent", "dd-trace-python/2.18.0");
+        then.status(200).body(r#"{}"#);
+    });
+
+    common::client_for(&server)
+        .send_traces(
+            Bytes::from_static(b""),
+            0,
+            TraceFormat::MsgpackV5,
+            TraceSendOptions::default(),
+        )
+        .await
+        .unwrap();
+
+    mock.assert();
+}
+
+#[tokio::test]
+async fn test_token_injected_when_set() {
+    let server = MockServer::start();
+    let mock = server.mock(|when, then| {
+        when.method(PUT)
+            .path("/v0.5/traces")
+            .header("x-datadog-test-session-token", "my-token");
+        then.status(200).body(r#"{}"#);
+    });
+
+    common::ensure_crypto_provider();
+    let client = AgentClient::builder()
+        .http("localhost", server.port())
+        .language_metadata(LanguageMetadata::new(
+            "python", "3.12.1", "CPython", "2.18.0",
+        ))
+        .test_agent_session_token("my-token")
+        .build()
+        .unwrap();
+
+    client
+        .send_traces(
+            Bytes::from_static(b""),
+            0,
+            TraceFormat::MsgpackV5,
+            TraceSendOptions::default(),
+        )
+        .await
+        .unwrap();
+
+    mock.assert();
+}
diff --git a/libdd-agent-client/tests/stats.rs b/libdd-agent-client/tests/stats.rs
new file mode 100644
index 0000000000..81a3839780
--- /dev/null
+++ b/libdd-agent-client/tests/stats.rs
@@ -0,0 +1,41 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+mod common;
+
+use bytes::Bytes;
+use httpmock::prelude::*;
+
+#[tokio::test]
+async fn puts_to_v06_stats() {
+    let server = MockServer::start();
+    let mock = server.mock(|when, then| {
+        when.method(PUT).path("/v0.6/stats");
+        then.status(200).body("");
+    });
+
+    common::client_for(&server)
+        .send_stats(Bytes::from_static(b"\x80"))
+        .await
+        .unwrap();
+
+    mock.assert();
+}
+
+#[tokio::test]
+async fn sets_msgpack_content_type() {
+    let server = MockServer::start();
+    let mock = server.mock(|when, then| {
+        when.method(PUT)
+            .path("/v0.6/stats")
+            .header("Content-Type", "application/msgpack");
+        then.status(200).body("");
+    });
+
+    common::client_for(&server)
+        .send_stats(Bytes::from_static(b"\x80"))
+        .await
+        .unwrap();
+
+    mock.assert();
+}
diff --git a/libdd-agent-client/tests/telemetry.rs b/libdd-agent-client/tests/telemetry.rs
new file mode 100644
index 0000000000..e663f77e49
--- /dev/null
+++ b/libdd-agent-client/tests/telemetry.rs
@@ -0,0 +1,55 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+mod common;
+
+use bytes::Bytes;
+use httpmock::prelude::*;
+use libdd_agent_client::TelemetryRequest;
+
+#[tokio::test]
+async fn posts_to_telemetry_proxy() {
+    let server = MockServer::start();
+    let mock = server.mock(|when, then| {
+        when.method(POST)
+            .path("/telemetry/proxy/api/v2/apmtelemetry");
+        then.status(202).body("");
+    });
+
+    common::client_for(&server)
+        .send_telemetry(TelemetryRequest {
+            request_type: "app-started".to_string(),
+            api_version: "v2".to_string(),
+            debug: false,
+            body: Bytes::from_static(b"{}"),
+        })
+        .await
+        .unwrap();
+
+    mock.assert();
+}
+
+#[tokio::test]
+async fn injects_per_request_headers() {
+    let server = MockServer::start();
+    let mock = server.mock(|when, then| {
+        when.method(POST)
+            .path("/telemetry/proxy/api/v2/apmtelemetry")
+            .header("DD-Telemetry-Request-Type", "app-started")
+            .header("DD-Telemetry-API-Version", "v2")
+            .header("DD-Telemetry-Debug-Enabled", "false");
+        then.status(202).body("");
+    });
+
+    common::client_for(&server)
+        .send_telemetry(TelemetryRequest {
+            request_type: "app-started".to_string(),
+            api_version: "v2".to_string(),
+            debug: false,
+            body: Bytes::from_static(b"{}"),
+        })
+        .await
+        .unwrap();
+
+    mock.assert();
+}
diff --git a/libdd-agent-client/tests/traces.rs b/libdd-agent-client/tests/traces.rs
new file mode 100644
index 0000000000..7dd0fe3791
--- /dev/null
+++ b/libdd-agent-client/tests/traces.rs
@@ -0,0 +1,173 @@
+// Copyright 2026-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+mod common;
+
+use bytes::Bytes;
+use httpmock::prelude::*;
+use libdd_agent_client::{TraceFormat, TraceSendOptions};
+
+#[tokio::test]
+async fn v5_puts_to_correct_endpoint() {
+    let server = MockServer::start();
+    let mock = server.mock(|when, then| {
+        when.method(PUT).path("/v0.5/traces");
+        then.status(200).body(r#"{"rate_by_service":{}}"#);
+    });
+
+    let resp = common::client_for(&server)
+        .send_traces(
+            Bytes::from_static(b"\x91\x90"),
+            1,
+            TraceFormat::MsgpackV5,
+            TraceSendOptions::default(),
+        )
+        .await
+        .unwrap();
+
+    mock.assert();
+    assert_eq!(resp.status, 200);
+}
+
+#[tokio::test]
+async fn v4_puts_to_v4_endpoint() {
+    let server = MockServer::start();
+    let mock = server.mock(|when, then| {
+        when.method(PUT).path("/v0.4/traces");
+        then.status(200).body(r#"{}"#);
+    });
+
+    common::client_for(&server)
+        .send_traces(
+            Bytes::from_static(b"\x91\x90"),
+            1,
+            TraceFormat::MsgpackV4,
+            TraceSendOptions::default(),
+        )
+        .await
+        .unwrap();
+
+    mock.assert();
+}
+
+#[tokio::test]
+async fn injects_trace_count_header() {
+    let server = MockServer::start();
+    let mock = server.mock(|when, then| {
+        when.method(PUT)
+            .path("/v0.5/traces")
+            .header("X-Datadog-Trace-Count", "42");
+        then.status(200).body(r#"{}"#);
+    });
+
+    common::client_for(&server)
+        .send_traces(
+            Bytes::from_static(b"\x91\x90"),
+            42,
+            TraceFormat::MsgpackV5,
+            TraceSendOptions::default(),
+        )
+        .await
+        .unwrap();
+
+    mock.assert();
+}
+
+#[tokio::test]
+async fn injects_send_real_http_status_header() {
+    let server = MockServer::start();
+    let mock = server.mock(|when, then| {
+        when.method(PUT)
+            .path("/v0.5/traces")
+            .header("Datadog-Send-Real-Http-Status", "true");
+        then.status(200).body(r#"{}"#);
+    });
+
+    common::client_for(&server)
+        .send_traces(
+            Bytes::from_static(b""),
+            0,
+            TraceFormat::MsgpackV5,
+            TraceSendOptions::default(),
+        )
+        .await
+        .unwrap();
+
+    mock.assert();
+}
+
+#[tokio::test]
+async fn computed_top_level_injects_header() {
+    let server = MockServer::start();
+    let mock = server.mock(|when, then| {
+        when.method(PUT)
+            .path("/v0.5/traces")
+            .header("Datadog-Client-Computed-Top-Level", "yes");
+        then.status(200).body(r#"{}"#);
+    });
+
+    common::client_for(&server)
+        .send_traces(
+            Bytes::from_static(b""),
+            0,
+            TraceFormat::MsgpackV5,
+            TraceSendOptions {
+                computed_top_level: true,
+            },
+        )
+        .await
+        .unwrap();
+
+    mock.assert();
+}
+
+#[tokio::test]
+async fn parses_rate_by_service() {
+    let server = MockServer::start();
+    server.mock(|when, then| {
+        when.method(PUT).path("/v0.5/traces");
+        then.status(200)
+            .body(r#"{"rate_by_service":{"service:env":0.75}}"#);
+    });
+
+    let resp = common::client_for(&server)
+        .send_traces(
+            Bytes::from_static(b""),
+            0,
+            TraceFormat::MsgpackV5,
+            TraceSendOptions::default(),
+        )
+        .await
+        .unwrap();
+
+    assert_eq!(
+        resp.rate_by_service
+            .as_ref()
+            .and_then(|m| m.get("service:env")),
+        Some(&0.75)
+    );
+}
+
+#[tokio::test]
+async fn returns_http_error_on_5xx() {
+    let server = MockServer::start();
+    server.mock(|when, then| {
+        when.method(PUT).path("/v0.5/traces");
+        then.status(503).body("overloaded");
+    });
+
+    let err = common::client_for(&server)
+        .send_traces(
+            Bytes::from_static(b""),
+            0,
+            TraceFormat::MsgpackV5,
+            TraceSendOptions::default(),
+        )
+        .await
+        .unwrap_err();
+
+    assert!(matches!(
+        err,
+        libdd_agent_client::SendError::HttpError { status: 503, .. }
+    ));
+}
diff --git a/libdd-http-client/src/request.rs b/libdd-http-client/src/request.rs
index 5b27cc2f1d..3d38384492 100644
--- a/libdd-http-client/src/request.rs
+++ b/libdd-http-client/src/request.rs
@@ -134,6 +134,13 @@ impl HttpRequest {
         self
     }
 
+    /// Append headers to this request.
+    #[inline]
+    pub fn with_headers<'a, K, V>(mut self, it: impl IntoIterator<Item = (K, V)>) -> Self where K: Into<String>, V: Into<String> {
+        self.headers.extend(it.into_iter().map(|(k, v)| (k.into(), v.into())));
+        self
+    }
+
     /// Set the request body.
     #[inline]
     pub fn with_body(mut self, body: impl Into<bytes::Bytes>) -> Self {