diff --git a/DESCRIPTION b/DESCRIPTION
index 092a284b..aa50961c 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -92,11 +92,12 @@ Collate:
     'params.R'
     'provider-any.R'
     'provider-aws.R'
+    'provider-claude.R'
     'provider-openai-compatible.R'
     'provider-azure.R'
+    'provider-azure-anthropic.R'
     'provider-claude-files.R'
     'provider-claude-tools.R'
-    'provider-claude.R'
     'provider-google.R'
     'provider-cloudflare.R'
     'provider-databricks.R'
diff --git a/NAMESPACE b/NAMESPACE
index e748db40..61198380 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -37,6 +37,7 @@ export(batch_chat_text)
 export(chat)
 export(chat_anthropic)
 export(chat_aws_bedrock)
+export(chat_azure_anthropic)
 export(chat_azure_openai)
 export(chat_claude)
 export(chat_cloudflare)
diff --git a/NEWS.md b/NEWS.md
index 40420b0d..40006637 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,6 @@
 # ellmer (development version)
 
+* New `chat_azure_anthropic()` enables chatting with Anthropic Claude models hosted on Azure AI Foundry (`*.services.ai.azure.com/anthropic` endpoints), with the same Azure authentication options as `chat_azure_openai()`.
 * Fixed three bugs that caused errors when streaming web search results: Claude's `citations_delta` events were mishandled, `server_tool_use` input wasn't parsed from JSON during streaming, and OpenAI's `web_search_call` failed for non-search action types like `open_page` (#941).
 * `chat_aws_bedrock()` gains a `cache` parameter for prompt caching. The default, `"auto"`, enables caching for models known to support it (Anthropic Claude and Amazon Nova) and disables it otherwise (#954).
 * Built-in tools (e.g., `openai_tool_web_search()`, `claude_tool_web_search()`) now include `description` and `annotations` properties, making their metadata consistent with user-defined tools created by `tool()` (#942).
diff --git a/R/provider-azure-anthropic.R b/R/provider-azure-anthropic.R
new file mode 100644
index 00000000..71afcd99
--- /dev/null
+++ b/R/provider-azure-anthropic.R
@@ -0,0 +1,168 @@
+#' @include provider-azure.R
+#' @include provider-claude.R
+NULL
+
+# https://learn.microsoft.com/en-us/azure/foundry/foundry-models/concepts/endpoints
+
+#' Chat with an Anthropic Claude model hosted on Azure AI Foundry
+#'
+#' [Azure AI Foundry](https://azure.microsoft.com/en-us/products/ai-foundry)
+#' hosts Anthropic Claude models accessible via the
+#' `*.services.ai.azure.com/anthropic` endpoint, using the Anthropic Messages
+#' API format.
+#'
+#' Unlike [chat_azure_openai()], which targets `*.openai.azure.com` endpoints
+#' and uses the OpenAI chat completions format, this function targets Azure AI
+#' Foundry's Anthropic-compatible endpoint.
+#'
+#' ## Authentication
+#'
+#' `chat_azure_anthropic()` supports API keys via the `AZURE_ANTHROPIC_API_KEY`
+#' environment variable and the `credentials` parameter. It also supports:
+#'
+#' - Azure service principals (when the `AZURE_TENANT_ID`, `AZURE_CLIENT_ID`,
+#'   and `AZURE_CLIENT_SECRET` environment variables are set).
+#' - Interactive Entra ID authentication, like the Azure CLI.
+#' - Viewer-based credentials on Posit Connect. Requires the \pkg{connectcreds}
+#'   package.
+#'
+#' @param endpoint Azure AI Foundry endpoint URL with protocol and hostname,
+#'   i.e. `https://{your-project}.services.ai.azure.com/anthropic`. Defaults
+#'   to the value of the `AZURE_ANTHROPIC_ENDPOINT` environment variable.
+#' @param model The **deployment name** for the model you want to use.
+#' @param credentials `r api_key_param("AZURE_ANTHROPIC_API_KEY")`
+#' @inheritParams chat_anthropic
+#' @inherit chat_openai return
+#' @family chatbots
+#' @export
+#' @examples
+#' \dontrun{
+#' chat <- chat_azure_anthropic(
+#'   endpoint = "https://your-project.services.ai.azure.com/anthropic",
+#'   model = "your-deployment-name"
+#' )
+#' chat$chat("Tell me three jokes about statisticians")
+#' }
+chat_azure_anthropic <- function(
+  endpoint = azure_anthropic_endpoint(),
+  model,
+  params = NULL,
+  system_prompt = NULL,
+  credentials = NULL,
+  cache = c("5m", "1h", "none"),
+  beta_headers = character(),
+  api_args = list(),
+  api_headers = character(),
+  echo = NULL
+) {
+  check_string(endpoint)
+  check_string(model)
+  params <- params %||% params()
+  cache <- arg_match(cache)
+  echo <- check_echo(echo)
+
+  credentials <- as_credentials(
+    "chat_azure_anthropic",
+    default_azure_anthropic_credentials(),
+    credentials = credentials
+  )
+
+  provider <- ProviderAzureAnthropic(
+    name = "Azure/Anthropic",
+    base_url = paste0(gsub("/$", "", endpoint), "/v1"),
+    model = model,
+    params = params,
+    credentials = credentials,
+    extra_args = api_args,
+    extra_headers = api_headers,
+    beta_headers = beta_headers,
+    cache = cache
+  )
+
+  Chat$new(provider = provider, system_prompt = system_prompt, echo = echo)
+}
+
+ProviderAzureAnthropic <- new_class(
+  "ProviderAzureAnthropic",
+  parent = ProviderAnthropic
+)
+
+azure_anthropic_endpoint <- function() {
+  key_get("AZURE_ANTHROPIC_ENDPOINT")
+}
+
+default_azure_anthropic_credentials <- function() {
+  azure_scope <- "https://cognitiveservices.azure.com/.default"
+
+  # Detect viewer-based credentials from Posit Connect.
+  if (has_connect_viewer_token(scope = azure_scope)) {
+    return(function() {
+      token <- connectcreds::connect_viewer_token(scope = azure_scope)
+      list(Authorization = paste("Bearer", token$access_token))
+    })
+  }
+
+  # Detect Azure service principals.
+  tenant_id <- Sys.getenv("AZURE_TENANT_ID")
+  client_id <- Sys.getenv("AZURE_CLIENT_ID")
+  client_secret <- Sys.getenv("AZURE_CLIENT_SECRET")
+  if (nchar(tenant_id) && nchar(client_id) && nchar(client_secret)) {
+    client <- oauth_client(
+      client_id,
+      token_url = paste0(
+        "https://login.microsoftonline.com/",
+        tenant_id,
+        "/oauth2/v2.0/token"
+      ),
+      secret = client_secret,
+      auth = "body",
+      name = "ellmer-azure-anthropic-sp"
+    )
+    return(function() {
+      token <- oauth_token_cached(
+        client,
+        oauth_flow_client_credentials,
+        flow_params = list(scope = azure_scope),
+        reauth = is_testing()
+      )
+      list(Authorization = paste("Bearer", token$access_token))
+    })
+  }
+
+  # If we have an API key, include it in the credentials.
+  api_key <- Sys.getenv("AZURE_ANTHROPIC_API_KEY")
+  if (nchar(api_key)) {
+    return(\() api_key)
+  }
+
+  # Masquerade as the Azure CLI.
+  client_id <- "04b07795-8ddb-461a-bbee-02f9e1bf7b46"
+  if (is_interactive() && !is_hosted_session()) {
+    client <- oauth_client(
+      client_id,
+      token_url = "https://login.microsoftonline.com/common/oauth2/v2.0/token",
+      secret = "",
+      auth = "body",
+      name = paste0("ellmer-", client_id)
+    )
+    return(function() {
+      token <- oauth_token_cached(
+        client,
+        oauth_flow_auth_code,
+        flow_params = list(
+          auth_url = "https://login.microsoftonline.com/common/oauth2/v2.0/authorize",
+          scope = paste(azure_scope, "offline_access"),
+          redirect_uri = "http://localhost:8400",
+          auth_params = list(prompt = "select_account")
+        )
+      )
+      list(Authorization = paste("Bearer", token$access_token))
+    })
+  }
+
+  if (is_testing()) {
+    testthat::skip("no Azure credentials available")
+  }
+
+  cli::cli_abort("No Azure credentials are available.")
+}
diff --git a/man/chat_anthropic.Rd b/man/chat_anthropic.Rd
index 66cc5738..89aa4be5 100644
--- a/man/chat_anthropic.Rd
+++ b/man/chat_anthropic.Rd
@@ -148,6 +148,7 @@ chat$chat("Tell me three jokes about statisticians")
 \seealso{
 Other chatbots: 
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
diff --git a/man/chat_aws_bedrock.Rd b/man/chat_aws_bedrock.Rd
index 29e1840a..ffa7a070 100644
--- a/man/chat_aws_bedrock.Rd
+++ b/man/chat_aws_bedrock.Rd
@@ -118,6 +118,7 @@ chat$chat("Tell me three jokes about statisticians")
 \seealso{
 Other chatbots: 
 \code{\link{chat_anthropic}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
diff --git a/man/chat_azure_anthropic.Rd b/man/chat_azure_anthropic.Rd
new file mode 100644
index 00000000..8b5e2c87
--- /dev/null
+++ b/man/chat_azure_anthropic.Rd
@@ -0,0 +1,116 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/provider-azure-anthropic.R
+\name{chat_azure_anthropic}
+\alias{chat_azure_anthropic}
+\title{Chat with an Anthropic Claude model hosted on Azure AI Foundry}
+\usage{
+chat_azure_anthropic(
+  endpoint = azure_anthropic_endpoint(),
+  model,
+  params = NULL,
+  system_prompt = NULL,
+  credentials = NULL,
+  cache = c("5m", "1h", "none"),
+  beta_headers = character(),
+  api_args = list(),
+  api_headers = character(),
+  echo = NULL
+)
+}
+\arguments{
+\item{endpoint}{Azure AI Foundry endpoint URL with protocol and hostname,
+i.e. \verb{https://\{your-project\}.services.ai.azure.com/anthropic}. Defaults
+to the value of the \code{AZURE_ANTHROPIC_ENDPOINT} environment variable.}
+
+\item{model}{The \strong{deployment name} for the model you want to use.}
+
+\item{params}{Common model parameters, usually created by \code{\link[=params]{params()}}.}
+
+\item{system_prompt}{A system prompt to set the behavior of the assistant.}
+
+\item{credentials}{Override the default credentials. You generally should not need this argument; instead set the \code{AZURE_ANTHROPIC_API_KEY} environment variable. The best place to set this is in \code{.Renviron},
+which you can easily edit by calling \code{usethis::edit_r_environ()}.
+
+If you do need additional control, this argument takes a zero-argument function that returns either a string (the API key), or a named list (added as additional headers to every request).}
+
+\item{cache}{How long to cache inputs? Defaults to "5m" (five minutes).
+Set to "none" to disable caching or "1h" to cache for one hour.
+
+See details below.}
+
+\item{beta_headers}{Optionally, a character vector of beta headers to opt-in
+claude features that are still in beta.}
+
+\item{api_args}{Named list of arbitrary extra arguments appended to the body
+of every chat API call. Combined with the body object generated by ellmer
+with \code{\link[=modifyList]{modifyList()}}.}
+
+\item{api_headers}{Named character vector of arbitrary extra headers appended
+to every chat API call.}
+
+\item{echo}{One of the following options:
+\itemize{
+\item \code{none}: don't emit any output (default when running in a function).
+\item \code{output}: echo text and tool-calling output as it streams in (default
+when running at the console).
+\item \code{all}: echo all input and output.
+}
+
+Note this only affects the \code{chat()} method.}
+}
+\value{
+A \link{Chat} object.
+}
+\description{
+\href{https://azure.microsoft.com/en-us/products/ai-foundry}{Azure AI Foundry}
+hosts Anthropic Claude models accessible via the
+\verb{*.services.ai.azure.com/anthropic} endpoint, using the Anthropic Messages
+API format.
+}
+\details{
+Unlike \code{\link[=chat_azure_openai]{chat_azure_openai()}}, which targets \verb{*.openai.azure.com} endpoints
+and uses the OpenAI chat completions format, this function targets Azure AI
+Foundry's Anthropic-compatible endpoint.
+\subsection{Authentication}{
+
+\code{chat_azure_anthropic()} supports API keys via the \code{AZURE_ANTHROPIC_API_KEY}
+environment variable and the \code{credentials} parameter. It also supports:
+\itemize{
+\item Azure service principals (when the \code{AZURE_TENANT_ID}, \code{AZURE_CLIENT_ID},
+and \code{AZURE_CLIENT_SECRET} environment variables are set).
+\item Interactive Entra ID authentication, like the Azure CLI.
+\item Viewer-based credentials on Posit Connect. Requires the \pkg{connectcreds}
+package.
+}
+}
+}
+\examples{
+\dontrun{
+chat <- chat_azure_anthropic(
+  endpoint = "https://your-project.services.ai.azure.com/anthropic",
+  model = "your-deployment-name"
+)
+chat$chat("Tell me three jokes about statisticians")
+}
+}
+\seealso{
+Other chatbots: 
+\code{\link{chat_anthropic}()},
+\code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_openai}()},
+\code{\link{chat_cloudflare}()},
+\code{\link{chat_databricks}()},
+\code{\link{chat_deepseek}()},
+\code{\link{chat_github}()},
+\code{\link{chat_google_gemini}()},
+\code{\link{chat_groq}()},
+\code{\link{chat_huggingface}()},
+\code{\link{chat_mistral}()},
+\code{\link{chat_ollama}()},
+\code{\link{chat_openai}()},
+\code{\link{chat_openai_compatible}()},
+\code{\link{chat_openrouter}()},
+\code{\link{chat_perplexity}()},
+\code{\link{chat_portkey}()}
+}
+\concept{chatbots}
diff --git a/man/chat_azure_openai.Rd b/man/chat_azure_openai.Rd
index 64fb46af..48c8ed90 100644
--- a/man/chat_azure_openai.Rd
+++ b/man/chat_azure_openai.Rd
@@ -89,6 +89,7 @@ chat$chat("Tell me three jokes about statisticians")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
 \code{\link{chat_deepseek}()},
diff --git a/man/chat_cloudflare.Rd b/man/chat_cloudflare.Rd
index 139416eb..0f80ca81 100644
--- a/man/chat_cloudflare.Rd
+++ b/man/chat_cloudflare.Rd
@@ -78,6 +78,7 @@ chat$chat("Tell me three jokes about statisticians")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_databricks}()},
 \code{\link{chat_deepseek}()},
diff --git a/man/chat_databricks.Rd b/man/chat_databricks.Rd
index 9bb467f2..84996ffc 100644
--- a/man/chat_databricks.Rd
+++ b/man/chat_databricks.Rd
@@ -89,6 +89,7 @@ chat$chat("Tell me three jokes about statisticians")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_deepseek}()},
diff --git a/man/chat_deepseek.Rd b/man/chat_deepseek.Rd
index a2965b7a..77a7a5d7 100644
--- a/man/chat_deepseek.Rd
+++ b/man/chat_deepseek.Rd
@@ -74,6 +74,7 @@ chat$chat("Tell me three jokes about statisticians")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
diff --git a/man/chat_github.Rd b/man/chat_github.Rd
index 255bcf25..9f664500 100644
--- a/man/chat_github.Rd
+++ b/man/chat_github.Rd
@@ -83,6 +83,7 @@ chat$chat("Tell me three jokes about statisticians")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
diff --git a/man/chat_google_gemini.Rd b/man/chat_google_gemini.Rd
index efbfcb8f..6ecd38c0 100644
--- a/man/chat_google_gemini.Rd
+++ b/man/chat_google_gemini.Rd
@@ -113,6 +113,7 @@ chat$chat("Tell me three jokes about statisticians")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
diff --git a/man/chat_groq.Rd b/man/chat_groq.Rd
index 72a6ba94..d5c83d88 100644
--- a/man/chat_groq.Rd
+++ b/man/chat_groq.Rd
@@ -69,6 +69,7 @@ chat$chat("Tell me three jokes about statisticians")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
diff --git a/man/chat_huggingface.Rd b/man/chat_huggingface.Rd
index 565cb007..0314bbe2 100644
--- a/man/chat_huggingface.Rd
+++ b/man/chat_huggingface.Rd
@@ -77,6 +77,7 @@ chat$chat("Tell me three jokes about statisticians")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
diff --git a/man/chat_mistral.Rd b/man/chat_mistral.Rd
index f4238746..e7830686 100644
--- a/man/chat_mistral.Rd
+++ b/man/chat_mistral.Rd
@@ -74,6 +74,7 @@ chat$chat("Tell me three jokes about statisticians")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
diff --git a/man/chat_ollama.Rd b/man/chat_ollama.Rd
index 622da336..cb472cca 100644
--- a/man/chat_ollama.Rd
+++ b/man/chat_ollama.Rd
@@ -90,6 +90,7 @@ chat$chat("Tell me three jokes about statisticians")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
diff --git a/man/chat_openai.Rd b/man/chat_openai.Rd
index 7f660b04..60a6de65 100644
--- a/man/chat_openai.Rd
+++ b/man/chat_openai.Rd
@@ -97,6 +97,7 @@ chat$chat("Tell me three funny jokes about statisticians")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
diff --git a/man/chat_openai_compatible.Rd b/man/chat_openai_compatible.Rd
index 794d29b4..94637b1f 100644
--- a/man/chat_openai_compatible.Rd
+++ b/man/chat_openai_compatible.Rd
@@ -81,6 +81,7 @@ chat$chat("What is the difference between a tibble and a data frame?")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
diff --git a/man/chat_openrouter.Rd b/man/chat_openrouter.Rd
index f5ceac9e..ef3f5ac0 100644
--- a/man/chat_openrouter.Rd
+++ b/man/chat_openrouter.Rd
@@ -66,6 +66,7 @@ chat$chat("Tell me three jokes about statisticians")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
diff --git a/man/chat_perplexity.Rd b/man/chat_perplexity.Rd
index dc2e9364..8c4b627e 100644
--- a/man/chat_perplexity.Rd
+++ b/man/chat_perplexity.Rd
@@ -75,6 +75,7 @@ chat$chat("Tell me three jokes about statisticians")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
diff --git a/man/chat_portkey.Rd b/man/chat_portkey.Rd
index 20d11a40..cb5c500f 100644
--- a/man/chat_portkey.Rd
+++ b/man/chat_portkey.Rd
@@ -81,6 +81,7 @@ chat$chat("Tell me three jokes about statisticians")
 Other chatbots: 
 \code{\link{chat_anthropic}()},
 \code{\link{chat_aws_bedrock}()},
+\code{\link{chat_azure_anthropic}()},
 \code{\link{chat_azure_openai}()},
 \code{\link{chat_cloudflare}()},
 \code{\link{chat_databricks}()},
diff --git a/tests/testthat/test-provider-azure-anthropic.R b/tests/testthat/test-provider-azure-anthropic.R
new file mode 100644
index 00000000..215b450d
--- /dev/null
+++ b/tests/testthat/test-provider-azure-anthropic.R
@@ -0,0 +1,104 @@
+# Defaults ----------------------------------------------------------------
+
+test_that("model is required", {
+  withr::local_envvar(AZURE_ANTHROPIC_API_KEY = "key")
+  expect_error(
+    chat_azure_anthropic("https://example.services.ai.azure.com/anthropic"),
+    "model"
+  )
+})
+
+test_that("trailing slash in endpoint is handled correctly", {
+  withr::local_envvar(AZURE_ANTHROPIC_API_KEY = "key")
+  chat <- chat_azure_anthropic(
+    endpoint = "https://example.services.ai.azure.com/anthropic/",
+    model = "claude-sonnet-4-6"
+  )
+  expect_no_match(chat$get_provider()@base_url, "//v1")
+  expect_match(chat$get_provider()@base_url, "/v1$")
+})
+
+# Authentication ----------------------------------------------------------
+
+test_that("Azure Anthropic request headers are generated correctly", {
+  turn <- UserTurn(
+    contents = list(ContentText("What is 1 + 1?"))
+  )
+  endpoint <- "https://example.services.ai.azure.com/anthropic"
+
+  p <- ProviderAzureAnthropic(
+    name = "Azure/Anthropic",
+    base_url = paste0(endpoint, "/v1"),
+    model = "claude-sonnet-4-6",
+    params = list(),
+    extra_args = list(),
+    extra_headers = character(),
+    credentials = \() "key",
+    beta_headers = character(),
+    cache = "none"
+  )
+  req <- chat_request(p, FALSE, list(turn))
+  headers <- req_get_headers(req, "reveal")
+
+  # Uses x-api-key and anthropic-version, same as standard Anthropic API
+  expect_equal(headers$`x-api-key`, "key")
+  expect_equal(headers$`anthropic-version`, "2023-06-01")
+  expect_null(headers$`api-key`)
+  # No api-version query parameter
+  expect_no_match(req$url, "api-version")
+})
+
+test_that("beta headers are forwarded correctly", {
+  endpoint <- "https://example.services.ai.azure.com/anthropic"
+
+  p <- ProviderAzureAnthropic(
+    name = "Azure/Anthropic",
+    base_url = paste0(endpoint, "/v1"),
+    model = "claude-sonnet-4-6",
+    params = list(),
+    extra_args = list(),
+    extra_headers = character(),
+    credentials = \() "key",
+    beta_headers = c("feature-a", "feature-b"),
+    cache = "none"
+  )
+  req <- base_request(p)
+  headers <- req_get_headers(req)
+  expect_equal(headers$`anthropic-beta`, "feature-a,feature-b")
+})
+
+test_that("service principal authentication requests look correct", {
+  withr::local_envvar(
+    AZURE_TENANT_ID = "aaaa0a0a-bb1b-cc2c-dd3d-eeeeee4e4e4e",
+    AZURE_CLIENT_ID = "id",
+    AZURE_CLIENT_SECRET = "secret"
+  )
+  local_mocked_responses(function(req) {
+    summary <- request_summary(req)
+    expect_match(
+      summary$url,
+      "login.microsoftonline.com/aaaa0a0a-bb1b-cc2c-dd3d-eeeeee4e4e4e"
+    )
+    expect_match(summary$body$grant_type, "client_credentials")
+    expect_match(summary$body$scope, "cognitiveservices.azure.com")
+    expect_match(summary$body$client_id, "id")
+    expect_match(summary$body$client_secret, "secret")
+    response_json(body = list(access_token = "token"))
+  })
+  source <- default_azure_anthropic_credentials()
+  expect_equal(source(), list(Authorization = "Bearer token"))
+})
+
+test_that("tokens can be requested from a Connect server", {
+  skip_if_not_installed("connectcreds")
+
+  connectcreds::local_mocked_connect_responses(token = "token")
+  credentials <- default_azure_anthropic_credentials()
+  expect_equal(credentials(), list(Authorization = "Bearer token"))
+})
+
+test_that("API key is read from AZURE_ANTHROPIC_API_KEY", {
+  withr::local_envvar(AZURE_ANTHROPIC_API_KEY = "my-key")
+  credentials <- default_azure_anthropic_credentials()
+  expect_equal(credentials(), "my-key")
+})