diff --git a/R/model.R b/R/model.R
index 79882226..0359678a 100644
--- a/R/model.R
+++ b/R/model.R
@@ -196,6 +196,7 @@ cmdstan_model <- function(stan_file = NULL, exe_file = NULL, compile = TRUE, ...
 #'  [`$hpp_file()`][model-method-compile] |  Return the file path to the `.hpp` file containing the generated C++ code. |
 #'  [`$save_hpp_file()`][model-method-compile] |  Save the `.hpp` file containing the generated C++ code. |
 #'  [`$expose_functions()`][model-method-expose_functions] |  Expose Stan functions for use in R. |
+#'  [`$cmdstan_defaults()`][model-method-cmdstan_defaults] |  Get CmdStan default argument values for a method. |
 #'
 #'  ## Diagnostics
 #'
@@ -2209,6 +2210,51 @@ expose_functions = function(global = FALSE, verbose = FALSE) {
 CmdStanModel$set("public", name = "expose_functions", value = expose_functions)
 
 
+#' Get CmdStan default argument values
+#'
+#' @name model-method-cmdstan_defaults
+#' @aliases cmdstan_defaults
+#' @family CmdStanModel methods
+#'
+#' @description The `$cmdstan_defaults()` method of a [`CmdStanModel`]
+#'   object queries the compiled model binary for the default argument
+#'   values used by a given inference method. The returned list uses
+#'   cmdstanr-style argument names (e.g., `iter_sampling` instead of
+#'   CmdStan's `num_samples`).
+#'
+#'   The model must be compiled before calling this method.
+#'
+#' @param method (string) The inference method whose defaults to
+#'   retrieve. One of `"sample"`, `"optimize"`, `"variational"`,
+#'   `"pathfinder"`, or `"laplace"`.
+#' @return A named list of default argument values for the specified
+#'   method, with cmdstanr-style argument names.
+#'
+#' @template seealso-docs
+#'
+#' @examples
+#' \dontrun{
+#' mod <- cmdstan_model(file.path(cmdstan_path(),
+#'                                "examples/bernoulli/bernoulli.stan"))
+#' mod$cmdstan_defaults("sample")
+#' mod$cmdstan_defaults("optimize")
+#' }
+#'
+cmdstan_defaults <- function(method = c("sample", "optimize", "variational",
+                                        "pathfinder", "laplace")) {
+  method <- match.arg(method)
+  if (length(self$exe_file()) == 0 || !file.exists(self$exe_file())) {
+    stop(
+      "'$cmdstan_defaults()' requires a compiled model. ",
+      "Please compile the model first with '$compile()'.",
+      call. = FALSE
+    )
+  }
+  parse_cmdstan_args(self$exe_file(), method)
+}
+CmdStanModel$set("public", name = "cmdstan_defaults", value = cmdstan_defaults)
+
+
 
 # internal ----------------------------------------------------------------
 assert_valid_stanc_options <- function(stanc_options) {
@@ -2289,10 +2335,10 @@ model_variables <- function(stan_file, include_paths = NULL, allow_undefined = F
   variables
 }
 
-
 is_variables_method_supported <- function(mod) {
   mod$has_stan_file() && file.exists(mod$stan_file())
 }
+
 resolve_exe_path <- function(dir = NULL,
                              private_dir = NULL,
                              self_exe_file = NULL,
@@ -2329,3 +2375,199 @@ resolve_exe_path <- function(dir = NULL,
   }
   exe
 }
+
+# cmdstan_defaults() helpers
+
+#' Parse CmdStan default argument values from model binary
+#'
+#' Runs a CmdStan model binary with `help-all` to extract valid arguments
+#' and their default values for a given inference method, returning them
+#' with cmdstanr argument names.
+#'
+#' @noRd
+#' @param model_binary Path to the CmdStan model binary.
+#' @param method Inference method: `"sample"`, `"optimize"`,
+#'   `"variational"`, `"pathfinder"`, or `"laplace"`.
+#' @return A named list with cmdstanr-style argument names and default
+#'   values.
+parse_cmdstan_args <- function(model_binary, method) {
+  withr::with_path(
+    c(
+      toolchain_PATH_env_var(),
+      tbb_path()
+    ),
+    ret <- wsl_compatible_run(
+      command = wsl_safe_path(model_binary),
+      args = c(method, "help-all"),
+      error_on_status = FALSE
+    )
+  )
+  # CmdStan may write help text to stdout or stderr depending on the platform
+  raw <- paste0(ret$stdout, ret$stderr)
+  output <- strsplit(raw, "\r?\n")[[1]]
+
+  argument_map <- map_cmdstan_to_cmdstanr(method)
+  cmdstan_keys <- unname(argument_map)
+  public_names <- names(argument_map)
+
+  defaults <- list()
+  n <- length(output)
+  # Track the current hierarchical argument key using section indentation.
+  section_indents <- integer(0)
+  section_names <- character(0)
+
+  for (i in seq_len(n)) {
+    line <- output[i]
+    content <- trimws(line)
+
+    # Skip blank lines so they don't reset the section stack
+    if (!nzchar(content)) next
+
+    indent <- nchar(sub("^(\\s*).*", "\\1", line))
+
+    # Drop sections at deeper or equal indentation
+    while (length(section_indents) > 0 &&
+           section_indents[[length(section_indents)]] >= indent) {
+      section_indents <- section_indents[-length(section_indents)]
+      section_names <- section_names[-length(section_names)]
+    }
+
+    section_name <- parse_cmdstan_section_name(content)
+    if (!is.null(section_name)) {
+      section_indents <- c(section_indents, indent)
+      section_names <- c(section_names, section_name)
+      next
+    }
+
+    arg_name <- parse_cmdstan_arg_name(content)
+    if (!is.null(arg_name)) {
+
+      # Build the full dotted argument key: method.section1.section2...arg_name
+      # The top-level method heading (e.g. "sample") is tracked as a section,
+      # so it becomes the first segment of the key.
+      full_key <- paste(c(section_names, arg_name), collapse = ".")
+
+      # Check if this full argument key matches one of our target arguments
+      match_idx <- match(full_key, cmdstan_keys, nomatch = 0L)
+
+      if (match_idx > 0L) {
+        default_value <- find_cmdstan_default_value(output, i, n)
+        defaults[[public_names[[match_idx]]]] <- default_value
+      }
+    }
+  }
+
+  defaults
+}
+
+#' Parse CmdStan section name from a help-all line
+#' @noRd
+parse_cmdstan_section_name <- function(line) {
+  match <- regmatches(line, regexec("^([a-z_][a-z0-9_]*)$", line))[[1]]
+  if (length(match) >= 2) match[2] else NULL
+}
+
+#' Parse CmdStan argument name from a help-all line
+#' @noRd
+parse_cmdstan_arg_name <- function(line) {
+  match <- regmatches(line, regexec("^([a-z_][a-z0-9_]*)=", line))[[1]]
+  if (length(match) >= 2) match[2] else NULL
+}
+
+#' Find CmdStan default value following a help-all argument line
+#' @noRd
+find_cmdstan_default_value <- function(output, line_idx, n_lines) {
+  default_value <- NULL
+
+  for (j in (line_idx + 1):min(line_idx + 5, n_lines)) {
+    next_content <- trimws(output[j])
+    if (grepl("^Defaults to", next_content)) {
+      default_value <- parse_default_value(next_content)
+      break
+    }
+    # Stop if we hit another argument
+    if (grepl("^[a-z_][a-z0-9_]*=", next_content)) break
+  }
+
+  default_value
+}
+
+#' Parse default value from "Defaults to ..." line
+#' @noRd
+parse_default_value <- function(line) {
+  val_str <- sub("^Defaults to\\s*", "", line)
+  if (val_str %in% c("true", "false")) return(val_str == "true")
+  if (grepl("^-?[0-9]+$", val_str)) return(as.integer(val_str))
+  if (grepl("^-?[0-9]*\\.?[0-9]+([eE][+-]?[0-9]+)?$", val_str)) return(as.numeric(val_str))
+  val_str
+}
+
+#' Map CmdStan argument names to CmdStanR argument names
+#' @noRd
+map_cmdstan_to_cmdstanr <- function(method) {
+  switch(method,
+         sample = c(
+           iter_sampling = "sample.num_samples",
+           iter_warmup = "sample.num_warmup",
+           save_warmup = "sample.save_warmup",
+           thin = "sample.thin",
+           adapt_engaged = "sample.adapt.engaged",
+           adapt_delta = "sample.adapt.delta",
+           init_buffer = "sample.adapt.init_buffer",
+           term_buffer = "sample.adapt.term_buffer",
+           window = "sample.adapt.window",
+           save_metric = "sample.adapt.save_metric",
+           max_treedepth = "sample.hmc.nuts.max_depth",
+           metric = "sample.hmc.metric",
+           metric_file = "sample.hmc.metric_file",
+           step_size = "sample.hmc.stepsize"
+         ),
+         optimize = c(
+           algorithm = "optimize.algorithm",
+           jacobian = "optimize.jacobian",
+           iter = "optimize.iter",
+           init_alpha = "optimize.lbfgs.init_alpha",
+           tol_obj = "optimize.lbfgs.tol_obj",
+           tol_rel_obj = "optimize.lbfgs.tol_rel_obj",
+           tol_grad = "optimize.lbfgs.tol_grad",
+           tol_rel_grad = "optimize.lbfgs.tol_rel_grad",
+           tol_param = "optimize.lbfgs.tol_param",
+           history_size = "optimize.lbfgs.history_size"
+         ),
+         variational = c(
+           algorithm = "variational.algorithm",
+           iter = "variational.iter",
+           grad_samples = "variational.grad_samples",
+           elbo_samples = "variational.elbo_samples",
+           eta = "variational.eta",
+           adapt_engaged = "variational.adapt.engaged",
+           adapt_iter = "variational.adapt.iter",
+           tol_rel_obj = "variational.tol_rel_obj",
+           eval_elbo = "variational.eval_elbo",
+           draws = "variational.output_samples"
+         ),
+         pathfinder = c(
+           init_alpha = "pathfinder.init_alpha",
+           tol_obj = "pathfinder.tol_obj",
+           tol_rel_obj = "pathfinder.tol_rel_obj",
+           tol_grad = "pathfinder.tol_grad",
+           tol_rel_grad = "pathfinder.tol_rel_grad",
+           tol_param = "pathfinder.tol_param",
+           history_size = "pathfinder.history_size",
+           draws = "pathfinder.num_psis_draws",
+           num_paths = "pathfinder.num_paths",
+           save_single_paths = "pathfinder.save_single_paths",
+           psis_resample = "pathfinder.psis_resample",
+           calculate_lp = "pathfinder.calculate_lp",
+           max_lbfgs_iters = "pathfinder.max_lbfgs_iters",
+           single_path_draws = "pathfinder.num_draws",
+           num_elbo_draws = "pathfinder.num_elbo_draws"
+         ),
+         laplace = c(
+           jacobian = "laplace.jacobian",
+           draws = "laplace.draws"
+         ),
+         character(0)
+  )
+}
+
diff --git a/_pkgdown.yml b/_pkgdown.yml
index 123d2191..af774887 100644
--- a/_pkgdown.yml
+++ b/_pkgdown.yml
@@ -95,6 +95,7 @@ reference:
       - read_cmdstan_csv
       - write_stan_json
       - write_stan_file
+      - print_stan_file
       - draws_to_csv
       - as_mcmc.list
       - as_draws.CmdStanMCMC
diff --git a/man/CmdStanModel.Rd b/man/CmdStanModel.Rd
index 0b21ac5c..7057014e 100644
--- a/man/CmdStanModel.Rd
+++ b/man/CmdStanModel.Rd
@@ -30,6 +30,7 @@ methods, many of which have their own (linked) documentation pages:
    \code{\link[=model-method-compile]{$hpp_file()}} \tab Return the file path to the \code{.hpp} file containing the generated C++ code. \cr
    \code{\link[=model-method-compile]{$save_hpp_file()}} \tab Save the \code{.hpp} file containing the generated C++ code. \cr
    \code{\link[=model-method-expose_functions]{$expose_functions()}} \tab Expose Stan functions for use in R. \cr
+   \code{\link[=model-method-cmdstan_defaults]{$cmdstan_defaults()}} \tab Get CmdStan default argument values for a method. \cr
 }
 
 }
diff --git a/man/cmdstanr-package.Rd b/man/cmdstanr-package.Rd
index c2ccbb1d..e6479f57 100644
--- a/man/cmdstanr-package.Rd
+++ b/man/cmdstanr-package.Rd
@@ -34,22 +34,22 @@ algorithms, and writing results to output files.
 \subsection{Advantages of RStan}{
 \itemize{
 \item Allows other developers to distribute R packages with \emph{pre-compiled}
-Stan programs (like \strong{rstanarm}) on CRAN. (Note: As of 2023, this can
-mostly be achieved with CmdStanR as well. See \href{https://mc-stan.org/cmdstanr/articles/cmdstanr-internals.html#developing-using-cmdstanr}{Developing using CmdStanR}.)
-\item Avoids use of R6 classes, which may result in more familiar syntax for
-many R users.
+Stan programs (like \strong{rstanarm}) on CRAN. (Note: As of 2023, this
+can mostly be achieved with CmdStanR as well. See \href{https://mc-stan.org/cmdstanr/articles/cmdstanr-internals.html#developing-using-cmdstanr}{Developing using CmdStanR}.)
+\item Avoids use of R6 classes, which may result in more familiar syntax
+for many R users.
 \item CRAN binaries available for Mac and Windows.
 }
 }
 
 \subsection{Advantages of CmdStanR}{
 \itemize{
-\item Compatible with latest versions of Stan. Keeping up with Stan releases
-is complicated for RStan, often requiring non-trivial changes to the
-\strong{rstan} package and new CRAN releases of both \strong{rstan} and
-\strong{StanHeaders}. With CmdStanR the latest improvements in Stan will be
-available from R immediately after updating CmdStan using
-\code{cmdstanr::install_cmdstan()}.
+\item Compatible with latest versions of Stan. Keeping up with Stan
+releases is complicated for RStan, often requiring non-trivial
+changes to the \strong{rstan} package and new CRAN releases of both
+\strong{rstan} and \strong{StanHeaders}. With CmdStanR the latest improvements
+in Stan will be available from R immediately after updating CmdStan
+using \code{cmdstanr::install_cmdstan()}.
 \item Running Stan via external processes results in fewer unexpected
 crashes, especially in RStudio.
 \item Less memory overhead.
diff --git a/man/model-method-check_syntax.Rd b/man/model-method-check_syntax.Rd
index 68366fb5..5725defd 100644
--- a/man/model-method-check_syntax.Rd
+++ b/man/model-method-check_syntax.Rd
@@ -78,6 +78,7 @@ The Stan and CmdStan documentation:
 }
 
 Other CmdStanModel methods: 
+\code{\link{model-method-cmdstan_defaults}},
 \code{\link{model-method-compile}},
 \code{\link{model-method-diagnose}},
 \code{\link{model-method-expose_functions}},
diff --git a/man/model-method-cmdstan_defaults.Rd b/man/model-method-cmdstan_defaults.Rd
new file mode 100644
index 00000000..fa45b200
--- /dev/null
+++ b/man/model-method-cmdstan_defaults.Rd
@@ -0,0 +1,65 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/model.R
+\name{model-method-cmdstan_defaults}
+\alias{model-method-cmdstan_defaults}
+\alias{cmdstan_defaults}
+\title{Get CmdStan default argument values}
+\usage{
+cmdstan_defaults(
+  method = c("sample", "optimize", "variational", "pathfinder", "laplace")
+)
+}
+\arguments{
+\item{method}{(string) The inference method whose defaults to
+retrieve. One of \code{"sample"}, \code{"optimize"}, \code{"variational"},
+\code{"pathfinder"}, or \code{"laplace"}.}
+}
+\value{
+A named list of default argument values for the specified
+method, with cmdstanr-style argument names.
+}
+\description{
+The \verb{$cmdstan_defaults()} method of a \code{\link{CmdStanModel}}
+object queries the compiled model binary for the default argument
+values used by a given inference method. The returned list uses
+cmdstanr-style argument names (e.g., \code{iter_sampling} instead of
+CmdStan's \code{num_samples}).
+
+The model must be compiled before calling this method.
+}
+\examples{
+\dontrun{
+mod <- cmdstan_model(file.path(cmdstan_path(),
+                               "examples/bernoulli/bernoulli.stan"))
+mod$cmdstan_defaults("sample")
+mod$cmdstan_defaults("optimize")
+}
+
+}
+\seealso{
+The CmdStanR website
+(\href{https://mc-stan.org/cmdstanr/}{mc-stan.org/cmdstanr}) for online
+documentation and tutorials.
+
+The Stan and CmdStan documentation:
+\itemize{
+\item Stan documentation: \href{https://mc-stan.org/users/documentation/}{mc-stan.org/users/documentation}
+\item CmdStan User’s Guide: \href{https://mc-stan.org/docs/cmdstan-guide/}{mc-stan.org/docs/cmdstan-guide}
+}
+
+Other CmdStanModel methods: 
+\code{\link{model-method-check_syntax}},
+\code{\link{model-method-compile}},
+\code{\link{model-method-diagnose}},
+\code{\link{model-method-expose_functions}},
+\code{\link{model-method-format}},
+\code{\link{model-method-generate-quantities}},
+\code{\link{model-method-laplace}},
+\code{\link{model-method-optimize}},
+\code{\link{model-method-pathfinder}},
+\code{\link{model-method-sample}},
+\code{\link{model-method-sample_mpi}},
+\code{\link{model-method-variables}},
+\code{\link{model-method-variational}}
+}
+\concept{CmdStanModel methods}
diff --git a/man/model-method-compile.Rd b/man/model-method-compile.Rd
index 14871ef5..1dd12463 100644
--- a/man/model-method-compile.Rd
+++ b/man/model-method-compile.Rd
@@ -146,6 +146,7 @@ The Stan and CmdStan documentation:
 
 Other CmdStanModel methods: 
 \code{\link{model-method-check_syntax}},
+\code{\link{model-method-cmdstan_defaults}},
 \code{\link{model-method-diagnose}},
 \code{\link{model-method-expose_functions}},
 \code{\link{model-method-format}},
diff --git a/man/model-method-diagnose.Rd b/man/model-method-diagnose.Rd
index c7117ef1..a9bb6a6a 100644
--- a/man/model-method-diagnose.Rd
+++ b/man/model-method-diagnose.Rd
@@ -146,6 +146,7 @@ The Stan and CmdStan documentation:
 
 Other CmdStanModel methods: 
 \code{\link{model-method-check_syntax}},
+\code{\link{model-method-cmdstan_defaults}},
 \code{\link{model-method-compile}},
 \code{\link{model-method-expose_functions}},
 \code{\link{model-method-format}},
diff --git a/man/model-method-expose_functions.Rd b/man/model-method-expose_functions.Rd
index b7d42231..92c105bb 100644
--- a/man/model-method-expose_functions.Rd
+++ b/man/model-method-expose_functions.Rd
@@ -70,6 +70,7 @@ The Stan and CmdStan documentation:
 
 Other CmdStanModel methods: 
 \code{\link{model-method-check_syntax}},
+\code{\link{model-method-cmdstan_defaults}},
 \code{\link{model-method-compile}},
 \code{\link{model-method-diagnose}},
 \code{\link{model-method-format}},
diff --git a/man/model-method-format.Rd b/man/model-method-format.Rd
index 4a8af83b..9d28973e 100644
--- a/man/model-method-format.Rd
+++ b/man/model-method-format.Rd
@@ -86,6 +86,7 @@ The Stan and CmdStan documentation:
 
 Other CmdStanModel methods: 
 \code{\link{model-method-check_syntax}},
+\code{\link{model-method-cmdstan_defaults}},
 \code{\link{model-method-compile}},
 \code{\link{model-method-diagnose}},
 \code{\link{model-method-expose_functions}},
diff --git a/man/model-method-generate-quantities.Rd b/man/model-method-generate-quantities.Rd
index 4f7c87bf..e2131f63 100644
--- a/man/model-method-generate-quantities.Rd
+++ b/man/model-method-generate-quantities.Rd
@@ -184,6 +184,7 @@ The Stan and CmdStan documentation:
 
 Other CmdStanModel methods: 
 \code{\link{model-method-check_syntax}},
+\code{\link{model-method-cmdstan_defaults}},
 \code{\link{model-method-compile}},
 \code{\link{model-method-diagnose}},
 \code{\link{model-method-expose_functions}},
diff --git a/man/model-method-laplace.Rd b/man/model-method-laplace.Rd
index e94c0f64..6977e301 100644
--- a/man/model-method-laplace.Rd
+++ b/man/model-method-laplace.Rd
@@ -238,6 +238,7 @@ https://mc-stan.org/docs/cmdstan-guide/
 \seealso{
 Other CmdStanModel methods: 
 \code{\link{model-method-check_syntax}},
+\code{\link{model-method-cmdstan_defaults}},
 \code{\link{model-method-compile}},
 \code{\link{model-method-diagnose}},
 \code{\link{model-method-expose_functions}},
diff --git a/man/model-method-optimize.Rd b/man/model-method-optimize.Rd
index f9fbb5c5..07f3c841 100644
--- a/man/model-method-optimize.Rd
+++ b/man/model-method-optimize.Rd
@@ -363,6 +363,7 @@ https://mc-stan.org/docs/cmdstan-guide/
 \seealso{
 Other CmdStanModel methods: 
 \code{\link{model-method-check_syntax}},
+\code{\link{model-method-cmdstan_defaults}},
 \code{\link{model-method-compile}},
 \code{\link{model-method-diagnose}},
 \code{\link{model-method-expose_functions}},
diff --git a/man/model-method-pathfinder.Rd b/man/model-method-pathfinder.Rd
index a7b3c15e..58036c17 100644
--- a/man/model-method-pathfinder.Rd
+++ b/man/model-method-pathfinder.Rd
@@ -382,6 +382,7 @@ https://mc-stan.org/docs/cmdstan-guide/
 \seealso{
 Other CmdStanModel methods: 
 \code{\link{model-method-check_syntax}},
+\code{\link{model-method-cmdstan_defaults}},
 \code{\link{model-method-compile}},
 \code{\link{model-method-diagnose}},
 \code{\link{model-method-expose_functions}},
diff --git a/man/model-method-sample.Rd b/man/model-method-sample.Rd
index dd8a1b43..f5285024 100644
--- a/man/model-method-sample.Rd
+++ b/man/model-method-sample.Rd
@@ -448,6 +448,7 @@ https://mc-stan.org/docs/cmdstan-guide/
 \seealso{
 Other CmdStanModel methods: 
 \code{\link{model-method-check_syntax}},
+\code{\link{model-method-cmdstan_defaults}},
 \code{\link{model-method-compile}},
 \code{\link{model-method-diagnose}},
 \code{\link{model-method-expose_functions}},
diff --git a/man/model-method-sample_mpi.Rd b/man/model-method-sample_mpi.Rd
index b8620ecb..b0cc6bc9 100644
--- a/man/model-method-sample_mpi.Rd
+++ b/man/model-method-sample_mpi.Rd
@@ -343,6 +343,7 @@ details on MPI support in Stan.
 
 Other CmdStanModel methods: 
 \code{\link{model-method-check_syntax}},
+\code{\link{model-method-cmdstan_defaults}},
 \code{\link{model-method-compile}},
 \code{\link{model-method-diagnose}},
 \code{\link{model-method-expose_functions}},
diff --git a/man/model-method-variables.Rd b/man/model-method-variables.Rd
index 87e9d73e..1415fdc8 100644
--- a/man/model-method-variables.Rd
+++ b/man/model-method-variables.Rd
@@ -38,6 +38,7 @@ mod$variables()
 \seealso{
 Other CmdStanModel methods: 
 \code{\link{model-method-check_syntax}},
+\code{\link{model-method-cmdstan_defaults}},
 \code{\link{model-method-compile}},
 \code{\link{model-method-diagnose}},
 \code{\link{model-method-expose_functions}},
diff --git a/man/model-method-variational.Rd b/man/model-method-variational.Rd
index 41fb890c..684b152b 100644
--- a/man/model-method-variational.Rd
+++ b/man/model-method-variational.Rd
@@ -353,6 +353,7 @@ https://mc-stan.org/docs/cmdstan-guide/
 \seealso{
 Other CmdStanModel methods: 
 \code{\link{model-method-check_syntax}},
+\code{\link{model-method-cmdstan_defaults}},
 \code{\link{model-method-compile}},
 \code{\link{model-method-diagnose}},
 \code{\link{model-method-expose_functions}},
diff --git a/tests/testthat/test-model-cmdstan-defaults.R b/tests/testthat/test-model-cmdstan-defaults.R
new file mode 100644
index 00000000..608bd3e3
--- /dev/null
+++ b/tests/testthat/test-model-cmdstan-defaults.R
@@ -0,0 +1,140 @@
+set_cmdstan_path()
+mod <- testing_model("bernoulli")
+
+expected_cmdstan_defaults <- list(
+  sample = list(
+    iter_sampling = 1000L,
+    iter_warmup = 1000L,
+    save_warmup = FALSE,
+    thin = 1L,
+    adapt_engaged = TRUE,
+    adapt_delta = 0.8,
+    init_buffer = 75L,
+    term_buffer = 50L,
+    window = 25L,
+    save_metric = FALSE,
+    max_treedepth = 10L,
+    metric = "diag_e",
+    metric_file = "",
+    step_size = 1L
+  ),
+  optimize = list(
+    algorithm = "lbfgs",
+    init_alpha = 0.001,
+    tol_obj = 1e-12,
+    tol_rel_obj = 10000L,
+    tol_grad = 1e-08,
+    tol_rel_grad = 1e+07,
+    tol_param = 1e-08,
+    history_size = 5L,
+    jacobian = FALSE,
+    iter = 2000L
+  ),
+  variational = list(
+    algorithm = "meanfield",
+    iter = 10000L,
+    grad_samples = 1L,
+    elbo_samples = 100L,
+    eta = 1L,
+    adapt_engaged = TRUE,
+    adapt_iter = 50L,
+    tol_rel_obj = 0.01,
+    eval_elbo = 100L,
+    draws = 1000L
+  ),
+  pathfinder = list(
+    init_alpha = 0.001,
+    tol_obj = 1e-12,
+    tol_rel_obj = 10000L,
+    tol_grad = 1e-08,
+    tol_rel_grad = 1e+07,
+    tol_param = 1e-08,
+    history_size = 5L,
+    draws = 1000L,
+    num_paths = 4L,
+    save_single_paths = FALSE,
+    psis_resample = TRUE,
+    calculate_lp = TRUE,
+    max_lbfgs_iters = 1000L,
+    single_path_draws = 1000L,
+    num_elbo_draws = 25L
+  ),
+  laplace = list(
+    jacobian = TRUE,
+    draws = 1000L
+  )
+)
+
+expect_cmdstan_defaults <- function(method, expected) {
+  args <- mod$cmdstan_defaults(method)
+  expect_type(args, "list")
+  expect_named(args)
+  expect_setequal(names(args), names(expected))
+
+  for (name in names(expected)) {
+    expect_identical(args[[name]], expected[[name]], info = paste0(method, "$", name))
+  }
+}
+
+test_that("cmdstan_defaults() errors for uncompiled model", {
+  mod_uncompiled <- cmdstan_model(
+    stan_file = testing_stan_file("bernoulli"),
+    compile = FALSE
+  )
+  expect_error(
+    mod_uncompiled$cmdstan_defaults("sample"),
+    "'$cmdstan_defaults()' requires a compiled model",
+    fixed = TRUE
+  )
+})
+
+test_that("cmdstan_defaults() errors for invalid method", {
+  expect_error(
+    mod$cmdstan_defaults("bogus"),
+    "'arg' should be one of",
+    fixed = TRUE
+  )
+})
+
+test_that("cmdstan_defaults() returns expected names and values", {
+  for (method in names(expected_cmdstan_defaults)) {
+    expect_cmdstan_defaults(method, expected_cmdstan_defaults[[method]])
+  }
+})
+
+# internal helpers --------------------------------------------------------
+
+test_that("parse_default_value() parses booleans", {
+  expect_identical(parse_default_value("Defaults to true"), TRUE)
+  expect_identical(parse_default_value("Defaults to false"), FALSE)
+})
+
+test_that("parse_default_value() parses integers", {
+  expect_identical(parse_default_value("Defaults to 1000"), 1000L)
+  expect_identical(parse_default_value("Defaults to -1"), -1L)
+  expect_identical(parse_default_value("Defaults to 0"), 0L)
+})
+
+test_that("parse_default_value() parses doubles", {
+  expect_identical(parse_default_value("Defaults to 0.8"), 0.8)
+  expect_identical(parse_default_value("Defaults to 1e-6"), 1e-6)
+  expect_identical(parse_default_value("Defaults to -0.5"), -0.5)
+})
+
+test_that("parse_default_value() returns strings for non-numeric values", {
+  expect_identical(parse_default_value("Defaults to lbfgs"), "lbfgs")
+  expect_identical(parse_default_value("Defaults to diagonal_e"), "diagonal_e")
+})
+
+test_that("map_cmdstan_to_cmdstanr() returns named character for valid methods", {
+  for (method in c("sample", "optimize", "variational", "pathfinder", "laplace")) {
+    mapping <- map_cmdstan_to_cmdstanr(method)
+    expect_type(mapping, "character")
+    expect_true(length(mapping) > 0, info = method)
+    expect_named(mapping)
+  }
+})
+
+test_that("map_cmdstan_to_cmdstanr() returns empty for unknown method", {
+  expect_length(map_cmdstan_to_cmdstanr("unknown"), 0)
+})