diff --git a/R-package/R/xgb.load.R b/R-package/R/xgb.load.R
index bda4e7e07..d98041908 100644
--- a/R-package/R/xgb.load.R
+++ b/R-package/R/xgb.load.R
@@ -5,7 +5,7 @@
 #' @param modelfile the name of the binary input file.
 #'
 #' @details
-#' The input file is expected to contain a model saved in an xgboost-internal binary format
+#' The input file is expected to contain a model saved in an xgboost model format
 #' using either \code{\link{xgb.save}} or \code{\link{cb.save.model}} in R, or using some
 #' appropriate methods from other xgboost interfaces. E.g., a model trained in Python and
 #' saved from there in xgboost format, could be loaded from R.
@@ -38,6 +38,13 @@ xgb.load <- function(modelfile) {
   handle <- xgb.Booster.handle(modelfile = modelfile)
   # re-use modelfile if it is raw so we do not need to serialize
   if (typeof(modelfile) == "raw") {
+    warning(
+      paste(
+        "The support for loading raw booster with `xgb.load` will be ",
+        "discontinued in upcoming release. Use `xgb.load.raw` or",
+        " `xgb.unserialize` instead. "
+      )
+    )
     bst <- xgb.handleToBooster(handle, modelfile)
   } else {
     bst <- xgb.handleToBooster(handle, NULL)
diff --git a/R-package/R/xgb.save.raw.R b/R-package/R/xgb.save.raw.R
index 967a31482..48fdbca45 100644
--- a/R-package/R/xgb.save.raw.R
+++ b/R-package/R/xgb.save.raw.R
@@ -4,6 +4,14 @@
 #' Save xgboost model from xgboost or xgb.train
 #'
 #' @param model the model object.
+#' @param raw_format The format for encoding the booster.  Available options are
+#' \itemize{
+#'     \item \code{json}: Encode the booster into JSON text document.
+#'     \item \code{ubj}:  Encode the booster into Universal Binary JSON.
+#'     \item \code{deprecated}: Encode the booster into old customized binary format.
+#' }
+#'
+#' Right now the default is \code{deprecated} but will be changed to \code{ubj} in upcoming release.
 #'
 #' @examples
 #' data(agaricus.train, package='xgboost')
@@ -17,7 +25,8 @@
 #' pred <- predict(bst, test$data)
 #'
 #' @export
-xgb.save.raw <- function(model) {
+xgb.save.raw <- function(model, raw_format = "deprecated") {
   handle <- xgb.get.handle(model)
-  .Call(XGBoosterModelToRaw_R, handle)
+  args <- list(format = raw_format)
+  .Call(XGBoosterSaveModelToRaw_R, handle, jsonlite::toJSON(args, auto_unbox = TRUE))
 }
diff --git a/R-package/demo/basic_walkthrough.R b/R-package/demo/basic_walkthrough.R
index 6c7f79a03..31f79fb57 100644
--- a/R-package/demo/basic_walkthrough.R
+++ b/R-package/demo/basic_walkthrough.R
@@ -63,7 +63,7 @@ print(paste("sum(abs(pred2-pred))=", sum(abs(pred2 - pred))))
 # save model to R's raw vector
 raw <- xgb.save.raw(bst)
 # load binary model to R
-bst3 <- xgb.load(raw)
+bst3 <- xgb.load.raw(raw)
 pred3 <- predict(bst3, test$data)
 # pred3 should be identical to pred
 print(paste("sum(abs(pred3-pred))=", sum(abs(pred3 - pred))))
diff --git a/R-package/src/init.c b/R-package/src/init.c
index 9cfa1ac3f..2af072221 100644
--- a/R-package/src/init.c
+++ b/R-package/src/init.c
@@ -24,12 +24,12 @@ extern SEXP XGBoosterEvalOneIter_R(SEXP, SEXP, SEXP, SEXP);
 extern SEXP XGBoosterGetAttrNames_R(SEXP);
 extern SEXP XGBoosterGetAttr_R(SEXP, SEXP);
 extern SEXP XGBoosterLoadModelFromRaw_R(SEXP, SEXP);
+extern SEXP XGBoosterSaveModelToRaw_R(SEXP handle, SEXP config);
 extern SEXP XGBoosterLoadModel_R(SEXP, SEXP);
 extern SEXP XGBoosterSaveJsonConfig_R(SEXP handle);
 extern SEXP XGBoosterLoadJsonConfig_R(SEXP handle, SEXP value);
 extern SEXP XGBoosterSerializeToBuffer_R(SEXP handle);
 extern SEXP XGBoosterUnserializeFromBuffer_R(SEXP handle, SEXP raw);
-extern SEXP XGBoosterModelToRaw_R(SEXP);
 extern SEXP XGBoosterPredict_R(SEXP, SEXP, SEXP, SEXP, SEXP);
 extern SEXP XGBoosterPredictFromDMatrix_R(SEXP, SEXP, SEXP);
 extern SEXP XGBoosterSaveModel_R(SEXP, SEXP);
@@ -59,12 +59,12 @@ static const R_CallMethodDef CallEntries[] = {
   {"XGBoosterGetAttrNames_R",     (DL_FUNC) &XGBoosterGetAttrNames_R,     1},
   {"XGBoosterGetAttr_R",          (DL_FUNC) &XGBoosterGetAttr_R,          2},
   {"XGBoosterLoadModelFromRaw_R", (DL_FUNC) &XGBoosterLoadModelFromRaw_R, 2},
+  {"XGBoosterSaveModelToRaw_R",   (DL_FUNC) &XGBoosterSaveModelToRaw_R,   2},
   {"XGBoosterLoadModel_R",        (DL_FUNC) &XGBoosterLoadModel_R,        2},
   {"XGBoosterSaveJsonConfig_R",   (DL_FUNC) &XGBoosterSaveJsonConfig_R,   1},
   {"XGBoosterLoadJsonConfig_R",   (DL_FUNC) &XGBoosterLoadJsonConfig_R,   2},
   {"XGBoosterSerializeToBuffer_R",     (DL_FUNC) &XGBoosterSerializeToBuffer_R,     1},
   {"XGBoosterUnserializeFromBuffer_R", (DL_FUNC) &XGBoosterUnserializeFromBuffer_R, 2},
-  {"XGBoosterModelToRaw_R",       (DL_FUNC) &XGBoosterModelToRaw_R,       1},
   {"XGBoosterPredict_R",          (DL_FUNC) &XGBoosterPredict_R,          5},
   {"XGBoosterPredictFromDMatrix_R", (DL_FUNC) &XGBoosterPredictFromDMatrix_R, 3},
   {"XGBoosterSaveModel_R",        (DL_FUNC) &XGBoosterSaveModel_R,        2},
diff --git a/R-package/src/xgboost_R.cc b/R-package/src/xgboost_R.cc
index 9921bb74b..5f7bd6c19 100644
--- a/R-package/src/xgboost_R.cc
+++ b/R-package/src/xgboost_R.cc
@@ -429,21 +429,6 @@ XGB_DLL SEXP XGBoosterSaveModel_R(SEXP handle, SEXP fname) {
   return R_NilValue;
 }
 
-XGB_DLL SEXP XGBoosterModelToRaw_R(SEXP handle) {
-  SEXP ret;
-  R_API_BEGIN();
-  bst_ulong olen;
-  const char *raw;
-  CHECK_CALL(XGBoosterGetModelRaw(R_ExternalPtrAddr(handle), &olen, &raw));
-  ret = PROTECT(allocVector(RAWSXP, olen));
-  if (olen != 0) {
-    memcpy(RAW(ret), raw, olen);
-  }
-  R_API_END();
-  UNPROTECT(1);
-  return ret;
-}
-
 XGB_DLL SEXP XGBoosterLoadModelFromRaw_R(SEXP handle, SEXP raw) {
   R_API_BEGIN();
   CHECK_CALL(XGBoosterLoadModelFromBuffer(R_ExternalPtrAddr(handle),
@@ -453,6 +438,22 @@ XGB_DLL SEXP XGBoosterLoadModelFromRaw_R(SEXP handle, SEXP raw) {
   return R_NilValue;
 }
 
+XGB_DLL SEXP XGBoosterSaveModelToRaw_R(SEXP handle, SEXP json_config) {
+  SEXP ret;
+  R_API_BEGIN();
+  bst_ulong olen;
+  char const *c_json_config = CHAR(asChar(json_config));
+  char const *raw;
+  CHECK_CALL(XGBoosterSaveModelToBuffer(R_ExternalPtrAddr(handle), c_json_config, &olen, &raw))
+  ret = PROTECT(allocVector(RAWSXP, olen));
+  if (olen != 0) {
+    std::memcpy(RAW(ret), raw, olen);
+  }
+  R_API_END();
+  UNPROTECT(1);
+  return ret;
+}
+
 XGB_DLL SEXP XGBoosterSaveJsonConfig_R(SEXP handle) {
   const char* ret;
   R_API_BEGIN();
diff --git a/R-package/src/xgboost_R.h b/R-package/src/xgboost_R.h
index 786514593..7d6edb648 100644
--- a/R-package/src/xgboost_R.h
+++ b/R-package/src/xgboost_R.h
@@ -209,11 +209,21 @@ XGB_DLL SEXP XGBoosterSaveModel_R(SEXP handle, SEXP fname);
 XGB_DLL SEXP XGBoosterLoadModelFromRaw_R(SEXP handle, SEXP raw);
 
 /*!
- * \brief save model into R's raw array
+ * \brief Save model into R's raw array
+ *
  * \param handle handle
- * \return raw array
+ * \param json_config JSON encoded string storing parameters for the function.  Following
+ *                    keys are expected in the JSON document:
+ *
+ *     "format": str
+ *       - json: Output booster will be encoded as JSON.
+ *       - ubj:  Output booster will be encoded as Univeral binary JSON.
+ *       - deprecated: Output booster will be encoded as old custom binary format.  Do now use
+ *         this format except for compatibility reasons.
+ *
+ * \return Raw array
  */
-XGB_DLL SEXP XGBoosterModelToRaw_R(SEXP handle);
+XGB_DLL SEXP XGBoosterSaveModelToRaw_R(SEXP handle, SEXP json_config);
 
 /*!
  * \brief Save internal parameters as a JSON string
diff --git a/R-package/tests/testthat/test_io.R b/R-package/tests/testthat/test_io.R
new file mode 100644
index 000000000..f4990352f
--- /dev/null
+++ b/R-package/tests/testthat/test_io.R
@@ -0,0 +1,39 @@
+context("Test model IO.")
+## some other tests are in test_basic.R
+require(xgboost)
+require(testthat)
+
+data(agaricus.train, package = "xgboost")
+data(agaricus.test, package = "xgboost")
+train <- agaricus.train
+test <- agaricus.test
+
+test_that("load/save raw works", {
+  nrounds <- 8
+  booster <- xgboost(
+    data = train$data, label = train$label,
+    nrounds = nrounds, objective = "binary:logistic"
+  )
+
+  json_bytes <- xgb.save.raw(booster, raw_format = "json")
+  ubj_bytes <- xgb.save.raw(booster, raw_format = "ubj")
+  old_bytes <- xgb.save.raw(booster, raw_format = "deprecated")
+
+  from_json <- xgb.load.raw(json_bytes)
+  from_ubj <- xgb.load.raw(ubj_bytes)
+
+  ## FIXME(jiamingy): Should we include these 3 lines into `xgb.load.raw`?
+  from_json <- list(handle = from_json, raw = NULL)
+  class(from_json) <- "xgb.Booster"
+  from_json <- xgb.Booster.complete(from_json, saveraw = TRUE)
+
+  from_ubj <- list(handle = from_ubj, raw = NULL)
+  class(from_ubj) <- "xgb.Booster"
+  from_ubj <- xgb.Booster.complete(from_ubj, saveraw = TRUE)
+
+  json2old <- xgb.save.raw(from_json, raw_format = "deprecated")
+  ubj2old <- xgb.save.raw(from_ubj, raw_format = "deprecated")
+
+  expect_equal(json2old, ubj2old)
+  expect_equal(json2old, old_bytes)
+})