diff --git a/.chloggen/elasticsearchexporter_mapping-mode-default-otel.yaml b/.chloggen/elasticsearchexporter_mapping-mode-default-otel.yaml
new file mode 100644
index 0000000000000..5e57161de45be
--- /dev/null
+++ b/.chloggen/elasticsearchexporter_mapping-mode-default-otel.yaml
@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: breaking
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: elasticsearchexporter
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Change default `mapping::mode` config to `otel`
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [37241]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: The new default, OTel mapping mode, requires Elasticsearch 8.12+. To retain the old behavior, explicitly set `mapping::mode` to `none`.
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]
diff --git a/exporter/elasticsearchexporter/README.md b/exporter/elasticsearchexporter/README.md
index b70b4bcbd7feb..6df70c38405f3 100644
--- a/exporter/elasticsearchexporter/README.md
+++ b/exporter/elasticsearchexporter/README.md
@@ -158,7 +158,7 @@ The Elasticsearch exporter supports several document schemas and preprocessing
 behaviours, which may be configured through the following settings:
 
 - `mapping`:
-  - `mode` (default=none): The default mapping mode. Valid modes are:
+  - `mode` (default=otel): The default mapping mode. Valid modes are:
     - `none`
     - `ecs`
     - `otel`
@@ -177,7 +177,12 @@ See below for a description of each mapping mode.
 
 #### OTel mapping mode
 
-Requires Elasticsearch 8.12 or above.
+The default and recommended "OTel-native" mapping mode.
+
+Requires Elasticsearch 8.12 or above[^1], works best with Elasticsearch 8.16 or above[^2].
+
+[^1]: as it uses the undocumented `require_data_stream` bulk API parameter supported from Elasticsearch 8.12
+[^2]: Elasticsearch 8.16 contains a built-in `otel-data` plugin
 
 In `otel` mapping mode, the Elasticsearch Exporter stores documents in Elastic's preferred
 "OTel-native" schema. In this mapping mode, documents use the original attribute names and
@@ -188,9 +193,7 @@ and `data_stream.namespace`. Instead of serializing these values under the `*att
 they are put at the root of the document, to conform with the conventions of the data stream naming
 scheme that maps these as `constant_keyword` fields.
 
-`data_stream.dataset` will always be appended with `.otel`. It is recommended to use with
-`*_dynamic_index::enabled: true` (e.g. `logs_dynamic_index::enabled`) to route documents to data stream
-`${data_stream.type}-${data_stream.dataset}-${data_stream.namespace}`.
+`data_stream.dataset` will always be appended with `.otel` if [dynamic data stream routing mode](#elasticsearch-document-routing) is active.
 
 Span events are stored in separate documents. They will be routed with `data_stream.type` set to
 `logs` if `traces_dynamic_index::enabled` is `true`.
@@ -516,3 +519,16 @@ This gives the exporter the opportunity to group all related metrics into the sa
 
 2. Otherwise, check your metrics pipeline setup for misconfiguration that causes an actual violation of the [single writer principle](https://opentelemetry.io/docs/specs/otel/metrics/data-model/#single-writer).
  This means that the same metric with the same dimensions is sent from multiple sources, which is not allowed in the OTel metrics data model.
+
+### flush failed (400) illegal_argument_exception
+
+Symptom: bulk indexer logs an error that indicates "bulk indexer flush error" with bulk request returning HTTP 400 and an error type of `illegal_argument_exception`, similar to the following.
+
+```
+error   elasticsearchexporter@v0.120.1/bulkindexer.go:343       bulk indexer flush error        {"otelcol.component.id": "elasticsearch", "otelcol.component.kind": "Exporter", "otelcol.signal": "logs", "error": "flush failed (400): {\"error\":{\"type\":\"illegal_argument_exception\",\"caused_by\":{}}}"}
+```
+
+This may happen when you use [OTel mapping mode](#otel-mapping-mode) (the default mapping mode from v0.122.0, or explicitly by configuring `mapping::mode: otel`) sending to Elasticsearch version < 8.12.
+
+To resolve this, it is recommended to upgrade your Elasticsearch to 8.12+, ideally 8.16+.
+Alternatively, try other mapping modes, but the document structure will be different.
diff --git a/exporter/elasticsearchexporter/config_test.go b/exporter/elasticsearchexporter/config_test.go
index e36f15ee86db3..e4bc453a916b0 100644
--- a/exporter/elasticsearchexporter/config_test.go
+++ b/exporter/elasticsearchexporter/config_test.go
@@ -109,7 +109,7 @@ func TestConfig(t *testing.T) {
 					RetryOnStatus:   []int{http.StatusTooManyRequests, http.StatusInternalServerError},
 				},
 				Mapping: MappingsSettings{
-					Mode:         "none",
+					Mode:         "otel",
 					AllowedModes: []string{"bodymap", "ecs", "none", "otel", "raw"},
 				},
 				LogstashFormat: LogstashFormatSettings{
@@ -184,7 +184,7 @@ func TestConfig(t *testing.T) {
 					RetryOnStatus:   []int{http.StatusTooManyRequests, http.StatusInternalServerError},
 				},
 				Mapping: MappingsSettings{
-					Mode:         "none",
+					Mode:         "otel",
 					AllowedModes: []string{"bodymap", "ecs", "none", "otel", "raw"},
 				},
 				LogstashFormat: LogstashFormatSettings{
@@ -259,7 +259,7 @@ func TestConfig(t *testing.T) {
 					RetryOnStatus:   []int{http.StatusTooManyRequests, http.StatusInternalServerError},
 				},
 				Mapping: MappingsSettings{
-					Mode:         "none",
+					Mode:         "otel",
 					AllowedModes: []string{"bodymap", "ecs", "none", "otel", "raw"},
 				},
 				LogstashFormat: LogstashFormatSettings{
diff --git a/exporter/elasticsearchexporter/exporter_test.go b/exporter/elasticsearchexporter/exporter_test.go
index 8b61a0537b0aa..9002952c6dc56 100644
--- a/exporter/elasticsearchexporter/exporter_test.go
+++ b/exporter/elasticsearchexporter/exporter_test.go
@@ -363,6 +363,7 @@ func TestExporterLogs(t *testing.T) {
 		})
 
 		exporter := newTestLogsExporter(t, server.URL, func(cfg *Config) {
+			cfg.Mapping.Mode = "none"
 			cfg.LogsDynamicIndex.Enabled = true
 		})
 		logs := newLogsWithAttributes(
@@ -1734,6 +1735,7 @@ func TestExporterTraces(t *testing.T) {
 		})
 
 		exporter := newTestTracesExporter(t, server.URL, func(cfg *Config) {
+			cfg.Mapping.Mode = "none"
 			cfg.TracesDynamicIndex.Enabled = true
 		})
 
diff --git a/exporter/elasticsearchexporter/factory.go b/exporter/elasticsearchexporter/factory.go
index a78e6d176717e..755894697827a 100644
--- a/exporter/elasticsearchexporter/factory.go
+++ b/exporter/elasticsearchexporter/factory.go
@@ -84,7 +84,7 @@ func createDefaultConfig() component.Config {
 			},
 		},
 		Mapping: MappingsSettings{
-			Mode:         "none",
+			Mode:         "otel",
 			AllowedModes: slices.Sorted(maps.Keys(canonicalMappingModes)),
 		},
 		LogstashFormat: LogstashFormatSettings{