diff --git a/tsdb/head_append.go b/tsdb/head_append.go
index 17bb5de835..e673466ccc 100644
--- a/tsdb/head_append.go
+++ b/tsdb/head_append.go
@@ -1059,7 +1059,7 @@ func (a *headAppenderBase) log() error {
 	defer func() { a.head.putBytesBuffer(buf) }()
 
 	var rec []byte
-	var enc record.Encoder
+	enc := record.Encoder{EnableSTStorage: a.head.opts.EnableSTStorage.Load()}
 
 	if len(a.seriesRefs) > 0 {
 		rec = enc.Series(a.seriesRefs, buf)
@@ -1743,7 +1743,7 @@ func (a *headAppenderBase) Commit() (err error) {
 			samplesPerChunk: h.opts.SamplesPerChunk,
 		},
 		oooEnc: record.Encoder{
-			EnableSTStorage: false,
+			EnableSTStorage: h.opts.EnableSTStorage.Load(),
 		},
 	}
 
diff --git a/tsdb/head_test.go b/tsdb/head_test.go
index 2cee989e40..91cd742330 100644
--- a/tsdb/head_test.go
+++ b/tsdb/head_test.go
@@ -7267,3 +7267,117 @@ func TestHistogramStalenessConversionMetrics(t *testing.T) {
 		})
 	}
 }
+
+// TestHeadAppender_WALEncoder_EnableSTStorage verifies that when EnableSTStorage
+// is true the WAL encoder writes SamplesV2 records, and when false it writes
+// plain Samples (V1) records. The bug was that log() always created a zero-value
+// record.Encoder (EnableSTStorage=false), ignoring the head option.
+func TestHeadAppender_WALEncoder_EnableSTStorage(t *testing.T) {
+	for _, enableST := range []bool{false, true} {
+		t.Run(fmt.Sprintf("enableSTStorage=%v", enableST), func(t *testing.T) {
+			opts := newTestHeadDefaultOptions(DefaultBlockDuration, false)
+			opts.EnableSTStorage.Store(enableST)
+			h, w := newTestHeadWithOptions(t, compression.None, opts)
+
+			lbls := labels.FromStrings("foo", "bar")
+			app := h.AppenderV2(context.Background())
+			for ts := int64(100); ts < 110; ts++ {
+				_, err := app.Append(0, lbls, 0, ts, float64(ts), nil, nil, storage.AOptions{})
+				require.NoError(t, err)
+			}
+			require.NoError(t, app.Commit())
+			require.NoError(t, h.Close())
+
+			// Read WAL segments directly and check the sample record type.
+			sr, err := wlog.NewSegmentsReader(w.Dir())
+			require.NoError(t, err)
+			defer func() { require.NoError(t, sr.Close()) }()
+
+			dec := record.NewDecoder(labels.NewSymbolTable(), promslog.NewNopLogger())
+			r := wlog.NewReader(sr)
+
+			var foundSampleRecord bool
+			for r.Next() {
+				rt := dec.Type(r.Record())
+				switch rt {
+				case record.Samples:
+					require.False(t, enableST, "WAL contains Samples (V1) record but EnableSTStorage=true, expected SamplesV2")
+					foundSampleRecord = true
+				case record.SamplesV2:
+					require.True(t, enableST, "WAL contains SamplesV2 record but EnableSTStorage=false, expected Samples (V1)")
+					foundSampleRecord = true
+				}
+			}
+			require.NoError(t, r.Err())
+			require.True(t, foundSampleRecord, "no sample record found in WAL")
+		})
+	}
+}
+
+// TestHeadAppender_WBLEncoder_EnableSTStorage verifies that when EnableSTStorage
+// is true the WBL encoder writes SamplesV2 records for out-of-order samples, and
+// when false it writes plain Samples (V1) records. The bug was that collectOOORecords()
+// always created record.Encoder{EnableSTStorage: false}, ignoring the head option.
+func TestHeadAppender_WBLEncoder_EnableSTStorage(t *testing.T) {
+	for _, enableST := range []bool{false, true} {
+		t.Run(fmt.Sprintf("enableSTStorage=%v", enableST), func(t *testing.T) {
+			dir := t.TempDir()
+			wal, err := wlog.NewSize(nil, nil, filepath.Join(dir, "wal"), 32768, compression.None)
+			require.NoError(t, err)
+			wbl, err := wlog.NewSize(nil, nil, filepath.Join(dir, wlog.WblDirName), 32768, compression.None)
+			require.NoError(t, err)
+
+			opts := DefaultHeadOptions()
+			opts.ChunkRange = DefaultBlockDuration
+			opts.ChunkDirRoot = dir
+			opts.OutOfOrderTimeWindow.Store(60 * time.Minute.Milliseconds())
+			opts.EnableSTStorage.Store(enableST)
+
+			h, err := NewHead(nil, nil, wal, wbl, opts, nil)
+			require.NoError(t, err)
+			require.NoError(t, h.Init(0))
+			t.Cleanup(func() { _ = h.Close() })
+
+			lbls := labels.FromStrings("foo", "bar")
+
+			// Append an in-order sample to establish head maxt.
+			app := h.AppenderV2(context.Background())
+			_, err = app.Append(0, lbls, 0, 200, 200, nil, nil, storage.AOptions{})
+			require.NoError(t, err)
+			require.NoError(t, app.Commit())
+
+			// Append OOO samples; these are written to the WBL.
+			app = h.AppenderV2(context.Background())
+			for ts := int64(100); ts < 110; ts++ {
+				_, err = app.Append(0, lbls, 0, ts, float64(ts), nil, nil, storage.AOptions{})
+				require.NoError(t, err)
+			}
+			require.NoError(t, app.Commit())
+
+			require.NoError(t, h.Close())
+
+			// Read WBL segments directly and check the sample record type.
+			sr, err := wlog.NewSegmentsReader(filepath.Join(dir, wlog.WblDirName))
+			require.NoError(t, err)
+			defer func() { require.NoError(t, sr.Close()) }()
+
+			dec := record.NewDecoder(labels.NewSymbolTable(), promslog.NewNopLogger())
+			r := wlog.NewReader(sr)
+
+			var foundSampleRecord bool
+			for r.Next() {
+				rt := dec.Type(r.Record())
+				switch rt {
+				case record.Samples:
+					require.False(t, enableST, "WBL contains Samples (V1) record but EnableSTStorage=true, expected SamplesV2")
+					foundSampleRecord = true
+				case record.SamplesV2:
+					require.True(t, enableST, "WBL contains SamplesV2 record but EnableSTStorage=false, expected Samples (V1)")
+					foundSampleRecord = true
+				}
+			}
+			require.NoError(t, r.Err())
+			require.True(t, foundSampleRecord, "no sample record found in WBL")
+		})
+	}
+}