diff --git a/internal/crdbtest/crdb.go b/internal/crdbtest/crdb.go
index 51bfdf9254..444c364245 100644
--- a/internal/crdbtest/crdb.go
+++ b/internal/crdbtest/crdb.go
@@ -14,6 +14,7 @@ import (
 	"io"
 	"math/rand/v2"
 	"slices"
+	"strings"
 	"time"
 	"unsafe"
 
@@ -517,7 +518,8 @@ const (
 )
 
 var KeySchema = colblk.KeySchema{
-	Name: "crdb1",
+	Name:       "crdb1",
+	HeaderSize: 1,
 	ColumnTypes: []colblk.DataType{
 		cockroachColRoachKey:       colblk.DataTypePrefixBytes,
 		cockroachColMVCCWallTime:   colblk.DataTypeUint,
@@ -525,12 +527,7 @@ var KeySchema = colblk.KeySchema{
 		cockroachColUntypedVersion: colblk.DataTypeBytes,
 	},
 	NewKeyWriter: func() colblk.KeyWriter {
-		kw := &cockroachKeyWriter{}
-		kw.roachKeys.Init(16)
-		kw.wallTimes.Init()
-		kw.logicalTimes.InitWithDefault()
-		kw.untypedVersions.Init()
-		return kw
+		return makeCockroachKeyWriter()
 	},
 	InitKeySeekerMetadata: func(meta *colblk.KeySeekerMetadata, d *colblk.DataBlockDecoder) {
 		ks := (*cockroachKeySeeker)(unsafe.Pointer(meta))
@@ -541,14 +538,64 @@ var KeySchema = colblk.KeySchema{
 	},
 }
 
+// suffixTypes is a bitfield indicating what kind of suffixes are present in a
+// block.
+type suffixTypes uint8
+
+const (
+	// hasMVCCSuffixes is set if there is at least one key with an MVCC suffix in
+	// the block.
+	hasMVCCSuffixes suffixTypes = (1 << iota)
+	// hasEmptySuffixes is set if there is at least one key with no suffix in the block.
+	hasEmptySuffixes
+	// hasNonMVCCSuffixes is set if there is at least one key with a non-empty,
+	// non-MVCC sufffix.
+	hasNonMVCCSuffixes
+)
+
+func (s suffixTypes) String() string {
+	var suffixes []string
+	if s&hasMVCCSuffixes != 0 {
+		suffixes = append(suffixes, "mvcc")
+	}
+	if s&hasEmptySuffixes != 0 {
+		suffixes = append(suffixes, "empty")
+	}
+	if s&hasEmptySuffixes != 0 {
+		suffixes = append(suffixes, "non-mvcc")
+	}
+	if len(suffixes) == 0 {
+		return "none"
+	}
+	return strings.Join(suffixes, ",")
+}
+
 type cockroachKeyWriter struct {
 	roachKeys       colblk.PrefixBytesBuilder
 	wallTimes       colblk.UintBuilder
 	logicalTimes    colblk.UintBuilder
 	untypedVersions colblk.RawBytesBuilder
+	suffixTypes     suffixTypes
 	prevSuffix      []byte
 }
 
+func makeCockroachKeyWriter() *cockroachKeyWriter {
+	kw := &cockroachKeyWriter{}
+	kw.roachKeys.Init(16)
+	kw.wallTimes.Init()
+	kw.logicalTimes.InitWithDefault()
+	kw.untypedVersions.Init()
+	return kw
+}
+
+func (kw *cockroachKeyWriter) Reset() {
+	kw.roachKeys.Reset()
+	kw.wallTimes.Reset()
+	kw.logicalTimes.Reset()
+	kw.untypedVersions.Reset()
+	kw.suffixTypes = 0
+}
+
 func (kw *cockroachKeyWriter) ComparePrev(key []byte) colblk.KeyComparison {
 	var cmpv colblk.KeyComparison
 	cmpv.PrefixLen = int32(Split(key)) // TODO(jackson): Inline
@@ -596,6 +643,13 @@ func (kw *cockroachKeyWriter) WriteKey(
 		kw.logicalTimes.Set(row, uint64(logicalTime))
 	}
 	kw.untypedVersions.Put(untypedVersion)
+	if wallTime != 0 || logicalTime != 0 {
+		kw.suffixTypes |= hasMVCCSuffixes
+	} else if len(untypedVersion) == 0 {
+		kw.suffixTypes |= hasEmptySuffixes
+	} else {
+		kw.suffixTypes |= hasNonMVCCSuffixes
+	}
 }
 
 func (kw *cockroachKeyWriter) MaterializeKey(dst []byte, i int) []byte {
@@ -610,13 +664,6 @@ func (kw *cockroachKeyWriter) MaterializeKey(dst []byte, i int) []byte {
 	return AppendTimestamp(dst, kw.wallTimes.Get(i), uint32(kw.logicalTimes.Get(i)))
 }
 
-func (kw *cockroachKeyWriter) Reset() {
-	kw.roachKeys.Reset()
-	kw.wallTimes.Reset()
-	kw.logicalTimes.Reset()
-	kw.untypedVersions.Reset()
-}
-
 func (kw *cockroachKeyWriter) WriteDebug(dst io.Writer, rows int) {
 	fmt.Fprint(dst, "prefixes: ")
 	kw.roachKeys.WriteDebug(dst, rows)
@@ -630,6 +677,8 @@ func (kw *cockroachKeyWriter) WriteDebug(dst io.Writer, rows int) {
 	fmt.Fprint(dst, "untyped suffixes: ")
 	kw.untypedVersions.WriteDebug(dst, rows)
 	fmt.Fprintln(dst)
+	fmt.Fprint(dst, "suffix types: ")
+	fmt.Fprintln(dst, kw.suffixTypes.String())
 }
 
 func (kw *cockroachKeyWriter) NumColumns() int {
@@ -665,12 +714,17 @@ func (kw *cockroachKeyWriter) Finish(
 	}
 }
 
+func (kw *cockroachKeyWriter) FinishHeader(buf []byte) {
+	buf[0] = byte(kw.suffixTypes)
+}
+
 type cockroachKeySeeker struct {
 	roachKeys       colblk.PrefixBytes
 	roachKeyChanged colblk.Bitmap
 	mvccWallTimes   colblk.UnsafeUints
 	mvccLogical     colblk.UnsafeUints
 	untypedVersions colblk.RawBytes
+	suffixTypes     suffixTypes
 }
 
 // Assert that the cockroachKeySeeker fits inside KeySeekerMetadata.
@@ -685,6 +739,7 @@ func (ks *cockroachKeySeeker) init(d *colblk.DataBlockDecoder) {
 	ks.mvccWallTimes = bd.Uints(cockroachColMVCCWallTime)
 	ks.mvccLogical = bd.Uints(cockroachColMVCCLogical)
 	ks.untypedVersions = bd.RawBytes(cockroachColUntypedVersion)
+	ks.suffixTypes = suffixTypes(d.KeySchemaHeader(1)[0])
 }
 
 // IsLowerBound is part of the KeySeeker interface.
diff --git a/sstable/block/block.go b/sstable/block/block.go
index 18fcab5f8c..a4e886d9ac 100644
--- a/sstable/block/block.go
+++ b/sstable/block/block.go
@@ -157,7 +157,7 @@ type Metadata [MetadataSize]byte
 
 // MetadataSize is the size of the metadata. The value is chosen to fit a
 // colblk.DataBlockDecoder and a CockroachDB colblk.KeySeeker.
-const MetadataSize = 328
+const MetadataSize = 336
 
 // Assert that MetadataSize is a multiple of 8. This is necessary to keep the
 // block data buffer aligned.
diff --git a/sstable/block/testdata/flush_governor b/sstable/block/testdata/flush_governor
index e2c25b7f4c..ba68ec09a9 100644
--- a/sstable/block/testdata/flush_governor
+++ b/sstable/block/testdata/flush_governor
@@ -29,8 +29,8 @@ should not flush
 init target-block-size=1000 size-class-aware-threshold=60 size-classes=(820, 1020, 1320, 1820)
 ----
 low watermark: 600
-high watermark: 1460
-boundaries: [660 960]
+high watermark: 1452
+boundaries: [652 952]
 
 # Should not flush when the "after" block fits in the same size class.
 should-flush size-before=600 size-after=650
@@ -89,8 +89,8 @@ boundaries: []
 init target-block-size=32768 jemalloc-size-classes
 ----
 low watermark: 19661
-high watermark: 40600
-boundaries: [20120 24216 28312 32408]
+high watermark: 40592
+boundaries: [20112 24208 28304 32400]
 
 # We should flush to avoid exceeding the boundary.
 should-flush size-before=32000 size-after=32766
diff --git a/sstable/colblk/block.go b/sstable/colblk/block.go
index 8908f0b739..4e57860285 100644
--- a/sstable/colblk/block.go
+++ b/sstable/colblk/block.go
@@ -184,9 +184,9 @@ func (h Header) Encode(buf []byte) {
 // blockHeaderSize returns the size of the block header, including column
 // headers, for a block with the specified number of columns and optionally a
 // custom header size.
-func blockHeaderSize(cols int, customHeaderSize int) uint32 {
+func blockHeaderSize(cols int, customHeaderSize uint32) uint32 {
 	// Each column has a 1-byte DataType and a 4-byte offset into the block.
-	return uint32(blockHeaderBaseSize + cols*columnHeaderSize + customHeaderSize)
+	return uint32(blockHeaderBaseSize+cols*columnHeaderSize) + customHeaderSize
 }
 
 // DecodeHeader reads the block header from the provided serialized columnar
@@ -217,7 +217,7 @@ func (e *blockEncoder) reset() {
 
 // init initializes the block encoder with a buffer of the specified size and
 // header.
-func (e *blockEncoder) init(size int, h Header, customHeaderSize int) {
+func (e *blockEncoder) init(size int, h Header, customHeaderSize uint32) {
 	if cap(e.buf) < size {
 		e.buf = crbytes.AllocAligned(size)
 	} else {
diff --git a/sstable/colblk/data_block.go b/sstable/colblk/data_block.go
index 2685e3e2cf..681c1b64aa 100644
--- a/sstable/colblk/data_block.go
+++ b/sstable/colblk/data_block.go
@@ -33,7 +33,10 @@ import (
 // attributes inlined within the data block. For inlined-values, the
 // user-defined value columns would be implicitly null.
 type KeySchema struct {
-	Name         string
+	Name string
+	// KeySchema implementations can optionally make use a fixed-sized custom
+	// header inside each block.
+	HeaderSize   uint32
 	ColumnTypes  []DataType
 	NewKeyWriter func() KeyWriter
 
@@ -63,7 +66,7 @@ type KeySeekerMetadata [KeySeekerMetadataSize]byte
 
 // KeySeekerMetadataSize is chosen to fit the CockroachDB key seeker
 // implementation.
-const KeySeekerMetadataSize = 168
+const KeySeekerMetadataSize = 176
 
 // A KeyWriter maintains ColumnWriters for a data block for writing user keys
 // into the database-specific key schema. Users may define their own key schema
@@ -90,6 +93,8 @@ type KeyWriter interface {
 	// MaterializeKey appends the zero-indexed row'th key written to dst,
 	// returning the result.
 	MaterializeKey(dst []byte, row int) []byte
+	// FinishHeader serializes an internal header of exactly KeySchema.HeaderSize bytes.
+	FinishHeader(dst []byte)
 }
 
 // KeyComparison holds information about a key and its comparison to another a
@@ -177,6 +182,7 @@ var defaultSchemaColumnTypes = []DataType{
 func DefaultKeySchema(comparer *base.Comparer, prefixBundleSize int) KeySchema {
 	return KeySchema{
 		Name:        fmt.Sprintf("DefaultKeySchema(%s,%d)", comparer.Name, prefixBundleSize),
+		HeaderSize:  0,
 		ColumnTypes: defaultSchemaColumnTypes,
 		NewKeyWriter: func() KeyWriter {
 			kw := &defaultKeyWriter{comparer: comparer}
@@ -300,6 +306,8 @@ func (w *defaultKeyWriter) Size(rows int, offset uint32) uint32 {
 	return offset
 }
 
+func (w *defaultKeyWriter) FinishHeader([]byte) {}
+
 func (w *defaultKeyWriter) Finish(col, rows int, offset uint32, buf []byte) (nextOffset uint32) {
 	switch col {
 	case defaultKeySchemaColumnPrefix:
@@ -464,6 +472,7 @@ const (
 // contained within the block. This is used by iterators to avoid the need to
 // grow key buffers while iterating over the block, ensuring that the key buffer
 // is always sufficiently large.
+// This is serialized immediately after the KeySchema specific header.
 const dataBlockCustomHeaderSize = 4
 
 // Init initializes the data block writer.
@@ -571,7 +580,7 @@ func (w *DataBlockEncoder) Rows() int {
 
 // Size returns the size of the current pending data block.
 func (w *DataBlockEncoder) Size() int {
-	off := blockHeaderSize(len(w.Schema.ColumnTypes)+dataBlockColumnMax, dataBlockCustomHeaderSize)
+	off := blockHeaderSize(len(w.Schema.ColumnTypes)+dataBlockColumnMax, dataBlockCustomHeaderSize+w.Schema.HeaderSize)
 	off = w.KeyWriter.Size(w.rows, off)
 	off = w.trailers.Size(w.rows, off)
 	off = w.prefixSame.InvertedSize(w.rows, off)
@@ -607,11 +616,12 @@ func (w *DataBlockEncoder) Finish(rows, size int) (finished []byte, lastKey base
 	// to represent when the prefix changes.
 	w.prefixSame.Invert(rows)
 
-	w.enc.init(size, h, dataBlockCustomHeaderSize)
-
-	// Write the max key length in the custom header.
-	binary.LittleEndian.PutUint32(w.enc.data()[:dataBlockCustomHeaderSize], uint32(w.maximumKeyLength))
+	w.enc.init(size, h, dataBlockCustomHeaderSize+w.Schema.HeaderSize)
 
+	// Write the key schema custom header.
+	w.KeyWriter.FinishHeader(w.enc.data()[:w.Schema.HeaderSize])
+	// Write the max key length in the data block custom header.
+	binary.LittleEndian.PutUint32(w.enc.data()[w.Schema.HeaderSize:w.Schema.HeaderSize+dataBlockCustomHeaderSize], uint32(w.maximumKeyLength))
 	w.enc.encode(rows, w.KeyWriter)
 	w.enc.encode(rows, &w.trailers)
 	w.enc.encode(rows, &w.prefixSame)
@@ -864,18 +874,23 @@ func (d *DataBlockDecoder) PrefixChanged() Bitmap {
 	return d.prefixChanged
 }
 
+// KeySchemaHeader returns the KeySchema-specific header of fixed size.
+func (d *DataBlockDecoder) KeySchemaHeader(schemaHeaderSize uint32) []byte {
+	return d.d.data[:schemaHeaderSize]
+}
+
 // Init initializes the data block reader with the given serialized data block.
 func (d *DataBlockDecoder) Init(schema *KeySchema, data []byte) {
 	if uintptr(unsafe.Pointer(unsafe.SliceData(data)))&7 != 0 {
 		panic("data buffer not 8-byte aligned")
 	}
-	d.d.Init(data, dataBlockCustomHeaderSize)
+	d.d.Init(data, dataBlockCustomHeaderSize+schema.HeaderSize)
 	d.trailers = d.d.Uints(len(schema.ColumnTypes) + dataBlockColumnTrailer)
 	d.prefixChanged = d.d.Bitmap(len(schema.ColumnTypes) + dataBlockColumnPrefixChanged)
 	d.values = d.d.RawBytes(len(schema.ColumnTypes) + dataBlockColumnValue)
 	d.isValueExternal = d.d.Bitmap(len(schema.ColumnTypes) + dataBlockColumnIsValueExternal)
 	d.isObsolete = d.d.Bitmap(len(schema.ColumnTypes) + dataBlockColumnIsObsolete)
-	d.maximumKeyLength = binary.LittleEndian.Uint32(data[:dataBlockCustomHeaderSize])
+	d.maximumKeyLength = binary.LittleEndian.Uint32(data[schema.HeaderSize:])
 }
 
 // Describe descirbes the binary format of the data block, assuming f.Offset()
diff --git a/testdata/event_listener b/testdata/event_listener
index 5e4e0a2923..cd326ee930 100644
--- a/testdata/event_listener
+++ b/testdata/event_listener
@@ -232,7 +232,7 @@ Backing tables: 0 (0B)
 Virtual tables: 0 (0B)
 Local tables size: 2.1KB
 Compression types: snappy: 3
-Block cache: 2 entries (768B)  hit rate: 0.0%
+Block cache: 2 entries (784B)  hit rate: 0.0%
 Table cache: 0 entries (0B)  hit rate: 50.0%
 Secondary cache: 0 entries (0B)  hit rate: 0.0%
 Snapshots: 0  earliest seq num: 0
diff --git a/testdata/ingest b/testdata/ingest
index 7d4f364e99..29eb2e3b9a 100644
--- a/testdata/ingest
+++ b/testdata/ingest
@@ -53,7 +53,7 @@ Backing tables: 0 (0B)
 Virtual tables: 0 (0B)
 Local tables size: 569B
 Compression types: snappy: 1
-Block cache: 3 entries (1.0KB)  hit rate: 18.2%
+Block cache: 3 entries (1.1KB)  hit rate: 18.2%
 Table cache: 1 entries (760B)  hit rate: 50.0%
 Secondary cache: 0 entries (0B)  hit rate: 0.0%
 Snapshots: 0  earliest seq num: 0
diff --git a/testdata/metrics b/testdata/metrics
index a9ae92b744..cd66bfe2f7 100644
--- a/testdata/metrics
+++ b/testdata/metrics
@@ -75,7 +75,7 @@ Backing tables: 0 (0B)
 Virtual tables: 0 (0B)
 Local tables size: 589B
 Compression types: snappy: 1
-Block cache: 2 entries (700B)  hit rate: 0.0%
+Block cache: 2 entries (716B)  hit rate: 0.0%
 Table cache: 1 entries (760B)  hit rate: 0.0%
 Secondary cache: 0 entries (0B)  hit rate: 0.0%
 Snapshots: 0  earliest seq num: 0
@@ -132,7 +132,7 @@ Backing tables: 0 (0B)
 Virtual tables: 0 (0B)
 Local tables size: 595B
 Compression types: snappy: 1
-Block cache: 2 entries (700B)  hit rate: 33.3%
+Block cache: 2 entries (716B)  hit rate: 33.3%
 Table cache: 2 entries (1.5KB)  hit rate: 66.7%
 Secondary cache: 0 entries (0B)  hit rate: 0.0%
 Snapshots: 0  earliest seq num: 0
@@ -176,7 +176,7 @@ Backing tables: 0 (0B)
 Virtual tables: 0 (0B)
 Local tables size: 595B
 Compression types: snappy: 1
-Block cache: 2 entries (700B)  hit rate: 33.3%
+Block cache: 2 entries (716B)  hit rate: 33.3%
 Table cache: 2 entries (1.5KB)  hit rate: 66.7%
 Secondary cache: 0 entries (0B)  hit rate: 0.0%
 Snapshots: 0  earliest seq num: 0
@@ -217,7 +217,7 @@ Backing tables: 0 (0B)
 Virtual tables: 0 (0B)
 Local tables size: 595B
 Compression types: snappy: 1
-Block cache: 2 entries (700B)  hit rate: 33.3%
+Block cache: 2 entries (716B)  hit rate: 33.3%
 Table cache: 1 entries (760B)  hit rate: 66.7%
 Secondary cache: 0 entries (0B)  hit rate: 0.0%
 Snapshots: 0  earliest seq num: 0