diff --git a/src/crypto/cipher/benchmark_test.go b/src/crypto/cipher/benchmark_test.go
index 181d08c9b14699..1a5b1b1ddd552d 100644
--- a/src/crypto/cipher/benchmark_test.go
+++ b/src/crypto/cipher/benchmark_test.go
@@ -65,12 +65,12 @@ func BenchmarkAESGCM(b *testing.B) {
 	}
 }
 
-func benchmarkAESStream(b *testing.B, mode func(cipher.Block, []byte) cipher.Stream, buf []byte) {
+func benchmarkAESStream(b *testing.B, mode func(cipher.Block, []byte) cipher.Stream, buf []byte, keySize int) {
 	b.SetBytes(int64(len(buf)))
 
-	var key [16]byte
+	key := make([]byte, keySize)
 	var iv [16]byte
-	aes, _ := aes.NewCipher(key[:])
+	aes, _ := aes.NewCipher(key)
 	stream := mode(aes, iv[:])
 
 	b.ResetTimer()
@@ -87,15 +87,20 @@ const almost1K = 1024 - 5
 const almost8K = 8*1024 - 5
 
 func BenchmarkAESCTR(b *testing.B) {
-	b.Run("50", func(b *testing.B) {
-		benchmarkAESStream(b, cipher.NewCTR, make([]byte, 50))
-	})
-	b.Run("1K", func(b *testing.B) {
-		benchmarkAESStream(b, cipher.NewCTR, make([]byte, almost1K))
-	})
-	b.Run("8K", func(b *testing.B) {
-		benchmarkAESStream(b, cipher.NewCTR, make([]byte, almost8K))
-	})
+	for _, keyBits := range []int{128, 192, 256} {
+		keySize := keyBits / 8
+		b.Run(strconv.Itoa(keyBits), func(b *testing.B) {
+			b.Run("50", func(b *testing.B) {
+				benchmarkAESStream(b, cipher.NewCTR, make([]byte, 50), keySize)
+			})
+			b.Run("1K", func(b *testing.B) {
+				benchmarkAESStream(b, cipher.NewCTR, make([]byte, almost1K), keySize)
+			})
+			b.Run("8K", func(b *testing.B) {
+				benchmarkAESStream(b, cipher.NewCTR, make([]byte, almost8K), keySize)
+			})
+		})
+	}
 }
 
 func BenchmarkAESCBCEncrypt1K(b *testing.B) {
diff --git a/src/crypto/cipher/ctr_aes_test.go b/src/crypto/cipher/ctr_aes_test.go
index 9b7d30e2164422..1d8ae78674ebe2 100644
--- a/src/crypto/cipher/ctr_aes_test.go
+++ b/src/crypto/cipher/ctr_aes_test.go
@@ -17,6 +17,7 @@ import (
 	"crypto/internal/boring"
 	"crypto/internal/cryptotest"
 	fipsaes "crypto/internal/fips140/aes"
+	"encoding/binary"
 	"encoding/hex"
 	"fmt"
 	"math/rand"
@@ -117,6 +118,60 @@ func makeTestingCiphers(aesBlock cipher.Block, iv []byte) (genericCtr, multibloc
 	return cipher.NewCTR(wrap(aesBlock), iv), cipher.NewCTR(aesBlock, iv)
 }
 
+// TestCTR_AES_blocks8FastPathMatchesGeneric ensures the overlow aware branch
+// produces identical keystreams to the generic counter walker across
+// representative IVs, including near-overflow cases.
+func TestCTR_AES_blocks8FastPathMatchesGeneric(t *testing.T) {
+	key := make([]byte, aes.BlockSize)
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, ok := block.(*fipsaes.Block); !ok {
+		t.Skip("requires crypto/internal/fips140/aes")
+	}
+
+	keystream := make([]byte, 8*aes.BlockSize)
+
+	testCases := []struct {
+		name string
+		hi   uint64
+		lo   uint64
+	}{
+		{"Zero", 0, 0},
+		{"NearOverflowMinus7", 1, ^uint64(0) - 7},
+		{"NearOverflowMinus6", 2, ^uint64(0) - 6},
+		{"Overflow", 0, ^uint64(0)},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			var iv [aes.BlockSize]byte
+			binary.BigEndian.PutUint64(iv[0:8], tc.hi)
+			binary.BigEndian.PutUint64(iv[8:], tc.lo)
+
+			generic, multiblock := makeTestingCiphers(block, iv[:])
+
+			genericOut := make([]byte, len(keystream))
+			multiblockOut := make([]byte, len(keystream))
+
+			generic.XORKeyStream(genericOut, keystream)
+			multiblock.XORKeyStream(multiblockOut, keystream)
+
+			if !bytes.Equal(multiblockOut, genericOut) {
+				t.Fatalf("mismatch for iv %#x:%#x\n"+
+					"asm keystream: %x\n"+
+					"gen keystream: %x\n"+
+					"asm counters: %x\n"+
+					"gen counters: %x",
+					tc.hi, tc.lo, multiblockOut, genericOut,
+					extractCounters(block, multiblockOut),
+					extractCounters(block, genericOut))
+			}
+		})
+	}
+}
+
 func randBytes(t *testing.T, r *rand.Rand, count int) []byte {
 	t.Helper()
 	buf := make([]byte, count)
@@ -297,3 +352,12 @@ func TestCTR_AES_multiblock_XORKeyStreamAt(t *testing.T) {
 		})
 	}
 }
+
+func extractCounters(block cipher.Block, keystream []byte) []byte {
+	blockSize := block.BlockSize()
+	res := make([]byte, len(keystream))
+	for i := 0; i < len(keystream); i += blockSize {
+		block.Decrypt(res[i:i+blockSize], keystream[i:i+blockSize])
+	}
+	return res
+}
diff --git a/src/crypto/internal/fips140/aes/_asm/ctr/ctr_amd64_asm.go b/src/crypto/internal/fips140/aes/_asm/ctr/ctr_amd64_asm.go
index 775d4a8acc5969..e3dbdf66d70e1c 100644
--- a/src/crypto/internal/fips140/aes/_asm/ctr/ctr_amd64_asm.go
+++ b/src/crypto/internal/fips140/aes/_asm/ctr/ctr_amd64_asm.go
@@ -40,19 +40,79 @@ func ctrBlocks(numBlocks int) {
 	bswap := XMM()
 	MOVOU(bswapMask(), bswap)
 
-	blocks := make([]VecVirtual, 0, numBlocks)
+	blocks := make([]VecVirtual, numBlocks)
+
+	// For the 8-block case we optimize counter generation. We build the first
+	// counter as usual, then check whether the remaining seven increments will
+	// overflow. When they do not (the common case) we keep the work entirely in
+	// XMM registers to avoid expensive general-purpose -> XMM moves. Otherwise
+	// we fall back to the traditional scalar path.
+	if numBlocks == 8 {
+		for i := range blocks {
+			blocks[i] = XMM()
+		}
 
-	// Lay out counter block plaintext.
-	for i := 0; i < numBlocks; i++ {
-		x := XMM()
-		blocks = append(blocks, x)
-
-		MOVQ(ivlo, x)
-		PINSRQ(Imm(1), ivhi, x)
-		PSHUFB(bswap, x)
-		if i < numBlocks-1 {
-			ADDQ(Imm(1), ivlo)
-			ADCQ(Imm(0), ivhi)
+		base := XMM()
+		tmp := GP64()
+		addVec := XMM()
+
+		MOVQ(ivlo, blocks[0])
+		PINSRQ(Imm(1), ivhi, blocks[0])
+		MOVAPS(blocks[0], base)
+		PSHUFB(bswap, blocks[0])
+
+		// Check whether any of these eight counters will overflow.
+		MOVQ(ivlo, tmp)
+		ADDQ(Imm(uint64(numBlocks-1)), tmp)
+		slowLabel := fmt.Sprintf("ctr%d_slow", numBlocks)
+		doneLabel := fmt.Sprintf("ctr%d_done", numBlocks)
+		JC(LabelRef(slowLabel))
+
+		// Fast branch: create an XMM increment vector containing the value 1.
+		// Adding it to the base counter yields each subsequent counter.
+		XORQ(tmp, tmp)
+		INCQ(tmp)
+		PXOR(addVec, addVec)
+		PINSRQ(Imm(0), tmp, addVec)
+
+		for i := 1; i < numBlocks; i++ {
+			PADDQ(addVec, base)
+			MOVAPS(base, blocks[i])
+		}
+		JMP(LabelRef(doneLabel))
+
+		Label(slowLabel)
+		ADDQ(Imm(1), ivlo)
+		ADCQ(Imm(0), ivhi)
+		for i := 1; i < numBlocks; i++ {
+			MOVQ(ivlo, blocks[i])
+			PINSRQ(Imm(1), ivhi, blocks[i])
+			if i < numBlocks-1 {
+				ADDQ(Imm(1), ivlo)
+				ADCQ(Imm(0), ivhi)
+			}
+		}
+
+		Label(doneLabel)
+
+		// Convert little-endian counters to big-endian after the branch since
+		// both paths share the same shuffle sequence.
+		for i := 1; i < numBlocks; i++ {
+			PSHUFB(bswap, blocks[i])
+		}
+	} else {
+		// Lay out counter block plaintext.
+		for i := 0; i < numBlocks; i++ {
+			x := XMM()
+			blocks[i] = x
+
+			MOVQ(ivlo, x)
+			PINSRQ(Imm(1), ivhi, x)
+			PSHUFB(bswap, x)
+			if i < numBlocks-1 {
+				ADDQ(Imm(1), ivlo)
+				ADCQ(Imm(0), ivhi)
+			}
 		}
 	}
 
diff --git a/src/crypto/internal/fips140/aes/ctr_amd64.s b/src/crypto/internal/fips140/aes/ctr_amd64.s
index e6710834dd27e6..deef3e7705a5b3 100644
--- a/src/crypto/internal/fips140/aes/ctr_amd64.s
+++ b/src/crypto/internal/fips140/aes/ctr_amd64.s
@@ -286,41 +286,68 @@ TEXT ·ctrBlocks8Asm(SB), $0-48
 	MOVOU  bswapMask<>+0(SB), X0
 	MOVQ   SI, X1
 	PINSRQ $0x01, DI, X1
+	MOVAPS X1, X8
 	PSHUFB X0, X1
+	MOVQ   SI, R8
+	ADDQ   $0x07, R8
+	JC     ctr8_slow
+	XORQ   R8, R8
+	INCQ   R8
+	PXOR   X9, X9
+	PINSRQ $0x00, R8, X9
+	PADDQ  X9, X8
+	MOVAPS X8, X2
+	PADDQ  X9, X8
+	MOVAPS X8, X3
+	PADDQ  X9, X8
+	MOVAPS X8, X4
+	PADDQ  X9, X8
+	MOVAPS X8, X5
+	PADDQ  X9, X8
+	MOVAPS X8, X6
+	PADDQ  X9, X8
+	MOVAPS X8, X7
+	PADDQ  X9, X8
+	MOVAPS X8, X8
+	JMP    ctr8_done
+
+ctr8_slow:
 	ADDQ   $0x01, SI
 	ADCQ   $0x00, DI
 	MOVQ   SI, X2
 	PINSRQ $0x01, DI, X2
-	PSHUFB X0, X2
 	ADDQ   $0x01, SI
 	ADCQ   $0x00, DI
 	MOVQ   SI, X3
 	PINSRQ $0x01, DI, X3
-	PSHUFB X0, X3
 	ADDQ   $0x01, SI
 	ADCQ   $0x00, DI
 	MOVQ   SI, X4
 	PINSRQ $0x01, DI, X4
-	PSHUFB X0, X4
 	ADDQ   $0x01, SI
 	ADCQ   $0x00, DI
 	MOVQ   SI, X5
 	PINSRQ $0x01, DI, X5
-	PSHUFB X0, X5
 	ADDQ   $0x01, SI
 	ADCQ   $0x00, DI
 	MOVQ   SI, X6
 	PINSRQ $0x01, DI, X6
-	PSHUFB X0, X6
 	ADDQ   $0x01, SI
 	ADCQ   $0x00, DI
 	MOVQ   SI, X7
 	PINSRQ $0x01, DI, X7
-	PSHUFB X0, X7
 	ADDQ   $0x01, SI
 	ADCQ   $0x00, DI
 	MOVQ   SI, X8
 	PINSRQ $0x01, DI, X8
+
+ctr8_done:
+	PSHUFB X0, X2
+	PSHUFB X0, X3
+	PSHUFB X0, X4
+	PSHUFB X0, X5
+	PSHUFB X0, X6
+	PSHUFB X0, X7
 	PSHUFB X0, X8
 	MOVUPS (CX), X0
 	PXOR   X0, X1