diff --git a/lib/bcoin/miner.js b/lib/bcoin/miner.js
index a82c34ca..a5f0b4b5 100644
--- a/lib/bcoin/miner.js
+++ b/lib/bcoin/miner.js
@@ -339,8 +339,6 @@ Miner.prototype.mineBlock = function mineBlock(version, callback) {
  */
 
 function MinerBlock(options) {
-  var i;
-
   if (!(this instanceof MinerBlock))
     return new MinerBlock(options);
 
@@ -348,77 +346,96 @@ function MinerBlock(options) {
   this.workerPool = options.workerPool;
   this.tip = options.tip;
   this.height = options.tip.height + 1;
-  this.target = utils.fromCompact(options.target).toArrayLike(Buffer, 'le', 32);
+  this.bits = options.target;
+  this.target = utils.fromCompact(this.bits).toArrayLike(Buffer, 'le', 32);
   this.extraNonce = new bn(0);
   this.iterations = 0;
   this.coinbaseFlags = options.coinbaseFlags;
   this.witness = options.witness;
   this.address = options.address;
-  this.witnessNonce = null;
   this.network = bcoin.network.get(options.network);
 
-  // Create a coinbase
-  this.coinbase = new bcoin.mtx();
+  this.coinbase = new bcoin.tx();
+  this.coinbase.mutable = true;
 
-  this.coinbase.addInput({
-    prevout: {
-      hash: constants.NULL_HASH,
-      index: 0xffffffff
-    },
-    coin: null,
-    script: bcoin.script.fromArray([
-      // Height (required in v2+ blocks)
-      bcoin.script.array(this.height),
-      // extraNonce - incremented when
-      // the nonce overflows.
-      bcoin.script.array(0),
-      // Add a nonce to ensure we don't
-      // collide with a previous coinbase
-      // of ours. This isn't really
-      // necessary nowdays due to bip34
-      // (used above).
-      bcoin.script.array(utils.nonce()),
-      // Let the world know this little
-      // miner succeeded.
-      new Buffer(this.coinbaseFlags, 'utf8')
-    ]),
-    witness: new bcoin.witness(),
-    sequence: 0xffffffff
-  });
+  this.block = new bcoin.block();
+  this.block.mutable = true;
 
-  this.coinbase.addOutput({
-    address: this.address,
-    value: 0
-  });
+  this._init();
+}
 
-  // Create our block
-  this.block = new bcoin.block({
-    mutable: true,
-    version: options.version,
-    prevBlock: this.tip.hash,
-    merkleRoot: constants.NULL_HASH,
-    ts: Math.max(bcoin.now(), this.tip.ts + 1),
-    bits: options.target,
-    nonce: 0,
-    height: this.height
-  });
+/**
+ * Initialize the block.
+ * @private
+ */
 
-  this.block.addTX(this.coinbase);
+MinerBlock.prototype._init = function _init() {
+  var options = this.options;
+  var block = this.block;
+  var cb = this.coinbase;
+  var i, input, output, hash, witnessNonce;
+
+  // Coinbase input.
+  input = new bcoin.input();
+
+  // Height (required in v2+ blocks)
+  input.script.set(0, new bn(this.height));
+
+  // extraNonce - incremented when
+  // the nonce overflows.
+  input.script.set(1, this.extraNonce);
+
+  // Add a nonce to ensure we don't
+  // collide with a previous coinbase
+  // of ours. This isn't really
+  // necessary nowdays due to bip34
+  // (used above).
+  input.script.set(2, utils.nonce());
+
+  // Let the world know this little
+  // miner succeeded.
+  input.script.set(3, this.coinbaseFlags);
+
+  input.script.compile();
+
+  cb.inputs.push(input);
+
+  // Reward output.
+  output = new bcoin.output();
+  output.script = bcoin.script.fromAddress(this.address);
+
+  cb.outputs.push(output);
+
+  // If we're using segwit, we need to
+  // set up the nonce and commitment.
+  if (this.witness) {
+    // Our witness nonce is the hash256
+    // of the previous block hash.
+    hash = new Buffer(this.tip.hash, 'hex');
+    witnessNonce = utils.hash256(hash);
+
+    // Set up the witness nonce.
+    input.witness.set(0, witnessNonce);
+    input.witness.compile();
+
+    // Commitment output.
+    cb.outputs.push(new bcoin.output());
+  }
+
+  // Setup our block.
+  block.version = options.version;
+  block.prevBlock = this.tip.hash;
+  block.merkleRoot = constants.NULL_HASH;
+  block.ts = Math.max(bcoin.now(), this.tip.ts + 1);
+  block.bits = this.bits;
+  block.nonce = 0;
+  block.height = this.height;
+
+  block.addTX(cb);
 
   if (options.txs) {
     for (i = 0; i < options.txs.length; i++)
-      this.block.addTX(options.txs[i]);
-  }
-
-  if (this.witness) {
-    // Set up the witness nonce and
-    // commitment output for segwit.
-    this.witnessNonce = utils.hash256(new Buffer(this.tip.hash, 'hex'));
-    this.coinbase.inputs[0].witness.items[0] = this.witnessNonce;
-    this.coinbase.addOutput({
-      script: new bcoin.script(),
-      value: 0
-    });
+      block.addTX(options.txs[i]);
   }
 
   // Update coinbase since our coinbase was added.
@@ -436,20 +453,29 @@ utils.inherits(MinerBlock, EventEmitter);
 
 MinerBlock.prototype.updateCommitment = function updateCommitment() {
   var output = this.coinbase.outputs[1];
-  var hash = this.block.getCommitmentHash();
-  var commit = bcoin.script.createCommitment(hash, this.coinbaseFlags);
-  output.script = commit;
+  var flags = this.coinbaseFlags;
+  var hash;
+
+  // Recalculate witness merkle root.
+  hash = this.block.getCommitmentHash();
+
+  // Update commitment.
+  output.script = bcoin.script.fromCommitment(hash, flags);
 };
 
 /**
- * Update the extranonce and coinbase reward.
+ * Update the extra nonce and coinbase reward.
  */
 
 MinerBlock.prototype.updateCoinbase = function updateCoinbase() {
   var input = this.coinbase.inputs[0];
   var output = this.coinbase.outputs[0];
+
+  // Update extra nonce.
   input.script.set(1, this.extraNonce);
   input.script.compile();
+
+  // Update reward.
   output.value = this.block.getReward(this.network);
 };
 
@@ -465,7 +491,10 @@ MinerBlock.prototype.updateMerkle = function updateMerkle() {
   if (this.witness)
     this.updateCommitment();
 
+  // Update timestamp.
   this.block.ts = Math.max(bcoin.now(), this.tip.ts + 1);
+
+  // Recalculate merkle root.
   this.block.merkleRoot = this.block.getMerkleRoot('hex');
 };
 
@@ -609,8 +638,6 @@ MinerBlock.prototype.mine = function mine(callback) {
     if (!self.findNonce())
       return self.mine(callback);
 
-    self.block.txs[0] = self.block.txs[0].toTX();
-
     return callback(null, self.block);
   }, 100);
 };
@@ -622,7 +649,6 @@ MinerBlock.prototype.mine = function mine(callback) {
 
 MinerBlock.prototype.mineSync = function mineSync() {
   while (!this.findNonce());
-  this.block.txs[0] = this.block.txs[0].toTX();
   return this.block;
 };
 
diff --git a/lib/bcoin/script.js b/lib/bcoin/script.js
index f9d877a6..772f8ede 100644
--- a/lib/bcoin/script.js
+++ b/lib/bcoin/script.js
@@ -2568,7 +2568,7 @@ Script.fromAddress = function fromAddress(address) {
  * @returns {Script}
  */
 
-Script.createCommitment = function createCommitment(hash, flags) {
+Script.fromCommitment = function fromCommitment(hash, flags) {
   var p;
 
   if (!flags)