diff --git a/web3/builder_api_callsigs.nim b/web3/builder_api_callsigs.nim
index c05167f..8c72112 100644
--- a/web3/builder_api_callsigs.nim
+++ b/web3/builder_api_callsigs.nim
@@ -1,6 +1,10 @@
-# https://github.com/flashbots/mev-boost/blob/thegostep/docs/docs/milestone-1.md#api-docs
-
 import ethtypes, builder_api_types, engine_api_types
 
-proc builder_getPayloadHeaderV1(payloadId: PayloadID): ExecutionPayloadHeaderV1
-proc builder_proposeBlindedBlockV1(blck: SignedBlindedBeaconBlock): ExecutionPayloadV1
+# https://github.com/flashbots/mev-boost/blob/thegostep/docs/docs/milestone-1.md#api-docs
+# but not what's in the actual code
+# proc builder_getPayloadHeaderV1(payloadId: PayloadID): ExecutionPayloadHeaderV1
+# proc builder_proposeBlindedBlockV1(blck: SignedBlindedBeaconBlock): ExecutionPayloadV1
+
+# https://github.com/flashbots/mev-boost/blob/thegostep/docs/lib/service.go
+proc builder_getPayloadHeaderV1(payloadId: PayloadID): ExecutionPayloadWithTxRootV1
+proc builder_proposeBlindedBlockV1(blck: SignedBlindedBeaconBlock): ExecutionPayloadWithTxRootV1
diff --git a/web3/builder_api_types.nim b/web3/builder_api_types.nim
index 1be133f..959656b 100644
--- a/web3/builder_api_types.nim
+++ b/web3/builder_api_types.nim
@@ -1,47 +1,57 @@
 import
+  stint,
   ethtypes
 
 export
   ethtypes
 
 type
-  # https://github.com/ethereum/consensus-specs/blob/v1.1.9/specs/bellatrix/beacon-chain.md#executionpayloadheader
-  ExecutionPayloadHeaderV1* = object
-    parent_hash*: FixedBytes[32]
-    fee_recipient*: Address
-    state_root*: FixedBytes[32]
-    receipts_root*: FixedBytes[32]
-    logs_bloom*: FixedBytes[256]
+  # https://github.com/flashbots/mev-boost/blob/thegostep/docs/lib/types.go#L34
+  ExecutionPayloadWithTxRootV1* = object
+    parentHash*: FixedBytes[32]
+    feeRecipient*: Address
+    stateRoot*: FixedBytes[32]
+    receiptsRoot*: FixedBytes[32]
+    logsBloom*: string # FixedBytes[256]
     random*: FixedBytes[32]
-    block_number*: Quantity
-    gas_limit*: Quantity
-    gas_used*: Quantity
+    blockNumber*: Quantity
+    gasLimit*: Quantity
+    gasUsed*: Quantity
     timestamp*: Quantity
-    extra_data*: string    # List[byte, MAX_EXTRA_DATA_BYTES]
-    base_fee_per_gas*: FixedBytes[32]  # base fee introduced in EIP-1559, little-endian serialized
+    extraData*: string    # List[byte, MAX_EXTRA_DATA_BYTES]
+    baseFeePerGas*: Uint256  # base fee introduced in EIP-1559, little-endian serialized
+    blockHash*: FixedBytes[32]
+    #transactions: seq[string]
+    transactionsRoot*: FixedBytes[32]
 
-  # https://github.com/flashbots/mev-boost/blob/thegostep/docs/docs/milestone-1.md#blindedbeaconblockbody
-  BlindedBeaconBlockBody* = object
-    randao_reveal*: FixedBytes[96]
-    eth1_data*: string # Eth1Data
-    graffiti*: FixedBytes[32]
-    proposer_slashings*: string # List[ProposerSlashing, MAX_PROPOSER_SLASHINGS]
-    attester_slashings*: string # List[AttesterSlashing, MAX_ATTESTER_SLASHINGS]
-    attestations*: string # List[Attestation, MAX_ATTESTATIONS]
-    voluntary_exits*: string # List[SignedVoluntaryExit, MAX_VOLUNTARY_EXITS]
-    sync_aggregate*: string # SyncAggregate
-    execution_payload_header*: ExecutionPayloadHeaderV1
+  ExecutionPayloadHeaderOnlyBlockHash* = object
+    # Another of these either-snake-or-camel definitions
+    # also why use common.Hash elsewhere but string here as block type? Either
+    # works, but.
+    blockHash*: string
+
+  # https://github.com/flashbots/mev-boost/blob/thegostep/docs/lib/types.go#L26
+  BlindedBeaconBlockBodyPartial* = object
+    execution_payload_header*: ExecutionPayloadHeaderOnlyBlockHash
+    # Either snake_case or camelCase is allowed, or both:
+    # https://github.com/flashbots/mev-boost/blob/thegostep/docs/lib/service.go#L157
 
   # https://github.com/flashbots/mev-boost/blob/thegostep/docs/docs/milestone-1.md#blindedbeaconblock
+  # https://github.com/flashbots/mev-boost/blob/thegostep/docs/lib/types.go#L17
   BlindedBeaconBlock* = object
-    slot*: Quantity
+    # These are snake case, while, e.g. ExecutionPayloadWithTxRootV1 is
+    # camelCase. And others, such as BlindedBeaconBlockBodyPartial, can be either
+    # proposer_index, parent_root, and state_root are all strings for MEV
+    slot*: Quantity    # MEV builder service uses string here
     proposer_index*: Quantity
     parent_root*: FixedBytes[32]
     state_root*: FixedBytes[32]
-    body*: BlindedBeaconBlockBody
+    # The MEV sevice only decodes BlindedBeaconBlockBodyPartial
+    # https://github.com/flashbots/mev-boost/blob/thegostep/docs/lib/service.go#L149
+    body*: BlindedBeaconBlockBodyPartial
 
   # https://github.com/flashbots/mev-boost/blob/thegostep/docs/docs/milestone-1.md#signedblindedbeaconblock
+  # https://github.com/flashbots/mev-boost/blob/thegostep/docs/lib/types.go#L11
   SignedBlindedBeaconBlock* = object
     message*: BlindedBeaconBlock
-    signature*: FixedBytes[96]
-    
+    signature*: FixedBytes[96]  # the MEV builder API service uses string here