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Partial fills let you execute only a portion of a quoted order size. This is useful when combining RFQ liquidity with other sources (e.g. AMM fallback), or when market conditions change and you only need part of the originally requested size.
Partial fills are only supported for self-execution (gasless=false). Gasless quotes cannot be partially filled.

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How It Works

The quote response includes a partialFillOffset field that tells you where in the transaction calldata to modify the fill amount. By default, quotes are filled fully - to partially fill, you replace the taker amount at that offset with your desired amount. Partial fill amounts must be less than the original taker_amount in the quote, specified in base units (same as the original quote), and encoded as a 64-character hex string (32 bytes, zero-padded).

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Understanding the Calldata Structure

The partialFillOffset is a word index (0-indexed) counting 32-byte segments in the encoded calldata. Each word is 32 bytes = 64 hex characters. 
0x           // Hex prefix (2 characters)
4dcebcba     // Function selector (8 characters)
[word 0]     // First 32-byte word (64 characters)
[word 1]     // Second 32-byte word (64 characters)
...
[word N]     // filledTakerAmount (64 characters) ← partialFillOffset = N
The position in the hex string is: 
position = 10 + (offset × 64)
where 10 accounts for the 0x prefix (2 chars) and the 4-byte function selector (8 chars).

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Step by Step

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1. Request a Quote

import httpx

NETWORK = "ethereum"

resp = httpx.get(
    f"https://api.bebop.xyz/pmm/{NETWORK}/v3/quote",
    params={
        "sell_tokens": "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
        "buy_tokens": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
        "sell_amounts": "1000000000000000000",  # 1 WETH
        "taker_address": "0xYourWalletAddress",
        "gasless": "false",
    },
)
quote = resp.json()
Key fields in the response:
FieldDescription
sellTokens.<token>.amountOriginally requested amount
tx.dataOriginal calldata
partialFillOffsetWord index where filledTakerAmount lives in the calldata

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2. Calculate Your Partial Fill Amount

Decide how much of the original order you want to fill. The amount must be in base units and less than the original taker_amount: 
sell_token = list(quote["sellTokens"].keys())[0]
original_amount = int(quote["sellTokens"][sell_token]["amount"])

# Fill 50% of the original order
fill_amount = original_amount // 2

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3. Modify the Calldata

Replace the fill amount in the transaction calldata at the position indicated by partialFillOffset: 
def apply_partial_fill(tx_data: str, offset: int, fill_amount: int) -> str:
    pos = 10 + offset * 64
    return (
        tx_data[:pos]
        + f"{fill_amount:064x}"
        + tx_data[pos + 64:]
    )

modified_data = apply_partial_fill(
    quote["tx"]["data"],
    quote["partialFillOffset"],
    fill_amount,
)

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4. Sign and Broadcast

From here, the flow is the same as the standard self-execution quickstart - use the modified calldata in the transaction, sign, and submit: 
from eth_account import Account
from web3 import Web3

PRIVATE_KEY = "0x<your_private_key>"
RPC_URL = "https://eth.llamarpc.com"

w3 = Web3(Web3.HTTPProvider(RPC_URL))
account = Account.from_key(PRIVATE_KEY)

# Submit with the modified calldata
tx = quote["tx"]
tx["data"] = modified_data
tx["nonce"] = w3.eth.get_transaction_count(account.address)
tx["chainId"] = quote["chainId"]

signed_tx = w3.eth.account.sign_transaction(tx, account.key)
tx_hash = w3.eth.send_raw_transaction(signed_tx.raw_transaction)
print(f"Partial fill transaction: {tx_hash.hex()}")

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Full Example

import httpx
from eth_account import Account
from web3 import Web3

PRIVATE_KEY = "0x<your_private_key_hex>"
NETWORK = "ethereum"
RPC_URL = "https://eth.llamarpc.com"
FILL_PERCENT = 50  # Fill 50% of the quoted amount

# --- 1. Request a self-execution quote ---

taker_address = "0x2e7E7cc62919eAf4c502dAC34753cFc5A29e9693"

quote_resp = httpx.get(
    f"https://api.bebop.xyz/pmm/{NETWORK}/v3/quote",
    params={
        "sell_tokens": "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
        "buy_tokens": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
        "sell_amounts": "1000000000000000000",  # 1 WETH
        "taker_address": taker_address,
        "gasless": "false",
    },
)
quote = quote_resp.json()

sell_token = list(quote["sellTokens"].keys())[0]
original_amount = int(quote["sellTokens"][sell_token]["amount"])
buy_token = list(quote["buyTokens"].values())[0]
print(
    f'Quote: sell 1 WETH -> buy ~{int(buy_token["amount"]) / 10 ** buy_token["decimals"]:.2f} USDC'
)

# --- 2. Calculate partial fill amount ---

fill_amount = original_amount * FILL_PERCENT // 100
print(f"Partial fill: {FILL_PERCENT}% -> {fill_amount} base units")

# --- 3. Splice the calldata ---

def apply_partial_fill(tx_data: str, offset: int, amount: int) -> str:
    pos = 10 + offset * 64
    return tx_data[:pos] + f"{amount:064x}" + tx_data[pos + 64 :]

modified_data = apply_partial_fill(
    quote["tx"]["data"], quote["partialFillOffset"], fill_amount
)

# --- 4. Sign and submit with modified calldata ---

w3 = Web3(Web3.HTTPProvider(RPC_URL))
account = Account.from_key(PRIVATE_KEY)

tx = quote["tx"]
tx["data"] = modified_data
tx["nonce"] = w3.eth.get_transaction_count(account.address)
tx["chainId"] = quote["chainId"]

signed_tx = w3.eth.account.sign_transaction(tx, account.key)
tx_hash = w3.eth.send_raw_transaction(signed_tx.raw_transaction)
print(f"Partial fill submitted: {tx_hash.hex()}")