Last Look

What Is Last Look?

Last look is a practice in electronic trading where a market maker or liquidity provider (LP) receives a client's trade request and then gets a final opportunity to accept or reject it before execution. During this brief hold window, the LP can check whether the price has moved against them since the quote was issued. If it has, they reject the trade. If the price is still favorable or unchanged, they fill it.

The practice originated in foreign exchange markets during the early days of electronic trading. When dealers transitioned from voice-based to screen-based execution, they needed a mechanism to guard against stale prices and verify credit availability. The FX Global Code, maintained by the Global Foreign Exchange Committee (GFXC), formally defines last look under Principle 17 as "a practice utilized in Electronic Trading Activities whereby a Market Participant receiving a trade request has a final opportunity to accept or reject the request against its quoted price."

What began as a risk management tool has become one of the most contentious topics in market microstructure. Critics argue that last look gives LPs a free option at the client's expense: the LP can observe the direction of the market during the hold window and cherry-pick which trades to fill.

How It Works

A last look transaction follows a specific sequence that differs from standard firm-quote execution:

1. The LP streams a quoted price to the client (or responds to an RFQ)
2. The client accepts the price and submits a trade request
3. The LP receives the request and starts its hold timer (the last look window)
4. During the window, the LP checks whether the market has moved against the quoted price
5. The LP decides to accept or reject based on price movement, credit checks, and internal risk limits
6. If accepted, the trade executes at the originally quoted price. If rejected, the client must seek a new quote

The hold window has shortened considerably over time. Data from NEX Markets showed that average hold times among top liquidity providers on EBS Direct fell from 93 milliseconds to 37 milliseconds over an 18-month period. XTX Markets, one of the largest non-bank FX market makers, moved to a zero-hold-time model, arguing that modern systems can complete a price validity check in roughly five milliseconds.

The Free Option Problem

The core controversy centers on what economists call the free option problem. During the hold window, the LP holds a costless option on the trade: if the market moves in the LP's favor, they accept. If it moves against them, they reject. The client bears all the downside of this asymmetry.

Consider a client requesting to buy EUR/USD at 1.1000. During a 50-millisecond hold window:

• If EUR/USD drops to 1.0998, the LP accepts: they sell at 1.1000 and can immediately hedge at 1.0998, locking in a 2-pip profit
• If EUR/USD rises to 1.1002, the LP rejects: the client must now buy at a worse price, experiencing slippage

This asymmetric outcome means the LP profits from volatility during the window while the client absorbs the cost. The longer the hold time, the larger the free option value.

Symmetric vs. Asymmetric Last Look

Not all last look implementations work the same way. The distinction between symmetric and asymmetric application matters:

The FX Global Code discourages asymmetric application. Principle 17 states that any hold time beyond what is needed for a legitimate price validity check is contrary to good market practice.

Last Look in Crypto Markets

Last look has migrated from traditional FX into crypto markets, primarily through two channels:

• OTC desks: institutional crypto OTC desks that evolved from FX dealing operations often carry over last look practices. When a client requests a large block trade, the desk may hold the request briefly before confirming execution
• RFQ platforms: crypto request-for-quote systems, where clients solicit competing quotes from multiple dealers, may allow quoting parties a last look window before their quotes become firm

On-chain decentralized exchanges operate differently. An AMM executes against a deterministic pricing formula: there is no counterparty to reject the trade. However, on-chain execution introduces its own form of information asymmetry through maximal extractable value (MEV). Validators and block builders can observe pending transactions and reorder them for profit, a dynamic that parallels the informational advantage of last look in traditional markets.

Connection to MEV and Fair Ordering

The debate over last look in traditional finance mirrors the fair ordering debate in crypto. Both center on the same question: should a privileged party be allowed to observe pending orders and act on that information before execution?

• In FX, the LP sees the client's order during the hold window and can reject or pre-hedge
• In crypto, a block builder sees pending mempool transactions and can front-run, sandwich, or reorder them

Both scenarios involve adverse selection: the informed party (LP or block builder) selectively engages with order flow based on private information about price direction. High-frequency trading firms exploit this in both contexts, using speed advantages to identify and capture mispriced orders before slower participants can react.

Firm Quotes vs. Last Look

The alternative to last look is the firm-quote (or firm-liquidity) model. On a firm venue, every quoted price is immediately executable. When a client hits a quote, the trade executes without any review window.

Six of the largest non-bank FX market makers, including Citadel Securities, Jump Trading, and Virtu Financial, have publicly called for last look to be abolished in favor of firm pricing. Their argument: modern technology makes the risk-management justification obsolete.

Use Cases

Despite the controversy, last look serves legitimate functions in certain market conditions:

• Latency arbitrage protection: when a client exploits stale quotes using faster market data feeds, last look lets the LP reject trades that are only profitable because of speed advantages, not genuine trading intent
• Credit risk management: the hold window allows the LP to verify that the counterparty has sufficient credit before committing to the trade, preventing exposure to uncreditworthy counterparties
• Tighter spreads for retail flow: because LPs can filter out toxic order flow, they can afford to quote tighter bid-ask spreads to genuine retail and corporate clients
• Illiquid market conditions: during periods of extreme volatility or thin liquidity, last look prevents LPs from being forced to honor quotes that are wildly out of date, which could otherwise cause them to withdraw from the market entirely

Risks and Considerations

Regulatory Enforcement

Regulators have taken action against abusive last look practices. Barclays was fined $150 million by the New York Department of Financial Services in 2015 for using last look to systematically reject client trades. Credit Suisse received a $135 million fine in 2017, partly for failing to disclose its last look practices to clients. These cases established that non-disclosure of last look and asymmetric application can constitute market misconduct.

Hidden Execution Costs

For price takers (clients), last look introduces hidden costs that do not appear in standard best execution analysis. A client may see a tight quoted spread but experience high rejection rates, forcing them to execute at worse prices. The effective cost of trading includes not just the spread but also the cost of rejected trades and subsequent slippage.

Information Leakage

Every rejected trade reveals the client's intent to the LP. Even when a trade is rejected, the LP now knows the client wanted to buy or sell a specific size at a specific price. This information can influence the LP's own positioning. The UK Investment Association has called this a form of payment for order flow in reverse: instead of paying for the right to see orders, the LP gets that information for free through the last look window.

Impact on Market Structure

When last look is widespread, it changes which participants can profitably provide liquidity. Firm-quote venues reward market makers who price accurately in real time. Last look venues reward market makers who are best at filtering order flow after the fact. This can lead to a market structure where the fastest rejectors, rather than the best pricers, dominate liquidity provision.

Why It Matters for Crypto

As institutional participants bring traditional market-making practices into crypto, understanding last look is essential for evaluating execution quality. Traders using OTC desks or RFQ platforms should ask whether the LP retains last look rights and what the hold window duration is.

For on-chain protocols, the last look debate informs the design of fair ordering mechanisms and order flow auctions. Solutions like encrypted mempools and batch auctions aim to eliminate the information advantage that parallels last look in decentralized systems. For a deeper analysis of how market structure affects execution quality in crypto, see the research on DeFi perpetual DEX market structure.

This glossary entry is for informational purposes only and does not constitute financial or investment advice. Always do your own research before using any protocol or technology.