Fee Structure

PAX offers two account types: free tier and λ tier. Every PAX participant has access to both account types with free tier as the default. Use of the λ API is fee-based and opt-in.

Account	Order entry (REST)	λ programs	WebSocket feeds	Fees	Rebates
λ	Yes	Yes	Yes	Yes	No
Free tier	Yes	No	Yes	No	When paired with λ

For λ accounts, all orders – whether placed over the network using the PAX limit order API or placed from on-chip by a λ program – are subject to a fee when filled. See Lambda API access for how λ accounts are used.

Free tier rebates

Free tier accounts are not charged a fee for trading.

Category	Counterparty	Rebate
Maker or Taker	λ tier	1/2 of λ fee [1]
Maker or Taker	Free tier	No rebate

Note 1. The free tier rebate is capped at a maximum of 0.25 bps and is normally 1/2 of the fee paid by the λ counterparty order.

λ tier fees

Category	Counterparty	Fee
Maker	λ or free tier	1/4 of spread [2]
Taker	λ or free tier	0.5 bps [3]

Note 2. The λ maker fee is capped at a maximum of 2 bps and is normally 1/4 of the spread based on that order’s limit price and the opposite side best price at the time of the fill.

Note 3. PAX will introduce λ priority tiers at 1.0 bps, 1.5 bps, 3.0 bps, and 4.5 bps. The λ priority tiers are opt-in and fairly price priority to match the size of the opportunity.

Fee & rebate calculations

For fee calculation, a λ maker’s spread is the difference between its limit price and the best price on the other side of the book at the time of the fill, with a minimum of 1 tick. If the opposite side is empty, the maker pays the 2 bps cap. The 1 tick minimum applies, for example, when the maker is filled by a GTC limit order that rests its remaining quantity after taking.

Fees and rebates are calculated on each fill’s value and settled in USDC. Fees round up and rebates round down to the nearest 0.000001 USDC.

Each order status update reports the fee or rebate for that fill in fee_rebate, in quote asset native units: negative for a fee, positive for a rebate.

Common scenarios

Taker	Maker	Scenario
Free tier	λ	Market makers use λs to quote new price levels & to cancel to avoid bad fills.
λ	Free tier	Free tier limit orders naturally pair with HFT takers using λ programs.
λ	λ	Unlikely because λ makers cancel on the same market signals that λ takers act on.
Free tier	Free tier	Unlikely because time priority naturally pairs free tier orders with λ orders.