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# HF-20210515
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The May 2021 protocol upgrade was the first to be comprised of [CHIPs ](#chips ).
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## CHIPs
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A CasH Improvement Proposal (CHIP) is a change request for the BitcoinCash protocol.
CHIPs can be written and published by any member of the BitcoinCash community.
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They are evaluated publicly, giving the authors an opportunity to make any clarifications or adjustments based on feedback from the rest of the community.
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Once there is sufficient support for a CHIP amongst node developers, it is scheduled for release in a future protocol upgrade.
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Changes from multiple CHIPs may be included in a single protocol upgrade.
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## Contents
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The May 2021 protocol upgrade is comprised the following CHIPs:
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1. [Unconfirmed Transaction Chain Limit ](/protocol/forks/chips/2021-05-unconfirmed-transaction-chain-limit )
2. [Multiple OP_RETURNs for Bitcoin Cash ](/protocol/forks/chips/2021-05-multiple-op-returns-for-bitcoin-cash )
