Subject: [bitcoindev] CTV + CSFS: a letter

From: James O'Beirne <[email-masked]>
Date: Mon, 9 Jun 2025 04:40:52 -0700 (PDT)

Good morning,

A letter has been published advocating for the final review and
activation of OP_CHECKTEMPLATEVERIFY (BIP-119) and OP_CHECKSIGFROMSTACK
(BIP-348). 

The full text of the letter can be found at https://ctv-csfs.com. It is
reproduced below.

---

To the technical bitcoin community,

We believe that the best next step for bitcoin would be to activate
OP_CHECKTEMPLATEVERIFY (CTV, BIP-119) and OP_CHECKSIGFROMSTACK (CSFS,
BIP-348). These opcodes enable functionality for a broad set of uses
that will allow bitcoin to preserve and expand its role as a scarce,
censorship-resistant store of value.

While there are a few promising proposals to improve bitcoin at the
consensus layer which may someday be deployed, we believe that CTV and
CSFS are uniquely well reviewed, simple, and have been proven to be both
safe and widely demanded.

CTV was first formalized in BIP-119 over 5 years ago. Despite many
attempts at refinement or replacement, it has remained the most widely
preferred method for enforcing pregenerated transaction sequences using
consensus. It unlocks valuable functionality for scaling solutions,
vaults, congestion control, non-custodial mining, discreet log
contracts, and more.

CSFS is a primitive opcode that has been deployed to Blockstream’s
Elements for at least 8 years. It represents no significant
computational burden over bitcoin’s most often used opcode, OP_CHECKSIG.
It can be combined with CTV to implement ln-symmetry, a longstanding
improvement to Lightning. It also unlocks a variety of other use cases.

We respectfully ask Bitcoin Core contributors to prioritize the review
and integration of CTV (PR #31989 or similar) and CSFS (PR #32247 or
similar) within the next six months. We believe this timeline allows for
rigorous final review and activation planning.

This request isn't meant to suggest that these contributors dictate the
consensus process, but rather it is an acknowledgement that before these
opcodes can be activated, they must be implemented in the most widely
used bitcoin client.

As application and protocol developers, we are convinced of the
significant benefits that these changes would bring to end users of
bitcoin – even if only considering their use for layer 1 security and
layer 2 scaling solutions. We are optimistic that given the limited size
and scope of these changes in both concept and implementation, they
represent a realistic next step in the continuing and important work of
preserving bitcoin's unique promise.

Signed, 

Abdel (Starkware)
Andrew Poelstra (@apoelstra)
Ben Carman (@benthecarman)
Ben Kaufman (@ben-kaufman)
Brandon Black (@reardencode)
Brian Langel (for Five Bells)
Buck Perley (@puckberley)
Calle (Cashu)
Calvin Kim (@kcalvinalvin)
Chun Wang (f2pool)
Christian Decker (@cdecker)
Coinjoined Chris (Bitsurance.eu)
Evan Kaloudis (for Zeus)
fiatjaf (@fiatjaf)
Floppy (@1440000bytes)
Gary Krause (@average-gary)
Harsha Goli (@arshbot)
Hunter Beast (@cryptoquick)
Jad Mubaslat (@champbronc2)
James O’Beirne (@jamesob)
Jameson Lopp (@jlopp)
Johan Halseth (@halseth)
Luke Childs (@lukechilds)
Matt Black (for Atomic Finance)
Michael Tidwell (@miketwenty1)
Nick Hansen (for Luxor Mining)
Nitesh (@nitesh_btc)
nvk (@nvk)
Owen Kemeys (for Foundation)
Paul Sztorc (@psztorc)
Portland.HODL (for MARA Pool)
Rijndael (@rot13maxi)
Rob Hamilton (@rob1ham)
Robin Linus (@RobinLinus)
Sanket Kanjalkar (@sanket1729)
Sean Ryan (Anchorage)
Seth for Privacy (for Cake Wallet)
Simanta Gautam (Alpen Labs)
Steven Roose (@stevenroose)
stutxo (@stutxo)
Talip (@otaliptus)
mononaut (@mononautical)
vnprc (@vnprc)

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