* [bitcoindev] Fly Client Proposal @ 2026-04-29 21:00 Zac Mitton 2026-04-30 18:52 ` [bitcoindev] " Super Testnet 2026-05-03 16:56 ` Tom Harding 0 siblings, 2 replies; 8+ messages in thread From: Zac Mitton @ 2026-04-29 21:00 UTC (permalink / raw) To: Bitcoin Development Mailing List [-- Attachment #1.1: Type: text/plain, Size: 849 bytes --] Hi, Ive been looking into FlyClient first described here <https://www.youtube.com/watch?v=BPNs9EVxWrA&t=8386s>. I don't see any BIPs, or previous discussion in this forum about it either. On bitcoin It could allow a light-client to verify the entire work of the heaviest chain with a single ~100KB proof. It can theoretically be done as a soft-fork by injecting a single hash into the coinbase tx (similar to how segwit is committed to). What do you guy's think? -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to bitcoindev+unsubscribe@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/edb5d954-37f6-4b57-a3ce-70d92d6a9407n%40googlegroups.com. [-- Attachment #1.2: Type: text/html, Size: 1209 bytes --] ^ permalink raw reply [flat|nested] 8+ messages in thread
* [bitcoindev] Re: Fly Client Proposal 2026-04-29 21:00 [bitcoindev] Fly Client Proposal Zac Mitton @ 2026-04-30 18:52 ` Super Testnet 2026-05-01 8:42 ` Nuh.dev 2026-05-03 16:56 ` Tom Harding 1 sibling, 1 reply; 8+ messages in thread From: Super Testnet @ 2026-04-30 18:52 UTC (permalink / raw) To: Bitcoin Development Mailing List [-- Attachment #1.1: Type: text/plain, Size: 1670 bytes --] Seems pretty cool. It looks like it has similar trust assumptions as a standard light client: the light client trusts the merkle root once it is buried under several blocks of proof of work, believing that an attacker is unlikely to do all that work just to fool a light client (especially when they could have been actually mining bitcoin with all that hashrate). A nice property is that, to get started, a fly client does not have to download a variable number of block headers (namely, all of them, however many there are), only a constant number of block headers, and it's a pretty small total number. That property seems to make fly clients more efficient than standard light clients. On Wednesday, April 29, 2026 at 5:03:36 PM UTC-4 Zac Mitton wrote: > Hi, Ive been looking into FlyClient first described here > <https://www.youtube.com/watch?v=BPNs9EVxWrA&t=8386s>. I don't see any > BIPs, or previous discussion in this forum about it either. > > On bitcoin It could allow a light-client to verify the entire work of the > heaviest chain with a single ~100KB proof. > > It can theoretically be done as a soft-fork by injecting a single hash > into the coinbase tx (similar to how segwit is committed to). > > What do you guy's think? > -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to bitcoindev+unsubscribe@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/1283ada3-6231-4e18-b8a3-056a8f142babn%40googlegroups.com. [-- Attachment #1.2: Type: text/html, Size: 2421 bytes --] ^ permalink raw reply [flat|nested] 8+ messages in thread
* [bitcoindev] Re: Fly Client Proposal 2026-04-30 18:52 ` [bitcoindev] " Super Testnet @ 2026-05-01 8:42 ` Nuh.dev 2026-05-02 19:23 ` Zac Mitton 0 siblings, 1 reply; 8+ messages in thread From: Nuh.dev @ 2026-05-01 8:42 UTC (permalink / raw) To: Bitcoin Development Mailing List [-- Attachment #1.1: Type: text/plain, Size: 2222 bytes --] FlyClient is very useful compared to SPV client, especially for blockchains with much more headers per day than Bitcoin. But fortunately, this is one of the few soft forks that we don't actually need, because we can substitute with a STARK proof as you can see here; https://github.com/starkware-bitcoin/raito ... so any energy for gathering consensus for a soft fork, before Bitcoin ossifies forever, is better spent elsewhere. On Thursday, 30 April 2026 at 21:55:05 UTC+3 Super Testnet wrote: > Seems pretty cool. It looks like it has similar trust assumptions as a > standard light client: the light client trusts the merkle root once it is > buried under several blocks of proof of work, believing that an attacker is > unlikely to do all that work just to fool a light client (especially when > they could have been actually mining bitcoin with all that hashrate). A > nice property is that, to get started, a fly client does not have to > download a variable number of block headers (namely, all of them, however > many there are), only a constant number of block headers, and it's a pretty > small total number. That property seems to make fly clients more efficient > than standard light clients. > > On Wednesday, April 29, 2026 at 5:03:36 PM UTC-4 Zac Mitton wrote: > >> Hi, Ive been looking into FlyClient first described here >> <https://www.youtube.com/watch?v=BPNs9EVxWrA&t=8386s>. I don't see any >> BIPs, or previous discussion in this forum about it either. >> >> On bitcoin It could allow a light-client to verify the entire work of the >> heaviest chain with a single ~100KB proof. >> >> It can theoretically be done as a soft-fork by injecting a single hash >> into the coinbase tx (similar to how segwit is committed to). >> >> What do you guy's think? >> > -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to bitcoindev+unsubscribe@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/69c7bb7f-5bf5-40f1-a2fd-a985ec88ddd7n%40googlegroups.com. [-- Attachment #1.2: Type: text/html, Size: 3133 bytes --] ^ permalink raw reply [flat|nested] 8+ messages in thread
* [bitcoindev] Re: Fly Client Proposal 2026-05-01 8:42 ` Nuh.dev @ 2026-05-02 19:23 ` Zac Mitton 2026-05-02 21:24 ` Nuh.dev 0 siblings, 1 reply; 8+ messages in thread From: Zac Mitton @ 2026-05-02 19:23 UTC (permalink / raw) To: Bitcoin Development Mailing List [-- Attachment #1.1: Type: text/plain, Size: 2892 bytes --] It makes sense that a STARK proof can do similar, however the 2 benefits to this would be that (1) This doesnt require (any) more strict assumptions which I'm assuming STARKS do, and (2) just the sheer simplicity of its design. Sorry to bring up a touchy topic but is the STARK version quantum safe, for instance? The flyclient version requires no new cryptographic assumptions beyond the "honest mining majority" used currently. Admittedly my dumb brain understands it better. I assume it would get grouped into some larger softfork rollout... On Friday, May 1, 2026 at 5:03:47 AM UTC-4 Nuh.dev wrote: > FlyClient is very useful compared to SPV client, especially for > blockchains with much more headers per day than Bitcoin. But fortunately, > this is one of the few soft forks that we don't actually need, because we > can substitute with a STARK proof as you can see here; > https://github.com/starkware-bitcoin/raito ... so any energy for > gathering consensus for a soft fork, before Bitcoin ossifies forever, is > better spent elsewhere. > > On Thursday, 30 April 2026 at 21:55:05 UTC+3 Super Testnet wrote: > >> Seems pretty cool. It looks like it has similar trust assumptions as a >> standard light client: the light client trusts the merkle root once it is >> buried under several blocks of proof of work, believing that an attacker is >> unlikely to do all that work just to fool a light client (especially when >> they could have been actually mining bitcoin with all that hashrate). A >> nice property is that, to get started, a fly client does not have to >> download a variable number of block headers (namely, all of them, however >> many there are), only a constant number of block headers, and it's a pretty >> small total number. That property seems to make fly clients more efficient >> than standard light clients. >> >> On Wednesday, April 29, 2026 at 5:03:36 PM UTC-4 Zac Mitton wrote: >> >>> Hi, Ive been looking into FlyClient first described here >>> <https://www.youtube.com/watch?v=BPNs9EVxWrA&t=8386s>. I don't see any >>> BIPs, or previous discussion in this forum about it either. >>> >>> On bitcoin It could allow a light-client to verify the entire work of >>> the heaviest chain with a single ~100KB proof. >>> >>> It can theoretically be done as a soft-fork by injecting a single hash >>> into the coinbase tx (similar to how segwit is committed to). >>> >>> What do you guy's think? >>> >> -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to bitcoindev+unsubscribe@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/4cd9d2bd-28f8-47a5-95f5-a7c9ae222835n%40googlegroups.com. [-- Attachment #1.2: Type: text/html, Size: 4248 bytes --] ^ permalink raw reply [flat|nested] 8+ messages in thread
* [bitcoindev] Re: Fly Client Proposal 2026-05-02 19:23 ` Zac Mitton @ 2026-05-02 21:24 ` Nuh.dev 0 siblings, 0 replies; 8+ messages in thread From: Nuh.dev @ 2026-05-02 21:24 UTC (permalink / raw) To: Bitcoin Development Mailing List [-- Attachment #1.1: Type: text/plain, Size: 3828 bytes --] Yes, STARK proofs are post quantum secure, as they don't require much more than polynomials and hash functions, and they don't have trust assumptions like SNARKs, which is why they are called scalable Transparent arguments of knowledge. STARKs are not too difficult to vaguely understand, and in fact they aren't too different from FlyClient, both start from an interactive proof, then use Fiat-Shamir heuristic too convert it into a non-interactive proof, the major difference is that FlyClient does that over a specific function (sum of Work), whereas STARK needs to prove arbitrary functions, usually a CPU instruction set. Finally, there will most likely not be any future soft forks, not even string concatenation in Script, so we are lucky this one doesn't need consensus change. On Saturday, 2 May 2026 at 23:07:22 UTC+3 Zac Mitton wrote: > It makes sense that a STARK proof can do similar, however the 2 benefits > to this would be that (1) This doesnt require (any) more strict assumptions > which I'm assuming STARKS do, and (2) just the sheer simplicity of its > design. Sorry to bring up a touchy topic but is the STARK version quantum > safe, for instance? The flyclient version requires no new cryptographic > assumptions beyond the "honest mining majority" used currently. > > Admittedly my dumb brain understands it better. I assume it would get > grouped into some larger softfork rollout... > > On Friday, May 1, 2026 at 5:03:47 AM UTC-4 Nuh.dev wrote: > >> FlyClient is very useful compared to SPV client, especially for >> blockchains with much more headers per day than Bitcoin. But fortunately, >> this is one of the few soft forks that we don't actually need, because we >> can substitute with a STARK proof as you can see here; >> https://github.com/starkware-bitcoin/raito ... so any energy for >> gathering consensus for a soft fork, before Bitcoin ossifies forever, is >> better spent elsewhere. >> >> On Thursday, 30 April 2026 at 21:55:05 UTC+3 Super Testnet wrote: >> >>> Seems pretty cool. It looks like it has similar trust assumptions as a >>> standard light client: the light client trusts the merkle root once it is >>> buried under several blocks of proof of work, believing that an attacker is >>> unlikely to do all that work just to fool a light client (especially when >>> they could have been actually mining bitcoin with all that hashrate). A >>> nice property is that, to get started, a fly client does not have to >>> download a variable number of block headers (namely, all of them, however >>> many there are), only a constant number of block headers, and it's a pretty >>> small total number. That property seems to make fly clients more efficient >>> than standard light clients. >>> >>> On Wednesday, April 29, 2026 at 5:03:36 PM UTC-4 Zac Mitton wrote: >>> >>>> Hi, Ive been looking into FlyClient first described here >>>> <https://www.youtube.com/watch?v=BPNs9EVxWrA&t=8386s>. I don't see any >>>> BIPs, or previous discussion in this forum about it either. >>>> >>>> On bitcoin It could allow a light-client to verify the entire work of >>>> the heaviest chain with a single ~100KB proof. >>>> >>>> It can theoretically be done as a soft-fork by injecting a single hash >>>> into the coinbase tx (similar to how segwit is committed to). >>>> >>>> What do you guy's think? >>>> >>> -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to bitcoindev+unsubscribe@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/85d0e4fb-26d5-44be-8c1b-461607b2fc28n%40googlegroups.com. [-- Attachment #1.2: Type: text/html, Size: 5347 bytes --] ^ permalink raw reply [flat|nested] 8+ messages in thread
* [bitcoindev] Re: Fly Client Proposal 2026-04-29 21:00 [bitcoindev] Fly Client Proposal Zac Mitton 2026-04-30 18:52 ` [bitcoindev] " Super Testnet @ 2026-05-03 16:56 ` Tom Harding [not found] ` <CAOsDwYbfZXKe_dcNoL_t2DSrWokUXC2OJh33J8=CDHmO=n3AhA@mail.gmail.com> 1 sibling, 1 reply; 8+ messages in thread From: Tom Harding @ 2026-05-03 16:56 UTC (permalink / raw) To: Bitcoin Development Mailing List [-- Attachment #1.1: Type: text/plain, Size: 1304 bytes --] In the linked presentation by Benedict Bünz, it's worth listening to the first audience question/answer. Questioner is spot on that an SPV client polling the network to gain probabilistic confidence of unspentness could easily subsume the task of gaining input inclusion proofs from the network, with no forking change necessary. On Wednesday, April 29, 2026 at 2:03:36 PM UTC-7 Zac Mitton wrote: > Hi, Ive been looking into FlyClient first described here > <https://www.youtube.com/watch?v=BPNs9EVxWrA&t=8386s>. I don't see any > BIPs, or previous discussion in this forum about it either. > > On bitcoin It could allow a light-client to verify the entire work of the > heaviest chain with a single ~100KB proof. > > It can theoretically be done as a soft-fork by injecting a single hash > into the coinbase tx (similar to how segwit is committed to). > > What do you guy's think? > -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to bitcoindev+unsubscribe@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/0aadce7a-b08b-4fd2-8bae-37df1cfc54afn%40googlegroups.com. [-- Attachment #1.2: Type: text/html, Size: 2091 bytes --] ^ permalink raw reply [flat|nested] 8+ messages in thread
[parent not found: <CAOsDwYbfZXKe_dcNoL_t2DSrWokUXC2OJh33J8=CDHmO=n3AhA@mail.gmail.com>]
* Re: [bitcoindev] Re: Fly Client Proposal [not found] ` <CAOsDwYbfZXKe_dcNoL_t2DSrWokUXC2OJh33J8=CDHmO=n3AhA@mail.gmail.com> @ 2026-05-04 16:26 ` Tom Harding 2026-05-04 22:34 ` Zac Mitton 0 siblings, 1 reply; 8+ messages in thread From: Tom Harding @ 2026-05-04 16:26 UTC (permalink / raw) To: Zac Mitton; +Cc: Bitcoin Development Mailing List [-- Attachment #1: Type: text/plain, Size: 2042 bytes --] Zac, That's probably because the question, and my post, are off-topic. They are not about FlyClient, which is not interesting to me because bitcoin's header chain is tiny. Instead they touch on two techniques which would improve on most historical implementations of SPV clients by adding protocol support for them. Sorry for the distraction. Tom On 5/3/26 12:26, Zac Mitton wrote: > Tom I can’t seem to grok the question or your explanation of it. Could > you spell it out for us in detail? > > > Thanks, Zac > > On Sun, May 3, 2026 at 12:58 PM Tom Harding <tomh@thinlink.com> wrote: > > In the linked presentation by Benedict Bünz, it's worth listening > to the first audience question/answer. Questioner is spot on that > an SPV client polling the network to gain probabilistic confidence > of unspentness could easily subsume the task of gaining input > inclusion proofs from the network, with no forking change necessary. > > On Wednesday, April 29, 2026 at 2:03:36 PM UTC-7 Zac Mitton wrote: > > Hi, Ive been looking into FlyClient first described here > <https://www.youtube.com/watch?v=BPNs9EVxWrA&t=8386s>. I don't > see any BIPs, or previous discussion in this forum about it > either. > > On bitcoin It could allow a light-client to verify the entire > work of the heaviest chain with a single ~100KB proof. > > It can theoretically be done as a soft-fork by injecting a > single hash into the coinbase tx (similar to how segwit is > committed to). > > What do you guy's think? > > -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to bitcoindev+unsubscribe@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/4516f3ab-0715-4dd9-825c-eed4eac3065a%40thinlink.com. [-- Attachment #2: Type: text/html, Size: 4327 bytes --] ^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [bitcoindev] Re: Fly Client Proposal 2026-05-04 16:26 ` Tom Harding @ 2026-05-04 22:34 ` Zac Mitton 0 siblings, 0 replies; 8+ messages in thread From: Zac Mitton @ 2026-05-04 22:34 UTC (permalink / raw) To: Tom Harding; +Cc: Bitcoin Development Mailing List [-- Attachment #1: Type: text/plain, Size: 2396 bytes --] Ok, Let's keep this thread about Flyclient on Bitcoin. The challenges related to actually getting a soft-fork into bitcoin are best discussed elsewhere. If anyone has information related to progress on this, or implementation ideas please help by posting here or DMing me. I will try to aggregate. On Mon, May 4, 2026 at 12:26 PM Tom Harding <tomh@thinlink.com> wrote: > Zac, > > That's probably because the question, and my post, are off-topic. They > are not about FlyClient, which is not interesting to me because bitcoin's > header chain is tiny. > > Instead they touch on two techniques which would improve on most > historical implementations of SPV clients by adding protocol support for > them. > > Sorry for the distraction. > > Tom > > > On 5/3/26 12:26, Zac Mitton wrote: > > Tom I can’t seem to grok the question or your explanation of it. Could you > spell it out for us in detail? > > > Thanks, Zac > > On Sun, May 3, 2026 at 12:58 PM Tom Harding <tomh@thinlink.com> wrote: > >> In the linked presentation by Benedict Bünz, it's worth listening to the >> first audience question/answer. Questioner is spot on that an SPV client >> polling the network to gain probabilistic confidence of unspentness could >> easily subsume the task of gaining input inclusion proofs from the network, >> with no forking change necessary. >> >> On Wednesday, April 29, 2026 at 2:03:36 PM UTC-7 Zac Mitton wrote: >> >>> Hi, Ive been looking into FlyClient first described here >>> <https://www.youtube.com/watch?v=BPNs9EVxWrA&t=8386s>. I don't see any >>> BIPs, or previous discussion in this forum about it either. >>> >>> On bitcoin It could allow a light-client to verify the entire work of >>> the heaviest chain with a single ~100KB proof. >>> >>> It can theoretically be done as a soft-fork by injecting a single hash >>> into the coinbase tx (similar to how segwit is committed to). >>> >>> What do you guy's think? >>> >> >> -- You received this message because you are subscribed to the Google Groups "Bitcoin Development Mailing List" group. To unsubscribe from this group and stop receiving emails from it, send an email to bitcoindev+unsubscribe@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/bitcoindev/CAOsDwYYw7bfRdfr5AsPWM1WmN7BePrvYDRQ2WRWhNpVcDHeo%2BA%40mail.gmail.com. [-- Attachment #2: Type: text/html, Size: 4566 bytes --] ^ permalink raw reply [flat|nested] 8+ messages in thread
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2026-04-29 21:00 [bitcoindev] Fly Client Proposal Zac Mitton
2026-04-30 18:52 ` [bitcoindev] " Super Testnet
2026-05-01 8:42 ` Nuh.dev
2026-05-02 19:23 ` Zac Mitton
2026-05-02 21:24 ` Nuh.dev
2026-05-03 16:56 ` Tom Harding
[not found] ` <CAOsDwYbfZXKe_dcNoL_t2DSrWokUXC2OJh33J8=CDHmO=n3AhA@mail.gmail.com>
2026-05-04 16:26 ` Tom Harding
2026-05-04 22:34 ` Zac Mitton
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