The Grammar of Bitcoin's Extensibility比特币的扩展性语法学 · 升级插槽的字节级解剖

Bitcoin doesn't add a feature by inventing a new byte. It reserves slots in advance, then fills them — and the block explorer still shows each filled slot under its pre-activation name. This is a field guide to those slots, read off real on-chain bytes: which one CAT, CSFS, CTV, APO and INTERNALKEY each plug into, and how many Bitcoin still holds unopened.

▶ Open the Upgrade-Slot Explorer

🎛 Interactive explorer

Pick an opcode, see its real leaf bytes, watch which reserved slot it plugs into, and why the explorer shows its pre-activation "fossil" name. Real signet bytes.

📖 The essay · English

Peel the onion from the address inward: witness version → leaf version → the opcode slot (NOP vs OP_SUCCESS) → the 0x01 hat → the empty annex → count the unopened slots.

📖 文章 · 中文

从地址往里剥洋葱:witness version → leaf version → opcode 槽(NOP vs OP_SUCCESS）→ 0x01 帽子 → 空 annex → 数一数还剩几个没拆封的插槽。

The onion, at a glance

Layer 1
witness version — in the address, 5120…; v2–v16 empty
Layer 2
leaf version — control block & 0xfe; c0/c1 is just y-parity
Layer 3
the opcode slot — NOP (CTV) vs OP_SUCCESS (CAT/CSFS/IK)
Layer 4/5
sighash + pubkey prefix — APO's 0x01 hat; 32 vs 33 bytes
Layer 6
the annex 0x50 — the empty pocket, still unused

Read on

Companion signet series (opcode by opcode): medium.com/@aaron.recompile
Sibling piece: What a Signature Can See (the sighash playground)
Specs: BIP-342 (tapscript/OP_SUCCESS) · BIP-119 (CTV) · BIP-118 (APO) · runs on signet

About

Aaron Zhang

Author of Mastering Taproot.

Bitcoin Developer, Educator and Investor.