{
  "$schema": "https://degreesofsatoshi.com/encyclopedia/schemas/article-v1.json",
  "schemaVersion": "1.0.0",
  "id": "bitcoin-block-reorganizations",
  "canonical": "https://degreesofsatoshi.com/encyclopedia/bitcoin-block-reorganizations/",
  "collection": "bitcoin",
  "title": "Bitcoin reorganizations: when a confirmed transaction changes branch",
  "description": "Follow what happens when a Bitcoin node switches to a valid branch with more accumulated work and why a transaction’s confirmation count can change.",
  "aliases": [],
  "dates": {
    "published": "2026-10-02",
    "modified": "2026-10-02",
    "verified": "2026-10-02T18:15:23.891Z",
    "dataAsOf": "2026-10-02"
  },
  "authorship": {
    "publisher": "Degrees of Satoshi editorial project",
    "process": "AI-assisted research and drafting with a separate automated source-verification pass; no external expert or named human review is implied."
  },
  "quickAnswer": {
    "text": "A Bitcoin block reorganization occurs when a node changes its active chain to a competing valid branch with more accumulated proof of work. Blocks from the former branch stop contributing confirmations. Their transactions may appear in the new branch, become pending again or conflict with transactions now confirmed.",
    "claimId": "bitcoin-block-reorganizations-quick-answer",
    "sourceIds": [
      "bitcoin-dev-blockchain",
      "bitcoin-whitepaper"
    ]
  },
  "keyFacts": [
    {
      "label": "Selection",
      "value": "The relevant measure is accumulated proof of work, not simply a count of blocks.",
      "sourceIds": [
        "bitcoin-dev-blockchain"
      ],
      "id": "selection",
      "claimId": "bitcoin-block-reorganizations-fact-selection"
    },
    {
      "label": "Depth",
      "value": "Confirmations describe a transaction’s position in the chain currently accepted by the observer.",
      "sourceIds": [
        "bitcoin-dev-blockchain"
      ],
      "id": "depth",
      "claimId": "bitcoin-block-reorganizations-fact-depth"
    },
    {
      "label": "Conflict",
      "value": "A transaction from a displaced block is not guaranteed to confirm again.",
      "sourceIds": [
        "bitcoin-dev-blockchain",
        "bitcoin-dev-transactions"
      ],
      "id": "conflict",
      "claimId": "bitcoin-block-reorganizations-fact-conflict"
    }
  ],
  "prerequisites": [
    "bitcoin-confirmations"
  ],
  "sections": [
    {
      "id": "fork",
      "heading": "How two competing tips can arise",
      "sourceIds": [
        "bitcoin-dev-blockchain"
      ],
      "paragraphs": [
        "Two miners can find valid blocks extending the same parent before either block has reached everyone. Different nodes may temporarily see different tips. A later extension can make one branch the preferred chain.",
        "This temporary competition is different from a deliberate change to consensus rules. Nodes still validate the candidate branch under the rules they enforce."
      ]
    },
    {
      "id": "payment",
      "heading": "Re-read the actual payment after a reorganization",
      "sourceIds": [
        "bitcoin-dev-transactions",
        "bitcoin-dev-blockchain"
      ],
      "paragraphs": [
        "A payment previously shown in a block may also be included in the replacement branch, possibly at another height. If it is absent and its inputs are still available, it may be eligible for rebroadcast. If the new chain contains a conflicting spend, that original payment cannot also spend the same outputs.",
        "A wallet should evaluate the transaction and its inputs rather than assume every displaced payment simply returns to the same pending queue."
      ]
    },
    {
      "id": "risk",
      "heading": "Depth reduces ordinary reversal risk without an absolute promise",
      "sourceIds": [
        "bitcoin-whitepaper"
      ],
      "paragraphs": [
        "The white paper models how an attacker’s chance of catching up changes with depth under specified hash-power assumptions. That model is not a universal guarantee for every network condition.",
        "A confirmation policy depends on value, threat assumptions and tolerance for delay. No fixed number transforms proof-of-work settlement into mathematical irreversibility."
      ]
    }
  ],
  "faq": [
    {
      "question": "Can a confirmation count go down?",
      "answer": "Yes. It can change when the observer’s accepted chain changes. Check the transaction’s actual block location and whether a conflicting spend exists.",
      "sourceIds": [
        "bitcoin-dev-blockchain",
        "bitcoin-dev-transactions"
      ]
    }
  ],
  "claims": [
    {
      "id": "bitcoin-block-reorganizations-quick-answer",
      "articleSlug": "bitcoin-block-reorganizations",
      "statement": "A Bitcoin block reorganization occurs when a node changes its active chain to a competing valid branch with more accumulated proof of work. Blocks from the former branch stop contributing confirmations. Their transactions may appear in the new branch, become pending again or conflict with transactions now confirmed.",
      "sourceIds": [
        "source-190b9fe0eec933dc",
        "source-0e46aca4dbc5a030"
      ],
      "sourceLocators": [
        {
          "sourceId": "source-190b9fe0eec933dc",
          "locator": "Proof Of Work; Block Height And Forking; Transaction Data"
        },
        {
          "sourceId": "source-0e46aca4dbc5a030",
          "locator": "Sections 4–5 and 7–11"
        }
      ],
      "scope": {
        "collection": "bitcoin",
        "dataAsOf": "2026-10-02",
        "blockHeight": null
      },
      "qualification": "",
      "evidenceStatus": "documented",
      "verification": {
        "status": "verified",
        "method": "independent automated source review",
        "checkedAt": "2026-10-02T18:15:23.891Z",
        "reviewer": "Independent automated verification agent verify_bitcoin_stablecoins_100",
        "notes": [
          "Checked developer-guide Block Height And Forking and white-paper sections 4–5 and 11. Valid-chain selection concerns accumulated work, and displaced transactions may be included, pending or conflicting.",
          "The attacker catch-up model is qualified by its assumptions. No fixed confirmation depth is described as mathematical irreversibility."
        ]
      }
    },
    {
      "id": "bitcoin-block-reorganizations-fact-selection",
      "articleSlug": "bitcoin-block-reorganizations",
      "statement": "Selection: The relevant measure is accumulated proof of work, not simply a count of blocks.",
      "sourceIds": [
        "source-190b9fe0eec933dc"
      ],
      "sourceLocators": [
        {
          "sourceId": "source-190b9fe0eec933dc",
          "locator": "Proof Of Work; Block Height And Forking; Transaction Data"
        }
      ],
      "scope": {
        "collection": "bitcoin",
        "dataAsOf": "2026-10-02",
        "blockHeight": null
      },
      "qualification": "",
      "evidenceStatus": "documented",
      "verification": {
        "status": "verified",
        "method": "independent automated source review",
        "checkedAt": "2026-10-02T18:15:23.891Z",
        "reviewer": "Independent automated verification agent verify_bitcoin_stablecoins_100",
        "notes": [
          "Checked developer-guide Block Height And Forking and white-paper sections 4–5 and 11. Valid-chain selection concerns accumulated work, and displaced transactions may be included, pending or conflicting.",
          "The attacker catch-up model is qualified by its assumptions. No fixed confirmation depth is described as mathematical irreversibility."
        ]
      }
    },
    {
      "id": "bitcoin-block-reorganizations-fact-depth",
      "articleSlug": "bitcoin-block-reorganizations",
      "statement": "Depth: Confirmations describe a transaction’s position in the chain currently accepted by the observer.",
      "sourceIds": [
        "source-190b9fe0eec933dc"
      ],
      "sourceLocators": [
        {
          "sourceId": "source-190b9fe0eec933dc",
          "locator": "Proof Of Work; Block Height And Forking; Transaction Data"
        }
      ],
      "scope": {
        "collection": "bitcoin",
        "dataAsOf": "2026-10-02",
        "blockHeight": null
      },
      "qualification": "",
      "evidenceStatus": "documented",
      "verification": {
        "status": "verified",
        "method": "independent automated source review",
        "checkedAt": "2026-10-02T18:15:23.891Z",
        "reviewer": "Independent automated verification agent verify_bitcoin_stablecoins_100",
        "notes": [
          "Checked developer-guide Block Height And Forking and white-paper sections 4–5 and 11. Valid-chain selection concerns accumulated work, and displaced transactions may be included, pending or conflicting.",
          "The attacker catch-up model is qualified by its assumptions. No fixed confirmation depth is described as mathematical irreversibility."
        ]
      }
    },
    {
      "id": "bitcoin-block-reorganizations-fact-conflict",
      "articleSlug": "bitcoin-block-reorganizations",
      "statement": "Conflict: A transaction from a displaced block is not guaranteed to confirm again.",
      "sourceIds": [
        "source-190b9fe0eec933dc",
        "source-b282fdecc069b74d"
      ],
      "sourceLocators": [
        {
          "sourceId": "source-190b9fe0eec933dc",
          "locator": "Proof Of Work; Block Height And Forking; Transaction Data"
        },
        {
          "sourceId": "source-b282fdecc069b74d",
          "locator": "P2PKH Script Validation; Transaction Fees And Change"
        }
      ],
      "scope": {
        "collection": "bitcoin",
        "dataAsOf": "2026-10-02",
        "blockHeight": null
      },
      "qualification": "",
      "evidenceStatus": "documented",
      "verification": {
        "status": "verified",
        "method": "independent automated source review",
        "checkedAt": "2026-10-02T18:15:23.891Z",
        "reviewer": "Independent automated verification agent verify_bitcoin_stablecoins_100",
        "notes": [
          "Checked developer-guide Block Height And Forking and white-paper sections 4–5 and 11. Valid-chain selection concerns accumulated work, and displaced transactions may be included, pending or conflicting.",
          "The attacker catch-up model is qualified by its assumptions. No fixed confirmation depth is described as mathematical irreversibility."
        ]
      }
    }
  ],
  "sources": [
    {
      "id": "bitcoin-dev-blockchain",
      "label": "Bitcoin Developer Guide: Block Chain",
      "publisher": "Bitcoin developer documentation contributors",
      "url": "https://developer.bitcoin.org/devguide/block_chain.html",
      "locator": "Proof Of Work; Block Height And Forking; Transaction Data",
      "note": "Block headers, transaction Merkle trees and competing valid branches.",
      "version": null,
      "checkedAt": "2026-10-02T17:03:41.181Z",
      "contentSha256": "0102eb1bda0d084051a86735e4b293dadc5a93b2bee93ad71c62cfeb855f1583",
      "recordId": "source-190b9fe0eec933dc"
    },
    {
      "id": "bitcoin-whitepaper",
      "label": "Bitcoin: A Peer-to-Peer Electronic Cash System",
      "publisher": "Satoshi Nakamoto",
      "url": "https://bitcoin.org/bitcoin.pdf",
      "locator": "Sections 4–5 and 7–11",
      "note": "Most-work chain selection, Merkle inclusion, SPV limits and transaction change.",
      "version": "2008 paper",
      "checkedAt": "2026-10-02T17:03:41.335Z",
      "contentSha256": "b1674191a88ec5cdd733e4240a81803105dc412d6c6708d53ab94fc248f4f553",
      "recordId": "source-0e46aca4dbc5a030"
    },
    {
      "id": "bitcoin-dev-transactions",
      "label": "Bitcoin Developer Guide: Transactions",
      "publisher": "Bitcoin developer documentation contributors",
      "url": "https://developer.bitcoin.org/devguide/transactions.html",
      "locator": "P2PKH Script Validation; Transaction Fees And Change",
      "note": "UTXO inputs, transaction outputs, change and the difference paid as a fee.",
      "version": null,
      "checkedAt": "2026-10-02T17:03:41.190Z",
      "contentSha256": "449ae88ea59f9b198c398d3f5f56f83a92cd6be1638fa6681a1fdeea164892c0",
      "recordId": "source-b282fdecc069b74d"
    }
  ],
  "related": {
    "articles": [
      "bitcoin-confirmations",
      "double-spending",
      "51-percent-attack"
    ],
    "dossiers": [],
    "wallets": []
  },
  "revisionHistory": [
    {
      "date": "2026-10-02",
      "kind": "published",
      "summary": "Initial Bitcoin encyclopedia entry at this permanent URL."
    },
    {
      "date": "2026-10-02",
      "kind": "publishing-format",
      "summary": "Added reusable claims, explicit source locators, and matching Markdown and JSON. This publishing change does not itself establish factual verification."
    }
  ],
  "citation": "Degrees of Satoshi editorial project. “Bitcoin reorganizations: when a confirmed transaction changes branch.” Published 2026-10-02; updated 2026-10-02. https://degreesofsatoshi.com/encyclopedia/bitcoin-block-reorganizations/"
}