diff --git a/proving/igneum-prove/elf/prior/igneum-prove-aggregator.elf b/proving/igneum-prove/elf/prior/igneum-prove-aggregator.elf
new file mode 100644
index 000000000..a6d068225
Binary files /dev/null and b/proving/igneum-prove/elf/prior/igneum-prove-aggregator.elf differ
diff --git a/proving/igneum-prove/elf/prior/igneum-prove-aggregator.vk b/proving/igneum-prove/elf/prior/igneum-prove-aggregator.vk
new file mode 100644
index 000000000..51e8c6c00
Binary files /dev/null and b/proving/igneum-prove/elf/prior/igneum-prove-aggregator.vk differ
diff --git a/proving/igneum-prove/elf/prior/igneum-prove-program.elf b/proving/igneum-prove/elf/prior/igneum-prove-program.elf
new file mode 100644
index 000000000..8db866f14
Binary files /dev/null and b/proving/igneum-prove/elf/prior/igneum-prove-program.elf differ
diff --git a/proving/igneum-prove/elf/prior/igneum-prove-program.vk b/proving/igneum-prove/elf/prior/igneum-prove-program.vk
new file mode 100644
index 000000000..3c052ce7f
Binary files /dev/null and b/proving/igneum-prove/elf/prior/igneum-prove-program.vk differ
diff --git a/proving/igneum-prove/host/src/bin/pin.rs b/proving/igneum-prove/host/src/bin/pin.rs
index 93a4bd6e3..29ec4e7c6 100644
--- a/proving/igneum-prove/host/src/bin/pin.rs
+++ b/proving/igneum-prove/host/src/bin/pin.rs
@@ -70,10 +70,32 @@ fn main() -> Result<()> {
     let out = arg("--out").map(PathBuf::from).unwrap_or_else(|| here.join("elf"));
     std::fs::create_dir_all(&out)?;
     let host = std::process::Command::new("uname").arg("-a").output().ok().map(|o| String::from_utf8_lossy(&o.stdout).trim().to_string()).unwrap_or_else(|| "unknown".into());
+    // Key succession (docs/design/key-succession.md, 8 October 2026): a pin over an existing elf/ moves the pair it
+    // holds to elf/prior/ and writes the manifest's `prior` block (the same per-program fields) and a `succession`
+    // block naming both pairs' ids; the top-level shard and aggregator stay the newest pair. At most two pairs live:
+    // a pin over an elf/ that already carries prior/ replaces prior/ with the current pair. The node reads H, W and
+    // the next ids from its object, never from the manifest; `succession` is for the served manifest and its check.
+    // `--no-prior` keeps today's shape (the bootstrap, or a pin that replaces a pair never served).
+    let keep_prior = !args.iter().any(|a| a == "--no-prior");
+    let prior = if keep_prior && out.join("manifest.json").exists() {
+        let current: serde_json::Value = serde_json::from_str(&std::fs::read_to_string(out.join("manifest.json"))?)?;
+        let prior_dir = out.join("prior");
+        std::fs::create_dir_all(&prior_dir)?;
+        for name in ["igneum-prove-program", "igneum-prove-aggregator"] {
+            for ext in ["elf", "vk"] {
+                let f = format!("{name}.{ext}");
+                std::fs::copy(out.join(&f), prior_dir.join(&f)).with_context(|| format!("move {f} to prior/"))?;
+            }
+        }
+        println!("RESULT pin: the pair pinned at {} moved to {} (prior)", current["pinned_at"].as_str().unwrap_or("?"), prior_dir.display());
+        Some(serde_json::json!({ "shard": current["shard"], "aggregator": current["aggregator"], "pinned_at": current["pinned_at"] }))
+    } else {
+        None
+    };
     let light = LightProver::new();
     let shard = pin_one(&light, &from, &out, "igneum-prove-program")?;
     let aggregator = pin_one(&light, &from, &out, "igneum-prove-aggregator")?;
-    let manifest = serde_json::json!({
+    let mut manifest = serde_json::json!({
         "format": "igneum-prove-elf-manifest-v1",
         "sp1_crate_version": "6.8.1",
         "sp1_circuit_version": sp1_sdk::SP1_CIRCUIT_VERSION,
@@ -82,6 +104,26 @@ fn main() -> Result<()> {
         "shard": shard,
         "aggregator": aggregator,
     });
+    if let Some(p) = prior {
+        manifest["succession"] = serde_json::json!({
+            "prior_shard_program_id": p["shard"]["program_id"],
+            "prior_aggregator_id": p["aggregator"]["program_id"],
+            "next_shard_program_id": manifest["shard"]["program_id"],
+            "next_aggregator_id": manifest["aggregator"]["program_id"],
+        });
+        manifest["prior"] = p;
+    } else {
+        // no pair to carry: prior/ is a copy of the current pair so the host's include_bytes compile, the manifest
+        // names no `prior` (the in-process verifier reads it as absent)
+        let prior_dir = out.join("prior");
+        std::fs::create_dir_all(&prior_dir)?;
+        for name in ["igneum-prove-program", "igneum-prove-aggregator"] {
+            for ext in ["elf", "vk"] {
+                let f = format!("{name}.{ext}");
+                std::fs::copy(out.join(&f), prior_dir.join(&f))?;
+            }
+        }
+    }
     std::fs::write(out.join("manifest.json"), format!("{}\n", serde_json::to_string_pretty(&manifest)?))?;
     println!("RESULT pin: manifest written to {}; rebuild the host so it embeds these files", out.join("manifest.json").display());
     Ok(())
diff --git a/proving/igneum-prove/host/src/pinned.rs b/proving/igneum-prove/host/src/pinned.rs
index c87256d1e..2843a2b4b 100644
--- a/proving/igneum-prove/host/src/pinned.rs
+++ b/proving/igneum-prove/host/src/pinned.rs
@@ -26,6 +26,13 @@ pub const SHARD_VK_BYTES: &[u8] = include_bytes!("../../elf/igneum-prove-program
 pub const AGG_ELF_BYTES: &[u8] = include_bytes!("../../elf/igneum-prove-aggregator.elf");
 pub const AGG_VK_BYTES: &[u8] = include_bytes!("../../elf/igneum-prove-aggregator.vk");
 pub const MANIFEST_JSON: &str = include_str!("../../elf/manifest.json");
+/// Key succession (docs/design/key-succession.md, 8 October 2026): the prior pair's files under `elf/prior/` (the same
+/// names), present in every tree (a copy of the current pair until a pin moves one there, the manifest then naming no
+/// `prior`); the host embeds them so a node carries both pairs across a succession window.
+pub const PRIOR_SHARD_ELF_BYTES: &[u8] = include_bytes!("../../elf/prior/igneum-prove-program.elf");
+pub const PRIOR_SHARD_VK_BYTES: &[u8] = include_bytes!("../../elf/prior/igneum-prove-program.vk");
+pub const PRIOR_AGG_ELF_BYTES: &[u8] = include_bytes!("../../elf/prior/igneum-prove-aggregator.elf");
+pub const PRIOR_AGG_VK_BYTES: &[u8] = include_bytes!("../../elf/prior/igneum-prove-aggregator.vk");
 
 /// One pinned program: file names, hashes and the program id (`agg::vk_bytes` of the verifying key's `hash_u32`).
 #[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq)]
@@ -47,6 +54,29 @@ pub struct Manifest {
     pub pinned_on: String,
     pub shard: PinnedProgram,
     pub aggregator: PinnedProgram,
+    /// Key succession: the pair pinned before this one (`elf/prior/`), present only once a pin has moved one there.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub prior: Option<PriorPair>,
+    /// Key succession: both pairs' ids as the served manifest carries them (the node reads H, W and the next ids
+    /// from its object, never from here).
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub succession: Option<Succession>,
+}
+
+/// The prior pair's block: the same per-program fields as the top level and the time it was pinned.
+#[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq)]
+pub struct PriorPair {
+    pub shard: PinnedProgram,
+    pub aggregator: PinnedProgram,
+    pub pinned_at: String,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq)]
+pub struct Succession {
+    pub prior_shard_program_id: String,
+    pub prior_aggregator_id: String,
+    pub next_shard_program_id: String,
+    pub next_aggregator_id: String,
 }
 
 impl Manifest {
@@ -78,6 +108,17 @@ pub struct Pinned {
     pub agg_vk: SP1VerifyingKey,
     pub shard_id: B256,
     pub agg_id: B256,
+    /// Key succession: the prior pair (its two verifying keys and ids) when the manifest carries a `prior` block and
+    /// the embedded prior files hash to it; `None` on today's shape.
+    pub prior: Option<PriorKeys>,
+}
+
+/// The prior pair as loaded: the keys and the ids derived from them.
+pub struct PriorKeys {
+    pub shard_vk: SP1VerifyingKey,
+    pub agg_vk: SP1VerifyingKey,
+    pub shard_id: B256,
+    pub agg_id: B256,
 }
 
 impl Pinned {
@@ -95,7 +136,35 @@ impl Pinned {
         let agg_id = program_id_of(&agg_vk);
         check_id("shard", shard_id, &manifest.shard.program_id)?;
         check_id("aggregator", agg_id, &manifest.aggregator.program_id)?;
-        Ok(Self { manifest, shard_vk, agg_vk, shard_id, agg_id })
+        let prior = match &manifest.prior {
+            Some(p) => {
+                check_file("prior shard ELF", PRIOR_SHARD_ELF_BYTES, &p.shard.elf_sha256)?;
+                check_file("prior shard verifying key", PRIOR_SHARD_VK_BYTES, &p.shard.vk_sha256)?;
+                check_file("prior aggregator ELF", PRIOR_AGG_ELF_BYTES, &p.aggregator.elf_sha256)?;
+                check_file("prior aggregator verifying key", PRIOR_AGG_VK_BYTES, &p.aggregator.vk_sha256)?;
+                let pvk: SP1VerifyingKey = bincode::deserialize(PRIOR_SHARD_VK_BYTES).context("the embedded prior shard verifying key does not deserialize")?;
+                let pavk: SP1VerifyingKey = bincode::deserialize(PRIOR_AGG_VK_BYTES).context("the embedded prior aggregator verifying key does not deserialize")?;
+                let (psid, paid) = (program_id_of(&pvk), program_id_of(&pavk));
+                check_id("prior shard", psid, &p.shard.program_id)?;
+                check_id("prior aggregator", paid, &p.aggregator.program_id)?;
+                if let Some(s) = &manifest.succession {
+                    check_id("succession prior shard", psid, &s.prior_shard_program_id)?;
+                    check_id("succession prior aggregator", paid, &s.prior_aggregator_id)?;
+                    check_id("succession next shard", shard_id, &s.next_shard_program_id)?;
+                    check_id("succession next aggregator", agg_id, &s.next_aggregator_id)?;
+                }
+                Some(PriorKeys { shard_vk: pvk, agg_vk: pavk, shard_id: psid, agg_id: paid })
+            }
+            None => None,
+        };
+        Ok(Self { manifest, shard_vk, agg_vk, shard_id, agg_id, prior })
+    }
+
+    pub fn prior_shard_elf(&self) -> Option<Elf> {
+        self.prior.as_ref().map(|_| Elf::Static(PRIOR_SHARD_ELF_BYTES))
+    }
+    pub fn prior_agg_elf(&self) -> Option<Elf> {
+        self.prior.as_ref().map(|_| Elf::Static(PRIOR_AGG_ELF_BYTES))
     }
 
     pub fn shard_elf(&self) -> Elf {
diff --git a/tools/ci/release-manifest-check.mjs b/tools/ci/release-manifest-check.mjs
index 0cbcdcae3..5b90ddd34 100644
--- a/tools/ci/release-manifest-check.mjs
+++ b/tools/ci/release-manifest-check.mjs
@@ -28,6 +28,21 @@ if (existsSync(elfp)) {
   const e = JSON.parse(readFileSync(elfp, 'utf8'));
   for (const [a, b] of [['shard_program_id', e.shard.program_id], ['shard_elf_sha256', e.shard.elf_sha256], ['shard_vk_sha256', e.shard.vk_sha256], ['aggregator_program_id', e.aggregator.program_id], ['aggregator_elf_sha256', e.aggregator.elf_sha256], ['aggregator_vk_sha256', e.aggregator.vk_sha256], ['sp1_circuit_version', e.sp1_circuit_version], ['sp1_crate_version', e.sp1_crate_version], ['pinned_at', e.pinned_at]])
     if (m.proving[a] !== b) fails.push(`manifest: proving.${a} is ${m.proving[a]}, the ELF manifest says ${b}`);
+  // key succession (docs/design/key-succession.md, 8 October 2026): the served manifest carries the prior pair and the
+  // succession block exactly as the ELF manifest does; a `prior` present on one side only is a refusal, absent on both is
+  // today's shape
+  const ep = e.prior && typeof e.prior === 'object' ? e.prior : null;
+  const mp = m.proving.prior && typeof m.proving.prior === 'object' ? m.proving.prior : null;
+  if (!!ep !== !!mp) fails.push(`manifest: proving.prior is ${mp ? 'present' : 'absent'} but the ELF manifest's prior is ${ep ? 'present' : 'absent'}`);
+  if (ep && mp) {
+    for (const [a, b] of [['shard_program_id', ep.shard?.program_id], ['shard_elf_sha256', ep.shard?.elf_sha256], ['shard_vk_sha256', ep.shard?.vk_sha256], ['aggregator_program_id', ep.aggregator?.program_id], ['aggregator_elf_sha256', ep.aggregator?.elf_sha256], ['aggregator_vk_sha256', ep.aggregator?.vk_sha256], ['pinned_at', ep.pinned_at]])
+      if (mp[a] !== b) fails.push(`manifest: proving.prior.${a} is ${mp[a]}, the ELF manifest's prior says ${b}`);
+    const es = e.succession || {}, ms = m.proving.succession || {};
+    for (const k of ['prior_shard_program_id', 'prior_aggregator_id', 'next_shard_program_id', 'next_aggregator_id'])
+      if (ms[k] !== es[k]) fails.push(`manifest: proving.succession.${k} is ${ms[k]}, the ELF manifest says ${es[k]}`);
+    for (const k of ['succession_daa', 'succession_window_daa'])
+      if (!(k in m.proving) || !(Number.isInteger(m.proving[k]) || m.proving[k] === 'never')) fails.push(`manifest: proving.${k} must be an integer DAA or "never" when a prior pair is carried`);
+  }
 }
 const vercel = JSON.parse(readFileSync(join(site, 'vercel.json'), 'utf8'));
 if (!(vercel.rewrites || []).some(r => r.source === '/release.json' && r.destination === '/release-manifest.json')) fails.push('vercel.json: no rewrite /release.json -> /release-manifest.json');