diff --git a/packages/beacon-node/src/chain/blocks/importBlock.ts b/packages/beacon-node/src/chain/blocks/importBlock.ts
index bfb9cecf9d4b..3cedce0700b2 100644
--- a/packages/beacon-node/src/chain/blocks/importBlock.ts
+++ b/packages/beacon-node/src/chain/blocks/importBlock.ts
@@ -281,6 +281,18 @@ export async function importBlock(
   const newHead = this.recomputeForkChoiceHead(ForkchoiceCaller.importBlock);
   const currFinalizedEpoch = this.forkChoice.getFinalizedCheckpoint().epoch;
 
+  // Prune the gloas payload-envelope cache below the new head's parent so it stays bounded during
+  // syncing. On a synced node, cache holds just 2 entries — head (parent for
+  // next-slot production) and head.parent (proposer-boost-reorg fallback)
+  if (fork >= ForkSeq.gloas) {
+    callInNextEventLoop(() => {
+      const newHeadParent = this.forkChoice.getBlockHexDefaultStatus(newHead.parentRoot);
+      if (newHeadParent) {
+        this.seenPayloadEnvelopeInputCache.pruneBelowParent(newHeadParent);
+      }
+    });
+  }
+
   if (newHead.blockRoot !== oldHead.blockRoot) {
     // Set head state as strong reference
     this.regen.updateHeadState(newHead, postState);
diff --git a/packages/beacon-node/src/chain/prepareNextSlot.ts b/packages/beacon-node/src/chain/prepareNextSlot.ts
index ec6474c0d046..ced08b44ad97 100644
--- a/packages/beacon-node/src/chain/prepareNextSlot.ts
+++ b/packages/beacon-node/src/chain/prepareNextSlot.ts
@@ -217,16 +217,6 @@ export class PrepareNextSlotScheduler {
           });
         }
 
-        if (ForkSeq[fork] >= ForkSeq.gloas) {
-          // Cutoff = slot of the parent of the block we'll actually build on (post-reorg).
-          // Steady state: cache holds just 2 entries — head (parent for next-slot production)
-          // and head.parent (proposer-boost-reorg fallback). Anything older is evicted.
-          const updatedHeadParent = this.chain.forkChoice.getBlockHexDefaultStatus(updatedHead.parentRoot);
-          if (updatedHeadParent) {
-            this.chain.seenPayloadEnvelopeInputCache.pruneBelowParent(updatedHeadParent);
-          }
-        }
-
         this.computeStateHashTreeRoot(updatedPrepareState, isEpochTransition);
 
         // If emitPayloadAttributes is true emit a SSE payloadAttributes event for
diff --git a/packages/beacon-node/src/chain/seenCache/seenPayloadEnvelopeInput.ts b/packages/beacon-node/src/chain/seenCache/seenPayloadEnvelopeInput.ts
index 496a76503799..a297c9f6546c 100644
--- a/packages/beacon-node/src/chain/seenCache/seenPayloadEnvelopeInput.ts
+++ b/packages/beacon-node/src/chain/seenCache/seenPayloadEnvelopeInput.ts
@@ -1,5 +1,5 @@
 import {ChainForkConfig} from "@lodestar/config";
-import {CheckpointWithHex, IForkChoice, ProtoBlock} from "@lodestar/fork-choice";
+import {CheckpointWithHex, IForkChoice, PayloadStatus, ProtoBlock} from "@lodestar/fork-choice";
 import {computeStartSlotAtEpoch} from "@lodestar/state-transition";
 import {RootHex} from "@lodestar/types";
 import {Logger} from "@lodestar/utils";
@@ -154,9 +154,14 @@ export class SeenPayloadEnvelopeInput {
 
   pruneBelowParent(parentBlock: ProtoBlock): void {
     for (const block of this.forkChoice.getAllAncestorBlocks(parentBlock.blockRoot, parentBlock.payloadStatus)) {
-      if (block.slot < parentBlock.slot) {
+      // Only evict once the payload is FULL (revealed/imported) — on an EMPTY/PENDING branch we may
+      // still need to download the FULL envelope (see #9475), and evicting would make payload-by-root
+      // sync throw "Missing PayloadEnvelopeInput for known block".
+      if (block.slot < parentBlock.slot && block.payloadStatus === PayloadStatus.FULL) {
         const input = this.payloadInputs.get(block.blockRoot);
-        if (input) {
+        // ...and don't evict while columns are still being gathered: writeDataColumnsToDb awaits the
+        // same hasComputedAllData() before persisting. Such entries are pruned by a later call.
+        if (input?.hasComputedAllData()) {
           this.evictPayloadInput(input);
           this.logger?.verbose("SeenPayloadEnvelopeInput.pruneBelowParent deleted", {
             slot: block.slot,
diff --git a/packages/beacon-node/test/unit/chain/seenCache/seenPayloadEnvelopeInput.test.ts b/packages/beacon-node/test/unit/chain/seenCache/seenPayloadEnvelopeInput.test.ts
index 3623a936ace9..ba83abdfb594 100644
--- a/packages/beacon-node/test/unit/chain/seenCache/seenPayloadEnvelopeInput.test.ts
+++ b/packages/beacon-node/test/unit/chain/seenCache/seenPayloadEnvelopeInput.test.ts
@@ -8,7 +8,7 @@ import {ChainEventEmitter} from "../../../../src/chain/emitter.js";
 import {SeenPayloadEnvelopeInput} from "../../../../src/chain/seenCache/seenPayloadEnvelopeInput.js";
 import {SerializedCache} from "../../../../src/util/serializedCache.js";
 import {getMockedClock} from "../../../mocks/clock.js";
-import {config, generateBlock} from "../../../utils/blocksAndData.js";
+import {config, generateBlock, generateBlockWithColumnSidecars} from "../../../utils/blocksAndData.js";
 
 describe("SeenPayloadEnvelopeInput", () => {
   let cache: SeenPayloadEnvelopeInput;
@@ -50,6 +50,21 @@ describe("SeenPayloadEnvelopeInput", () => {
     return rootHex;
   }
 
+  // Block with blob commitments + non-empty sampledColumns and no columns added, so the input
+  // reports hasComputedAllData() === false.
+  function addPayloadInputNotComputed(slot: number): string {
+    const {block, rootHex} = generateBlockWithColumnSidecars({forkName: ForkName.gloas, slot});
+    cache.add({
+      blockRootHex: rootHex,
+      block,
+      forkName: ForkName.gloas,
+      sampledColumns: [0, 1],
+      custodyColumns: [0, 1],
+      timeCreatedSec: Date.now() / 1000,
+    });
+    return rootHex;
+  }
+
   function protoBlock(blockRoot: RootHex, slot: number): ProtoBlock {
     return {
       slot,
@@ -86,6 +101,31 @@ describe("SeenPayloadEnvelopeInput", () => {
     expect(cache.get(newRootHex)).toBeDefined();
   });
 
+  it("pruneBelowParent keeps ancestor payload inputs whose payload is not yet FULL", () => {
+    const oldRootHex = addPayloadInput(1);
+    const newRootHex = addPayloadInput(2);
+    const parentBlock = protoBlock(newRootHex, 2);
+    const emptyAncestor: ProtoBlock = {...protoBlock(oldRootHex, 1), payloadStatus: PayloadStatus.EMPTY};
+
+    vi.mocked(forkChoice.getAllAncestorBlocks).mockReturnValue([parentBlock, emptyAncestor]);
+    cache.pruneBelowParent(parentBlock);
+
+    expect(cache.get(oldRootHex)).toBeDefined();
+  });
+
+  it("pruneBelowParent keeps ancestor payload inputs that have not computed all data", () => {
+    const oldRootHex = addPayloadInputNotComputed(1);
+    const newRootHex = addPayloadInput(2);
+    // precondition: the ancestor input is still gathering columns
+    expect(cache.get(oldRootHex)?.hasComputedAllData()).toBe(false);
+
+    const parentBlock = protoBlock(newRootHex, 2);
+    vi.mocked(forkChoice.getAllAncestorBlocks).mockReturnValue([parentBlock, protoBlock(oldRootHex, 1)]);
+    cache.pruneBelowParent(parentBlock);
+
+    expect(cache.get(oldRootHex)).toBeDefined();
+  });
+
   it("pruneBelowParent keeps payload inputs at the parent slot", () => {
     const rootHex = addPayloadInput(1);
     const parentBlock = protoBlock(rootHex, 1);