diff --git a/crates/server/src/http/v1/post_execution_proof_requests.rs b/crates/server/src/http/v1/post_execution_proof_requests.rs
index d306d41..92be0d3 100644
--- a/crates/server/src/http/v1/post_execution_proof_requests.rs
+++ b/crates/server/src/http/v1/post_execution_proof_requests.rs
@@ -4,7 +4,7 @@ use std::{collections::HashSet, sync::Arc};
 
 use axum::{Json, extract::State};
 use bytes::Bytes;
-use tracing::{info_span, instrument};
+use tracing::{debug, info_span, instrument};
 use zkboost_types::{
     Decode, MainnetEthSpec, NewPayloadRequest, ProofRequestQuery, ProofRequestResponse, TreeHash,
 };
@@ -14,7 +14,7 @@ use crate::{
         AppState,
         v1::{ErrorResponse, Query},
     },
-    proof::ProofServiceMessage,
+    proof::{ProofServiceMessage, zkvm::zkVMInstance},
 };
 
 #[instrument(skip_all)]
@@ -44,6 +44,22 @@ pub(crate) async fn post_execution_proof_requests(
         }
     }
 
+    // Reject proof generation requests for verifier-only instances early,
+    // before wasting resources on witness fetching.
+    for proof_type in &proof_types {
+        if let Some(zkvm) = state.zkvms.get(proof_type)
+            && matches!(zkvm, zkVMInstance::Verifier { .. })
+        {
+            debug!(
+                %proof_type,
+                "rejecting proof request: verifier-only instance"
+            );
+            return Err(ErrorResponse::bad_request(format!(
+                "proof generation not supported for verifier-only zkvm '{proof_type}'"
+            )));
+        }
+    }
+
     let new_payload_request = NewPayloadRequest::<MainnetEthSpec>::from_ssz_bytes(&body)
         .map(Arc::new)
         .map_err(|e| ErrorResponse::bad_request(format!("invalid SSZ body: {e:?}")))?;
diff --git a/crates/server/src/server.rs b/crates/server/src/server.rs
index f10431f..0355328 100644
--- a/crates/server/src/server.rs
+++ b/crates/server/src/server.rs
@@ -79,10 +79,22 @@ impl zkBoostServer {
         let mut zkvms = HashMap::new();
         for zkvm_config in &config.zkvm {
             let instance = zkVMInstance::new(zkvm_config).await?;
+            let mode = match zkvm_config {
+                crate::config::zkVMConfig::Ere { .. } => "prover",
+                crate::config::zkVMConfig::Mock { .. } => "mock",
+                crate::config::zkVMConfig::Verifier { .. } => "verifier-only",
+            };
             info!(
                 proof_type = %zkvm_config.proof_type(),
+                mode,
                 "zkvm instance created"
             );
+            if matches!(zkvm_config, crate::config::zkVMConfig::Verifier { .. }) {
+                info!(
+                    proof_type = %zkvm_config.proof_type(),
+                    "verifier-only mode: proof generation requests will be rejected"
+                );
+            }
             zkvms.insert(zkvm_config.proof_type(), instance);
         }
         set_programs_loaded(zkvms.len());