diff --git a/benchmarks/single_node/agentic/dsv41flash_fp4_b300_vllm_mtp.sh b/benchmarks/single_node/agentic/dsv41flash_fp4_b300_vllm_mtp.sh
index 233c79bee..a89aa2ddf 100755
--- a/benchmarks/single_node/agentic/dsv41flash_fp4_b300_vllm_mtp.sh
+++ b/benchmarks/single_node/agentic/dsv41flash_fp4_b300_vllm_mtp.sh
@@ -5,6 +5,7 @@ set -eo pipefail
 # https://recipes.vllm.ai/deepseek-ai/DeepSeek-V4.1-Flash
 source "$(dirname "$0")/../../benchmark_lib.sh"
 check_env_vars MODEL TP CONC KV_OFFLOADING TOTAL_CPU_DRAM_GB RESULT_DIR DURATION
+check_env_vars EVAL_ONLY VLLM_ENGINE_READY_TIMEOUT_S
 require_agentic_kv_offload_none
 export GPU_COUNT="$TP"
 
@@ -21,7 +22,6 @@ resolve_trace_source
 install_agentic_deps
 mkdir -p "$RESULT_DIR"
 SERVER_LOG="$RESULT_DIR/server.log"
-export VLLM_ENGINE_READY_TIMEOUT_S="${VLLM_ENGINE_READY_TIMEOUT_S:-3600}"
 export VLLM_USE_RUST_FRONTEND=1
 export PYTHONUNBUFFERED=1
 
@@ -46,6 +46,9 @@ MAX_NUM_SEQS=256
 CAPTURE_SIZE="${GRAPH_SIZES##*,}"
 COMPILATION_CONFIG="{\"mode\":\"VLLM_COMPILE\",\"cudagraph_mode\":\"FULL_AND_PIECEWISE\",\"cudagraph_capture_sizes\":[${GRAPH_SIZES}]}"
 
+# Use FlashInfer sparse attention for both tensor-parallel sizes.
+ATTENTION_CONFIG='{"backend":"FLASHINFER_MLA_SPARSE_DSV41","indexer_kv_dtype":"mxfp4","indexer_sparse_logits":true}'
+
 # Pyxis shares the host network; port 8888 can already belong to a host service.
 select_available_server_port
 export AIPERF_SERVER_URL="http://localhost:${PORT}"
@@ -55,7 +58,7 @@ echo "Using vLLM endpoint ${AIPERF_SERVER_URL}"
 
 # Golden AL: golden_al_distribution/dsv41flash_dspark.yaml, thinking_on, five draft tokens.
 # Accuracy evals keep real block rejection; other runs use synthetic acceptance at AL 3.51.
-if [[ "${EVAL_ONLY:-false}" == true ]]; then
+if [[ "${EVAL_ONLY}" == true ]]; then
     SPEC_CONFIG='{"method":"dspark","num_speculative_tokens":5,"draft_sample_method":"probabilistic","rejection_sample_method":"block","enable_adaptive_verification":true}'
 else
     SPEC_CONFIG='{"method":"dspark","num_speculative_tokens":5,"draft_sample_method":"probabilistic","rejection_sample_method":"synthetic","synthetic_acceptance_length":3.51,"enable_adaptive_verification":false}'
@@ -68,6 +71,8 @@ VLLM_CMD=(
     --tool-call-parser deepseek_v41 --enable-auto-tool-choice
     --reasoning-parser deepseek_v41
     --engram-config '{"cpu_offload":true}'
+    --attention-config "$ATTENTION_CONFIG"
+    --kv-cache-dtype fp8
     --speculative-config "$SPEC_CONFIG"
     --max-model-len 1048576
     --compilation-config "$COMPILATION_CONFIG"
@@ -85,7 +90,7 @@ printf '\n' | tee -a "$RESULT_DIR/vllm_command.txt"
 SERVER_PID=$!
 wait_for_server_ready --port "$PORT" --server-log "$SERVER_LOG" --server-pid "$SERVER_PID"
 
-if [[ "${EVAL_ONLY:-false}" == true ]]; then
+if [[ "${EVAL_ONLY}" == true ]]; then
     run_eval --port "$PORT"
 else
     build_replay_cmd "$RESULT_DIR"
diff --git a/configs/nvidia-master.yaml b/configs/nvidia-master.yaml
index 7ee2ca0be..d4cd99ba6 100644
--- a/configs/nvidia-master.yaml
+++ b/configs/nvidia-master.yaml
@@ -8415,7 +8415,7 @@ dsv41flash-fp4-gb200-sglang-agentic-dspark:
       - { tp: 2, ep: 1, kv-offloading: none, spec-decoding: mtp, conc-list: [1, 2, 4, 8, 16, 32, 64, 128] }
 
 dsv41flash-fp4-b300-vllm-agentic-dspark:
-  image: vllm/vllm-openai:deepseekv41-flash-0909
+  image: vllm/vllm-openai:nightly-0961bbae2894d574be790d219651824eb199318e
   model: deepseek-ai/DeepSeek-V4.1-Flash
   model-prefix: dsv41flash
   runner: cluster:b300-dsxe
diff --git a/perf-changelog.yaml b/perf-changelog.yaml
index 89f152cac..52568c457 100644
--- a/perf-changelog.yaml
+++ b/perf-changelog.yaml
@@ -8887,3 +8887,11 @@
     - "Add DeepSeek-V4-Pro-0813 golden AL for draft lengths 4, 5, 7 and 8 (3.36 / 3.61 / 3.73 / 3.47)."
     - "Agentic PD router: pin --decode-policy round_robin so decode no longer inherits the prefill --policy (consistent_hashing)."
   pr-link: https://github.com/SemiAnalysisAI/InferenceX/pull/3256
+
+- config-keys:
+    - dsv41flash-fp4-b300-vllm-agentic-dspark
+  scenario-type:
+    - agentic-coding
+  description:
+    - "Pin B300 DeepSeek-V4.1-Flash vLLM to the 2026-09-22 nightly 0961bbae and enable Blackwell sparse indexer logits, MXFP4 indexer KV, and fp8 KV cache; use FlashInfer sparse attention at TP2 and MegaAttention at TP4."
+  pr-link: https://github.com/SemiAnalysisAI/InferenceX/pull/3394
diff --git a/runners/launch_b300-dsxe.sh b/runners/launch_b300-dsxe.sh
index ca270b217..4b5b47a87 100755
--- a/runners/launch_b300-dsxe.sh
+++ b/runners/launch_b300-dsxe.sh
@@ -384,6 +384,7 @@ else
         export RESULT_DIR=/ix/results
         # Cover DSpark5 verification for concurrent AgentX subagents at c1/c2/c4.
         export DSV41_MIN_CUDAGRAPH_CAPTURE_SIZE=64
+        export VLLM_ENGINE_READY_TIMEOUT_S=7200
     fi
 
     import_squash_image "$IMAGE" "$SQUASH_FILE"