claude-dev-suite Fee Estimation
Bitcoin tx fees are auctioned per-block. Wallets need to estimate the
fee rate (sat/vB) needed to confirm within n blocks.
Bitcoin Core's estimatesmartfee
bitcoin-cli estimatesmartfee 6 ECONOMICAL
Returns {"feerate": 0.00010000, "blocks": 6} (BTC/kvB → 10 sat/vB).
Algorithm (simplified)
- Track every tx that enters mempool with its first-seen fee rate.
- Track which fee rates resulted in confirmation within
nblocks. - For target
n: find lowest fee rate that successfully confirmed ≥ X% of historical txs withinnblocks.
Modes: ECONOMICAL (less aggressive), CONSERVATIVE (more buffer).
Limitations:
- Cold-start: needs ~3 hours of running for reliable estimates.
- Doesn't see network-wide mempool, only local.
- Slow to react to fee spikes (uses historical data).
Mempool-based estimation
Sample getrawmempool true:
mempool = bitcoind.getrawmempool(verbose=True)
# build histogram of (fee_rate, vsize)
# find fee rate where cumulative vsize from top fits in 1 MB block
target_rate_for_next_block = histogram.percentile(at_vsize=1_000_000)
This reflects current mempool state, not historical. Better during fee spikes; volatile during quiet periods.
External services
- mempool.space API:
GET /api/v1/fees/recommended→{ fastestFee, halfHourFee, hourFee, economyFee, minimumFee }. - mempool.space mempool blocks API:
/api/v1/fees/mempool-blocksshows projected next ~10 blocks with median fee rate per block. - BlockCypher, Esplora — similar.
External APIs offer real-time mempool view; trade-off is trust and availability.
Floor: incremental relay fee
incrementalrelayfee = 1 sat/vB (default)
Min fee rate for a tx to be relayed. RBF replacement must add at least this much per added vbyte beyond the original.
Smart-fee + smart-bump pattern
fee_rate = max(local_estimate(target=N),
external_api(target=N))
broadcast(tx, fee_rate)
sleep(check_interval)
if not confirmed:
new_rate = max(current_market_rate * bump_factor,
fee_rate + incrementalrelayfee + buffer)
rbf_replace(tx, new_rate)
bump_factor typically 1.5x for proactive bumps.
Fee floor for relay vs mining
- Relay: 1 sat/vB minimum (mempool admit).
- Mining: miners include highest-fee txs first, no theoretical floor (some pools mine 1 sat/vB; others have policies).
- Compact fee floor: even at near-empty mempool, miners include zero-fee txs only via private submission (mempool.space accelerator).
Special cases
Lightning anchor / commitment
Pre-signed commitment tx has fixed fee at signing time. To bump:
- Spend anchor output with high-fee child (CPFP).
- Effective fee rate = (parent_fee + child_fee) / (parent_vsize + child_vsize).
Mempool eviction
Bitcoin Core evicts tx with lowest fee when mempool is full
(maxmempool=300MB default). If your tx is evicted:
- Re-broadcast with same fee → may be re-rejected.
- Re-broadcast with bumped fee → admitted.
Per-block fee dynamics
- Fees follow block subsidy halvings loosely (more competition for fees as subsidy declines).
- Daily seasonality: fees lower on weekends, higher during US business hours.
- Event-driven spikes: ordinals waves (2023-2024), runes launch (April 2024) caused 1000+ sat/vB peaks.
Common bugs
- Using
estimatesmartfee 1(next-block) on a fresh node → returns -1 (insufficient history) → tx with no fee. - Hard-coding sat/vB → fails when fees spike.
- Not accounting for mempool min: on rejection from mempool, your tx
is silently lost; check
testmempoolacceptfirst. - Fee bumping without checking BIP125 rules → replacement rejected.