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Insider Trading Intelligence
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CS

Constantin Ionel Stefan

AMPX
CHIEF TECHNOLOGY OFFICER · AMPRIUS TECHNOLOGIES, INC. · CIK 0001940928
FILING MIX · LIFETIME42%/58%
BUYS
23
SELLS
32
TOTAL VALUE
$11.03M
COMPANIES
1
ACTIVE SINCE
Sep 2022
HOLDINGS NOW
801,310
AVG SELL PX
$10.47
TRADE KIND
SHOWING 55 / 55
Trades · vs SPY
Loading price series…
Performance · forward returns vs SPY
16 backtested trades · 8 horizons · 25 pending
Forward-return performance of every backtestable P/S trade by Constantin Ionel Stefan, measured at 8 horizons from 7 days to 2 years. Deduped per economic event so co-filings count once. Excess return = trade return minus SPY return over the same window.
HORIZONTRADESWIN RATEINSIDER RETURNSPY RETURNMEAN EXCESSMEDIAN EXCESST-STAT
7d16+31.25%+5.01%-0.10%+5.11%+6.07%—
14d16+43.75%+5.08%-0.32%+5.40%+1.65%—
30d16+75.00%+4.27%+0.23%+4.04%-9.77%—
60d16+31.25%+44.34%+0.03%+44.31%+35.08%—
90d16+25.00%+49.29%+3.77%+45.14%+62.02%—
180d16(5 pending)+18.18%+80.75%+10.37%+70.38%+36.45%—
1y16(8 pending)+25.00%+210.10%+18.24%+191.85%+136.47%—
2y16(12 pending)+0.00%+553.76%+46.21%+507.56%+489.39%—
How to read this: Insider Returnis the average raw return of the filer's trades over the horizon. SPY Return is what SPY did over those same windows — reference only, not a comparison. The headline alpha number is Mean Excess = Insider − SPY; green means the filer beat SPY, red means they trailed it. Win rate is the share of individual trades where the filer beat SPY. T-statvalues above 2 mean the alpha is unlikely to be chance given the sample size. "Pending" counts trades where the horizon hasn't elapsed yet; their stats are not included in the row average.
Holdings over time
AMPX · 801,310 shares · as of May 27, 2026
0310,381620,762931,1421,241,5232023202420252026SHARES HELD
Trading cadence · quarterly flow
BUY ● SELL ●
2022
2022
2023
2023
2023
2023
2024
2024
2024
2024
2025
2025
2025
2025
2026
2026
FLOW · 23 buys / 32 sellsCOVERAGE · 16 quarters
Form 4 filings · all activity
COMPANYTYPESHARESPRICEVALUEHELD AFTERTRADE DATEFILEDDETAILS
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
3,208$17.19$55.2K801,310May 27, 2026May 28, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
28,812$14.79$426.1K804,518May 21, 2026May 26, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASEGRANT
Stock grant
110,000——833,330Mar 4, 2026Mar 6, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
25,366$10.16$257.6K723,330Feb 23, 2026Feb 24, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASE
Chief Technology Officer
90$0.62$56748,786Jan 28, 2026Jan 30, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
90——0Jan 28, 2026Jan 30, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
39,690$12.00$476.4K748,696Jan 28, 2026Jan 30, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
39,600——0Jan 28, 2026Jan 30, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASE
Chief Technology Officer
39,600$0.05$2.0K788,386Jan 28, 2026Jan 30, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASE
Chief Technology Officer
1,600$0.05$80750,296Jan 23, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
1,600——39,600Jan 23, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
1,600$12.00$19.2K748,696Jan 23, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
72,795——0Jan 22, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASE
Chief Technology Officer
253,928$0.05$12.7K1,002,624Jan 22, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASE
Chief Technology Officer
72,795$0.45$32.8K1,075,419Jan 22, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
253,928——41,200Jan 22, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
492,827$12.04$5.93M748,696Jan 22, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASE
Chief Technology Officer
166,104$0.05$8.3K1,241,523Jan 22, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
166,104——0Jan 22, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
73,280$12.00$879.4K748,696Jan 21, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
41,563——90Jan 21, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
15,883——166,104Jan 21, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
15,834——295,128Jan 21, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASE
Chief Technology Officer
15,883$0.05$794821,976Jan 21, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASE
Chief Technology Officer
15,834$0.05$792806,093Jan 21, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASE
Chief Technology Officer
41,563$0.62$25.8K790,259Jan 21, 2026Jan 23, 2026 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
125,000——310,962Dec 11, 2025Dec 15, 2025 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASE
Chief Technology Officer
125,000$0.05$6.3K946,951Dec 11, 2025Dec 15, 2025 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
198,255$10.51$2.08M748,696Dec 11, 2025Dec 15, 2025 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
25,024$10.08$252.3K821,951Nov 21, 2025Nov 25, 2025 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
19,159$6.82$130.6K846,975Aug 21, 2025Aug 25, 2025 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
20,366$2.43$49.5K866,134May 21, 2025May 23, 2025 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASEGRANT
Stock grant
461,540——886,500Mar 19, 2025Mar 21, 2025 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASE
Chief Technology Officer
3,471$0.98$3.4K424,960Mar 14, 2025Mar 18, 2025 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
3,471——0Mar 14, 2025Mar 18, 2025 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
9,066$3.13$28.4K421,489Feb 21, 2025Feb 24, 2025 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
8,575$1.96$16.8K430,555Nov 21, 2024Nov 22, 2024 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASEGRANT
Stock grant
41,653——41,653Oct 23, 2024Oct 25, 2024 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASEGRANT
Stock grant
139,613——139,613Oct 23, 2024Oct 25, 2024 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASEGRANT
Stock grant
3,471——3,471Oct 23, 2024Oct 25, 2024 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
8,800$1.04$9.2K386,168Aug 21, 2024Aug 22, 2024 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
4,121$1.36$5.6K394,968May 22, 2024May 24, 2024 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
5,272$1.33$7.0K399,089May 21, 2024May 24, 2024 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASEGRANT
Stock grant
374,570——404,361Mar 19, 2024Mar 19, 2024 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
33,630$3.89$130.7K29,791Sep 15, 2023Sep 18, 2023 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
46,370$3.66$169.5K63,421Sep 14, 2023Sep 18, 2023 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
80,000——435,962Sep 9, 2023Sep 12, 2023 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASE
Chief Technology Officer
80,000$0.05$4.0K109,791Sep 9, 2023Sep 12, 2023 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
209$7.20$1.5K29,791Dec 14, 2022May 3, 2023 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
SALE
Chief Technology Officer
30,000——515,962Dec 14, 2022Dec 15, 2022 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASE
Chief Technology Officer
30,000$0.05$1.5K30,000Dec 14, 2022Dec 15, 2022 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASEGRANT
Stock grant
545,962——545,962Sep 14, 2022Sep 16, 2022 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASEGRANT
Stock grant
72,795——72,795Sep 14, 2022Sep 16, 2022 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASEGRANT
Stock grant
218,385——218,385Sep 14, 2022Sep 16, 2022 ↗View →
AMPX
AMPRIUS TECHNOLOGIES, INC.
PURCHASEGRANT
Stock grant
181,987——181,987Sep 14, 2022Sep 16, 2022 ↗View →
Other insiders · AMPX
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About this filer
CIK 0001940928
ROLE
Chief Technology Officer
PRIMARY
AMPX
COMPANIES
1
ACTIVE SINCE
Sep 2022
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