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Segments - Schedule of Segment Reporting Information, by Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Segment Reporting Information [Line Items]
Stock-based compensation	$ 2,824	$ 1,968
Direct external program expenses:	20,294	9,974
Net loss	(26,237)	(15,169)
Reportable segment
Segment Reporting Information [Line Items]
Personnel expenses excluding stock-based compensation	6,249	5,783
Stock-based compensation	2,824	1,968
Other research and development	1,198	1,129
General and administrative	4,091	3,044
Net loss	27,138	15,676
Reportable segment | ALTO-100
Segment Reporting Information [Line Items]
Direct external program expenses:	1,764	1,124
Reportable segment | ALTO-300
Segment Reporting Information [Line Items]
Direct external program expenses:	1,507	922
Reportable segment | ALTO-101
Segment Reporting Information [Line Items]
Direct external program expenses:	5,356	969
Reportable segment | ALTO-203
Segment Reporting Information [Line Items]
Direct external program expenses:	6	737
Reportable segment | ALTO-207
Segment Reporting Information [Line Items]
Direct external program expenses:	$ 4,143	$ 0

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