For German solo founders and small Mittelstand operators running AI-bookkeeping in 2026, the Buchhaltungssoftware choice resolves on Umsatz tier and Steuerberater relationship: DATEV (€20-€80/month plus Steuerberater-coupling) above €100K Umsatz where the Steuerberater workflow is binding, sevDesk (€8-€48/month) under €100K Umsatz as the cheapest path that produces a GoBD-compliant audit trail, and Lexware (€10-€40/month) as the legacy-Mittelstand fallback. The OPS-031 jurisdiction-neutral DIY-AI-bookkeeping case breaks at the moment the AI-drafted Buchungssatz must land in a tool that preserves the GoBD audit trail; the German-tool layer is the complement to the DIY-AI case. The OSS-Verfahren and reverse-charge VAT prompt-prefix is the operational discipline that prevents AI-VAT-error in 1 of 20 EU-cross-border invoices.

DE-specific sister to OPS-045 NL. Cohort: Kleinunternehmer, Einzelunternehmer, GmbH-Geschäftsführer, freiberuflich. Cadence 60-day. Trigger conditions: vendor product changes at DATEV, sevDesk, or Lexware affecting the AI-bookkeeping integration; ELSTER-side changes affecting USt-Voranmeldung filing flows; Bundesfinanzministerium guidance on AI-assisted bookkeeping under GoBD. Sister claims: OPS-045 (NL bookkeeping), OPS-031 (jurisdiction-neutral DIY case), OPS-049 (Mittelstand BetrVG/DSGVO deployment), OPS-037 (VAT). Note: published as OPS-055 (not OPS-050 as originally drafted) because OPS-050 was already taken by an unrelated local-SEO claim.