By August 24, 2026, HM Government will formally announce a binding multi-year commitment to raise UK defense spending to at least 2.5% of GDP, specifying a concrete timeline and fiscal pathway rather than an aspirational goal — moving beyond the current 2.3% target in formal government policy.

Four frameworks converge on a two-stage prediction: (1) formal announcement is highly probable (~0.72) given NATO summit forcing function, norm institutionalization pressure, and pre-existing Labour commitment; (2) the ‘binding’ multi-year qualifier is considerably less probable (~0.42–0.50) given UK constitutional constraints, Spending Review timing mismatch, and HM Treasury bond-market sensitivity inherited from the Truss episode. The question requires both: formal announcement AND binding quality. Under strict interpretation (Treasury-locked, OBR-scored fiscal path), multiplying P(announcement) × P(binding|announcement) yields ~0.30–0.36. The institutionalist framework’s critical correction applies here: UK political culture treats PM-level commitment as functionally binding even without statutory encoding, and the question’s ‘binding’ threshold may be satisfied by a formal policy declaration specifying 2.5% with a multi-year timeline attached. Under this looser but politically realistic interpretation, probability rises to ~0.42–0.48. Base rate (0.30) drawn from the historical UK pattern: defense commitments under NATO pressure consistently produce announcements that satisfy alliance audiences while deferring fiscal substance — the 2014 Wales 2% recommitment required creative accounting to nominally achieve over years. Adjusted upward from base rate to 0.42 given the strength of the current geopolitical forcing function, pre-existing government signaling, and multi-framework convergence on announcement probability. The Austrian accounting-elasticity insight provides an additional upward adjustment: if 2.5% can be reached definitionally through reclassification, the Treasury’s resistance is substantially lowered.