The shift toward unsignalled intervention raises the cost of holding short yen positions, since traders can no longer rely on jawboning to unwind ahead of MOF action. That heightens two-way risk for USD/JPY around any local data surprise or Fed repricing, with Thursday's US payrolls seen as a key swing factor given hopes a soft print could ease dollar strength without requiring direct intervention. The record 11.7 trillion yen spent in the previous late April to early May intervention window underscores the scale authorities are willing to deploy, though its effect proved short lived once the yen resumed its downtrend. A wide policy rate gap between the BOJ's 1% and the Fed's 3.50% to 3.75% continues to underpin the structural case for yen weakness regardless of intervention timing.---Japan is shifting to unsignalled, ambush-style intervention against yen short sellers rather than telegraphing risks in advance, sources tell Reuters, as the yen hits 40 year lows. Summary:Japanese officials are moving away from telegraphing intervention risk and toward unsignalled action designed to squeeze speculative yen short positions, sources sayAuthorities are avoiding any suggestion of a specific yen level that would trigger intervention, with timing instead focused on preventing excessive fallsThe yen slumped to a 40 year low of 162.66 per dollar on Tuesday and was trading near 162.50 in Tokyo on ThursdayJapan spent a record 11.7 trillion yen, around $72 billion, intervening between late April and early May, though the boost to the yen was quickly reversedBOJ Deputy Governor Ryozo Himino has warned that a weak yen may boost underlying inflation as import costs riseThe BOJ's quarterly tankan survey showed business sentiment at an eight year high and record corporate inflation expectations, reinforcing the case for further rate hikesThe BOJ's 1% policy rate remains far below the Fed's 3.50% to 3.75%, preserving a wide rate gap that continues to encourage yen sellingJapanese authorities are shifting toward a more targeted, unsignalled approach to currency intervention, aiming to squeeze speculators betting against the yen rather than telegraphing risks in advance, according to Reuters sources familiar with the matter. Where previous intervention was preceded by calibrated jawboning that gave traders room to unwind short positions ahead of time, the Ministry of Finance is now said to be prepared to step in abruptly, avoiding any suggestion of a specific exchange rate level that would trigger action.The approach is designed to use silence as a policy tool, keeping traders uncertain about timing and raising the cost of shorting the yen. Sources said the shift reflects a more aggressive MOF posture working in tandem with continued hawkish rhetoric from the Bank of Japan, which has ramped up warnings over the inflationary impact of yen weakness even after hiking rates last month. BOJ Deputy Governor Ryozo Himino said in June that currency moves are among the key factors affecting Japan's inflation outlook, warning that rising import costs from a weak yen may lift underlying price pressures, a view echoed by other board members.The currency's slide has continued despite Japan's record 11.7 trillion yen intervention between late April and early May. That effort briefly lifted the yen before it resumed its downtrend, slumping to a 40 year low of 162.66 per dollar on Tuesday and trading near 162.50 in Tokyo on Thursday. Because that earlier intervention was well flagged in advance, traders were able to avoid losses by unwinding short positions ahead of time, an opportunity authorities appear keen to eliminate going forward.Japan's top currency diplomat Atsushi Mimura has held off on verbal warnings since the last intervention, a silence one strategist said is likely deliberate, intended to make it harder for markets to gauge timing. Finance Minister Satsuki Katayama similarly avoided escalating rhetoric this week despite the yen's fresh lows, repeating only that Japan stood ready to respond appropriately to currency moves. Some officials are hoping Thursday's US jobs data could scale back market bets on further Fed tightening, which would ease dollar strength and help the yen without requiring direct intervention. If the data fails to shift that outlook, sources said the chances of intervention would rise.Washington's stance remains a key consideration, since intervention is typically justified only to counter disorderly market moves rather than a slow, grinding decline. US Treasury Secretary Scott Bessent has called for further BOJ rate hikes while staying quiet on Japan's prior intervention. With the BOJ's 1% policy rate still far below the Federal Reserve's 3.50% to 3.75%, the wide interest rate gap continues to support yen selling, a dynamic reinforced by the central bank's tankan survey this week, which showed business sentiment at an eight year high and corporate inflation expectations at record levels, strengthening the case for further BOJ tightening. This article was written by Eamonn Sheridan at investinglive.com.