Hearts of Iron 4 (HOI4) Update 1.17.1 Patch Notes – November 26, 2025

A new Hearts of Iron IV update 1.17.1 is available on PC (Steam). According to the official HOI4 patch notes, the latest update delivers major balance adjustments for China, Japan, and the Philippines, earlier submarine technologies, stronger focus-tree rewards, extensive AI naval improvements, and numerous UI polish fixes. Apart from this, HOI4 update 1.17.1 also stabilizes China–Japan mechanics, warlord behavior, doctrines, and naval systems.

HOI4 Update Patch Notes – November 26, 2025

Major Highlights (Most Important Changes)

• China and Japan receive broad balance reworks, including focus tree adjustments and goal reward boosts.

• Major submarine and engine tech timeline changes for earlier availability.

• Extensive AI naval and theater behavior improvements for Japan, USA, Italy, and UK.

• Large set of UI fixes improving tooltips, HQ handling, and navigation.

• Numerous critical bugfixes for crashes, focuses, doctrines, and Chinese warlord mechanics.

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Balance Changes

China & Japan Adjustments

• Adjusted surrender-limit bonuses for Chiang Kai-shek and Wang Jingwei.

• Japan receives a small mastery malus from Surprise Invasion.

• Added Densely Populated Rural Area modifier to additional Chinese states.

• “7075 Aluminium Alloy” now grants 5 aluminium in Osaka.

• “Develop New Fighters” increased air breakthrough and ahead-of-time reductions.

• “Shifting the Balance” updated with alternative requirements; incompatible advisors hidden.

• “Championing the Cause of Liberty” now adds a research slot.

• Added 15 tungsten to Fujian.

• “Chinese United Front” manifest now grants up to 10% core defense based on fulfillment.

• “Inefficient Economy” starting malus reduced from –40% to –35%.

Philippines Rebalance

• Subject surrender branch rebalance: lower resistance targets, higher garrison damage.

Focus & Goal Improvements

• Japanese focus “Military Ministers’ Attaché System” reduced to 35 days; AI updated.

• More lenient conditions for Military Infrastructure and Indifference is a Threat.

• Major reward increases for:

  • Maintain Control of the Coastline

  • Throw Out the Invaders

  • Align China

  • Control the Chinese Capitals

  • Organize the Resistance

• Reduced requirements + increased rewards for:

  • The Red Tide

  • Building up Guam

• Added more subjects to Eastern European Security.

• Added faction initiative reward to One Germany.

Technology Timeline Adjustments

• Basic Submarine Snorkel: 1939 (from 1940).

• Improved Submarine Snorkel: 1943 (from 1944).

• AIP-Diesel Engines: 1939 (from 1940).

• High-Speed Walter Engines: 1943 (from 1944).

• Improved Dual-Purpose Battery moved to 1940.

• Ice Composite Runways moved to 1944.

• Transport Ships now shown as requirement for Support Ships Special Project.

Subdoctrine & Mastery Tweaks

• Minor mastery bonus adjustments.

Gameplay Changes

• Dictator MacArthur remains in PHI if war with USA occurs.

• Taiyuan city repositioned; added level 1 land fort.

UI Fixes

• Naval HQ tooltip duplication fixed.

• Captured HQs now listed correctly and capturable after save-load.

• Fixed multiple tooltip, icon, and UI display issues:

  • Doctrine cost reduction

  • “Lack of Energy” output display

  • Faction theater icon

  • Naval dominance flag clickability

  • War summary closeability

  • Equipment stat breakdown

  • Naval leader window updates

  • Training XP-limit display

  • Garrison support slider usability

  • Missing faction influence country names

  • Naval commander assignment sorting issues

AI Improvements

• Japan auto-merges created China puppets into Reorganised Government.

• Better fleet homebase selection and naval objective targeting.

• Italy & UK, and USA & Japan now fight more historically intense naval wars.

• Convoy raiding evaluated per naval base, improving coverage logic.

• Fleets move to basing areas more reliably; fewer range-gate issues.

• Naval AI escalates more intelligently based on enemy presence.

Modding Enhancements

• Fixed crash in has_mastery_level when invalid subdoctrine used.

• Fixed multiplayer OOS issues.

• Fixed stacking battalion bonuses display in doctrines.

• Added max_track_columns and max_track_rows for multi-row doctrine tracks.

• Scripted GUI windows no longer disappear when switching countries.

• Doctrine list anchors properly with multiple rows.

• naval_dominance strategies can use AI areas to better distribute strike forces.

Crashes & Stability

• Fixed multiple crashes:

  • Battleplan crash

  • Nat China focus tree + German Civil War

  • Releasing a nation then creating new equipment design

  • Borderwar map icon hover (mac)

  • Carrier mission spam reducing network stability

  • Reinforce rate calculation

  • Submarine/airwing damage exploit and over-damage

  • Mastery unlock issues for PRC militia subdoctrine

China & Warlords

• Warlords can use Mining Commission after relevant focus.

• USA will not instantly peace out in Philippine War of Independence.

• Fixed Japan border war mission penalizing early victories.

• Added event enabling Retreat to Taiwan focus.

• Fixed autonomy-reduction decisions duplicating for warlords.

• Guangdong now targetable when puppeted via Liangguang incident.

• Xi’an Incident locked in 1939 start.

• United Front acceptance increased; PRC always accepts historically.

• Fixed factories returning to same state after evacuation.

• “Reclaim the North” now correctly grants cores on controlled states.

• Fixed multiple resource/production issues when becoming a puppet.

• Ensured warlords don’t capitulate before gaining PP to request United Front entry.

• Fixed China modifiers from “Well-timed Swoop of a Falcon”.

• Fixed Guerrilla state modifier disappearing incorrectly.

Japan

• Democratic Japan cannot invite non-democratic-led factions via decisions.

• “Fund the RIKEN Institute” availability fixed.

Global & Misc

• Incorrect unit animation fixes.

• Fixed doctrine reductions being consumed at 0 cost.

• Lock on Japan’s white peace offer to China (once only).

• Fixed faction theaters showing 0 countries incorrectly.

• Wrongly described battalions for air/ship goals corrected.

• Fixed multiple localization issues.

• Added US Naval Supply Hub to Norfolk.

• Fixed Danzig for Slovakia when Czech annexed earlier.

• Fixed Raj using invalid MIO.

• Fixed Iraqi advisor availability.

• Fixed template changes during raid missions.

• USA 1939 starting subdoctrines corrected.

• Can now draw offensive lines from naval invasion orders.

• Ensured Chiang Kai-shek succession events behave correctly.

Recently, a big Hearts of Iron IV update 1.12.10 was released that added adds Operation Sabre comes plenty of new bug fixes and some attention towards Bulgaria and Romania. Unfortunately, since the last update, many players were experiencing a number of issues when trying to play. Today’s Hearts of Iron 4 update 1.17.1 will fix a few of these issues.